Fatigue and Static Crack Growth Rate of Cr-Mn Stainless Steel in Aerated Brine Simulating Drilling Applications

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Directional drilling tools for oil and gas exploration is one industrial application where Manganese (Mn)-stabilized austenitic stainless steels with different amounts of other alloying elements like Chromium (Cr), Nickel (Ni) and Molybdenum (Mo) have found extensive use in spite of the demanding requirements in terms of mechanical properties and corrosion resistance. The limited resistance of this type of austenitic stainless steels to environmentally assisted cracking (EAC) in hot chloride (Cl-)-containing environments is well known. Chloride-bearing environments at elevated temperatures are not uncommon in drilling operations and can indeed challenge the EAC-resistance of CrMn-stainless steels

Product Number: 51323-19152-SG

Author: Ashwini Chandra, Helmuth Sarmiento Klapper, Ramgopal Thodla

Publication Date: 2023

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Austenitic stainless steels are commonly used in drilling equipment, where CrMn-stainless steels in particular have long tradition in this application due to its combination of high strength and ductility, good corrosion resistance and non-magnetic properties. The likelihood of encountering aggressive drilling environment related variables - higher salinity and temperature as well as loading conditions related to fatigue and steady state loading, necessitates an understanding the performance of such a material under these conditions. Fracture mechanics-based experiments were performed to understand the fatigue crack growth rate (FCGR) and static crack growth rate (SCGR) behavior of one CrMn austenitic stainless steel under simulated drilling environment. An aerated brine of pH 9.8 was evaluated, with the chloride content at 56,000 ppm and temperature at 50°C. Susceptibility to corrosion fatigue was concluded based on the observance of frequency dependence of FCGR, where an increase in FCGR was observed with decreasing frequency. Environmentally assisted cracking (EAC) susceptibility was also observed under static loading conditions. Chloride induced stress corrosion cracking is believed to be the mechanism of EAC.