Offshore - Enserch Exploration Partners, Ltd.
ORBITAL WELDING HANDLES PRESSURE OF UNDERSEA APPLICATION
Workers get weld head in position to weld the hydraulic tubing to the subsea template.
Featuring
Model 9

The fabrication of a subsea hydraulic control system used to regulate the flow of gas presented a challenge for Enserch Exploration Partners, Ltd. The joining method and type of steel tubing for the project needed to be chosen carefully because of the corrosive environment and because the control lines containing the hydraulic fluid would be subjected to operating pressures of about 10,000 lb/in.

Small-diameter seamless tubing (1/2 in. diameter, 0.065 in. wall thickness) of duplex alloy SAF 2507 was installed. The tubing was joined with Arc Machines' orbital welding equipment. Duplex stainless steel offered several advantages over 316L. The selection of duplex resulted in a significant savings in weight which was an important factor in the design to keep the template light enough for installation using the drilling rig cranes.

The two joining methods that were considered were manual GTA socket welds with filler and orbital GTA butt joint welding. Orbital welding was shown to offer several major advantages over manual socket welds. Since the filler material is usually added during welding of duplex materials, extensive weld qualification testing of the orbital, fusion-only, welds was done. The orbital GTA process was determined to be clearly superior.

The requirement was a fully penetrated weld, flat on the O.D. with no concavity, with uniform, even penetration around the entire weld circumference on the inside of the weld joint. No evidence of cracking or porosity was permitted nor found.

Find out how AMI's orbital welding equipment demonstrated the feasibility of using a fusion welding process on duplex alloys, realized a much lower reject rate than with manual welds, and increased the productivity rate.

Reprinted from The Welding Journal

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