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Topic 30: Extending the life of pipeline in the North Sea what are the Safety & Risk challenges

michael saiki's picture

The North Sea is experiencing another wave of technological advancement in the process of extending the life span of Existing pipelines.

A lot of the Pipelines in the North sea have reached or are close to the end of their design life and as usual the business minds who own these assets are taking steps to extend the life of the pipelines instead of just decommisioning, their argument is mainly economic i.e. the CAPEX involved. 

Is this not a potential disaster in the making. Can we properly extend the lives of pipelines and still optimize the safety case

Michael Saiki

Comments

mohamed.elkiki's picture

I agree with you Michael that this is a risky situation and most companies don't want to waste their money and business in replacing those pipes. However, when the reservoir reaches its end, it starts to produce more water which help in degradation of the pipeline. Also, the problem that face some companies is that to replace the pipeline they will have to shut the production and go in a very hard process which cause both loss of money for each day of stopping the production and also, replacing the pipe can produce more problems as new pipeline may have leak or something. Therefore, companies started to think that instead of replacing the pipes, they can protect it from degradation, corrosion and sour gases such as H2S. Here come the role of corrosion engineer. they can put surfactant, coat the pipes, cathodic protection and a lot of other techniques. However, i still agree with you Michael because even this techniques must be planned from the start of the project because it is very hard to do it while not planning. North sea has a lot of challenges because most of its projects started from very long time. However, the HSE are making check up on this pipeline to ensure that everything is safe and the risk percentage is very low.

Ambrose Ssentongo's picture

 

The risks exist indeed with pipeline life extension but I believe we now have methods and technologies to assess risk of failure of ageing pipelines, identify and apply appropriate inspection techniques (for example Risk and Reliability Based inspection  strategies), set economic inspection intervals to prevent failures, limit risks to an acceptable level, quantify the present integrity(using available design data and as-built data, Inspection data available, Loading and environmental data), predict the future integrity(using past and present operating conditions, forecast operating conditions ).

Operators can now safely extend the life of ageing pipelines by having a planned and structured approach to managing the integrity of these pipelines to ensure continued safe and efficient transportation for hydrocarbons.

 Ambrose Ssentongo

Refs

Extending the life of ageing pipelines by Paul A Henderson, Phil Hopkins,  and Andrew Cosham of Andrew Palmer and Associates, published 2001

Life Extension issues for Ageing Offshore installations, by A. Stacey HSE London, M. Birkinshaw HSE London, J.V Sharp Cranfield University Cranfield, 2008

 

Menelaos Michelakis's picture

Most of the platforms and pipelines we constructed many decades ago, (1970's), and this is the main problem of the UK sector. It is worthy mentioning that installations in the Norwegian sector, are in much better condition as well as the pipelines, because most of them were constructed later.

The problem has to do with money again, as mohamed stated, with profits lost, during repairing, or changing parts of the pipeline system. Preserving the pipeline system, seems to be the best option in my view. A corrosion engineer will be able to make good money in the UK sector of the North sea. Coating of the pipes, put surfactant and other possible solutions seems to be cheaper than changing parts of the pipeline system. This will be a logic action, considering that reservoirs are depleted, and the system will not be maintained for long time after repairs. So changing parts of the pipeline system, is a very expensive proceedure , compared to preservation techniques.

The probability of an accident to occur, is therefore, significant, as the pipeline system has reached at the end of its life. The companies will decide which is the best solution, and they must do it with respect to the life span of the existing system. An oil leekage, will ruin not only the environment but also the reputation of the company/ies involved.

Ref : A. Mather, Offshore engineering - An introduction

Andrew Allan's picture

One method of assessing the current integrity of a pipeline and to support justification for extended operation is to utilise an intelligent pigging tool capable of detecting the current wall thickness (and hence corrosion levels) along the length of the pipeline as well as detecting cracks and weld defects.  An intelligent pig can utilise a number of eletromagnetic and acoustic technologies to record data required by the operator.  A general overview of intelligent pigging technologies can be found on wikipedia (http://en.wikipedia.org/wiki/Pigging#Intelligent_pigging).

In building a picture of the current integrity of a pipeline, operators can then develop a strategy to prolong the life of the pipeline, getting authorisation from the Health and Safety executive to continue production.

It may be that given a recorded reduction in original design wall thickness following an intelligent pigging run, an operator decides to reduce the maximum allowable operating pressure of the pipeline such that the risk of overpressure due to corrosion at given areas of a pipeline is minimised.  This may involve adjustment of control settings and process conditions to meet these new goals.

Justification for continued operation may also be made based on the fact the actual steel grade used in fabrication was of a higher quality that that specified in design, and as such there is increased confidence that the integrity of the pipeline is sufficient to minimise the likelihood of a release.

Of course, in order to convince the HSE that the pipeline is still fit for operation for an extended period of time the arguement must be strong, with verifiable parameters such that the condition of the pipeline can be proven beyond doubt.

RossWinter's picture

As has been stated above the theoretical lifetime of many pipelines is up and they need are believed to need replacing. However with the advancements in technology, these pipes have been we maintained and made sure that they are in a good state of repair and this will theoretically extend their lifespan. It is relatively easy to monitor the pipes with ROV (Remote Operated Vehicles) which follow set pathways. The lifetime of the fossil fuel reserves in the North Sea are running out and many companies are reluctant to replace their pipes seeing as they won't get much use out of them, compared to the ones currently installed. However they need to look at the potential backlash of the cost of clear up and fines if these pipes do fail before they are improved or replaced.

Ross Winter Msc Renewable Energy

Kobina Gyan Budu's picture

Hello every one, while agreeing with you on some of the salient points raised, I will look at the
topic from a different perspective.
 
It is not always about the money/profit as perceived. When these extensions result in the release
of failure events, operations will come to a halt and it will cost the organisation more to manage
the undesired consequence that the perceived profit.

This is about knowing that the possibility of life extension is “doable” and using modern
technologies to make it happen. Even though in the event of doing this cost is saved, cost-saving
in itself should not be the driver. The onus is on both the organisation and the regulators to
ensure the extension exercise works. The organisation will have to demonstrate to the HSE that
they have done all possible to reduce all risks to ALARP. The HSE will have to scrutinise the
operations/safety case to satisfy itself before any possible certification.

Elvis.E.Osung's picture

Michael, this is indeed a safety issue. Engineering design estimates the limit of optimum functionality of a structure or material by the design life, though there are factors of safety involved, once this design life is exceeded, the behaviour of the material can no longer be predicted within the standard safety considerations. As pipelines in the North Sea are reaching the limit of their design life, maintaining pipeline integrity is pivotal to the continued and sustained production of oil in the North Sea. Subsea pipeline integrity management can be considered from two aspects Monitoring/Inspection and corrosion control. These two areas are not as expensive as decommissioning and replacing the pipelines, as funds will be lost due to production shut down and laying of new pipelines. Subsea pipeline assets in the North Sea require an extensive HSE inspection programme focused on life extension. There is also a need for detailed safety demonstration of continued safe operation. The truth remains that remedial efforts in corrosion management will not increase the life of the pipe endlessly and as such there should be a fair balance between functionality, safety and cost.

 

http://www.imeche.org/Libraries/Knowledge-Pressure_Systems/2377_s1512_offshore_pipelines_lr_1.sflb.ashx

 

Kobina Gyan Budu's picture

Elvis, I agree with you that “remedial efforts in corrosion management will not increase the life
of the pipe endlessly”. Of course the HSE/regulators will not grant endless extension certification.

The organisations will normally conduct thorough assessment of the piping facilities to establish
the existing integrity issues, evaluate defects and develop a robust plan for improvement to
sustain the extension. Some of the methods available include close-interval surveys, direct
current voltage gradient surveys (DCVGs) and Pipeline Current Mapping (PCM). A new safety
case will then be compiled for the HSE to consider.

The regulators (HSE) also have a duty of ensuring that the assessments conducted by the
organisations are credible (all clear risks identified, some eliminated/suppressed and sound
mitigating measures in place for the rest) and that piping system can survive the extension.
The responsibility will therefore be on the HSE to satisfy itself before issuing the licence for
extension. The HSE should be looking at the safety report with ALARP in mind and should they
find any activity intolerable, the organisation made to resolve before certification. When the
HSE/regulator validates the establishment of the necessary preparation to manage the safety and
risk challenges via the safety case, extensions will normally be given (for a relatively shorter
period).

michael saiki's picture

From the special lecture we had today i think the most fundamental question we need to ask about our assets is how much information do we have.  Beyond the fact that it has exceeded it design life or what is the basis for extending the life of these assets (economic or safety) is what data do we have,  how much of the assets state do we know, because that an asset has reached its design life does not mean it cannot be useful.

So we must ask ourselves whether the system has been properly preserved or if it still has the capacity to continue some additional number of years based on the projected reservoir characteristics, or that the systemeven though has not reached its design life may have failed because of insufficient design or maintenance  and so on.

