Failure pressure of a pressurized girth-welded super duplex stainless steel pipe in reverse osmosis desalination plants

Pressurized super duplex stainless steel grade S32750 pipe is the most important element in SWRO (Sea Water Reverse Osmosis) plants. This paper presents FE (finite element) analyses to investigate the residual stress distributions produced by the girth welding of the thin-walled super duplex stainless steel pipe and the failure pressure of the girth-welded super duplex steel pipe under internal pressure. FE simulation of the girth welding process was first performed to predict the weld-induced residual stresses employing a sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. The residual stresses were then incorporated into the 3-D elastic-plastic FE analyses to explore the failure behavior of the girth-welded super duplex steel pipe subjected to superimposed internal pressure. GPD (Global Plastic Deformation) was used as an indicator of the failure pressure. The FE results have shown that the failure of the girth-welded thin-walled super duplex stainless steel pipe under internal pressure occurs when the effective stress approaches at a certain level which is much lower than the ultimate tensile strength and the burst pressure is weakly influenced by the weld-induced residual stresses.