Subsea Integrity Management: Materials Selection & Monitoring

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.

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Failures Related to API 5CT High Strength Steels

American Petroleum Institute (API) 5CT high strength steels are extensively used for casing strings in  wells subjected to high cyclic hydraulic fracturing loads. While non-sour grades of API steel such as P110 casing strings have been used satisfactorily for well construction, standard API P110 connections have seen higher rates of failures than pipe body failures in shale wells that require hydraulic fracturing. P110 pipe body and connection failures have also been experienced in cases where poor manufacturing practices have been employed to produce P110 steel casings and connections  used in wells subjected to these high hydraulic fracturing loads.

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Collapse Strength of Casing Subjected to Combined Load

Triaxial evaluation of wellbore loads is used extensively for casing and tubing string design and analysis. A triaxial based collapse strength method was recently adopted by the American Petroleum Institute (API), and an addendum issued to API Technical Report 5C3 (TR 5C3). The triaxial based collapse formula incorporates internal pressure and axial load into the calculation of casing and tubing collapse strengths.  Casing and tubing that are subjected to combined loads have higher collapse strength than previous formulas would predict, permitting the use of thinner walled, or lower strength, pipe than formerly required.

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Well Integrity: A Holistic Approach to Annulus Pressure Management for Subsea Wells

Annulus Pressure Management refers to an engineered approach ensuring that casing annulus pressures do not challenge the well’s integrity during the life of the well. The aim is to maintain the casing pressure within the well’s mechanical design limits at all times by controlling the ‘A’ annulus pressure.

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