scope:

Technical Guidance

This Publication sets out the principles and practices of materials selection and corrosion control and provides information on lessons learned in the industry. Key aspects of welding and fabrication are also discussed. However, it should not be seen as an alternative to the involvement of suitably qualified materials and corrosion specialists in subsea or renewable energy projects. Indeed, the complexity of some of the issues involved is such that the document cannot always provide definitive recommendations, and the requirement for expert advice on materials issues will remain.

There are many associated topics that could affect materials performance and equipment integrity that are not addressed in any detail in this document, for example:

• welding and cladding procedures,

• weld defect acceptance criteria,

• non-destructive examination requirements,

• QA/QC procedures during component manufacture,

• verification and validation testing of assembled equipment,

• chemical treatment of hydrotest fluids,

• methods of deployment of equipment to avoid seawater ingress, and

• subsea connection procedures to avoid or minimise seawater ingress.

Extent of Application

This Publication relates to equipment fully immersed in seawater installed at or above the seabed for oil and gas production, including water, gas and chemical injection systems and their associated controls - essentially everything from the wellheads downstream to the delivery point to the surface facilities. The equipment is that typically associated with subsea developments, using either tie-backs to fixed platforms, or an arrangement of rigid or flexible risers to floating production units which could be semi-submersibles or monohull vessels. Similarly, Appendix A covers those elements of renewable energy facilities that are predominantly immersed in seawater.

The emphasis is on the identification and discussion of those materials- and corrosion-related issues which are specific to subsea equipment and which are not usually encountered in offshore platform-based designs utilising dry completions.

Outside the scope are:

• drilling and downhole equipment;

• items used only for the deployment, retrieval or maintenance of the permanently installed facilities (though the materials used for such equipment should be subjected to review, based on the principles in this document. At least one serious incident is known to have occurred due to rapid galvanic corrosion of aluminium components in deployment equipment.

Failures of high strength fasteners used in lifting and deployment equipment have also been reported);

• structural items and steel fabrications (Ref ISO 13628-15); and

• topside equipment if not part of the subsea envelope, e.g. risers.