In conclusion, the final decision to extend the life of an Asset depends on the data integrity. However, like you all have said the onus is on regulators to decide what is the acceptable benchmark for licensing the extension of the life of these assets or otherwise

Michael Saiki

oseghale lucas okohue's picture

This is an interesting topic that needs to be well researched before posting. Thanks to micheal an others who have contributed relevantly. Let me add some spice to this interesting discussion: Before we have a chat on pipeline extension in the North sea , I would like us to have a broader Understanding of this debate with respect to the initial pipe design at the North Sea. Pipelines are usually designed, coated and cathodically protected to ensure that the maintain their integrity over their required Engineered design life. The corrosion Engineer usually create an advenue for extention of this Engineered life. Now  subsea intergrity class we know that cathodic protection can be said to be a means of reducing the rate of corrosion on a metal surface as a result of exposure to the environment.  Cathodic protection is of two types1. Galvanic i.e. sacrificial anode…… In which the current used to drive this cells is generated from    the sacrificed anode and depends on the potential difference existing between the two electrodes        i.e. cathode and anode.  Materials used as sacrifice are mg, zn and al 2. Impressed current i.e. inert anode. Here electric power from an external source is used to drive the cell. Rectifier is then used to convert AC to DC. Now coming to “Extending the life of pipeline in the North Sea what are the Safety & Risk challenges" debate... In the North Sea most of their pipeline was protected from design to fulfil its Engineered designed life through coating and galvanic cathodic protection because of initial cost of implementation and maintenance of this pipelines and their facilities offshore. The Question here is should we use retrofitting method since it was galvanised initially or should we used impressed current for the cathodic protection. Let’s consider economics while arguing on this extension margin.

Mostafa Tantawi's picture

 Well to be Honest I didn't entirely read all the above posts but I have something to add here.

I would like to address the threats that accompanies the pipeline aging.


Threats in
an aged pipeline


Internal
Threats:

·        
Corrosion

·        
Erosion

·        
Wear

·        
Chemical and Physical Aging

·        
Creep

·        
Overpressure

·        
Under pressure

·        
Changes in Flow Characteristics

External
Threats

·        
External Corrosion

·        
Free Spans ( w.r.t Fatigue)

·        
Free Spans( w.r.t Trawl Pullover and hooking)

·        
Lateral Buckling

·        
Upheaval Buckling

·        
Expansion

·        
On-Bottom Stability

·        
Collapse

·        
Natural Hazards

·        
Incorrect Operations

·        
Compression

·        
Deteriorating Integrity of Supporting
Components( e.g. Buoyancy, mid water arches, pipe support)

·        
Deteriorating Integrity of Surrounding Infra
Structure

Well
Guys there is a whole standard for pipeline Life extension, it is really handy
and it is free over the internet NORSOK code y-002-u1


Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

Ajay.Kale's picture

 North Sea Pipelines network is most commissioned during year
1970-80.

 

Some of pipelines does or doesn’t accommodate modern safety
technologies.

It will be big challenge on extending the life of Pipeline
because of the cost.

The production in the North Sea has been dropped & need
to have proper estimate on cost of extending the life of pipe line and the
current as well as future oil or gas production.

The safety must be taken into account for extending life of
a pipeline because of their reliability.

Those old pipelines are now less reliable because they were
designed for a period of 20 to 25 years. The risk is at higher side.

The HSE regime needs to be tighter to maintain pipelines. HSE
creditable inspection can make sure safety as well as maintenance requirement
of pipelines.

If not we can see oil leakage in the North Sea (i.e. Gannet
alpha oil leak).

The integrity of pipeline is important & various
inspection methods using modern technology can achieved (use of ROV for
inspection of Pipelines).

Ajay Kale

Lee Soo Chyi's picture

It is reported 1069 steel lines operating in the North Sea and a total of 65 incidents which resulted in a leakage have been reported between the years 1971 to 2001. The main cause is corrosion [1]. Many subsea pipelines in North Sea are aging but required to remain in operation, often beyond their design lifetime. Extend life time means improve integrity of pipelines. Lifetime of pipelines can be extended provided we manage their integrity. This is necessary to keep pipelines operating safely and efficiently and minimize the downtime. However, while the need for integrity management is becoming stronger, there are often implementation difficulties. Many old pipelines were not designed to facilitate today’s monitoring and inspection technology and lack of good quality data. The integrity management may be started by review of operating record. It is however important to recognise that an accurate assessment depends on good quality data collected over the life of the pipeline. Good quality data requires preparation and cleanliness of the pipeline. Unfortunately, old pipelines do not fit these criteria. Most corrosion protection systems are designed based on the pipeline design life. An extension to the design life requires that the remaining life of the anodes and the condition of the anti-corrosion coating be assessed. The reference shown below provides a very good recommended practice for Integrity Management of Subsea Pipeline System. 

 

Reference:

[1] DNV-RP-F116 Integrity Management of Subsea Pipeline System, October 2009

 

Soo Chyi, Lee

Tilak Suresh Kumar's picture

As per DNV-RP-F116, Clause 3.6.2.

The overall life extension methodology is described as:
— define the premise for the extended operation, and identify few threats to the system
— assess the integrity of the system, in other words as far as possible quantify the current condition
— carry out a reassessment of the system based on the available information, current industry practice and available technology
— the reassessment can conclude that the integrity of the system is acceptable up to the end of the extended life, in
which case the process moves on to documentation and implementation. If the integrity is not acceptable, modifications
must be considered, and possibly the feasibility of the entire life extension.

 

Alan J Glennie's picture

Lee,

While the integrity management of pipelines is very important, the objective of an Integrity Management System (IMS) is to maintain the integrity of the system at an acceptable level. The operation of an IMS is not part of a life extension program. However, the data recorded by the IMS will be necessary for the process. From NORSOK U-009 (Ref 1) the life extension process can be summarised in the following steps:

1.       Define the life extension premise

2.       Assess the integrity of the system (current condition)

3.       Re-assess the system (new technologies, current industry practices)

4.       Conclude if life extension is acceptable

The data resulting from the IMS will be used during this process in step 2.

Ref 1: http://www.standard.no/PageFiles/19483/u009u1.pdf 

Monday Michael's picture

All pipelines are designed to strict standards or codes such as DNV, BS PD8010 and ASME. All pipelines have a design lifespan beyond which the pipeline may not be able to fulfill its design functions (i.e reliability and integrity). These pipelines are designed to withstand forces or conditions such as thermal expansion, spanning, upheaval buckling, trapping/entanglement by anchors and nets, etc. To further increase the reliability of the pipelines, they are regularly inspected and maintained; for example various in-line inspection methods (use of Intelligent Pigs) are used to check for loss of coating, cracks, bends, fatigue at the free ends, etc; the condition of the sacrificial anodes, which protects the pipelines against corrosion, is also checked for loss of anodic material.
Most of the design codes are conservative in approach coupled with the fact that a design safety factor is also applied; hence it is possible for the operational lifespan of the pipelines to be extended. However, a risk assessment for each failure mode should be carried out to determine if it is safe for the lifespan of the pipeline to be extended or for the pipeline to be replaced [1]. The risk assessment will amongst other things determine the likelihood of failure which could be in the form of burst, collapse, rupture, etc if the lifespan is extended. Any of these failure events will lead to undesirable consequences such as spillage of hydrocarbon products and contamination of the surrounding sea and subsequently huge fines to the organization, bad publicity as well as loss of goodwill. The cost of these could far outweigh the outright replacement of the pipelines.In addition to safety, the cost of extending the lifespan should be compared with the cost of replacement. It should be pointed out though that the overriding factor in extending the lifespan of the pipeline is safety and not cost! 
From the foregoing, the major challenge with extending the lifespan of a subsea pipeline is reliability and integrity management as pipelines with an extended lifespan are more likely to experience a failure event and consequently lead to undesirable consequences. Therefore, outright replacement is a safe and reliable option.
REFERENCES[1] http://www.penspenintegrity.com/downloads/virtual-library/extend-life-ag...

Kyeyune Joseph's picture

This is one way used by pipeline and field owners to sustain production especially in marginal fields, those close to depletion or those in challenging environments where construction of new pipelines is quite a hard task albeit being uneconomical. The strategy has been applied by Apache to Forties infield pipelines in the North Sea. Safety and risk challenges are involved and may include:
Pipeline integrity arising from its reliability is the biggest challenge. With age catching up on its operation, its reliability decreases basing on its design life. Additionally, pipeline extension comes at a time when flow rates are getting low. This has been realised in the Forties infield pipelines in the North Sea [1]. At flow rates lower than peak values, water entrainment occurs leading to pitting and corrosion especially at 6’Oclock position of the flowline. This can degrade maximum allowable working pressure significantly.


Loss of containment arising from various corrosion defects by carbon dioxide, sour streams as well as isolated localised defects like anchoring defects, impacts and natural hazards. This creates serious safety as well as environmental hazards and can attract penalty form regulators.


Lack of proper documentation regarding design specifications, corrosion monitoring and inhibition, pigging operations if any and risk assessment during past operation period is a serious challenges. This is common were a pipeline has changed ownership a number of times. Planning for operation life extension can then be tricky without such critical information.
Since the venture is cheaper than laying a new pipeline, in order to avert such safety and risky concerns, intelligent pigging can be used to assess pipeline condition. It is a vital tool before setting up a thorough corrosion management plan as well pipeline repair and maintenance strategy for any defects. Additionally, corrosion monitoring and chemical analysis at various spots like bends in flowlines can be done in order to ensure pipeline integrity.

References:
[1] Marsh, j., Teh, T., Ounnas, S. & Richardson, M. 2008, "Corrosion Management For Ageing Pipelines.—Experience From the Forties Field", SPE International Oilfield Corrosion Conference. Society of Petroleum Engineers, Aberdeen, UK, 27 May 2008.SPE 114141


Hudson, B. 2010, "Extending the Life of an Ageing Offshore Facility", Abu Dhabi International Petroleum Exhibition and Conference2010, Society of Petroleum Engineers, Abu Dhabi, UAE, 1-4 November 2010. SPE 138654

c.ejimuda's picture

 

  

I agree with Andrew's points in the use of intelligent pigging tool for pipeline integrity but my only concern is if using it is cost effective for small operators. Also, different pipeline integrity check/repair requires a new pig which will increase the overall cost of repair.

