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PRCI PR-3-629
- Corrosion Criteria for J-Tube Risers
- Report / Survey by Pipeline Research Council International, 10/30/1987
- Publisher: PRCI
$6.00$12.00
L51540e
Battelle Memorial Institute
Need: It has become apparent in recent years that a significant portion of the world's oil and gas will be produced offshore. As the percentage of offshore production increases, deeper and deeper water will be encountered. This will challenge the existing technology and require improvements. An important area that needs further investigation is the area of offshore pipelines and, in particular, risers.
Result: The state-of-the-art survey showed that a number of risers have been installed, using the J-tube method, in a variety of water depths and in a range of diameters. Many different coating types have been used, but neoprene appears to be the most popular. There was one reported riser failure after 10 years of service that was attributed to a damaged coating and an improperly set bottom plug. In the experimental program, two coating types were used, and the riser pipes were pulled through the J-tube test stand that was constructed in Houston; these were a two-part urethane and 1/2-inch thick neoprene. All the neoprene-coated joints studied in this program suffered only minimal damage, mostly abrasion. However, the urethane coating was scraped off and exposed bare steel. Consequently, it was concluded that neoprene is the better choice for J-tube risers.
Benefit: From the inhibitor studies, it was found that two commercial inhibitors reduced the corrosion rate of carbon steel in synthetic seawater while the third one actually increased the corrosion rate in some cases. It was also found that de-aeration was much more effective at reducing corrosion than inhibitor additions. In oxygen-free seawater, corrosion rates less than 3 mpy can be expected at the temperatures of operation; some inhibitors could lower it even further. Consequently, it is recommended that the annulus be sealed to exclude oxygen. Once the oxygen that is already there is consumed as a result of corrosion, further corrosion of the riser and the J-tube should be minimal.
Battelle Memorial Institute
Need: It has become apparent in recent years that a significant portion of the world's oil and gas will be produced offshore. As the percentage of offshore production increases, deeper and deeper water will be encountered. This will challenge the existing technology and require improvements. An important area that needs further investigation is the area of offshore pipelines and, in particular, risers.
Result: The state-of-the-art survey showed that a number of risers have been installed, using the J-tube method, in a variety of water depths and in a range of diameters. Many different coating types have been used, but neoprene appears to be the most popular. There was one reported riser failure after 10 years of service that was attributed to a damaged coating and an improperly set bottom plug. In the experimental program, two coating types were used, and the riser pipes were pulled through the J-tube test stand that was constructed in Houston; these were a two-part urethane and 1/2-inch thick neoprene. All the neoprene-coated joints studied in this program suffered only minimal damage, mostly abrasion. However, the urethane coating was scraped off and exposed bare steel. Consequently, it was concluded that neoprene is the better choice for J-tube risers.
Benefit: From the inhibitor studies, it was found that two commercial inhibitors reduced the corrosion rate of carbon steel in synthetic seawater while the third one actually increased the corrosion rate in some cases. It was also found that de-aeration was much more effective at reducing corrosion than inhibitor additions. In oxygen-free seawater, corrosion rates less than 3 mpy can be expected at the temperatures of operation; some inhibitors could lower it even further. Consequently, it is recommended that the annulus be sealed to exclude oxygen. Once the oxygen that is already there is consumed as a result of corrosion, further corrosion of the riser and the J-tube should be minimal.
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