Weld Reinforcement to Prevent Strain Concentrations in Regions of High-Low Misalignment
Publication Date: 2011-Jul-19
The IP.com Prior Art Database
Pipelines in areas subjected to ground movements can be designed with strain based designs. Strain based pipelines must have the capacity to tolerate longitudinal plastic strains without failure. The strain capacity of pipelines can be limited by the capacity of girth welds containing flaws and high-low misalignment. A method of increasing the strain capacity of pipelines is described. This method mitigates the effect of high low misalignment on strain capacity. Local reinforcement of the weld region is applied by the addition of weld passes adjacent to the cap of the weld. These extra weld passes prevent the concentration of strains and the formation of shear bands across welds with high-low misalignment.
Pipelines subjected to ground movements can be subjected to plastic deformations. For example, pipelines in discontinuous permafrost can be subjected to ground displacements resulting from frost heave or thaw settlement. Similarly, pipelines in seismic regions can be deformed by fault displacements or ground movements caused by soil liquefaction. In these and other conditions, strain based design is used to design the pipelines and the pipe and welds must be capable of withstanding the strains resulting from ground movements. A key failure mode that must be designed against is tensile rupture of welds containing flaws. High-low misalignment reduces the strain capacity of welds containing flaws because strains can concentrate in regions of high-low misalignment. A shear band can form across the weld due to strain concentrations caused by high low misalignment as shown in Figure 1. Preventing this strain concentration and high localized deformation in the weld regions that have high-low misalignment can increase strain capacity.
Figure 1. Illustration of the strain concentration that results in weld regions containing high low misalignment that are subjected to axial strains.
The effect of high-low misalignment on strain capacity can be mitigated by the addition of extra weld passes positioned to prevent strain localization. The weld passes are added on the OD of the pipe on the low side of the high-low misalignment as illustrated in Figure 2. The addition of these weld passes provides local reinforcement that prevents local deformation across the weld and reduces or eliminates the formation of the...