Operators are faced with the challenges of trying to extend the life of aging pipelines in the North Sea. The key point considered by operators is trying to maintain a balance between operational cost and the pipeline performance bearing in mind the safety and environmental implications .i.e. regulations.

Some of the hazards identified from ruptured pipelines include the loss of human lives, destruction of pipe network, existing facilities and huge impact on the environment. However, studies revealed that most of the pipeline failures are as a result of corrosion (Abd Murad, 2009).

There is no special method in extending the life of aging pipelines but with extensive operational experience a comprehensive pipeline integrity method can be determined.

According to Abd Murad, 2009 suggested four key research areas in extending the pipeline integrity. They include:

  • Assessment: This includes assessing the physical features of the pipeline. Considering the integrity and if the pipeline is corroded internally or externally. Some of the methods used for assessments include inline inspection (ILI) and External corrosion direct assessment (Abd Murad, 2009).

 

  • Monitoring: After assessing the integrity on the pipeline, there is a need for constant monitoring to ensure that the result from the assessment conducted is in order and if not, consider re-assessing again until desired result is achieved.

 

  • Mitigation: If the pipeline integrity is in doubt, further actions are required which includes modifications, excavation and repair and general maintenance of the aging pipeline (Abd Murad, 2009).

 

  • Life Extension: This includes using the information gathered during assessment, monitoring and mitigation in extending the life of aging pipeline. The result here will give you a better approach to adopt in carrying out life extension bearing in mind that no two pipelines have the same integrity issues.

 

I will recommend the use of Omnisens which uses the latest fibre optic DITEST technology in extending the life of aging pipeline because this method gives detailed information about the operational abnormality i.e. any changes during pipeline operation, detects the existence of a leak and producing a comprehensive report about the pipeline integrity (Abd Murad, 2009). See more details about the Omnisens on http://www.omnisens.ch/ditest/321-company.php

 

References:

Abd Murad, M. (2009) ‘ The Development of Structural Health Monitoring (SHM) Procedures for Structural Integrity and Maintenance Repair of Offshore Ageing Pipelines' 4th European - American Workshop on Reliability of NDE, 24th - 26th June 2009. BAM - Berlin, Germany [Online] Available at: http://212.8.206.21/article/reliability2009/Inhalt/th2a1.pdf [Accessed 23 October 2012]

Chukwumaijem M Ejimuda

MSC Safety and Reliability Engineering.

Mostafa Tantawi's picture

Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen


The Life
extension of pipelines must pass through a definite process in order to achieve
the proper level of knowledge and thus achieve the required integrity level


Existing
Integrity Assessment and life extension premise should be first identified in
order to know the scope and the battery life of you system; this will help you
to put a boundary of what level of integrity you need for the system. This is
the information gathering phase, where you gather all the information about the
existing system, and assess all the threats and have a look back on the history
of this pipeline and what threats it might gone through in its early age.


Deinyefa S. Ebikeme's picture

The idea of life extension period of pipelines should not be ruled out because it could help organisations make plans for cost (CAPEX) of decommissioning at last.

Pipelines are designed to operate in their active life (ASME), where its reliability is guaranteed and it is advisable to decommission these pipelines after this period. Any life extension program done on it will only extend its life within its total life (life extension = total life - active life) concerning other factors. This is done based on the level of awareness (information available) for such systems during their design phase and active life. During the life extension period, reliability isn't certained, and any threats accompanying pipelines ageing not properly assessed and tackled during integrity management will lead to catastrophy.This will in turn cause the organisation all form of losses that could have been avoided initially. In conclusion, to avoid the latter scenerio from occuring, the organisational safety case should address deeply all risks involved and legislative bodies have a vital role to play in checkmating their activities knowing that eventually all pipelines in Northsea will be decommissioned.

Deinyefa Stephen Ebikeme IBIYF

Ambrose Ssentongo's picture

Well Steven, ,one other positive point of view from the legislative point of view is that in 2011, the industry together with the HSE embarked on an effort to address issues concerned with asset ageing and life extension and part of that effort produced the “Guidance on management of asset ageing and life extension for UKCS oil and gas installations.” One of the critical objectives for the duty holder that the guidance emphasises is major accident prevention and continued safe operations. The guidance recognises existence of relevant legislation related to asset ageing and life extension(ALE) and therefore only serves to among others; complement existing industry legislation that addresses issues such as asset integrity and hydrocarbon release reduction; recognize and bridge duty holder management systems; seek to define what is included in the asset ageing and life extension bracket.

Reference

Guidance on management of UKCS oil and Gas installations, Oil & Gas UK, Issue 1, April 2012.

Robbie Potter's picture

In order to actually extend the service life of a subsea pipeline, the duration of life extension should be specified so that the initial design considerations can be re-assessed for the most current premises. This is defined in Norsok Standard U-009 as re-qualification[1].As alluded to in previous posts, re-qualification can increase the service life as a result of an increase in data quality. An increase in data quality should reduce the error range in the variables, which can be significant. Therefore, the calculated result (service life) can be significantly affected. In most cases, due to the application of conservatism this should result in an increase in the expected service life.Therefore, the cost implications of re-qualification may actually not be as significant as expected; which therefore significantly affects the practicability in terms of cost and benefit.

 

References:

[1]   Standards Norway (2011) NORSOK STANDARD U-009 Life Extension for Subsea Systems. Lysaker, Norway.

 

Robbie PotterMSc Subsea Engineering

Ambrose Ssentongo's picture

Well Robbie, I believe that as part of effort to assure quality of data, an integrity monitoring scheme (part of the Pipeline Integrity Management System) collates all the data from the various sources including condition monitoring, process control and production control to produce an overall review of the pipeline condition (since no one technique can provide sufficient information to give the complete picture of the pipeline’s condition). The collection and analysis of all this data is the major expected deliverable of the pipeline integrity monitoring scheme. To give the true picture of the pipeline condition the integrity monitoring scheme must identify those elements of the pipeline, which are at most risk to potential modes of failure. To achieve this advisably a Risk and Reliability Based Inspection Strategy should be adopted.

Ambrose Ssentongo

Refs:

http://www.penspenintegrity.com/downloads/virtual-library/extend-life-ag...

http://www.penspen.com/Downloads/Papers/Documents/TheStructuralIntegrity...

ikenna_ekekwe's picture

Extending pipeline operating life is a challenge which is not just peculiar to the North Sea alone. It is a challenge facing the worldwide oil and gas industry. The key issues involved in pipeline (internal and external) rehabilitation include inspection and evaluation of the pipeline condition, cathodic and anodic repair, chemical treatment, lining, coating repair and recoating procedure.

However, it will be important to note that the age of a pipeline is not a significant factor in the safety of a pipeline, so far as the pipeline is maintained and inspected correctly. Hence, provided effective integrity management is done, a pipeline can continue to safely operate even after extended life. Therefore, the main challenge is being able to properly determine the true picture of the pipeline condition.

 

Ikenna Ekekwe 

Mostafa Tantawi's picture

 I would Like to illustrate the Pipeline Extension process based on the NORSOK code


Step
1: Initiation of Lifetime process:


The
initiation of the process should start early before the service life of the
pipeline


Step
2: Defining the new Battery life of the system and Assessing the Integrity of
the system


The
battery life of the system is the proposed extended life of the system; i.e.
how many more years the system is required to work


Assessing
the Integrity of the system is gathering all the data required of the system,
that makes it possible to take the appropriate decision


Step3:
Reviewing data, apply modifications


Assessing
all the data and taking the decision if the integrity level is acceptable or
modifications must be implemented to the system


Step4:
Implementing


Implementing
the actions required( modification) to extend the service life of the system


Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

 

michael saiki's picture

 We all have agreed that the life of a pipeline is not more about the design life  or age of the pipelines but about the integrity of the system, how much data we have and know of these pipelines, but the puzzle again is how much can we really know of these pipelines, engineers have evolved Artificial Retrofiting and Impressed current techniques to extend its life, but,  as we move towards deeper and ultra deep waters how much we can know begins to diminish and assupmtions and guess work begin to influence our judgement. So as much as we at a distance say yea its not about age we should also say at a closer look, age cannot be ruled out. Especially when the reservoir has depleted tangibly and we now have large volumes of water produced which means higher corrosion rates.

So if we just say its about what we know then it is obvious that we can't know enough and we cant know completely what the specific details are. Thus we must  approach this technology with enough caution and without allowing the major driver to be Financial gain but value to the entire value Chain

Mostafa Tantawi's picture


Well, that’s a very good point Michael, the
key point here is how much do we know about the pipeline, well here when the
Integrity management really kicks in. If we managed to preserve our integrity
manage system throughout the pipeline life this will definitely help us to know
exactly the state of our pipeline. Pipeline maintenance is also an important
issue (e.g. regular pigging) and all comes into the integrity management
system. Inspection is one of the key measures that gives us an insight of how
our pipeline doing there are several methods of inspection, At a higher Level
we can differentiate them into External Inspection, Internal Inspection, and it
all comes to monitor the external and Internal threats.


Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

Babawale Onagbola's picture

Micheal, while i agree that pipeline life extension strategies and technologies should not be driven only by the anticipated financial gain for the asset owner, correct me if i am worng but I understand your last comment as saying that we dont have enough information on pipeline conditions and characteristics in deeper and utra deeper waters and as such technologies deployed for the life extension of pipelines are unreliable or purely based on assumptions. To start with, the uncertainty of operating at significantly deep depths will always allow for assumptions but the issue here is that these are carefully calculated assumptions. Operators employ the use of fibre optics temperature monitoring and strain monitoring to identify potential hot spots along the lenght of the pipeline and also monitor seabed erosion or displacements that could lead to buckling or flat out failures. My point is, technology is continually evolving and as such the amount of information recoverable from pipelines buried in deep water would soon be as good as onshore pipelines, therefore corrosion mitigation methods such as artificial retrofitting and impressed anodic current application are fairy reliable means of extending the useful life of offshore pipelines. I do not think the age of the pipelines in question are so much a factor as proper inspection and maintenance of the pipelines.

