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Evaluation of Methods to Alleviate Corrosion Fatigue in Type 135 Drill-Pipe Steel for Offshore-Drilling Applications Pages: 17 Published: Jan 1970
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View License Agreement Various methods of modifying the drilling environment and changing the response of the material to the environment were examined as potential methods of alleviating corrosion fatigue in Type 135 drill-pipe steel for use in offshore-drilling applications. The fatigue behavior of Type 135 steel specimens in seawater and in air was compared to the results obtained in deaerated seawater, freshwater and seawater drilling mud, inhibited drilling mud, and drilling mud with an elevated pH. No improvement in fatigue life resulted for any of the modified environments examined, several actually proving detrimental. Cathodic-protection studies were then conducted on specimens subjected to various applied current densities during fatigue cycling in seawater and a range of current densities that improved the fatigue behavior determined. The half-cell potential was determined for the steel in seawater and zinc selected as the sacrificial metal coating. Zinc-electroplated specimens fatigue tested in seawater showed a marked increase in fatigue life compared to that of uncoated specimens in seawater. Bare regions up to ⅜ in. wide were tolerated with no loss of protection and regions as large as ¾ in. wide still resulted in an improved fatigue-corrosion behavior. Thus, zinc electroplating of Type 135 drill-pipe steel resulted in a substantial improvement in fatigue behavior in a seawater environment. Alteration of the chemical environment resulted in no improvement of the fatigue behavior of uncoated specimens over that obtained in plain seawater. | ||
