CORRIB ONSHORE PIPELINE: ENHANCING SAFETY

PIPELINE SAFETYTo ensure The safeTy and long-Term inTegriTy of a pipeline The following key elemenTs musT be managed effecTively

1. design 2. consTrucTion 3. operaTion and mainTenance

The corrib pipeline projecT is applying besT indusTry pracTice To all of These aspecTs, wiTh safeTy as iTs firsT prioriTy.

1. DESIGN

The pipeline must be designed for the key operating parameters of pressure, flow rate and fluid to be transported.

• pressure The normal operating pressure of the onshore pipeline will be 90 to 100 bar. The maximum pressure in the pipeline onshore will be limited by the landfall valve facility to 144 bar. The pressure to which the onshore pipeline will be hydro-tested (strength tested using water as the test medium) is in excess of 500 bar. This provides a very significant margin of safety. as gas is produced from the corrib field and the gas reservoir is depleted, the operating pressure will decrease and is predicted to fall to 60 bar after 4 years, further enhancing the margin of safety.

• flow rate The pipeline has been designed to transport 10 million cubic metres per day at a velocity of 6 metres per second equivalent to 22 kilometres per hour.

• fluid The onshore pipeline will contain natural gas, hydrocarbon liquids, water and inhibitors that are injected at the wells. The inhibitors are used to protect the internal wall of the pipeline against corrosion, and to prevent the formation of gas hydrates, which can lead to pipeline or valve blockages.

The application of knowledge and experience gained over many years through operating pipeline systems similar to corrib will ensure the safe and stable operation of the pipeline.

The design must also take into account the terrain to be traversed, soil conditions such as stability and corrosivity and social factors such as land use and housing.

in areas of deep peat proven construction techniques similar to those used by bord gáis eireann for the mayo galway pipeline will be used to make sure the pipeline is stable.

The pipeline will be routed in compliance with separation distances specified in the relevant irish and international pipeline design codes. a quantified risk assessment of the onshore pipeline carried out by advantica on behalf of the then minister for communications, marine and natural resources in 2005, confirmed that the risks associated with the corrib onshore pipeline are acceptable according to international norms.

The onshore pipeline will have an outside diameter of 508mm / 20” and wall thickness of 27.1mm. To put this in context, the pipeline linking the ring main in galway to the terminal at bellanaboy has an outside diameter of 660mm / 26” and is 9mm thick. The corrib pipeline has been fabricated from high-grade carbon steel and will be capable of safely transporting the gas from the gas field to the terminal.

2. CONSTRuCTION

The construction of pipelines on land, whether in farm lands or bog, is a routine activity for the construction industry. The way any pipeline is constructed depends to a large extent on soil conditions and terrain. The geophysical and geotechnical characteristics of the route will be investigated and assessed before construction takes place. The construction methodologies proposed for the onshore pipeline will be described in the environmental impact statement (eis) submitted with the upcoming pipeline consent applications, which will be the subject of public consultation during the application process.

3. OPERATION AND MAINTENANCE

The offshore and onshore sections of the pipeline will be protected against internal and external corrosion throughout the lifetime of the operation. in order to prevent internal corrosion, inhibitor chemicals will be continuously injected into the pipeline at the offshore gas wells. The inhibitor will be pumped out to the wells via a small pipeline, which is incorporated into a group of service pipes and cables referred to as an umbilical, and is linked to the terminal.

The outside of the pipeline will be protected by a polypropylene thermoplastic coating, as well as an impressed voltage system. monitoring tools and techniques will be used to gather data to allow regular assessment of the internal and external condition of the pipe and to ensure its integrity throughout the lifetime of the operations. pipeline inspection tools that travel through the pipeline will be used to inspect the condition of the pipeline.

THE CORRIB GAS PARTNERS’ RESPONSE TO THE SAFETY REvIEw’S RECOMMENDATIONS

PIPELINE PRESSuRE:

advantica recommended a system to ensure that the onshore pipeline pressure could not exceed 144 bar, suggesting this to be a practical and effective measure to reduce risk in light of societal concerns that had been expressed.

in response to this recommendation The corrib gas partners have designed a landfall valve facility, which automatically shuts off the pressure from offshore in the very unlikely event that the pressure in the onshore pipeline should rise towards 144 bar.

GROuND STABILITY:

The potential for ground movement to damage the pipeline due to instability of peat and the possible unsuitability of peat for pipeline construction were reviewed by advantica.

Their report noted that peat is one of the most difficult materials in which to construct pipelines and concluded that the “recommendations made by agec (expert advisors on ground investigations along the pipeline route) should be followed in full and the proposed construction methods revised accordingly, in order that the ground stability issues are managed appropriately”.

THE ADvANTICA INDEPENDENT SAFETY REvIEw

in augusT 2005, The minisTer for communicaTions, marine and naTural resources commissioned a consulTanT company, advanTica, To carry ouT an independenT safeTy review To address concerns expressed by local residenTs regarding The safeTy of The onshore secTion of The corrib gas pipeline. The findings of this review were published in early may 2006 and concluded that: “proper consideration was given to safety issues in the selection process for the preferred design option and the locations of the landfall, pipeline route and terminal”.

