Finite Element Modelling of Reduced Pressure Electron Beam Stainless Steel Plate and Pipe Welds

Abstract

Rolls-Royce plc is conducting work to investigate the feasibility of using Reduced Pressure Electron Beam Welding (RPEB) for thick section welded joints in power plant construction. As part of the work, simple specimens have been manufactured at TWI ltd in order to develop welding parameters and conditions and to examine the achievable weld quality. Previous work in this project has shown good correlations between measured and predicted stresses in RPEB welds in ferritic components [5,6]. This paper describes Finite Element (FE) modelling that was carried out to try to predict the residual stress field generated by the welding process in three of the specimens. The first specimen that was modelled was a full penetration butt weld in 80 mm thick Type 316L plate (W17). The other two models were of circumferential butt welds in 14 inch nominal diameter Type 304L pipe. The first pipe model (W20) was a single pass, 360° weld, while the second (W22) featured a slope-up and slope-down each lasting for 16° either side of a 360° full penetration weld, giving a total weld of 392°. The modelling was carried out in Abaqus [1] using a DFLUX user subroutine to model the welding heat input as a cylindrical heat source, due to the reduced pressure during specimen manufacture, only radiation heat losses were considered. The built-in Chaboche mixed hardening model was used for both materials during the structural analysis. The residual stresses predicted by the FE modelling have been compared with the results of Deep Hole Drilling (DHD) that was carried out on the equivalent specimens. Full details of the measurements are reported in [4].