Welding residual stresses

The welding residual stress distributions in the longitudinal direction in longitudinal, T-type, and cross joints were measured using wire strain gauges and are shown in Fig. 6a. The maximum tensile stress was nearly equal to the 0 0.2 of the base metal, regardless of the kind of welded joints [%... 

Fig. 6. Effect of welding residual stress (a) on fracture strength (b).

Welding residual stresses and misfabrication hardly affect the fracture strength of notched plates. 

Dean, D. Hidekazu, M. (2006). Prediction of welding residual stress in multi-pass butt-welded modified 9Cr-lMo steel pipe considering phase transformation effects. Comp. Mater. Sci., Vol. 37, 209-219. 

Crevices significantly increase the probability for SCC due to the highly aggressive local environment that may form within the crevice. Creviced Alloy 600 has suffered IGSCC in the BWR (e g., nozzle safe ends, shroud head bolts, access hole covers). Alloy 182 has also experienced IGSCC in nozzle safe end applications where weld residual stresses and fairly high applied stresses were present. It must conservatively be assumed that Alloy 182 exposed to normal coolant conditions is susceptible to IGSCC. 

There are three primary sources of tensile stresses for RPVDs These are (1) fabrication induced stresses, (2) primary stresses, (3) and secondary stresses. Fabrication induced stresses consist of stresses introduced during manufacture and installation (i.e., fit-up and assembly in the shop or field plus those introduced by machining or forming operations and welding). As is the case for weld residual stresses, hard machining, abusive grinding can produce surface residual stresses near or above the yield point of the material. 

Whereas service related primary stresses and secondary stresses for RPVIs during normal operation are generally lower than weld residual stresses. 

Weld residual stresses can be reduced by a post-weld heat treatment (PWHT) during fabrication. To avoid sensitization, PWHT parameters have to be well controlled and adjusted to the materials and construction. 

There are numerous welds in the core spray internal piping with attendant weld sensitized heat-affected zones and weld residual stress that are potentially susceptible to IGSCC. In addition, a crevice exists at the lower end of both vertical pipe runs and at the core shroud penetration. The crevice on the vertical pipe is produced by a gap between the connecting sleeve to vertical pipe joint. 

Kanazawa, T., Oba, H., Susei, S. The effect of welding residual stress upon brittle fracture propagation, report ii. Japan Soc. Naval Arch. 110, 359-368 (1961)... 

The uncertainty in the definition of the system. Parameters such as the initial material conditions (e.g., thermally induced grain boundary sensitization, coolant purity, corrosion potential) are important, but the most significant uncertainty rests with the definition of the weld residual stress. 

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