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].

Development of Residual Stress Profiles for Defect Tolerance Assessments of Thick Section Electron Beam Welds

“…The 304L pipe weld RS fields are different from the 316L plate weld [9]. Although each stress component is symmetrical about weld centre-line, there is a distinct biasing of the tensile hoop and axial stress field in the inner half of the joint.…”

“…The Abaqus built-in Chaboche mixed hardening material model was used for both the Type 316L plate and the Type 304L pipe material [9]. The Type 316L material was modelled using a single back stress, while the Type 304L material used two back stress components.…”

“…Stress contour plots from the FE weld model analysis [9] are presented in Figure 8, showing a highly tri-axial tensile stress state in the centre of the weld. The central core is the last region to solidify and cool-down; consequently there is a high restraint to shrinkage.…”