Mostafa Tantawi's picture


One very
important methods of pipeline inspection is pigging, pigging has been used in
the industry for about 85 years, they were first made of wood or straw, and
were mainly used for cleaning, and from the squealing  sound of the “pig”, came the word pigging. They
are now considered a must in the pipeline specifications, all newly built
pipelines must have a pig launcher manifold. However in earlier days around 30
years ago, many old built pipelines (some of them are still in service) don’t
have a pigging structure, these pipelines are really hard to assess and to know
its condition, and some of the companies modified the layout and added pig
launcher just to assess the integrity of the pipelines.


Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

Tilak Suresh Kumar's picture

Adding to the above discussion, I agree with Mostafa Tantawi and others, who has clearly explained the views of pipeline life extension beyond their design life is possible with an effective integrigty management practice. 

In case of North Sea, most of the aging assets are complexly networked with rigid pipeline where design life has been exceeded, the dominant integrity issues are linked to internal and external corrosion. All of these issues can be controlled. However, this requires knowledgeable personnel, effective design, comprehensive testing, and effective corrosion-management systems.

This issue has been strongly argued by in a SPE Paper,"SPE 125060, Offshore Pipeline and Riser Integrity - The Big Issues". This paper is specific to the North sea environment & aging pipelines.

Tilak S.

(51232891) 

michael saiki's picture

We all have brought lots of perspectives to this discussion which is great and I feel more informed rather than just a one sided view. However, I believe that until we critically continue to evaluate and critisize what we already do and know we cannot effectively modify and improve  it. Like Mostafa has said Pigging is a method of  inspection and monitoring of the CP systems today.

Now, I am aware than these pipelines are not only designed against Corrosion, other design criteria are buckling, fatigue, creep and others. So are there also methods evolved to improve the or extend the pipeline resilience against these other criteria. Well if there are what are they.

Imagine if we have a dropped object making contact with the pipeline that has exceeded its design life. how will it respond to impact from dropped objects?

 

Emmanuel Mbata's picture

yes michael, there are. 

Managing the change or transition from the originally anticipated service life to a period of life extension requires special considerations and this includes the pipeline ability to withstand the criteria you mentioned above.

The act of life extension is regulated by HSE (i.e in UKCS). where assets or pipeline in this case is expected to be operated beyond their anticipated service life, duty holders should be able to demonstrate to the regulatory body that the asset has sufficient integrity and remains or is expected to remain fit-for-purpose for the specified life extension period. If not , they will not be granted permission to extend the life of that asset.

 

 

reference: http://www.oilandgasuk.co.uk/cmsfiles/modules/publications/pdfs/HS073.pdf 

Samira Bamdad's picture

As it has been previously stated, pipelines life extension
is normally based on outputs received from a PIG running through the pipeline
that should give the engineers a fairly good understanding of corrosion and
corrosion regimes inside the pipeline.

The point I wanted to mention is, not all the pipelines are
piggable when it gets towards the end of their lives. Once I came across a
short pipeline in North Sea, subject to survey for life extension, that had not
been surveyed for over 15 years and therefore there was no confidence in the
corrosion level inside the pipeline, hence there was a considerable risk associated
with pigging the pipeline. Due to the high risk of pigging, replacing the
pipeline and bearing the cost, was proposed to the operator as a better
solution.

Tilak Suresh Kumar's picture

Drop Object shall also be a part
of integrity, the following shall be considered:

1.)  
Implementing operational practices
before handling any loads that present a dropped object threat to the subsea
pipelines.

2.)  
Operating procedures to include
requirement for regular inspections of “Near Platform” zone of sub-sea
pipelines. Such inspection should be conducted after reported dropped objects incidents
to eliminate any potential of small leak development.

3.)  
Loads that present a dropped
object threat to the existing pipelines should be calculated as part of such
assessment and review of risks with the validity of assumptions related to drop
object and riser ship impact analysis in light of any changes proposed during
the design stage of the project.

Mostafa Tantawi's picture

I totally agree with Samira not all pipelines are piggable, aside from the risk of pigging of the pipeline, Not all of the old pipeline have pigging loops, those pipeline were not designed for pigging, some operators now tend to add a subsea pigging loop by changing a manifold and adding a pigging structure topside, but sometimes especially in deep water the intervention is so expensive. However now days it is almost a convention that pipeline should be designed to be piggable, not only adding pigging loops between pipelines but also design the pipelines not to have bottle necks for pigs, if there is a T connection (in manifolds mainly) this Tee connection should be barred so the pig would not trap in it, also the bend radius, for the bends to be piggable all bends should be long radius bends typically 6D. Also all the valves should be a FB valves which means they have the same diameter of the pipeline. Pigs are so sensitive to change of Diameter however there are some new multi diameter pigs introduced now days by 2 or 3 vendors.

Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

Maxwell Otobo's picture

The fact that most of the pipelines in the North Sea have either reached or are close to the end of their design life is one of the biggest issues faced today. As the pipeline approaches the end of its life span, so is the reservoir coming to the end of its life span as well where the production rate is fast declining.

The question here now is "Is it economically feasible to replace the pipelines?" or "should the lifespan of the pipeline be extended?"

Here, the pipeline engineers, safety engineers and production engineers have a major role to play which will contribute to the safety of the environment. The pipelines need to be critically assessed as well as the production life of the reservoir. If the pipelines show any risk of failure whatsoever, then they need to be replaced regardless of the cost involved because the money spent in replacing it will be nothing compared to the money that will be spent in cleaning up if any spill occurs as a result of the pipeline failure and also considering the marine/aquatic life.

Also as mentioned in a few posts above, not all pipelines can be pigged, in otherwords, life extension may seem impossible. The pipelines should be replaced depending on its state and integrity and the life of the field can also be extended on the other hand by EOR methods

Samira Bamdad's picture

To extend the life of a subsea asset, such as pipeline, all
the failure modes should be precisely identified and studied. Depending on the location
along the pipeline, the failure modes might varies as different sections are
exposed to different hazards with their associated frequency and consequence. For
example bends are more prone to erosion than straight sections of pipelines or
hot ends of the pipelines are more exposed to material degradation than the
cold end.

Hazard identification analysis techniques shall be adopted
to identify all potential hazards affecting the integrity, operability and serviceability
of a pipeline. Risk based inspection should be planned based on the failure
modes and mechanisms. The better the inspection data quality, the smaller the
associated uncertainties and hence the smaller risk will be achieved. 

Ambrose Ssentongo's picture

I agree with you Samira, especially in regards to adopting Risk Based Inspection (RBI) for risk analysis. RBI extends the operating life of equipment and piping, safely and cost effectively and achieves three major and important  goals that is; provide capability to define and quantify risk associated with process failures and therefore enable measures to be managed according to the most critical elements of the pipeline; allow management to review safety, environmental and business-interruption risks in an integrated, cost effective manner; and reduce the likelihood and consequence of failure by allocating resources to high risk parts. RBI provides a logical, documented, repeatable methodology for determining the optimum combination of inspection frequencies and inspection scopes. Its objective is to ensure focus of inspection to areas with high risk, while inspection in areas with low risk will be reduced or excluded from the normal inspection program and therefore result in significant inspection and maintenance cost reduction.

Ambrose Ssentongo

Ambrose Ssentongo's picture

In addition to what Tilak writes a few posts above, in trying to identify all failure modes and mechanisms, the location over the length of the pipe for which exposure to different hazards matters. Taking an example of dropped objects on which Tilak enlightens, these may be more likely adjacent to platforms than at mid line or another example is, bends may be more vulnerable to erosion than straight sections of the pipeline. Having in mind which sections are susceptible to which risks is helpful so to assist the HAZID and associated risk on integrity, the pipeline is divided into sections; Valves and fittings; Riser and Spool pieces; Safety zone; Mid-line; Shore approach. The associated risk is calculated using the concept of probability of failure and consequences  of the event so that then areas with high risk can be identified and critically analysed.

Refs

Extending the life of ageing pipelines by Paul A Henderson, Phil Hopkins,  and Andrew Cosham of Andrew Palmer and Associates, published 2001

Life Extension issues for Ageing Offshore installations, by A. Stacey HSE London, M. Birkinshaw HSE London, J.V Sharp Cranfield University Cranfield, 2008

Oil and Gas UK Guidance on management of Ageing and Life extension of UKCS Oil and Gas installations Issue 1, 2012 

Ambrose Ssentongo

chukwuemeka uzukwu's picture


Many of our offshore pipelines are
now either showing signs of age (e.g. corrosion), or are
approaching the end of their
design life. This problem can be addressed by using a variety

of engineering methods to predict
the remaining safe life of the pipelines. These methods
include both simple and complex
fitness for purpose analyses, but must consider other

aspects of the care of an ageing
asset, e.g. inspection and repair.
Offshore pipelines are expected to
operate safely and securely in a variety of hostile environments. At their
start of life, given they are designed and constructed to recognised

standards, their ‘day 1’ safety
and security will be excellent. However, as the pipelines age,
they will inevitably deteriorate
or become defective, and hence an Operator must be able to

both assess the significance of
this damage, and ensure that the pipelines do not fail as


they age.


