Dual-torch pipeline welding gains impetus offshore Brazil

• Key components of the Saturne 8-T welding system for larger diameter pipelines [25,012 bytes].
• Saturnax welding bugs in action [19,550 bytes].

However, sole owner ETPM is now left with a limited number of pipelay barges, and these are basically dedicated to West African and North Sea operations. It has been agreed therefore to let Serimer Dasa work with competing contractors in any other region of the world.

Serimer Dasa has wasted no time, already signing up with Preussag's Brazilian subsidiary Conduto to help out on an 80-km, 26-in. pipeline installation offshore Brazil. This will be performed using Petrobras' BGL-1 barge on the Pescada Field, and will also represent Serimer Dasa's first job in this region.

The company was created over 20 years ago when Brown & Root held a high degree of control over automated pipeline welding offshore. Following intervention by Total, their system was used under licence by ETPM for the Frigg line installation between Norway and the UK. Rather than resume this arrangement with Brown & Root for subsequent tasks, ETPM decided to develop its own system, just as Saipem (Passo) and, more recently, Allseas have done.

According to Serimer Dasa's chief executive officer, Alain Hersent, the key requirements were a good, productive welding system with a low repair rate. Reliability and efficiency were paramount due to the high costs of pipelay barges. The result was Saturne, a fully automated welding robot introduced in 1981and upgraded many times since.

The unique feature of Serimer Dasa's system was GMAW dual-torch welding. Two torches welding simultaneously doubles the rate of deposit, thereby achieving similar productivity to standard single torch systems, but with reduced manpower and welding station numbers. Also, says Hersent, post-heating the first torch's deposited material with a second torch boosts the weld's mechanical characteristics, and therefore its quality.

Saturne spawned Saturnax which was adopted on McDermott-ETPM's pipelay barges from the late 1980s. Saturnax comprises a self-propelled carriage guided on a pre-set ring around the pipeline joint, supporting a dual torch welding head. It comes with a fully integrated DC power/electronic control unit module and real time data acquisition and computerized quality control systems.

The lightweight bugs carrying the welding torches are designed for easy handling. There is no need to touch the welding carriages during operation as they are fully automated, except for the welding torch tracking relative to the joint bevel. If need be, the latter can be adjusted by remote control using a trigger on a small handset. For transportation purposes, Saturnax packs into a module measuring 5.5 ft by 5.5 ft by 6 ft, which also includes welding generators, electrical control cabinets and a quality control system. Each module is designed to support two Saturnax bugs (one welding station).

Saturnax is suited to small to large diameter lines, off and onshore. Last year, using only two stations on a barge never equipped before for automated welding, 309 welds/day were achieved on a 12-in. by 0.5-in. pipeline, with no subsequent repairs. Also in 1997, ETPM's DLB Polaris managed a record 391 welds in one day off Nigeria for Chevron Escravos, using three Saturnax stations on an 8-in. by 3/8-in. pipeline.

This year, Saturnax is lined up for five North Sea installations, ranging from a short 16-in. line for Conoco Phoenix to the 695-km, 42-in. Asgard gas export trunkline, which the LB 200 is due to start work on shortly. Here Saturnax will support the Saturne 8-Torch system, which is designed specifically for thick and large diameter pipes.

Saturne 8-T is an orbital welding robot comprising four bugs traveling around the pipe in a horseshoe ring format - each with a dual welding head welding a quarter of a circumference of the pipe. Unlike Saturnax, where the welder has to position the bug in the welding torch himself, Saturne 8-T is fully automated. Its computerized system also manages start-stop to the selected cycle sequence and other welding parameters pre-set for each pass. The operator simply has to concentrate on positioning the machine, watching the molten pool, selecting the automation cycle and general safety procedures.

Last year, LB 200 averaged 200 double-length joints per day, or 4,880 meters/day, on Statoil's 42-in. NorFra gas trunkline, using two Saturne 8-T and two Saturnax stations. "The only disruption came when the people on the barge were attempting to proceed too fast," says Hersent, "which led to the welding equipment being bumped into the rollers."

Serimer Dasa employs 100 people, is certified by DNV, and gained ISO 9001 recognition this February. Turnover is $15 million, with $0.5 to 1 million invested annually in R & D.

Offshore development trends demand further changes to the technology, says Hersent. "We have to improve productivity on specific pipelines - those with lots of alloys, chromium or duplex steels, which are subject to corrosion, particularly on subsea projects. These are very difficult to weld, so we need to improve our efficiency."

"Also, ETPM wants to go to deepwater pipelaying, including J-lay. We can weld horizontally with an S-curve, but we need to improve horizontal welds for vertical line laying. Our techniques must be faster than arc welding, which employs three to four stations."

Serimer Dasa's internal eight-torch welding clamp system, B'Cat, refined mid-1995 for large diameter lines, will probably not be promoted henceforth offshore. "We believe it's much better to weld from outside the pipeline," says Hersent. "The improvements proven during the NorFra installation showed that a low repair rate may be achieved with external welding only. If you use an internal machine and it breaks down, you have to remove it. If this process takes hours, it can cost you up to ten double joints."

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