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].
This paper describes finite element (FE) modelling and neutron diffraction (ND) measurements to investigate the development of residual stresses in two different geometries of ferritic weld. All specimens were produced using SA508 Grade 3 steel plates, depositing a low carbon SD3 weld filler by mechanised TIG welding. The FE analyses were carried out using Abaqus/VFT and the behaviour of the SA508 steel was modelled using a simplified (Leblond) phase transformation model with isotropic hardening using VFT’s UMAT-WELD subroutine, which includes the change in volume due to phase transformation. Single bead-on-plate specimens were manufactured using a range of mechanised TIG welding parameters. One pass and three pass groove welds were also produced, in order to investigate the cyclic hardening behaviour of the materials, as well as phase transformation effects in a multi-pass weld. FE analyses were then performed to determine how accurately these effects could be modelled. During manufacture, a number of thermocouples were attached to each of the specimens in order to calibrate the heat input to the FE models. The residual stresses in each of the bead on plate welds, as well as the groove weld after the first and the third passes, were then measured using ND at the middle of the plate. The ND measurements for the three pass weld showed no significant cyclic hardening behaviour although some was predicted by the FE analysis. Another key finding of the FE modelling that was seen in all of the models was that the phase transformation acts to reduce the stress levels in the deposited weld metal leaving the largest tensile stresses in a ring at the outer edge of the full heat affected zone (HAZ). There are plans to refine the FE studies using improved material properties when material testing of SA508 and SD3 are completed in the near future.
The computer simulation of multiple layering of welds is necessary to determine the distortion and residual stresses arising from the welding process. The welding simulation requires thermal and structural solutions, which are usually carried out in two simulations. Once solved, the thermal transient model temperature results are read in to the structural model to solve for component stresses. This paper describes the application of the Abaqus Weld Interface (AWI) plug-in for 2D axisymmetric simulation of the residual stresses generated in a Dissimilar Metal Weld (DMW) nozzle to pipe joint comprising of an Alloy 600 nozzle girth weld to a 316 LN Stainless Steel (SS) safe-end pipe. The test piece was manufactured for an ongoing programme within Rolls-Royce PLC. A mechanised Tungsten Inert Gas (TIG) welding process was employed depositing 83 weld bead passes. The weld filler material was Alloy 82. The AWI Graphical User Interface (GUI) simplifies and saves a large amount of time towards generating the Finite Element Models (FEMs). By using the AWI plug-in within Abaqus/CAE, the FEMs take approximately a month to generate and solve with significant time savings associated with setting up the surfaces for the welding bead sequences and matching the heat input to the actual specimen. The GUI rapidly creates both the thermal and structural input files for the Abaqus/Standard solver. However, modifications were made to the thermal and structural FEM model input files to suit the analysis pre-processing requirements for idealised conditions to match the test piece pipework conditions. FEM predictions captured the characteristic through-wall Weld Residual Stress (WRS) profiles measured by Deep Hole Drilling (DHD). The weld shrinkage was under estimated.
A previous paper (PVP2010-25649) presented work carried out to model a three pass groove weld in an SA508 plate using Abaqus with the VFT material model. The model used the SA508 physical and mechanical properties for both parent and weld metal, with phase transformation properties for a slightly different material as these were the only properties available at the time. A material properties testing programme has since been completed allowing the analysis to be rerun using a complete set of properties for both the parent metal (SA508) and the weld metal (SD3). Properties to describe the phase transformations on cooling from austenite were derived for a range of austenite grain sizes. This paper presents a sensitivity study comparing the predicted stresses and phase proportions when using the different properties, and the effects of using different properties for the two materials. With the updated material properties and by using separate properties for the parent and weld, the results have been improved significantly. The results show that, while changing the phase properties affected the predicted phase proportions and the stresses in the weld metal, the residual stress distribution in the parent metal, where the peak tensile stresses occur, did not change significantly.
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