 


EXTENDING LIFE
THROUGH BASELINE PLANNING AND SURVEYS


An Operator with an ageing asset
who wants to determine extended life beyond initial
design limits and ensure future
integrity must first of all conduct some type of baseline

survey against which the
performance of the pipeline can be judged. This may be a smart pig run, a
review of operating records, etc. It is however important to recognise that an
accurate assessment depends on
good quality data collected over the life of the pipeline.

Good quality data requires
preparation and cleanliness of the pipeline. API 1160 again gives
guidance, and recent proposed
legislation by the Railroad Commission of Texas is also informative:

 


RISK AND
RELIABILITY BASED INSPECTION STRATEGY


The aim of this strategy is to
answer the questions of what, where, how and when to
examine or test pipelines in order
to maintain the integrity of the pipeline.

To achieve this strategy a
structured approach must be used to identify the hazards that


threaten the integrity of the
pipeline, then analyse the risks associated with those hazards
and identify the inspection
techniques and tools to report on those hazards. Those hazards

that are more onerous can be
further analysed using reliability techniques.


 


CONCLUSIONS


We now have methods and
technologies to:


- assess risk of failure of ageing
pipelines


- identify and apply appropriate
inspection techniques


- set economic inspection intervals
to prevent failures


- limit risks to an acceptable level


- quantify the present integrity


- predict the future integrity, with
continued engineering effort


Operators can now safely extend
the life of ageing pipelines by having a planned and
structured approach to managing
the integrity of these pipelines to ensure continued safe

and efficient transportation for
hydrocarbons.

http://www04.abb.com/global/seitp/seitp202.nsf/0/001a63cdd274a7d5c12577d60026c217/$file/ADIPEC+paper+-+Extending+the+life+of+an+ageing+offshore+facility.pdf

http://www.stoprust.com/17extendingpipelinelife.htm 


Samira Bamdad's picture

Pigging and pipeline survey is one of the first steps prior
to making any decision regarding a pipeline life extension. However there are
lots of challenges associated with the pigging process that may result in
losing resources rather than gaining any.

One of the observations that should be done prior to pigging
is that the pig passage should be open to let the pig pass through the
pipeline. There was a case of a buried pipe-in-pipe that pig got lost in the
line as it was stuck behind a hydrate blockage and couldn’t be located. It took
lots of effort, cost and time to remove the hydrate blockage by means of water
and MEG flushing and impose extra expenses than what had planned to the
project, such that at some point the operator considered installing a new
pipeline instead!

Abdulazeez Bello's picture

Extending the design life of a pipeline poses a number of challenges,
one of which is the uncertainty in the present condition of the pipeline. Most
companies tend to focus on the major type of pipeline defect which can be
categorized into three classes: 
Operating related metal loss (corrosion), sharp-edged material flaws
with high stress concentration and blunt deformations of the pipeline roundness
which are normally done through physical or intelligent pigging.
 Defects associated with geometry (reduced
fatigue resistance due to stress concentration) and material properties (flaw
size) are not normally investigated / captured or when done the calculations or
methodologies used are far from accurate and this normally affects the reliability
of the risk assessments. Another challenge faced with ageing pipeline
Inspection is the archiving of data from in-line Inspection as the system often
fall short of the desired compatibility and accessibility of Inspection data.

Reference
Reber K., Schmid W., (2007) ’what are the real challenges in pipeline Inspection’
Pipeline technology Conference [Online] .Available at http://www.pipeline-conference.com/sites/default/files/papers/3.3%20Reber.pdf
[Accessed on   10 November, 2012]

farman oladi's picture

Increased usage of pipelines as a safe and usually cheapest method for transferring energy, like all other engineering equipments can, do and fail. Consequently pipelines should be maintained by means that are cost effective and prevent failure. Routine inspection and monitor through direct and indirect methods are already in practice. One of these methods is inline inspection of transmission pipelines. An instrument called "Pig" has been in usage more than 20 years.

Newer generation of " Smart " and "intelligent " pigs has been used to measure and collect pipeline data which includes Route Surveying , Leak Detection ,Loss of Coating , Detection and Sizing of Cracks , Metal Loss Defects and many other informative data. Since an intelligent Pig can also be operated in an operating pipeline, therefore there is no need to decommission the pipe line. These Pigs can operate in the media where Liquid or Gas are transferred.

These inspections will extend the life expectancy of the pipelines and will minimize unexpected and costly damages both to pipelines and installations. The method has been increasingly in use specially in underwater and underground pipelines where access is restricted.

Ref.: Penespen Integrity Library

http://www.penspenintegrity.com/downloads/virtual-library/pipeline-internal-inspection.pdf

Samira Bamdad's picture

Towards the end of a field life there might be gradual
changes in operational condition of the field. The level of produced water
would increase gradually that might have not been considered in the first
design since it had been out of the pipelines initial life span. Ignoring the
reassessing the new condition for the pipeline can be a serious source of
failure in a variety of aspects and increase the risk of life extension.

Higher produced water will result in higher temperature
profile and therefore higher axial force in the pipe wall thicknesses and
consequently there will be a higher risk of upheaval buckling for the buried
pipelines. Also, higher corrosion is expected due to increased water in the
pipeline content and it may cause extra plasticity in the pipeline at the
location of imperfection due to the combination of axial force and bending. This
should be accurately studied as it may result in a failure.

Trevor Strawbridge's picture

Pipeline Integrity management is coming more into the forefront these days even with newbuild projects. The schemes often include inteligent pigging and other clever tools available to measure the pipeline  (corrossion monitors, sand monitors etc) However, I am interested to see if Project teams reasearch the proposed corrosion inhibitors thoroughly before introducing them in the pipeline. There is a general concensous that Preferential Weld Corrosion is no issue providing the welding consumabe has a nickel content less than 1%. This is not the case as other elements including the base material (linepipe material) can also come into the equation. Operators need to be careful with their coice of corrosion inhibitors or the Pipeline integrity scheme will not prevent pipelines failing prematurely. The best mitigation is to perform flow loop testing on a represenative test weld using the corosion inhibitor to establish the potential preferences between weld and line pipe. Some further reading below

http://www.twi.co.uk/technical-knowledge/published-papers/preferential-weld-corrosion-effects-of-weldment-microstructure-and-composition-april-2005/

http://www.twi.co.uk/technical-knowledge/faqs/material-faqs/faq-what-are-the-causes-of-and-solutions-to-preferential-weld-corrosion-in-electric-resistance-welded-steel-pipe/

 Trevor

Samira Bamdad's picture

As Trevor has highlighted, corrosion inhibitors are one of
the interesting subjects that comes to the window as part of a life extension
study.

Towards the end of a field life, produced water content may
increase as a result of water injection due to life extension. The consequence
of having higher produced water inside the pipeline is higher temperature and consequently,
a different corrosion regime. To extend such pipeline life, a corrosion
inhibitor such as MEG, may needed to be added to the pipeline content. One of
the challenges is that not always the infra-structures are available to provide
the corrosion inhibitor or it may impose extra cost to the project.

Mostafa Tantawi's picture


In
addition to what Samira said, indeed pigging is one of the most important
maintenance and inspection methods in pipeline operation, that’s why pigging
schedules should be strictly adhered to; Reluctance in carrying out pigging
schedules can result in over formation of (wax, hydrates and scale). A
progressive pigging approach should be carried out when the pipeline hasn't
been recently pigged, this is a gentle pigging approach meaning that it starts
with Foam pigs, foam pigs are very flexible and can hardly stuck into any of
the previous formations, they have the tendency to elongate, however sometimes
foam pigs ( due its low weight and lack of support to pipeline walls) can disappear
within the pipeline, especially before the pig receiver, a carcass is installed
before the any wye to hold the pig in case it went to the wrong direction.


Pigs
should be properly designed to adhere to pipeline structure and conditions. Moreover
the pipeline should be properly designed for pigging (barred tees, 5D bends and
full bore valves)


Mostafa
Tantawi Masters of Subsea Engineering, University of Aberdeen

 

ROHIT NAIR's picture

I
agree to your point about the need for routine pigging but the problem is that
old pipelines were not designed for pigging as there are no access points and
also there are variable diameters of the pipeline. But advancement in technology
has paved way for far more advanced techniques like using a pipecrawler or a
Robotic Survey system generation 2.

 

ROBOTIC
SURVEY SYSTEM GENERATION 2:
(Rosen Group )

It is one of
the newest technologies built for the inspection of hydrocarbon pipelines. It
can be equipped with a high-resolution ultrasonic testing inspection unit. It
is a versatile system. It can be used for detecting various kinds of defects
like corrosion, mechanical or welding. It has the capacity to squeeze through
tight bends as well as high reduction capacity. It can pass the variable
diametric pipelines and also it can climb vertically because of its high
driving force. It can work in both directions - in the direction of product
flow or against the direction of product flow. The main advantage it has over
the pipeline crawler is that it has an onboard power source and thus tethering
is not required so continuous inspections can be carried out without the hassle
of the tether being extended too much

Reference

http://www.roseninspection.net/RosenInternet/InspectionServices/RoboticInspection/RSS/.

 

Rohit C Nair
Subsea Engineering
Student id- 51231896

Keqin Chen's picture

When the pipelines are approaching their design life or showing their aging
problems such as corrosion, it is not easy to decide the next measure. Should
we abandon it or continue to use it? Is it safe to continue and how can we do
to prolong the life of them?

Pipeline Integrity Management (PIM) is the inevitable
process to ensure a pipeline is safe and secure for the efficient
transportation of fluid. Its aim is to protect the investment, normal operation
and environment. By optimizing available resources, PIM involves all aspects in
the lifecycle of pipelines, i.e. design, management, inspection and maintenance
etc. Several important issues about PIM are listed below:

One of the important premises of PIM for an
operator with an ageing asset is that enough good quality data and related
survey about the performance of the pipeline has to be clarified firstly. The risk
based assessment and all failure modes and mechanisms of the pipeline should be
analyzed.

