Numerical weld modeling - a method for calculating weld-induced residual stresses

In the past, weld-induced residual stresses caused damage to numerous (powe r) plant parts, components and systems (Erve, M., Wesseling, U., Kilian, R. , Hardt, R., Brummer, G., Maier, V., Ilg, U., 1994. Cracking in Stabilized Austenitic Stainless Steel Piping of German Boiling Water Reactors - Charac teristic Features and Root Causes. 20. MPA-Seminar 1994, vol. 2, paper 29, pp.29.1-29.21). In the case of BWR nuclear power plants, this damage can be caused by the mechanism of intergranular stress corrosion cracking in aust enitic piping or the core shroud in the reactor pressure vessel and is trig gered chiefly by weld-induced residual stresses. One solution of this probl em that has been used in the past involves experimental measurements of res idual stresses in conjunction with weld optimization testing. However? the experimental analysis of all relevant parameters is an extremely tedious pr ocess. Numerical simulation using the finite element method (FEM) not only supplements this method but, in view of modern computer capacities, is also an equally valid alternative in its own right. This paper will demonstrate that the technique developed for numerical simulation of the welding proce ss has not only been properly verified and validated on austenitic pipe wel ds, but that it also permits making selective statements on improvements to the welding process. For instance, numerical simulation can provide inform ation on the starting point of welding for every weld bead, the effect of i nterpass cooling as far as a possible sensitization of the heat affected zo ne (HAZ) is concerned, the effect of gap width on the resultant weld residu al stresses? or the effect of the 'last pass heat sink welding' (welding of the final passes while simultaneously cooling the inner surface with water ) producing compressive stresses in the root area of a circumferential weld in an austenitic pipe. The computer program FERESA (finite element residua l stress analysis) was based on a commercially available ABAQUS code (Hibbi tt, Karlsson, Sorensen, Inc, 1997. ABAQUS user's manual, version 5,6). and can be used as a 2-D or 3-D FEM analysis; depending on task definition it c an provide a starting paint for a fracture mechanics safety analysis with a cceptable computing times. (C) 2001 Elsevier Science B.V. All rights reserv ed.