This paper addresses the question of what effect the pipe thickness has on weld residual stresses in 304 stainless steel piping. Two diameters are considered. These are nominal 4-in. and 10-in. diameters. Four pipe wall thicknesses corresponding to schedules 10, 40, 80, and 160 are examined for each pipe. The focus is on residual stress distributions on the pipe inner surface because this is a primary site for intergranular stress corrosion cracking in 304 stainless steel pipes. The trends in residual stress values are toward more compressive stresses at the pipe inner surface for thicker pipes with the same nominal diameter. Residual axial stresses for the thick 10-in. schedule 160 pipe were found to be compressive while those for the thinner schedule 80 pipe were tensile. X-ray residual stress data for a 6-in-dia schedule 160 pipe fall between the results for the 4-in. and 10-in. schedule 160 pipes and support the findings of the study.

Induction heating for stress improvement (IHSI) is a method for reducing the tensile weld induced stresses on the inner surfaces of the girth welded pipes. The process entails inductively heating the outside of a welded pipe while cooling the inner surface with flowing water. A 10-in. Schedule 80 Type 304 stainless steel pipe was selected for this study. Residual stresses due to welding were first determined using a finite element computational model. Several IHSI treatments subsequent to welding are then examined computationally to determine the effect of induction coil length and maximum outer surface temperatures on the final residual stress state. All IHSI treatments gave reduced inside surface tensile weld induced stresses on the inner surface. Longer coils and higher outer surface temperatures led to inner surface stresses that were more compressive.

Girth welding can produce tensile residual stresses on the pipe inner surface. Because tensile stresses enhance the possibility of stress corrosion cracking, methods for altering the weld-induced stress state are being investigated. One method, Induction Heating for Stress Improvement (IHSI), involves induction heating the pipe while cooling the inner surface. The method is being evaluated using both experimental and computational studies. This paper presents computational results of a 101.66-mm (4-in.) Schedule 80 stainless steel pipe. Results include comparisons of computed values for residual stresses with laboratory data. Computed values of residual stresses and laboratory data are in agreement and, for this case, clearly show that the IHSI process can change weld-induced tensile residual stresses to compressive values. A comparison of computational results for applying the IHSI process to a stress-free pipe and a welded pipe indicate that for geometry and process parameters considered here, the IHSI-induced compressive residual stresses on the pipe inner surface for these two cases are similar. The experimental results presented here show the feasibility of controlling weld-induced residual stresses. The computational results demonstrate a capability for predicting the observed stress behavior. The computational capability then provides an efficient tool to aid in developing ways for controlling residual stresses for other pipe sizes and weldment geometries.

The paper describes analysis related to cracks in rails using the finite element method. Attention has been focused on transverse fissure type of defects in railheads, although the approach is more generally applicable. Elastic stress intensity factors are calculated using the crack closure method and compared against values computed directly from node “opening” displacement. Analyses using idealized polynomial type of stress distributions for embedded cracks are viewed in the light of finite element results. A discussion of stresses that can occur in railheads with flaws for some load situations is included.