Centrifugal Compressors – Sulfide Stress Cracking

A prevalent problem is sulfide stress cracking of highly stressed components, especially impellers. It requires the presence of hydrogen sulfide, water in the liquid state, an acid pH, and tensile stress.

The use of inhibitors has been investigated, although in most cases the practical solution for operation in this environment has been a change of material.

Studies indicate that for materials with yield strengths between 100,000 to 110,000 psi, stress levels required for sulfide cracking are near the yield strength. In contrast, materials with yield strengths of 140,000 psi exhibited susceptibility at stresses as low as 30,000 psi.

Continuing studies have resulted in establishing the generally accepted API 617 guidelines, which limit material yield strength to 90,000 psi or less, and a hardness not exceeding Rockwell C22.

Note that in 1987, sulfide cracking caused the loss of a critical compressor supporting a major hydroprocessing facility, costing several million dollars. The cause was impeller stage pieces with too high a yield strength.

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