Under an extremely tight deadline, high-frequency induction (HFI) steel linepipe provided a high-quality, cost-effective replacement for a corroded pipeline section in the North Sea.
Richard Broughton, Corus Tubes, UK; and Mark Richardson, Apache North Sea Ltd.
It is important that companies acquiring maturing North Sea assets undertake integrity reviews of the infrastructure. Where these assets are showing signs of deterioration, the race is on to upgrade facilities in order to maximize access to remaining reserves.
Corus Tubes was contracted by Apache to supply high-quality, cost-effective pipeline to replace a corroded pipeline section in the North Sea within an extremely tight deadline. Corus Tubes supplied High-Frequency Induction (HFI) steel linepipe-an innovative solution that may have beneficial implications for future North Sea projects.
INTEGRITY MANAGEMENT
Forties Field is located in Block 21/10 in the central North Sea, about 178 km northeast of Aberdeen on the UK Continental Shelf. Originally discovered and operated by BP, Apache bought the field in 2003 and has since doubled production. The Forties infield pipelines are critical assets for exporting the field’s oil production. As part of the company’s integrity management campaign, it instigated inspections to assess the condition of the network.
The original Forties Bravo-to-Forties Charlie pipeline was installed in 1975 and was used to transport processed crude oil until December 2006, when its use was changed to the transportation of multiphase hydrocarbons and water. The pipeline had not been internally inspected for 17 years, and while the general state was serviceable, the results showed extensive corrosion.
While none of the reported corrosion features were assessed as being unsafe at the current maximum allowable operating pressure, the estimated remaining life for the pipeline was 2½ years. As the pipeline was operated at less than 30% of specified minimum yield stress, the most likely mode of failure was a leak due to future corrosion at the deepest defects.
To maximize production, protect the environment and improve integrity, Apache contracted Corus Tubes, based in Hartlepool, UK, to fabricate, coat and deliver 3.26 mi (5.25 km) of HFI-welded steel linepipe. This was to be completed within an extremely tight lead time of just nine weeks to meet a lay vessel window of opportunity.
The result was that the pipe was not only delivered three days ahead of the tight schedule, but was above the contracted specification in mechanical and dimensional properties.
INTEGRATED APPROACH
The manufacturer worked closely with subsea engineering and management contractor JP Kenny Caledonia Ltd, who, in accordance with the pipeline code of practice PD 8010 Part 2, created linepipe with a design life of 20 years. A total of 17,700 ft (5,400 m) of 14-in. (355.6-mm) OD linepipe was fabricated, coated and delivered by Corus Tubes from HFI-welded API 5L X52 steel with a wall thickness of 16 mm.
The HFI linepipe was manufactured to meet the following criteria:
- Wall thickness +/-5% (weld +8%) to nearest 0.1 mm
- Ovality < 0.75% nominal OD
- Diameter 0.5% of OD
- Straightness 1:1,000
- Length -0/+100 m
Due to the urgent nature of the project and the specific steel chemistry required, more than 1,000 metric tons of steel slab was cast before being hot-rolled into coil at Corus’ Strip Products facility in Port Talbot, South Wales. The steel coil was then transported by rail to Corus Tubes’ HFI mill in Hartlepool.
Often considered a new technology, HFI welding has been on the market for more than 20 years. The pipe is cold-formed from steel strip, and the manufacturing process involves “inducing” a current into the edges of the strip with the use of an induction coil, Fig. 1. The HFI weld is created with no filler material, and there is no direct electrical contact in the process.
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Fig. 1. Manufacturing HFI linepipe involves “inducing” a current into the edges of steel strip with the use of an induction coil. There is no direct electrical contact in the process.
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The innovative use of HFI for this reel-lay contract offered a number of key benefits: These included a consistently shorter procurement schedule and superior ovality and wall thickness tolerance to that of seamless linepipe, which significantly reduced costs at both the design and installation stages while maintaining exceptional product integrity.
To ensure reliability and integrity, the linepipe was put through rigorous tests before being cut to the required length. On completion of the pipe manufacture, the pipe joints were coated by BSR Pipeline Services (a Corus joint venture operation with Ramco located on the same site as the pipe mills in Hartlepool) with three-layer polypropylene and delivered to Technip’s Evanton spool base in the north of Scotland in preparation for spooling onto the Apache lay vessel.
The spool base received, inspected and fabricated six pipe stalks of 3,200 ft (976 m) comprised of between 77 and 80 pipe joints, and one of 600 ft (183 m) comprised of 15 pipe joints. The field joints were coated using mechanized three-layer polypropylene tape with flame-sprayed polypropylene on all repair welds, flanges and onshore tie-in welds. The pipe was received over a period of six days, and the stalks were completed a day after receipt of the final linepipe joints.
The project’s timeline was as follows:
- Day 1: The order for coated linepipe was placed.
- Day 35: Steel manufacture was completed at the Port Talbot plant.
- Day 36: The steel coil arrived at the 20-in. HFI pipe mill.
- Day 37: Pipe-making commenced at the Hartlepool mill.
- Day 42: Pipe-making was completed and the linepipe was dispatched to for coating.
- Day 57: Coating of all the pipe lengths was completed, and the pipe awaited dispatch to the Evanton spoolbase.
- Day 64: The coated pipe was delivered to the Evanton spoolbase for reeling onto the CSO Apache reel vessel.
- Day 69: The vessel commenced spooling of the linepipe for pipelay, Fig. 2.
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Fig. 2. The tight dimensional tolerances of the HFI-welded linepipe makes it very well-suited to the reeling process.
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The ambitious project was undertaken from a standing start with no personnel, materials or contracts in place, but in just over three months, 12 new contracts and agreements were signed, 108 specifications and procedures were produced and 31 vessel days were employed.
FAST-TRACK SUCCESS
Despite the ultra-fast-track nature of the project, the pipeline was installed within one day of the original baseline schedule. The final tie-in phase will be completed in April 2008 to coincide with a planned Forties Field shutdown. The speed of delivery is a major achievement compared with the last pipeline to be replaced in the field in 1994, which took over two years and exceeded its budget.
The Apache Forties project illustrates exceptional teamwork throughout the supply chain, resulting in the timely delivery of an innovative and successful solution. This collaborative approach will be key to future development of oil and gas reserves in maturing markets and proves that safety, quality and innovation need not be conflicting factors when working against the clock. 
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THE AUTHORS
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Richard Broughton is European sales manager for Corus Tubes. He has worked for Corus since 1993. He earned a Higher National Diploma (HND) in business and finance and is currently completing an MBA at Warwick University..
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Mark Richardson is the Subsea Projects manager for Apache North Sea Ltd. He has worked for Apache since the company’s takeover of Forties Field in 2004. He earned an MSc degree in offshore engineering and an MBA from Aberdeen Business School..
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