At the same time, PIM should comply with
the code such as ASME B31.8, API 1160, BS PD 8010,
DNV RP 116 and CEN 15174, and API 1160, refer to American
Petroleum Institute, “Managing System Integrity for Hazardous Liquid Pipelines”.

The following appropriate methods can be
done as the assessment of pipeline integrity:

 

  • Pressure test: to ensure the
    line can be safe to operate at the MOP (Maximum Operating Pressure) and below
  • In-line inspection: using “smart
    pigs” to assess the conditions of pipes in internal and external corrosion,
    crack-like defects, and deformation.
  •  ‘Direct assessment’: internal
    corrosion (ICDA), external corrosion (ECDA), and stress corrosion cracking
    (SCCDA).
  • Other new technology

 

 References:

 

1.      
Extending the Life of Ageing Pipelines, www.penspenintegrity.com

2.      
PIPELINE INTEGRITY MANAGEMENT,EXTERNAL CORROSION DIRECT ASSESSMENT, new.api.org

 

Keqin Chen

Msc of Oil and Gas Engineering

ID:51126368

Mostafa Tantawi's picture

The subsea pipeline incidents in the north sea is increasing with time, this appears clearly in the comparison between Parloc 2001 and Parloc 1996 Reports. In 1996 Report there were 212 (79 leaked) while in 2001 report there were 248 incidents (96 leaked). The main reason behind the increase of pipelines is corrosion, as in 1996 "35" incidents were caused by corrosion while in 2001 "49" incidents, this shows clearly that the effect of age appears in corrosion. The other cause of leakage was because of the dropped objects in both reports, also giving a hint that dropped objects is a serious safety issue that should be taken into account.


Reference

MACDONALD, M. (2003) PARLOC: 2001, The Updated Loss of
Containment Data for Offshore Pipelines. Energy
Institute, London
.

 

Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

Samira Bamdad's picture

Quite understandably, corrosion should be considered as a major cause for loss of integrity and leak. However, citing dropped object impact as another major cause of leak incidents is very interesting. I am very interested to know the actual number of incidents caused by dropped object impact.
The dropped object hit probabilities can be calculated using the methodology given in the DNV RP F107 and values easily found in the order of 10-3 or 10-4 per annum. Further to the relatively low probability, pipelines (especially if concrete coated) are quite robust in absorbing the impact energy. The eventuality of loss of containment as a result of dropped object impact may be fairly remote.

Sineenat Kruennumjai's picture

Topic 30; Can we properly extend the lives of pipelines and still optimize the safety case?
 
 The operators may want to extend the life of the pipeline beyond its original planned life. This situation occurs quite often in the oil and gas industry, for example the life time of well is longer than anticipated, or the increased in the production from new satellite fields and they have to be tied back to pipeline. The extension of pipelines can be safely achieved by using the methods of safety analysis or managing the integrity of ageing pipelines. This method can prove evidence that pipelines can be operating safety in their later life. There are six steps for managing the integrity of the ageing pipelines to ensure that they can safely use for transport hydrocarbons in their later life. 
 1.Assess the risk of failure of existing pipelines  
 2.Choose the inspection techniques for inspect pipelines (such as, intelligent pig)
 3.Set the intervals of inspection in order to prevent failures
 4.Limit hazard to an acceptable level
 5.Evaluate the present integrity
 6.Use the present integrity to predict the future integrity
 So, in my point of view if the operator can follow such approaches,  the extension life of pipelines can be safely done.

Sources; http://corrosion-doctors.org/Pipeline/Lifeextension.htm
http://www.penspenintegrity.com/downloads/virtual-library/extend-life-aging-pipelines.pdf

Posted By
Sineenat Kruennumjai
ID  51126536

Neil Fraser James Carr's picture

I do not understand how the extension of pipelines life optimises the safety case?

The safety case is an evolving document for all operators and risks must be assessed and dealt with throughout the installations existence however i feel that that the key safety factor here is the responsibility of the duty holder to maintain pipeline integrity utilising HSE guidance like KP4, the inclusion of goal setting documentation, inspection and asset integrity management.

Inspection data is only as good as it is interpreted and alll 6 of your approached are fair although none of them deal with the real issue, if the integrity falls below a certain level does what is acceptable not just move with it.

 

References

[1] http://www.hse.gov.uk/offshore/ageing/kp4-strategy.pdf(Accessed 26/11/2012)

 

Kelvin Arazu's picture

The consequences of using an old pipeline includes:

Loss of containment since the pipeline has past its design life spam.

Upheaval buckling and the pipe become susceptible to rupture because the pipe cannot accommodate the high temperature and pressure associated with hydrocarbon fluid.

Mitigation: to extending the life span of pipeline all the critical failure modes should be assessed given these factors,  

Defect severity:  Example location, depth, length, orientation

Financial/strategic, hence value of pipeline

Threat to environment & public relations

Regulatory/legal/insurance considerations

Failure/further failures consequences

I will suggest that for an operators to safely extend the life of ageing pipelines, the SIL of the aging pipeline should be raised by having a planned and structured approach to managing the integrity of these pipelines to ensure continued safe and efficient transportation for hydrocarbons.

Kevin K. Waweru's picture

As my colleagues have already expounded, the life extension of ageing pipeline assets is very much dependent on their integrity management during operation. The use of techniques such as intelligent PIG’s and corrosion inhibitors among others goes a long way in further reducing failure risks to ALARP.

In addition to quality integrity management, an operator’s confidence in their ageing pipeline assets will undoubtedly be enhanced by a critical understanding of the operating conditions to which the ageing pipelines are exposed. As Samira rightly points out, a depleting reservoir produces higher levels of water that accelerate corrosion rates. A fundamental understanding of such an operating environment is required in order to better manage the integrity of ageing assets.

High quality integrity management data has a direct impact on the degree of confidence an operator will have when seeking licence extensions for ageing assets subject to a critical understanding of their operating environment. The condition of the other components forming the systems of which the ageing pipelines are a part of is also paramount. Control valves, pressure vessels and power systems must also be monitored to ensure optimum operating conditions prevail at all times.

Kevin K. Waweru

MSc Oil & Gas Engineering

sreehariprabhu's picture

As my friends commented, life of a pipeline is one of the major factor to be considered. A fault in a pipeline may be due to corrosion, wear, creep, variaton in pressure, physical aging, buckling etc. The probability of these to happen may increase as the pipeline age increase. So it is important to measure and inspect the pipeline and make sure no defects occur. A pipeline leak may lead to the release of hydrocarbons in the sea which will affect the environment, marine life and also will lead to a bad face for the oil industry.

The integrity of pipelines must be made sure by regular inspections. On each inspection, it must be made sure that the pipeline integrity is fine till the next time of inspection. The methods as discussed earlier like intelligent pigging tool can detect the corrosion in a pipeline, cracks and also the weld defects. Thus by having a risk assessment on the old pipelines and by carrying out inspections will prevent from having an unfortunate incident in the North sea due to aging pipelines and hence we can extend the life of these pipelines.

Sreehari Ramachandra Prabhu

charlesggeorge's picture

 

 

Hi,

As we know one of the one of
the harsh environments in the world is the North Sea. It is very difficult for
inspection as well as the maintenance of the pipe line in such condition. Most
common method used is either the diver goes in the water or a
remotely operated vehicle (ROV). Mostly the risk challenge happen when the
driver is goes for the inspection of the pipeline under the sea. So that using
ROV will be a best option which will reduce risk and also can inspect the pipe
lines in sever conditions in the sea. Currently, Subsea pipeline inspections
have improved over the years but the vast majority of pipelines once laid
are never inspected unless something goes wrong. Regular maintenance and
inspections of pipelines are essential as a preventative measure which will
avoid oil spill which will affect the environment as well as the ecosystem in
the sea.

Charles George

Msc in Oil and Gas Engg

 

 

Joan.C.Isichei's picture

The need for extending the life of a pipeline beyond its original planned life, is commonplace in the oil and gas industry, owing to the following reasons[1];

Increased reserves from well tie-in.

Unexpected hike in oil and gas reserves. 

Working on extending the life of a pipeline gives rise to some safety and risk issues/challenges. Pipeline related risks are defined as the likelihood of a person becoming a casualty, as a result of a pipeline failure. 


RISK = FAILURE FREQUENCY  x  FAILURE CONSEQUENCES


The risk to the population living in the vicinity of a pipeline is defined in terms of both individual and societal risk:


1. Individual risk is defined as the risk of a person at a particular location becoming a casualty.

2. Societal risk is defined as the relationship between the frequency of an incident and the number of casualties that may result.


In most oil and gas facilities, the failures associated with work on pipeline life extension which are of uttermost concern, are those resulting in the rupture of said pipelines. Based on this, Some risk/safety challenges that arise from working on pipeline life extension include but are not limited to the following[2];


1. Rupturing and therefore, loss of containment of pipeline product which in turn leads to a loss in throughput revenue. 

2. Loss of containment or leakage can also lead to an explosion,

3. risk of personal injury or death and, 

4. pollution 

5. Vandalism and sabotage (on public pipeline rehabilitation sites).


Although risks can never be entirely eliminated, a thorough risk assessment should be carried out prior to pipeline life extension in order to mitigate the aforementioned risks.




