Failure analysis of a slot-welded impeller of recycle hydrogen centrifugal compressor

• The failure of the slot-welded impeller can be attributed to SSC accelerated by HIC.
• FV520B steel with banded δ ferrite does not match the optimal heat treatment.
• The corrosive environment is caused by hydrogen sulfide and condensed water vapor.
• The stress in the impeller strongly depends on shrink fit and centrifugal force.

A recently failed slot-welded impeller of recycle hydrogen centrifugal compressor has been investigated by material tests, theoretical calculation and numerical simulation, which focus on the environmental susceptibility of material, the corrosivity of environment and the characteristic components of the stress state. It is found that the matrix of FV520B precipitated hardening stainless steel used in the failed impeller did not match the optimal combination of strength, toughness and corrosion resistance, and large volumes of δ ferrite with banded appearance further increased the environmental susceptibility of material; the electrochemical corrosion environment came into being due to the presence of hydrogen sulfide and condensed water vapor in the recycle medium; the high hoop stress in the failed impeller was mainly caused by the shrink fit during manufacturing and the centrifugal force during operation. Based on these results, the failure of this slot-welded impeller can be mainly attributed to sulfide stress cracking (SSC), and hydrogen induced cracking (HIC) is found to accelerate SSC by breaking the continuity of material and hence increasing local stress. Additionally, the prevention and mitigation measures against failure have been discussed, which can provide some insight into improving the reliability of centrifugal compressor impeller.