Anomalous cracking of bearing balls under a liquid-butane environment

The causes of anomalous cracking of bearing balls experienced on the main bearings of a liquid-butane pump were investigated. The characteristic features of the cracked balls were (1) no scoring on ball surfaces; (2) no structural defects; (3) subsurface crack generation and intergranular growth; (4) no inclusions at the origins of the cracks. We suspected hydrogen embrittlement to be the reason for this phenomenon and the hydrogen concentration of cracked balls was measured. Amounts of hydrogen sufficient to cause the embrittlement were detected. We also measured the hydrogen concentration of balls tested under research-grade liquid butane by the four-ball rolling contact configuration. Although the cracking of balls was not reproduced, increased hydrogen concentrations were detected. The mechanisms of hydrogen diffusion into the balls are also discussed.