A pressure vessel, designed and tested under laboratory conditions for tens of thousands of cycles, failed in service after only a few cycles. Thousands of oscillatory pressure reversals have been measured at each loading. However, the predominance of the stress amplitudes were well below the critical threshold values necessary to initiate fatigue cracking.
Analysis has demonstrated that the disparity between lab cycling and field loading conditions cannot be explained simply by mechanical loading alone. Further investigation into the problem revealed that an extremely aggressive environment, the by-products of the internal combustion from within the pressure vessel, along with high temperatures, pressures, and other sources of high tensile loading all contribute to the short fatigue life of the vessel.