RESIDUAL-STRESS MEASUREMENT IN 304-STAINLESS-STEEL WELD OVERLAY PIPES

Welding overlay repair (WOR) is commonly employed to rebuild piping sy stems suffering from intergranular stress corrosion cracking (IGSCC). To understand the effects of this repair it is necessary to investigat e the distribution of residual stresses in the welded pipe. The overla y welding technique mush induce compressive residual stress at the inn er surface of the welded pipe to prevent of IGSCC. To understand the b ulk residual stress distribution, the stress profile as a function of location within wall is examined. In this study the full destructive r esidual stress measurement technique-a cutting and sectioning method-i s used to determine the residual stress distribution. The sample is ty pe 304 stainless steel weld overlay pipe with an outside diameter of 2 67 mm. A pipe segment is cut from the circular pipe; then a thin layer is removed axially from the inner to the outer surfaces until further sectioning is impractical. The total residual stress is calculated by adding the stress relieved by cutting the section away to the stress relieved by axially sectioning. The axial and hoop residual stresses a re compressive at the inner surface of the weld overlay pipe. Compress ive stress exists not only at the surface brit is also distributed ove r most of the pipe's cross section. On the one hand, the maximum compr essive hoop residual stress appears at the pipe's inner surface. The m agnitude approaches the yield strength of the material; the compressiv e stress exists from the inner surface our to 7.6 mm (0.3 in.) radiall y. On the other hand, compressive axial residual stress begins at dept hs greater than 2.5 mm (0.1 in.); its maximum value is located at 10.7 mm (0.42 in.) with magnitude close to four-tenths of yield strength. The thermal-mechanical induced crack closure from significant compress ive residual stress is discussed. This crack closure cart thus prevent IGSCC very effectively.