The acids used in downhole treatments are expected to induce severe corrosion attack on production tubing, downhole tools and casing, even though the anticipated contact times are kept short. To reduce the aggressive attack of the acid on tubing and casing materials, corrosion inhibitors are added to the acid solution. Even through inhibitors are known to provide some corrosion protection, they are usually effective only at high concentrations.
Development of an integrity management program is initiated during design phase, which includes selecting the appropriate materials, establishing requirements for corrosion, erosion, flow assurance and process along with associated maintenance, monitoring and surveillance requirements. In this GATEKEEPER, the philosophy around the materials selection and corrosion monitoring is discussed as the primary design barrier to corrosion and cracking in critical parts of a subsea system.
Titanium (Ti) alloys are attractive to subsea oil and gas operators due to their high strength, low density relative to steel, and innate corrosion resistance. The current primary application for Ti alloys has been in tapered stress joints (TSJs). Ti stress joints are a primary and sole barrier to loss of a riser and release of hydrocarbons into the environment. Therefore, the integrity of the TSJ is of utmost importance, and integrity loss of a TSJ carries a very high inherent risk.