Carbon dioxide/hydrogen sulfide corrosion under wet low-flow gas pipeline conditions in the presence of bicarbonate, chloride, and oxygen. Final report
The ability to transport wet, untreated natural gases through pipelines offshore or at other inaccessible locations is an important factor in the development of new gas fields. When a wet gas contains CO{sub 2} and H{sub 2}S, the internal corrosion rate of steel pipelines may be expected to increase. During the first program year, 1993, test solutions consisted of deaerated, pure water saturated with various partial pressures of H{sub 2}S and CO{sub 2}. Iron sulfide films formed on steel surfaces in H{sub 2}S-containing environments, and those films limited general corrosion rates to low levels. However, the sulfide films generally did not prevent pitting, and pitting was most severe when sulfide films did not completely cover steel surfaces. In the second year of the program, 1994, solution pH was maintained at 6.0 by addition of NaHCO{sub 3}. The results of these tests showed that an H{sub 2}S partial pressure as low as 0.5 psi can prevent pitting corrosion and limit general corrosion to low levels in stagnant, chloride-free, pH-6 solutions saturated with natural gases containing as much as 20 psi CO{sub 2}. However, in the presence of 1.0% chloride, 2.0 psi H{sub 2}S was not sufficient to prevent pitting for the same CO{sub 2} partial pressures. The 1995 experimental program concentrated on determining the effects of the oxygen concentration of wet natural gases on steel corrosion, and evaluating acceleration of corrosion rates at interfaces between liquid and gas phases. The most important findings of these tests were: that pitting corrosion can occur at rates as high as 20 to 30 mpy in stagnant water inside pipelines transporting natural gases with oxygen concentrations as low as 100 ppmv; and that susceptibility to both general corrosion and pitting was greater at liquid-vapor interfaces than on fully immersed specimens. Results of the 1996 test exposures showed that a slowly flowing solution increased general corrosion rates and reduced the pitting susceptibility of carbon steel. Finally, the results of this study of internal corrosion in wet gas pipelines indicate that there should be a guideline limiting oxygen contamination of pipelines gases to below 10 ppmv, and that chloride contamination should be monitored.
- Research Organization:
- Southwest Research Inst. (United States)
- Sponsoring Organization:
- American Gas Association, Inc., Arlington, VA (United States)
- OSTI ID:
- 325710
- Report Number(s):
- AGA--99001937; CNN: Contract PR-15-9313
- Country of Publication:
- United States
- Language:
- English
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