Residual stress measurement of new and in-service X70 pipelines by X-ray diffraction method

Based on the importance and complex working environment of X70 pipelines, stress measurement and analysis were done on an in-service process pipe, an anamorphic pipe in tunnel and three new welded pipes. Stresses in both the inner and outer walls of pipes were measured by X-ray diffraction, and thus the components of complex stress, internal pressure working stress, welding residual stress (WRS) and bending stress, were obtained by comparative analysis on stresses of various pipes. The results show that the maximum WRS occurs in the heat affected zone on inner wall, and its orientation is parallel to the weld seam. These maximum WRSs in various measured spots are mostly more than 0.80σ0.2 and up to 1.05σ0.2. However, on outer wall the stresses are less than 0.40σ0.2, and WRS appear in the weld area of 40 mm wide. For the tunnel pipeline, its maximum axial and circumference stresses were up to 0.93σ0.2 and 0.80σ0.2, respectively.