Considerations of Pipeline Tension Tie Problems

Two recent structural failures vividly illustrate problems experienced with the joint harness type tension ties commonly used on pipelines to prevent joint separation at flexible coupling locations. The transfer of imbalanced forces through joint harness tension tie bolts and lugs sets up high concentrations of streses in each element of the harness and the pipe wall. The tension tie bolt nut and washer pulled through the back plate of the joint harness lug in the first failure. The second failure occurred when the joint harness lug tore a section of pipe at the heel of the lug along the periphery of the lug to pipe weld. Both joint harnesses were designed using Table 19.7 or 19.8 in the AWWA M 11 Steel Pipe Manual. It is recommended that these joint harness design tables not be used until they can be further developed to better define limitations on pipe wall thickness, plate lug dimensions, pipeline configuration and construction practices.