Design of subsea manifolds for deep-water production, should minimise flange and threaded connections to eliminate potential leakage points because these manifolds are normally left unattended on the seabed for a long time and could be as long as 25 years depending on the life span of the oil field. Sending crew to conduct repair is close to impossible and as a result, all pipe work is fully welded. The challenge is to weld these small bore pipes using traditional welding method example GTAW. Due to the size and the accessibility of these weld joints orbital (fusion) welding is the alternative.
Despite the fact that this welding process has been in the market for many years, producing good weld joints remains a challenge because the welding procedure is very sensitive to the welding parameters. A slight variation in one of the welding parameters will result in poor welding quality and the weld joint has to be cut out, because repair is not permissible, not like traditional welded joints. The welding parameters are: the two parent metal itself, the voltage and current input, travel speed, quality of the purging gas, material and the vicinity cleanliness. In addition to the need to stringently control the welding parameters, tests on the production welds has to be conducted regularly to maintain high quality.
This paper describes in detail the challenges that we faced and the remedies implemented in performing this orbital welding on small bore pipes for various materials namely Duplex, Inconel, and Stainless Steel.
