Anti-HS Layer for Flexible Pipe: Full Scale Flowline Qualification Tests

Abstract

Abstract For more than 40 years, flexible pipes have been used for subsea oil and gas transportation. One of the main benefits of this technology is that, through an unbounded assembly of steel and polymer layers, the load bearing layers of the pipes are not in direct contact with the transported fluid and the corrosive components such as hydrogen sulphide (H2S). However, over a long period of time, small quantities of gas, including H2S, are able to permeate through the polymer pressure sheath and reach the metallic structural layers. To avoid this, a new polymer layer able to completely prevent H2S from reaching the annulus has been developed. This layer is called the anti-H2S layer. As part of the qualification program, an H2S exposure full scale test was performed. A flexible pipe structure with an anti-H2S layer was tested in harsh conditions, continuously exposed to gas containing methane mixed with 1.5% H2S and 5% CO2 at 200 bar (2902 psi) and 80°C (176°F) for 600 days. Several successful integrity tests were performed along the qualification program. After the H2S exposure test, the full scale prototype underwent a hydrostatic pressure test. Pipe dissection and laboratory material characterization were then performed to confirm the efficiency of the anti-H2S layer. The positive result obtained in the long term H2S exposure full scale test and qualification program demonstrate the efficiency of the anti-H2S layer. The use of the anti-H2S layer concept creates new opportunities in terms of flexible pipe design, especially for ultra deep water and very sour fluid transportation.