The shafts on two centrifugal pumps failed during use in a petroleum refinery. Light optical microscopy and scanning electron microscopy were used to analyze the damaged materials to determine the cause of failure. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.

Two oil-pump gears broke after four months of service in a gas compressor that operated at 1000 rpm and provided a discharge pressure of 7240 kPa (1050 psi). The compressor ran intermittently with sudden starts and stops. The large gear was sand cast from class 40 gray iron with a tensile strength of 290 MPa (42 ksi) at 207 HRB. The smaller gear was sand cast from ASTM A536, grade 100-70-03, ductile iron with a tensile strength of 696 MPa (101 ksi) at 241 HRB. Analysis (metallographic examination) supported the conclusion that excessive beam loading and a lack of ductility in the gray iron gear teeth were the primary causes of fracture. During subsequent rotation, fragments of gray iron damaged the mating ductile iron gear. Recommendations included replacing the large gear material with ASTM A536, grade 100-70-03, ductile iron normalized at 925 deg C (1700 deg F), air cooled, reheated to 870 deg C (1600 deg F), and oil quenched. The larger gear should be tempered to 200 to 240 HRB, and the smaller gear to 240 to 280 HRB.

Sucker-rod pumps are operating in very aggressive environments in oil well production. The combined effect of a corrosive environment and significant mechanical loads contribute to frequent cases of failure of the rod string during operation. Standards and recommendations have been developed to control and avoid those failures. This study presents various failure cases of sucker rods in different applications. The heat treatment of the steel material and the resulting microstructure are an important factor in the behavior of the sucker rod. A spheroidized microstructure presents a weaker resistance to corrosion affecting the rod life. Non-metallic inclusions are a pitting preferential site leading to fatigue crack initiation. Heterogeneous microstructure as banded martensite and ferrite/pearlite decreases the ductility of the material affecting the fatigue propagation resistance.

An oil scavenge pump was found to have failed when a protective shear neck fractured during the start of a jet engine. Visual inspection revealed that the driven gear in one of the bearing compartments was frozen as was the corresponding drive gear. Spacer wear and thermal discoloration (particularly on the driven gear) were also observed. The gears were made from 32Cr-Mo-V13 steel, hardened and nitrided to 750 to 950 HV. Micrographic inspection of the gear teeth revealed microstructural changes that, in context, appear to be the result of friction heating. The spacers consist of Cu alloy (AMS4845) bushings force fit into AA2024-T3 Al alloy spacing elements. It was found that uncontrolled fit interference between the two components had led to Cu alloy overstress. Thermal cycling under operating conditions yielded the material. The dilation was directed inward to the shaft, however, because the bushing had only a few microns of clearance. The effect caused the oil to squeeze out, resulting in metal-to-metal contact, and ultimately failure.