Sources

1. Pipeline Risk Management Manual: Ideas, Techniques, and Resources By W. Kent Muhlbauer.

2. TOTAL PIPELINE INTEGRITY by D G Jones, PII Group Limited

ROHIT NAIR's picture

I agree to your views about the ROV inspection mechanisms being
safer as it doesn’t involve the diver being employed and hence no safety
concerns. But the point is how can you increase the reliability of aged
pipelines by using ROV’s???? How can you find out the internal damage the pipe
is subjected to??? If u think intelligent pigging is an option then I am sorry
to say most of the old pipelines are unpiggable because:

·     
No access points

·     
Varying pipeline dimensions

·     
Flow limitations

·     
Unfavourable pipeline layout.

So how can you determine the reliability

ROHIT NAIR's picture

For extending the life of a
pipeline, it is necessary to have relevant datas associated with the pipeline.
For that, effective inspection of the pipelines has to be carried out for
determining what damages and deteriorations the pipeline has undergone since it
has been laid on the seabed. With old pipelines gathering this important datas
has always been a problem. But with development of technology, it has become
easy. The two important technological innovations which help us establish the
reliability of the pipelines are:

·      
Pipeline crawlers

·      
Robotic Survey system generation 2

 

These can easily pass through
variable diametric pipes and are equipped with the most advanced ultrasonic
inspection devices.

Rohit C Nair
Subsea Engineering
Student id- 51231896

ROHIT NAIR's picture

I agree to your views about the reliability being dependent on the information we collect during inspection of aged pipelines. But it is a very difficult process. How can you determine the internal corrosion the pipeline is subjected to. I would like to draw your attention towards the technological advancement in the inspection of pipelines.

PIPELINE CRAWLER:

A new type of tethered
intervention crawler has been developed which can be used for inspection of
pipelines considered to be unpiggable. They are unique in the sense that they
have single point of entry and recovery. They can also be used to evaluate
pipelines with variable dimensions as they have multi diameter tools. It
consists of a brush drive unit that is powered by an electric linear drive.
Pipeline crawlers are also able to generate multi tonne pulling force because
of the coupling of the suspension system with the brush drive. It has
bi-directional function which means it can operate in the direction of flow of
the product or in the direction opposite to the product flow. This is possible
because of the onboard power source and high levels of grip present on the bush
drive technology. The umbilical tether on the pipeline crawler helps handle the
motion, control and the data obtained by the crawler. It can run at a speed on
the scale of 0-900 meters per hour. It can also operate in low and medium
pressure environments.

            Removal of deposits inside the pipeline surface can also
be removed by controlling the speed and flow bypass capacities of the tool on
board the crawler. Thus the production unit need not be stopped for cleaning
operations. Once the pipelines are clean, the conventional inspection
techniques like magnetic flux leakage (MFL) can be carried out by fitting the
modular MFL packaged on the pipeline crawler.

Reference:

PIPE
CRAWLERS, . Available: www.pipecrawlers.com/pipeline-crawler-english.pdf.

 

Rohit C Nair
Subsea Engineering
Student id- 51231896

Samira Bamdad's picture

Risk associated with the life expansion may vary from case
to case. One of the common life extension cases is when a new field ties back
to an old flowline. While the old and new fields’ condition is fairly close,
the life extension study faces less risks compare to the case that the field pressure
or content chemical or any other parameter is different from the new field to
the old one; it turns the life extension case to be a very complicated
case.   Comprehensive studies and analyses should be performed
to assure that the risks are in control and the old pipeline situation is
compatible with the new chemical operational conditions.

William J. Wilson's picture

Samira, you mentioned comprehensive studies and analysis should be preformed to ensure that the old pipelines are compatible with the new chemical operations.  This is true and I believe that the industry does already carry out these studies during their new design stage.  The important factors which are raised by extending the life of a pipeline and introducing a new chemical operation are:
1. New hydro dynamics and corresponding turbulence of multiphase flow will influence the internal corrosion rate.
2. Effect of “water cut” (CO2 from water coming into contact with the steel wall of the pipe) increases corrosion
3. Hydrogen sulphide could be present in the new operation (especially if the pipe is re-located to a new well since 40% of all wells contain hydrogen sulphide) increasing corrosion.
To mitigate these issues would be a simple case of assessing the pipes original characteristics against its new/re-located purpose and by introducing passivating, cathodic, prescriptive, volatile or organic inhibitors) could reduce the corrosion impact of the new fluid being transported.

Reference: (40%) Y.Bai and Q. Bai Subsea Engineering Handbook.

William Wilson
MSc Subsea Engineering

VICTOR ETIM's picture


The reservoir fluid composition and external water
parameters like temperature, geological terrain and tidal action are major
hazards that must be address and mitigated againgst while considering the structural design phase of offshore
exploration. However valuable points have been raised by my colleagues but I will like to add the following points;

Potential hazards on hydrocarbon subsea pipelines could include: hydrate formation, wax deposition,
vortex induced vibrations, buckling and corrosion. A critical flow assurance
analysis using proven engineering simulating software for comprehensive structural
integrity analysis and retrofitting is always helpful in determining the
reliability of pipelines based on the required thermal performance, hydraulic strength
and safety of the environment.


As pointed out by Samirah, comprehensive compatibility
studies, HAZIDs and HAZOPs are essential for successful tieback operations to ensure reliability and safety.


VICTOR ITA
ETIM


51126236.
OGE.



adavis's picture

Though you lose some flow capacity, lining aging pipeline with high density polyethylene or other polymers seems to be an attractive solution for some applications. There are numerous companies who have devised ingenious solutions to place plastic liners inside aging pipe lines.  Some designs simply pull in a flexible pipe with an outer diameter which is slightly smaller than the inner diameter of the original pipe.  Other designs involve pulling in a polymer pipe with a temporarily reduced diameter which is “swaged” onto the inner diameter of the pipe by using a high temperature high pressure process.  Both options seem to promise extended life with minimal cost and risk.

William J. Wilson's picture

Adavis, Lining aging pipes seems like a novel solution to this problem and with my previous blog about reducing internal corrosion for introduction of a new chemical operations I think we have covered most of the angles related to the internal issues of old pipelines.  However, what about externally? How would you prevent further corrosion to the external pipelines?

There seems to be many aging metallic pipes in place which have many different types of external coatings as well as cathodic protection.  However, even these coatings are becoming old.  How can anyone be sure that these old pipe coatings isolate the external surface of the piping from the environment and prevent water ingress to the actual metal pipe?  I believe that more frequent inspections of pipelines will not improve longevity of the pipelines but it is a method of reducing the consequences of failure resulting in a safer system. Is there a simpler, cheaper, and safer solution to the external pipe corrosion and coating longevity  issue?

William Wilson
MSc Subsea Engineering

Kyle McFarlane's picture

In the oil and gas sector it is likely that assets will only be decommissioned provided the fields and wells they are working on are no longer financially viable or if the assets condition has reached too low a level to be worth maintaining.
The majority of assets with undergo life extension programmes in order to increase their design life and therefore ensure that production continues for as long as possible, at as low a price as possible whilst adhering to safety regulations.
In 2010 the HSE launched Key Programme 4 which is the "age and life extension programme" the fact that this programme has been launched shows the extent of the assets likely to be extended.
The decommissioned assets will provide a valuable insight to the condition of offshore plant and equipment and hopefully how these can be better managed to ensure that assets can be designed to last longer.

 

I think it is important to look at life extension as an oppurtunity to consider and discover a system, such as a pipelines condition, its suitability to have its design life extended or whether it should be decomissioned.  

Source
http://www.hse.gov.uk/offshore/ageing.htm

amir masoud bayat's picture

As my firends mentioned above, I assume that at first we needto know: Do we really need to extend the lifetime of pipelines? Which factors threat this issue?

There are several factors which lead to extend the life of a pipeline above its original lifespan. This may be because of unexpectedly more capacity from Oil and Gas fields or increase the reserves from new wells which need to be connected into pipeline. Thus the plan should be changed to extend the life of the pipeline in order to work in the remaining life of the field.

The key element for extending the lifespan of the pipeline is to determine the corrosion rate in the pipeline and using this reliable value to predict the degradation process in the future to understand what remedial action should be taken.

There are the other challenges in extending the life of pipelines; Review the date of pipeline such as past and present operation condition and forecast it for the future, inspection data available and identification all mechanisms and failure modes and recognize all events that could lead to failure.

References:

  http://corrosion-doctors.org/Pipeline/Lifeextension.htm

www.penspen.com

 

Catriona Ogg's picture

A couple of my classmates have mentioned anode retrofits as a means of extending the life of subsea pipelines.  I would like to expand on this process in a little more detail to highlight its validity.  One of the large commercial suppliers of retrofit anodes is Deepwater, who supply the RetroClampTM. These are clamps which are designed to easily click into place around a pipeline. They have new sacrificial anodes attached to the inside, which are electrically connected to the pipe once the clamp is secured in place.  These clamps can be attached individually or as an array for large-scale anode retrofit programs. RetroClamps are a fast, cost effective and practical means of conducting an anode retrofit. They can be installed used ROVs for deep sea networks and can also come fitted with current readers which can verify if the current requirements are being met by the system.

More information can be found here: http://www.stoprust.com/retro-clamp.htm 


I
can think of just one other disaster in the oil and gas industry that would be
as devastating to the environment as leakage of an active oil and gas subsea
pipeline, and that is a blow out during drilling or well work over on an
oil/gas well.


The
characteristics they both share is not just the type of fluid they release to
the atmosphere both also the fact that they are difficult to contain and leave
long footprint on the ecosystem.


The
issue of extending the life of subsea pipeline has the potential of destroying
the somewhat good record of subsea pipeline operation so far and must be given
careful considerations. The reason for this conclusion is that presently there
are no reliable methods for accessing the state/condition of subsea pipelines
and since this is the case, how can the adequate refurbishment measures be
implemented?



