Production of hydrocarbons reservoirs containing CO2/H2S is nowadays required. Increasing CO2/H2S contents above others cause a decreasing pH-value. For deep reservoirs high strength steels need to be used. Casing and tubing made of higher strength materials lead furthermore to a pronounced material saving due to reduced wall thickness.

Those requirements will be fulfilled on the one hand by sour gas resistance of steel and on the other hand by demands on mechanical properties of steel. This is also shown in the API Specification 5 CT, where a C110 grade is included.

Therefore investigations with various contents of microalloying elements Nb, V, Ti and B were performed. Different alloys in lab scale with approximately 130 kg were melted, bloc casted and afterwards rolled to plates according to the deformation grades at the rolling mill. Constant load and fracture mechanical testing was done to evaluate SSC resistance according to NACE Standard TM0177-2005 Method A and D. The specimens were tested in solution A (5 wt% NaCl, 0.5 wt% CH3COOH) with 100 % H2S concentration at 1 bar.

SEM and STEM studies were performed for further characterization of microstructure of materials. Different contents of microalloying elements resulted in different SSC resistance.

Subject
Test methods, Materials, Carbides, Microstructure, Fracture surfaces, Steel, Elements, Sulfide stress cracking, Fracture, Titanium alloys, Alloys, Cracks, Martensite
Keywords:
Oil Country Tubular Goods (OCTG), Sulfide Stress Cracking (SSC), C110 Api, NACE Method A and D tests
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2012
Association for Materials Protection and Performance (AMPP)
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