Abstract
In the oil and gas industry, it has been established that for pipelines fabricated with carbon steels, their limitation is related to H2S and CO2 environments, which is 7 to 10 psia of partial pressure of CO2. Therefore, in carbon steel cracking is shown, after 7 or 10 psia of partial pressure of CO2. The experimental work was performed under static conditions in autoclaves within a pH of 3 to 3.8; partial pressures of 16 - 96 psi for H2S and 15 - 53 psi for CO2, in the temperature range of 25°C - 150°C. It was observed that the average yielding stress used in Sulfide Stress Cracking (SSC) tests decreases with temperature increment. Hydrogen Induced Cracking (HIC) evaluations showed that X52 steel, under conditions, was not susceptible to HIC. Results of SSC did not show indications of cracking after exposure to sour solutions, except for the specimen exposed to high H2S and CO2 content (96 psi of H2S and 53 psi of CO2 of the partial pressure) and high temperature (150°C). Microcracks located between the upper and lower weld beads were also observed. However, the highest average corrosion rate was 0.27 mm/year (10.6 mpy), which occurred in samples exposed to 96 psi of H2S and 53 psi of CO2 at 150°C. Likewise, the highest localized corrosion (severe pitting attack) was obtained at the same environment with a corrosion rate of 4.2 mm/year (167 mpy). The oil and gas industry could use carbon steels pipelines in partial pressure higher than 10 psia.
Highlights
The acceptance criteria of NACE TM 0284 are: crack length ratio (CLR) less than of the 15%, crack thickness ratio (CTR) less than of the 5%, crack sensitivity ratio (CSR) less than 2%, the values obtained did not exceed the criteria established in NACE TM 0284
The Four Point Bent-Beam (FPBB) specimens were stressed up to 80% of the Actual Yield Strength (AYS) obtained at each test temperature
Vickers hardness measurements were made on the welded joints of X52 steel obtaining the maximum hardness in the weld beads (216 Hardness Vickers (HV)) which meets the requirements established in NACE MR 0175/ISO 15156
Summary
The oil and gas industry can provoke a wide variety of corrosive environments. The transportation of these corrosive fluids always results in the induce of failures in the production systems; this shows the need to perform qualification tests on candidate pipelines steels considered for the development of the Mexican field, due to the high concentrations of H2S and CO2 expected in the exploitation of mature fields. Sulfide stress cracking (SSC) is a major concern for most oil and gas pipeline operators for many years; research work still is done to develop strategies for a better management of this problem [1]-[7]. The SCC occurs due to the combination of three factors; a susceptible material, localized tensile stress above a threshold and exposure to corrosive environment. Sometimes due to environmental conditions, only corrosion occurs with no cracking [8]; in many times the cracks evolve from corrosion pitting [9]
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