A Micro Look Into Sucker Rod Material Selection for Fatigue Resistance


Mike Murray, Exceed Oilfield Equipment, Inc. 
Joshua Jackson, US Corrosion Services

Downhole sucker rod pumping conditions have changed in many aspects over the years. While downhole rod pumps, surface pumping units, automation, gas mitigation and sand control are constantly being improved, Sucker rods are one of the few products yet to catch up to the changes in our industry. Whether it be dwindling profit margins squeezed by operators with budgetary constraints, lack of capital to invest in new manufacturing processes, or a desire to simply maintain the status quo, sucker rod manufacturers have rarely taken a look at their product offering and manufacturing process to see if there areas for improvement. Automating the forging process, automating the threading process, and improving the shot peening quality control, have all been adopted by rod manufacturers to make existing rods more reliable. There are some manufacturers experimenting with more bold metallurgy to combat issues like corrosion. This is a step in the right direction. What all metallurgist are beginning to agree with is that the more you improve the granularity and microstructure of a steel, the more fatigue resistant that steel becomes once a stress riser is introduced in the form of corrosion or handling issues. When these stress risers occur, and they always occur in steel over time, all users hope that their rods will last the longest with those stress risers before ultimate failure. Exceed has contracted a third-party metallurgy lab to conduct a blind two-phase study to: 1) Observe the grain size of each sucker rod, from the major manufacturers in the market, to evaluate the effects of Normalized & Tempered rods vs Quenched & Tempered rods. 2.)Observe the fatigue resistance of each sucker rod through charpy impact notch tests. THE OBJECTIVE of this metallurgy lab study is to see if there is a correlation between the heat treatment process and the fatigue resistance of a sucker rod. This study may be objected by some of the manufacturers due to the inability of some to manufacture using both N&T and Q&T processes. Some are limited to only N&T or only Q&T. Exceed has the ability to produce both Q&T and N&T, so this test was encouraged to see if we should transition our focus to producing only the most fatigue resistant products, thus benefiting the end user. All manufacturers and rod designations will be kept anonymous and only steel type and heat treatment process will be listed in the study.