Life extension requires to extension of the period of
operation beyond its design life or intended use. The greatest challenge is
ensuring that the pipeline meet legal requirements. Assessing the pipelines meet
criteria is critical. The variance of standards of the pipeline from design
safety standards, the quality of the design and the quality of maintenance will
all impact on the pipeline’s current physical condition. The physical condition
of the pipeline will deteriorate over time from factors such as wear and
corrosion. Meeting legal requirements is one aspect as the safety standards
have become stricter overtime and sections of pipeline will not meet the
current criteria. Other sections of pipeline will have deteriorated and will not
the required safety requirements to have their life extension.  A good integrity management system will is
critical to ensure that the condition of  pipeline is remains it’s integrity to remain
to standards and does not fail.


James Parry
MSc Subsea Engineering

Alan J Glennie's picture

Much has been said previously about the main threat to subsea pipelines as being corrosion but not much has been said about the management of this. The pipeline are mainly carbon steel and are subject to corrosion on the inside and outside. To mitigate the external corrosion the pipeline is coated in an anti-corrosion coating, typically a plastic coating called 3LPP to prevent contact with the surrounding water.

To mitigate against damage to this coating and non-coated parts of the line a cathodic protection system is designed using anodes at set distances along the line. To mitigate the internal corrosion the operator can pump corrosion inhibitor chemicals into the line to reduce the effect but the corrosion cannot always be prevented e.g. erosion due to the flow. It is therefore required to ensure a corrosion allowance is built into the design of the line to cover the line over its design life. This allowance is at least 3mm and is added to the wall thickness required for pressure containment.

Most of the existing pipelines less than 14” in the UKCS were installed using the reeled methodology which involves spooling the pipe onto a large reel (15-18m radius hub) then installed into position on the sea bed. This installation methodology normally requires the pipe wall thickness to be increased in order to allow this methodology to be used. This results in a much thicker walled pipe and effectively a larger corrosion allowance. This could be justification for extending the life of an existing line past its design life.

Note: If the increase in wall thickness required for reeling is much more than that for pressure containment, there is an option to use a steel with less strength (and corrosion resistance) which could counter the additional wall thickness. Therefore the grade of steel must be taken into consideration. 

Samira Bamdad's picture

I’d like to add a couple of points to Alan’s argument regarding the designing of pipelines. It should be noted that flowlines subject to life expansion today, have been designed years ago, based on the codes and standards available at that time. However, the offshore technology is a very live science and the codes and standards are being updated very often to use the best of steel capacities.

Increasing the level of allowable plasticity and lower safety factors required by codes have resulted in smaller minimum wall thickness required and therefore the remaining thickness in the pipe after years of operation might be still acceptable to tolerate the pressure, referring to the new version of the codes. 

Alan J Glennie's picture

When designing a pipeline, the design life is usually dictated by the client requirements and is 25 years. Flow assurance data such as hydrocarbon composition, reservoir pressure and temperature is used to size the line and select the material. The pipe line is then designed for pressure containment, corrosion allowance, CP protection and installation loads, installed then commissioned during the CAPEX phase.

During the OPEX phase the pipeline is operated, inspected and maintained. This inspection and maintenance will be covered by ROV visual inspection of the coating for damage, anodes for depletion, identification of freespans along line and so on. In addition, if possible, wall thickness checks may be undertaken using intelligent PIGs. This makes up part of the asset integrity plan along with records of the chemical corrosion inhibitors used. If the operating company identifies that the life of the pipeline (design life) must be extended (to its new Service life) it is the responsibility of that company to demonstrate to Department of Energy and Climate Change (DECC) who review the justification and authorise the extension.

To do this the condition of the line should be determined. If possible, an intelligent PIG can be run up the line and the wall thickness measured. If this is not possible, samples of the hydrocarbon should be analysed and calculation of the corrosion made. A re-assessment of the reservoir data will be required to provide accurate data. There will now be masses of historical data (rather than predicted data during original design) in order to recalculate if the existing line has sufficient wall thickness in order to remain in operation for the desired new Service life. Once the process has been followed and the decision to extend made, an application to DECC will be made.

The process can be summarised as per the guidance document (Ref 1):

·         Long term planning

·         Identify potential asset extension issues (understand conditions, risk assess, review historical data)

·         Identify potential asset extension issues (gap analysis against current standards, best practices)

·         Review asset plant and equipment against degradation types

·         Develop extension scope

·         Assess costs and review options

·         Implement extension plan.

Ref 1: http://www.oilandgasuk.co.uk/publications/viewpub.cfm?frmPubID=436 

Samuel Bamkefa's picture

I have seen that a lot of us have focusssed on pigging. Pigging is a way to know the state (internal) of the pipeline and not necessarily to extend it. I think we should also look at rectification (if possible) and not just monitoring. So what happens after the state is known, both externally and internally?

On the issue of freespans in the pipeline. Due to seabed scouring by wave and current action, unsupported spans may have developed along the pipeline. There is more suceptibility to this as the pipeline ages the more.  This area can be susceptible to bar buckling and Vortex Induced Vibration. In order to extend the life of the pipeline, free span correction methods have to be adopted. This can be done by placing artificial supports under the pipeline at the critical points. A grout bag can be placed under the pipeline and cement slurry pumped into it. This solidifies and provides a support for the pipeline

In the case of dropped object, concrete mattresses can be placed over the pipeline at critical zones (within a particular radius of the platform). Like already mentioned, injection of corrosion inhibitors can be used to address internal corrosion as wel.

To answere Micheal's question of if we can extend the life of pipelines safely, I think it is very possible. It will all depend on the process we decide to follow and we go about it. A lot of the foregoing posts have giving insights into that

Samuel Bamkefa

Ahmed_Abdelkhalek's picture

I guess that the above discussions listed most of the factors that should be considered when assessing the possibility of extending the life of pipelines. However, I believe that a significantly important factor is not yet addressed which is geo-hazards.
Geo-hazards’ refer to natural phenomena that threaten man-made structures such as earthquakes, mudslides, faults landsides & soil liquefaction.
When justifying life extension for a pipeline it is important to check if newly discovered geo-hazards were identified along its route. The recent advances in geophysical surveying equipment enable the discovery of the subsurface geo-hazards that were identified and considered in the old design of the pipeline. In addition to geo-physical identified hazards, seismic activity has changed in some areas of the world. For instance in the Arabian Gulf, old structures and pipelines were not designed for earthquakes, and recently most operators are seeking to assess their existing assets to this newly considered geo-hazard.
So in addition to checking the physical properties of the pipeline (wall thickness and such) and the checking the pipeline operating conditions, it is crucial to appraise the original design criteria and especially the criteria which do not relate to the operation of the pipeline I only listed geo-hazards because I have come across this issue a lot in the past few years but other factors need to be considered like Fishing & Anchoring activities and changes in Metocean data.

[1] http://pipelinesinternational.com/news/a_global_perspective_on_pipeline_geohazards/079007/
[2] http://www.offshore-mag.com/articles/print/volume-71/issue-1/flowlines-__pipelines/survey-assesses-geohazards-for-record-subsea-pipeline.html
[3] NORSOK STANDARD Y-002 Life extension for transportation systems

Alan J Glennie's picture

The aim of a pipeline is to transport hydrocarbons from one place to another. The main hazard is the loss of containment of these hydrocarbons and the resultant environmental release. It has been said before that corrosion of the line is the main factor affecting failure of pipelines (Ref 1) and it is of the utmost importance to prevent this corrosion taking place.

Internal corrosion can take two forms, Sweet or Sour. Sweet corrosion results in fluids containing only CO2 (or a small trace or H2S) giving a general reduction in wall thickness and SOUR where the H2S level are higher which results in localised corrosion. If corrosion products are not deposited on the inner surface of the pipe several millimetres of millimetres of corrosion can occur. However, by good corrosion management i.e. the use of corrosion inhibitors the corrosion can be greatly reduced and the design life of the line achieved.

When many of the first pipelines were designed and the corrosion prediction models were conservative (Ref 4, p509). Since then the corrosion models, such as NORSOK, Shell and other companies) have become more accurate. As a result, corrosion allowances can be reduced to more realistic thicknesses.

Corrosion inhibitors are chemicals that prevent corrosion by attaching themselves to the inner surface of the line to form a film. Advances in inhibitor technologies has reduced the levels or expected corrosion in the lines both by erosion (Ref 2) and internal corrosion (Ref 3).

It can therefore be concluded that many pipelines nearing the end of their original design life have additional wall thickness attributed to expected corrosion rates that were over conservative. In addition, advances in inhibitor technologies since the 1970s has ensured that the corrosion levels are also less than expected. Both these point could suggest that existing pipelines are in relatively good condition if it can be proven that the correct dosages of inhibitors were used.

Ref 1: http://www.nrcan.gc.ca/science/story/6606

Ref 2: http://www.onepetro.org/mslib/servlet/onepetropreview?id=NACE-05292

Ref 3: http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6664750

Ref 4: Subsea Engineering Handbook (2012): Bai, Yong & Bai Qiang. Elsevier. 

Samira Bamdad's picture

There are risks associated with the reference point that
initially design has been done based upon which is the codes and standards. I’d
like to highlight here that many of the pipelines design aspects are performed using
papers, recommended practice and industry practice and none of them guaranty
the pipeline integrity. To extend a pipeline life, extra caution should be
included since the pipeline has become closer to the end of its life and risk
associated with the initial design is closer to failure. Design review based on
the latest knowledge contributing the current situation the pipeline can
improve the case. A good example is the pipeline upheaval buckling which for
many years was not a concern and not included in the design and it is
recommended to be considered if the pipeline is subject to the life extension.  

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