The corrib gas partners are committed to safety; it is their first priority. Therefore, recognizing that the implementation of advantica’s recommendations would further enhance the safety of the pipeline, they accepted the findings of the independent safety review and announced that they would adhere fully to advantica’s recommendations.

in response to this recommendation a technical report on the analysis of potential for ground instability (landslip analysis) has been prepared and submitted to The Technical advisory group (Tag) of the department of communications, energy and natural resources for their review. The detailed design for construction of the pipeline along the final route will incorporate the necessary support and stability measures determined through landslip analysis and detailed soil conditions data gathered from site investigation.

INTEGRITY MANAGEMENT PLAN:

The corrib gas pipeline project already had an integrity management plan, however, advantica recommended that the plan should include an operational and maintenance philosophy as well as the implementation of an independent audit and inspection regime before and during construction and in operation.

a draft pipeline integrity management system (pims) report incorporating these elements has been submitted to Tag for their review.

PIPELINE DESIGN CODES:

The onshore section of the corrib pipeline had been designed to british standard bs8010, but this standard has since been replaced by the european standard, pd 8010. advantica recommended that if the onshore pipeline was to be reclassified as a class 2 (suburban) pipeline, the pipeline design should be revised in accordance with

pd 8010. They also stated that the alternative approach of basing the revised pipeline design on the irish standard is en 14161, supplemented by the use of pd 8010 and is 328, would also be acceptable provided that the more onerous requirements of pd 8010 and is 328 were adopted where appropriate.

The use of irish standard is en 14161, associated with the use of the recommended parts of pd8010 & is 328 where they exceed is en 14161, have been agreed by Tag. These codes deal with pipeline operation and maintenance, as well as design, construction, testing and commissioning.

CONCLuSIONS

advantica’s report concluded: “provided that it can be demonstrated that the pressure in the onshore pipeline will be limited effectively, and that the recommendations made elsewhere in this report are followed, we believe that there will be a substantial safety margin in the pipeline design, and the pipeline design and proposed route should be accepted as meeting or exceeding international standards in terms of the acceptability of risk and international best practice for high pressure pipelines”.

Approx 83km from shore

wellheAd

wellheAd

wellheAd

wellheAd

wellheAdmAnifold

seA bed - Approx 350m below seA level pipeline

integrAted services umbilicAl

CONTROLLING PRESSuRE ALONG THE LENGTH OF THE PIPELINE in addiTion To normal operaTor conTrol, There

are Three independenT and auTomaTic levels of pressure proTecTion in place for The corrib onshore pipeline (see below):

the corrib resevoir - Approx 3000m below

the seA bed

1

2

Approx 9km inlAnd

bord gáis eireAnn pipeline

treAted wAter outfAll pipe [12.7km to seA]

AuTOMATIC SAFETY STEP 1: well control valves: the flow rate from each well will be controlled from the terminal by valves (known as chokes) located at each well-head on the seabed. These valves will be closed to fully stop the flow of gas if required.

AuTOMATIC SAFETY STEP 2: well shutdown valves: in the unlikely case that the control valves fail to close, there are additional subsea valves that will then be closed. in fact, for each individual well there are a total of three subsea isolation valves between the reservoir and the inlet to the offshore pipeline. These valves are fail safe, therefore in the event of an electrical failure in the control system, one of these valves would close. in the event of a hydraulic failure, all three would close.

AuTOMATIC SAFETY STEP 3: landfall valve facility: automatic shut-off feature to limit the pressure in the onshore pipeline. again, this valve is fail safe and would close in the event of failure.

The combination of these three levels of pressure protection exceeds industry ‘best practice’ and provides a level of safety above what would normally be required for a similar gas pipeline elsewhere in the world.

1

3

2

3

fig 1.0 (not to scAle)

NORMAL OPERATOR CONTROL: routine control adjustments from the control room.

NON-ROuTINE OPERATOR CONTROL: Alarm indicates to operator that pressure is rising above the normal range and will go to automatic closure if corrective control is not initiated.

CONTROLLING THE PRESSuRE ONSHORE: THE LANDFALL vALvE FACILITYBACkGROuND

The original pipeline design for the corrib project included an onshore isolation valve located at the landfall. This was intended to allow the onshore section of the pipeline to be isolated manually from the offshore section – for instance if maintenance was needed. in response to advantica’s recommendations, the corrib gas partners have undertaken to install an automatic landfall valve facility where the corrib pipeline comes ashore.

THE LANDFALL vALvE FACILITY IN BRIEF

The landfall valve facility is a system that will shut off the flow of gas automatically in the very unlikely event that the pressure in the pipeline rises towards 144 bar at the landfall. when activated, the shut-off valves close, resulting in complete isolation of the onshore section from the offshore section of the pipeline. The pressure in the onshore pipeline cannot rise above 144 bar.

