Just as workers had finished replacing a part in the hydraulic system of a rock crusher and were bringing the system up to working pressure, a connection failed and a pipe swung out and caught a worker on his shoulder, severely injuring him.

It was obvious to us, after examining the failed connection, that the threads on the new part were severely truncated and offered very little holding force.

The manufacturer's expert argued that the threads were stripped as a result of the accident. We argued they were manufactured that way. Microscopic examination showed circumferential striations on the thread tops that looked just like the machining marks that prepared the part for threading. There was precious little damage in the axial direction which would occur if the threads had been sheared off.

The other side then hired a second expert who argued that equations from a standard mechanical engineering handbook indicated that the fitting would not have failed at the pressure existing at the time of the failure. We researched the original source of those equations and found a caveat that they would not be accurate if the threads were much out of specification. Obviously, the threads were completely out of spec and the calculations were not applicable to this situation.

The case finally settled quite favorably just before trial. For a more in depth view of the case, please see our Fall 2007 newsletter in our publications section.