The upper mast of a workover rig had been telescoped into the lower mast and the lower mast was being laid down across the carrier cab for transport to a new location. Suddenly, the hydraulic cylinder base, which supported the weight of the compacted mast, collapsed as it was being laid over. There were no injuries, but there was significant workover rig damage .
Photograph A Sister workover rig with mast fully extended.
J.E.I Metallurgical was called to investigate the collapse. The short I-beam cross member used to support the hydraulic cylinder was removed for examination. There was a corroded hole through the cross beam support flange or web and through wall corrosion near the bottom. A view of the failed cross member is shown in Photograph B.
Photograph B Overall view of failed hydraulic cylinder cross beam.
For comparison, the frame of an earlier model workover rig was examined and photographed. The identically shaped cross member is shown in Photograph C.
Photograph C Earlier model workover rig frame and hydraulic cylinder structural support.
Examination of this exemplar hydraulic cylinder cross member revealed almost identical areas of corrosion. The rig insurer denied the claim sighting corrosion, wear and tear as opposed to overload resulting from operator error. Operator error was covered under the terms of the insurance policy.
Although there was obvious corrosion, the connections between the cross member flanges and the carrier frame exhibited larger amounts of permanent bending and deformation. Permanent bending and deformation are characteristics of overload failure and not corrosion.
One of the lower flange to carrier frame fractures is shown in Photograph D.
Photograph D Permanent deformation of lower flange.
Of importance is the presence of significant flange thickness and little evidence of flange thinning from corrosion in Photograph D. The very small variation in flange thickness is denoted with arrows.
A finite element analysis of the cross beam was conducted with allowance for corrosion thinning and web perforation.
In spite of the fact that some corrosion was present, the final conclusions were that the hydraulic cylinder cross member failure was the result of operator error and was not the result of corrosion.