Deep-penetration welds for a deep-water application

摘要

FMC Technology (UK) Ltd., a supplier of subsea systems for oil and petrochemical applications, fabricates wellhead control systems, also known as Christmas trees. A key issue in fabricating such control systems is the integrity of the hydraulic control lines that are critical to wellhead equipment operation. To increase the control line weld integrity for the company's West African subsea project, FMC's subcontractor, IFP Fluid Systems, developed a robust welding protocol with the use of the pressure-balanced orbital welding technique. Typical tubing sizes ranged from 0.250 inch OD to 0.500 in. OD in wall thicknesses of 0.049 in., 0.065 in., and 0.084 in. The majority was 0.375 in. OD with 0.065-in. wall thickness. The materials used were 316 stainless steel and duplex, the selection of which was determined by the working line pressure of the particular system and the corrosive environment. The project involved installing 13 Christmas trees that required an average 110 welds each.