Recent detailed observations of the performance of mooring chains for a floating production unit in tropical West African waters have shown severe localized corrosion (pitting) of the steel chain after only seven years of use. This paper describes the investigation of this phenomenon as part of the Joint Industry Project (JIP) research program SCORCH (Seawater Corrosion of Rope and Chain) funded by the major oil companies, most Classification Societies and various offshore operators and manufacturers. It is shown that there is a high likelihood that the chain has been subject to microbiologically influenced corrosion (MIC) as a result of the elevated levels of water pollution in the operational area. However, despite the large localized loss of steel in corrosion pits, the breaking load shows only a relatively small reduction compared to the Minimum Breaking Load specified in design guidelines.
The SCORCH (Seawater Corrosion of Rope and Chain) project is a Joint Industry Project (JIP), funded by the oil industry, for research into the corrosion of steel chain and wire rope as used in the offshore industry for mooring large floating platforms used for storage, production and offloading of oil, particularly in deeper waters. The JIP also will develop improved guidelines for offshore operations involving chain and wire rope. The vessels are either specially built or can be converted oil tanker ships (often minus propellers and rudder). In many cases they are moored to the sea floor using mooring system of 5 or more lines. These are connected to the vessel at a bow-mounted turret (or similar arrangement). Disconnection is possible in the event of a tropical cyclone threatening the vessel. Each mooring line typically is a series system, commencing at the vessel with a heavy-duty high-tensile steel chain. It runs through the splash zone into the immersion zone where typically it connects to galvanized wire rope (for deep waters).
