Oil and gas contractor Bonatti has selected an EFD Induction post-weld heat treatment (PWHT) solution to help build the world's longest 13% Cr onshore pipeline. The corrosion-resistant pipeline is part of the In Salah Southern Fields project (ISSF) in the Algerian Sahara desert.
This in turn is phase two of the larger In Salah Gas (ISG) project, which first came on-stream in July 2004. ISG, a joint venture between Statoil, BP and Sonatrach, is Algeria's third largest gas development, and currently has an annual production capacity of around nine billion cubic metres.
"This is a significant project for several reasons," says Stefano Migliavacca of EFD Induction in Italy. "To be selected by such a prestigious company as Bonatti confirms our ability to satisfy the most stringent criteria. The project also underscores the industry-wide acceptance of our PWHT solution for corrosion resistant alloys."
The Bonatti order involves two complete PWHT systems for on-site operation in the Saharan desert. Each system is truck-mounted, and comprises an EFD Induction 'Minac' 70/110 power source, specially designed induction coils for 8in-12in and 16in pipe, and chiller and quench units.
The two PWHT systems will be used for butt-to-butt welding of 13% Cr and 13% Cr to duplex steel. "Welding these heterogeneous materials is a technically advanced task," says Migliavacca. "But when used in conjunction with PWHT, such welding offers tremendous benefits. 13% Cr pipe, for example is extremely cost-effective because its strength means that lighter wall thicknesses can be used. Duplex on the other hand is extremely resistant to corrosion."
PWHT of 13% CR and duplex flowlines is necessary in order to minimise the risk of hydrogen induced stress cracking (HISC). Such cracking is caused by the presence of hydrogen in the pipe's heat affected zone. Although precautions are taken during the fabrication and welding stages to minimise hydrogen content, PWHT is still deemed the best way to achieve safe levels.
"A big factor behind Bonatti's decision is our proven experience in this specialised PWHT area," adds Migliavacca. "Our colleagues at EFD Induction in the UK, Jon Philpott in particular, had previously devised a PWHT solution for another In Salah contractor.
"It involved the supply of three truck-mounted PWHT units, which have now been operating in the tough Algerian environment for months. Philpott's expertise contributed greatly to the Bonatti solution, and helped convince them that EFD Induction was the right partner."
The PWHT units built for Bonatti are currently undergoing final testing. "We hope to get the units into action as soon as possible," says Migliavacca. "ISG is after all a critical project. Its seven fields not only supply key foreign and local markets with gas, it also involves the world's first full-scale carbon dioxide capture undertaking at a gas field. It's an honour to be part of such an exciting and meaningful initiative."