During completion of an oil well, the casing string became stuck and unmovable. A dangerous and improper procedure was attempted in order to loosen and free the casing string. Power to the rotating string was reversed and the pipe was slowly turned three, one-quarter reverse turns. Unfortunately, the 1170° of reverse rotation still did not free the casing. The reverse torque was held by the mechanical tongs and a short snubbing line, which is normally intended to be used as a tong hanger line. In this case, the hanger line was being used as a safety line.
An additional one-quarter reverse turn was attempted. During this maneuver, the snubbing line failed and because of the stored energy, the casing string began to unwind and the tong wire line also separated. The violent unwinding of the stored energy in the casing caused both wire ropes to fail. As a result, the tongs were slung around on the work deck causing injury to one worker and killing another.
The tongs and failed wire rope are shown in Photographs A and B.
Non-destructive visual and microscopic metallurgical examination revealed evidence of severe internal wire rope corrosion. External corrosion in wire ropes can be visually observed. However, internal wire rope corrosion can be hidden from view. The result can be a wire rope that visually appears usable, but because of internal corrosive attack, is much weaker than expected.
Ends of the failed corroded wire rope can be seen in Photograph C.
Wire ropes are very strong and low profile machines used in a wide variety of applications. They come in all shapes and sizes ranging from less than a 0.01-inch diameter to a half mile long with a 1-foot diameter! Many times the problem with a wire rope can be seen from the outside and is usually passed off as common wear and tear. However, physical damage to the outside of a wire rope generally means a lack maintenance or improper storage and is an easy way to tell if the wire rope is faulty. Ultimately, improper maintenance and/or improper storage will lead to wire rope failure.
J.E.I. is regularly requested to analyze wire rope failures and finds that often, poor inspection, improper maintenance and improper use are determined to be the root cause of these failures. If you have a wire rope(s) in question or need a wire rope failure analysis or a metallurgical evaluation, call us today!