Dissimilar welding between piping and valves in the offshore oil and gas industry

Abstract

ABSTRACT This article reviews different piping connections, such as flanged, wafer, hub and clamp, welded, and threaded. A bevel end welding connection is one of the most common pipe ends due to providing high joint efficiency and less risk of leakage. This type of pipe ending has a lean angle with the pipe surface and suitable for butt weld joints. For a butt weld joint, the pipe end is typically prepared according to ASME B16.25. Alternatively, a narrow gap welding technique with a 5° or 7° degree angle to the vertical line rather than 37.5° has been used to reduce the welding heat input and facilitate faster welding. Three case reviews are discussed in which industrial valves in the offshore industry are welded to the piping in different materials. The first case addresses the welding between a 38” oil export line in 22Cr duplex and pipeline valves in carbon steel material located on a platform in the North Sea, Norwegian continental shelf. The second case reviews subsea slab gate valves with remotely operated vehicle (ROV) operations located on subsea manifold mono-ethylene-glycol injection lines. The valves are supplied with pup pieces integral to the valve body in 25Cr duplex to be welded to API 5 LX65 carbon steel pipe. The third case reviews ¾” subsea ball valves with ROV operations located on subsea manifold chemical injection lines such as methanol. 25Cr super duplex valve materials should be welded to 6MO piping in this case. Welding techniques based on industrial experiences and past studies are proposed to solve the challenges in these three cases.