Session: MF-03-01 Welding Residual Stress and Distortion Simulation and Measurement-1

Paper Number: 155748

155748 - Full Scale Three-Dimensional Moving Arc Weld Analyses of Steam Generator Vessel With Effect of Post Weld Heat Treatment 

Abstract: 

Computational weld analysis was performed for a steam generator design using the Virtual Fabrication Technology (VFT^TM) computer code. The WRS field that develops from the welding process using a prescribed weld sequence is provided for the three large welds considered (divider plate top and bottom and the bowl closure weld).  Hoop (stresses in the direction of the weld) and in plane weld residual stresses are above yield for portions of the weld and heat affected zone because the weld process causes material hardening and because of the structural constraint in the steam generator design.  The WRS developed in the divider plate welds are decreased from application of the bowl weld.  An axisymmetric analysis was also performed of the bowl closure weld and the WRS field compared well with the full 3D solution for this weld for locations away from the weld start/stop locations.  The effect of cladding on the bowl was also considered and this increases the WRS field in the clad region compared to no cladding.

Some of the findings from this study include the following.
 

·         The WRS component field that develops in the steam generator are higher than yield within portions of the weld and heat affected zone.  This is due to material hardening and structural constraint.

·         The weld sequence of completing the bowl weld last results in a reduced WRS field in the divider plate welds and it thus considered the optimum sequence to use.

·         The effect of hydrotest pressure of 24.8 MPa has a rather small effect on reducing the WRS field.  Higher pressure would be required to reduce the WRS field more.

·         An axisymmetric solution of the bowl closure weld provides a reasonable prediction of the WRS field in this weld compared to full 3D solution.

·         The cladding applied to the bowl weld region increases the local hoop and axial stress in the bowl weld.  However, the OD hoop stress is reduced and the axial stress is reduced through the thickness.

 

The post weld heat treat (PWHT) analysis of the steam generator system also shows that the final residual stress field, after cool down, can be large and must be considered in a fitness for service assessment.

Presenting Author: Frederick (bud) Brust Engineering Mechanics Corporation of Columbus

Presenting Author Biography: F. W. (Bud) Brust works at Engineering Mechanics Corporation.

Authors:

Lance Hill EMC2
Frederick (bud) Brust Engineering Mechanics Corporation of Columbus
Jason Burr Westinghouse
Javier Grande Marlasca Westinghouse Electric Company