OTC 21371--New Anti H_2S Layer for Flexible Pipes

摘要

Flexible pipes are extensively used for oil and gas development and thus transport the corrosive fluids of the production flow. These corrosive components (water, carbon dioxide or hydrogen sulfide) do not enter in direct contact with the structural steel layers of the pipe. However, they will diffuse through the pressure sheath and may induce corrosion phenomena on the structural layers. H_2S gas could thus be present in the annulus. It is then necessary to use pressure vault and armour wires made of sour service steel grades instead of sweet service steel grades. In addition to the cost impact, the choice of these sour service steel grades with often lower mechanical performances has a direct influence on the overall design of the flexible pipe as they will result in structures with higher weight. Such a weight increase can be a disadvantage, for example in the case of ultra deep water applications. To prevent H_2S from reaching the annulus of the pipe, a new thermoplastic material was developed. Components in the sheath material react with H_2S and prevent it from diffusing and reaching the annulus. The use of this new ‘Anti-H_2S’ layer will ensure a H_2S free environment in the flexible pipe annulus. Considering that the steel layers will not be exposed to H_2S, no degradation linked to the presence of H_2S needs to be taken into account in the choice of the structural steel layers constitutive of the annulus. Consequently, the use of high steel grades layers with reduced thickness will be possible, reducing the cost and the weight of the flexible pipe. In addition, the ‘Anti-H_2S’ layer makes it possible to propose flexible pipes for applications with high H_2S contents, for which no solution could be proposed otherwise.