Pipe Whip—Bounding the Required Restraint Capacity

Energy balance methods commonly in use for the design of pipe whip restraints are based on the solution for the motion of a rigid-plastic pipe before impact against the restraint, with the assumption that after impact, the whipping portion of the pipe continues to rotate about the plastic hinge location determined for conditions before impact. Such energy balance methods are not necessarily conservative because: 1) the plastic hinge which forms in the pipe moves after impact on the restraint; and 2) elastic pipe deformations are not considered. Here, upper and lower bounds to the required restraint capacity are derived. In contrast to finite element methods, which are very time-consuming, the upper and lower bounds can be evaluated by simple hand calculations. Another advantage is that the required restraint capacity is calculated directly. No trial and error design is required. A numerical example shows that for a typical pipe and restraint, the upper and lower bounds differ by as little as 20 percent.