Mapping Multiple Components of the Residual Stress Tensor in a Large P91 Steel Pipe Girth Weld Using a Single Contour Cut

The contour method is applied in an innovative manner to measure the distribution of hoop residual stress in a large martensitic-ferritic steel pipe containing a multi-pass girth weld. First, a novel one-step wire electro-discharge machining cut is conducted to divide the pipe lengthways into two halves. The deformation of the cut halves is then measured and analysed in a way that simultaneously gives maps of hoop stress across the wall thickness on both sides of the pipe and automatically accounts for through-thickness hoop bending effects and how they may vary along the pipe. Finally the contour method results are combined with X-ray diffraction residual stress measurements using the principle of superposition to determine the distribution of the axial and radial residual stresses in the pipe. It is thereby demonstrated how the distribution of three direct components of the residual stress tensor in a welded pipe can be readily determined using a “hybrid” contour measurement approach.