Catastrophic failures of drill pipes are a major concern in HPHT drilling environments. The National Energy Technology Laboratory, U.S. Department of Energy and DNV, Columbus are investigating mechanisms of crack propagation in ultra-high strength low alloy (UHSLA) martensitic steel drill pipe under cyclic stress as functions of pH, H2S concentration and temperature in simulated production fluids. These fluids are deaerated 5% NaCl solution buffered with NaHCO3/Na2CO3 or CO2 in contact with 0.83 kPa H2S. Microscopic investigations of the pre-cracked sample surfaces after corrosion fatigue tests revealed the presence of additional cracks that had propagated in the bulk material in neutral pH solution at 20°C. This paper discusses effects of the production fluid temperature on susceptibility of the UHSLA steel to environmentally assisted cracking. Post-corrosion fatigue surface characterization methods, such as optical and scanning electron microscopy, were used in this study.

Subject
Scanning electron microscopy, Crack growth, Corrosion fatigue, Secondary cracks, Diffusion, Inspection, Corrosion cracking, Fatigue crack growth rate, Stress cracking, Corrosion products, Sodium chloride solution, Steel, Hydrogen
Keywords:
Ultra-high strength low alloy steel, sour environments, corrosion fatigue
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2014
Association for Materials Protection and Performance (AMPP)
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