Despite the fact that weld-induced residual stresses arise as a result of thermoplastic material deformation, current analyses of crack growth in welds assume that linear elastic fracture mechanics (LEFM) conditions are valid. In particular, the stress-intensity factor K, the LEFM-based measure of the crack driving force, is calculated using the linear superposition techniques that strictly hold for linear clastic material behavior. Another common idealization is that only the normal component of the residual stress field that acts on the crack plane is significant.

To assess the importance of these assumptions, a heuristic elastic-plastic fracture mechanics analysis procedure is developed in this paper and applied to determine the rate of stress-corrosion crack growth in an axially-loaded 102-mm (4-in.)-diameter girth-welded Type 304 stainless steel pipe. It is found that the more rigorous elastic-plastic analysis predicts higher crack growth rates than do the currently used LEFM-based calculations. It is concluded that more rigorous prediction methods may be needed for safety assessments of welded structures than those now in use.