A centrifugal gas pump in oil mine was used at elevated temperature and sour environment. The pump was submerged in water to certain height. The body of the pump was ductile cast iron containing 9wt% Ni. The ductile cast iron microstructure of pump body at the top contains Chunky graphite. The lower part of the pump contains spheroidal graphite. The pump was subjected to vibration and salts of the sea in addition to heat. The heat reduced the graphite size (Chunky type) of the upper part of the pump while the lower part of the pump (base) was submerged in water which prevented the reducing of graphites (spheroidal type). The effect of salts on the upper part of Chunky graphite plus the vibration created connected caves and severe crack initiators. The cracks during vibration propagated in the upper part forming severe cracks net in matrix, graphites and carbides. The heat induced aging phenomena to increase the hardness of the upper part of pump.