Axial Strains at a Girth Weld in a 914 mm Linepipe
High resolution neutron diffraction measurements have been made of axial strains in and adjacent to a multipass girth weld in a complete section of 914 mm (36″) linepipe. The experiments were carried out at the NRU reactor, Chalk River, with 1 mm wide apertures before and after the sample to define the location of the strain measurement. The diffraction angle was measured to a precision of ±0.003° leading to an accuracy of 1 in 104 in interplanar spacing. The strains were measured in the subset of grains whose  direction of the body centred cubic structure was aligned along the axis of the pipe. The strains were measured at ten positions through the 16 mm thickness of the pipe on the weld centre and offset by 4, 8, 20 and 50 mm from the weld centre. In addition, the spatial variation of axial strain as a function of axial distance from the weld centre was mapped out along the mid-thickness, near the root of the girth weld, and at the three-quarter-thickness position. The mid-thickness is in a state of tensile strain with respect to the outside and inside surfaces of the pipe. The effect is strongest at the weld centre and is less, though still present, well away from the weld. The strain peak at mid-thickness extends 5 mm from the weld centre, followed by a minimum at about 9 mm from the weld centre quite close to the edge of the weld. A further slight but extended maximum in strain is centred at 20 mm from the weld centre, well outside the weld. At a position 3 mm from the inside surface of the pipe, a broad strain minimum on the weld centre and a broad maximum centred at 20 mm from the weld centre are observed. The results are compared with strain gauge measurements on the weld surface and through-wall residual stress distributions measured using a layering technique.
KeywordsNeutron Diffraction Axial Strain Residual Strain Interplanar Spacing Seam Welding
Unable to display preview. Download preview PDF.