Evaluation of Dissimilar Socket Weld Connections

In the power industry, stainless steel is widely utilized for instrumentation tubing, while the small bore branch piping up to the root valves is either of carbon steel (A106 Gr. B, A106 Gr. C) or low alloy steel (A335 Gr. P11, A335 Gr. P22), or intermediate alloy steel (A335 Gr. P91). Stainless steel is not widely used for small bore piping. Generally, socket weld connections are employed in small bore piping applications as well as for pipe to tube adapter locations in instrumentation for sampling and sensing line applications. In this paper, socket weld connections at pipe to tube adapter locations are evaluated to determine the acceptability for higher temperature service applications. Finite element analysis methodology, based on axi-symmetric finite element models, is utilized to obtain thermal discontinuity stresses at the dissimilar socket weld connection. Taking into account the stress and cyclic considerations, the dissimilar socket weld connection is evaluated. Limitations and guidelines are provided concerning the acceptability for higher temperature service.