The landfall valve facility will be located at the landfall in glengad, (see fig 1.0) about 50 metres from the edge of the cliff. it will consist of a number of valves in the pipeline system, located below ground, together with some supporting equipment that will be placed above ground. To minimise visual impact the ground level of the installation will be lowered into the landscape in this area ensuring that very little of the facility will be visible from the public road.

HOw IT wORkS

The landfall valve facility will function as follows (see fig 2.0):

• Threepressuresensors/transmitters,locatedatthelandfallvalvefacility, continuously measure the pressure in the pipeline.

• Ifthesensorsdetectthegaspressureincreasingaboveacertainlevel, they send a series of ‘trip’ signals to a ‘control unit’.

• Thecontrolunitinturncommandsthetwoshutdownvalvestoclose.

• Theflowinthepipelinestops,ensuringthatthepressureontheonshore side does not rise any further.

This function is automatic and requires no human intervention. in the case of a control system malfunction or a loss of signal, the valves will also close automatically.

The pressure in the production system from the wells to the terminal will be controlled such that this safeguarding system should never have to operate. The system will be tested on a regular basis, typically with a full test once a year and partial tests of different components several times a year.

PROGRESSING THE LANDFALL vALvE FACILITY

The landfall valve facility will form a part of the modified onshore pipeline system, which requires consent from an bord pleanála under the strategic infrastructure act, and from the minister for communications, energy and natural resources under the gas act.

shutdown vAlves

v2

mAintenAnce isolAtion vAlve

v5

mAintenAnce isolAtion vAlve

v1

mAinline isolAtion vAlve

pt

pt

pt

v3 v4

pt pressure sensors. meAsure the pressure in the pipeline

control unit the control unit sends signAls to shutdown vAlves to close them when pressure ApproAches 144 bAr

v1 mAinline isolAtion vAlve. closed during normAl operAtion

v3 & v4 shutdown vAlves. will close AutomAticAlly when pressure ApproAches 144 bAr

v2 & v5 mAintenAnce isolAtion vAlves. open during normAl operAtion, closed when mAintenAnce of the shutdown vAlves is required.

offshore pipeline onshore pipeline

fig 2.0 (not to scAle)

control unit

LANDFALL vALvE FACILITY: QuESTIONS & ANSwERS

wHAT BACk uP PLANS ARE IN PLACE IF THE vALvES FAIL TO LIMIT THE PRESSuRE?

The valve itself is a backup system, which will only come into operation in very exceptional circumstances, for example if the terminal has to be shut down for any reason, in combination with the valves in the corrib field failing to operate as they should. The valve system will be designed with several layers of redundancy (safety), to make sure that the onshore pipeline system never experiences pressures above 144 bar.

it should be noted that the onshore pipeline was originally designed to withstand the highest occurring wellhead pressure, and that it will be tested to over 500 bar before the system is taken into operation. Thus, in the extremely unlikely event that all the above systems fail, the pipeline will contain the pressure and no gas will escape. The new design will have the pipeline rated at 144 bar, with a design factor of 0.3 which is the factor used for suburban areas.

wILL THERE BE ANY EMISSIONS RESuLTING FROM THE OPERATION OF THE LANDFALL vALvE FACILITY?

The operation of the landfall valve facility will not cause any emissions.

some of The mosT frequenTly asked quesTions on The landfall valve faciliTy are ouTlined below.

HOw wILL GAS LEAkS BE PREvENTED?

The design, manufacture, assembly, inspection and pressure testing will ensure that the potential for leaks is minimised. connections located below ground will be welded where possible. in addition, personnel from the terminal will carry out regular inspections and gas testing on the landfall valve facility

wHAT TYPE OF MAINTENANCE AND MONITORING PROGRAMMES ARE REQuIRED?

The landfall valve facility will be subject to a regular inspection and maintenance checks and testing, including visual and gas tests, valve closure and leakage tests, electronic checks, and communications checks. These will be set out in a planned maintenance schedule, which will form part of the pipeline integrity management scheme.

ARE SYSTEMS LIkE THIS uSED ELSEwHERE IN THE wORLD?

pressure limiting systems as described above are widely used across the world as means of protecting pipelines from over-pressure. similar equipment is incorporated into upstream flowlines from subsea fields to offshore platforms, between platforms offshore and between offshore and onshore facilities. others are used to protect distribution systems onshore. examples can be found in The netherlands (e.g. nogaT, moddergat pipelines in nam), where shut-off valves are used between offshore/onshore wells and pipelines. in some instances, these facilities are located in quite densely populated areas, with considerably smaller separation distances than those to be applied for the corrib pipeline.

wHO MONITORS THE SYSTEM wITHIN SHELL?

The operators working in the terminal will monitor and manage the operations. shell has internal and external audits of these systems. under current legislation, shell will be required to report on an annual basis the status and actions taken to ensure full technical integrity of the corrib gas pipeline system.

FOR FuRTHER INFORMATION PLEASE

visit: www.corribgas.ie contact: The corrib gas project, 52 lower leeson street, dublin 2.

Tel: 01-669-4100 email: info@corribgas.com