Oscar E. Martinez and John E. Stachowiak, Weatherford
Sucker rods are subjected to cyclic stress which leads to fatigue failure. It is well known that the shot peen process increases the fatigue life on metal parts. Although several manufacturers implemented shot peening in the sucker rod manufacturing for years, optimal parameters that yield a dramatic increase in fatigue life require extensive studies on both input parameters and comparative fatigue testing. This paper will discuss the steps and challenges involved in achieving the optimized shot peen process and benefits on the sucker rod fatigue life.| Optimum shot peening is achieved by iterating the process inputs such as shot size, shot metallurgy, shot velocity, the volume of shot and peening time. Each iteration is then evaluated by an axial fatigue test which replicates the downhole loading condition. The laboratory test results are then validated with field data to show increased runtime on sucker rods. The laboratory axial fatigue test showed that the optimized shot peen process increased the fatigue life of the sucker rod approximately 12 times as compared to shot blast processed rod. Sucker rod failures relating to fatigue were tracked for two years after the implementation of optimum shot peen parameters into the manufacturing process. The field data shows a decreasing trend in sucker rod failure rates which supports the laboratory results. This paper presents an insight into how an optimized shot peen process can help to improve the sucker rod quality from a fatigue perspective.