Residual Stress Measurement in 304 Stainless Steel Weld Overlay Pipes

Abstract

Welding overlay repair (WOR) is commonly employed to rebuild piping systems suffering from intergranular stress corrosion cracking (IGSCC). To understand the effects of this repair, it is necessary to investigate the distribution of residual stresses in the welded pipe. The overlay welding technique must induce compressive residual stress at the inner surface of the welded pipe to prevent of IGSCC. To understand the bulk residual stress distribution, the stress profile as a function of location within wall is examined. In this study the full destructive residual stress measurement technique—a cutting and sectioning method—is used to determine the residual stress distribution. The sample is type 304 stainless steel weld overlay pipe with an outside diameter of 267 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 are compressive at the inner surface of the weld overlay pipe. Compressive stress exists not only at the surface but is also distributed over most of the pipe’s cross section. On the one hand, the maximum compressive hoop residual stress appears at the pipe’s inner surface. The magnitude approaches the yield strength of the material; the compressive stress exists from the inner surface out to 7.6 mm (0.3 in.) radially. On the other hand, compressive axial residual stress begins at depths 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 compressive residual stress is discussed. This crack closure can thus prevent IGSCC very effectively.