Function
Identify and address corrosion and wear that occurs on anchors, mooring lines and jewellery.
Who supplies them
Ashtead Technology, HebDrone, Geo Oceans, InterMoor and Proceanic.
Key facts
Anchor inspection depends on the anchor type (see B.3.1 for further information). Drag embedment anchors are buried in the sea bed and so inspection usually involves checking burial depth. Suction anchors and driven pile anchors are inspected for corrosion where they protrude out of the sea bed.
Mooring chains are either inspected using general visual inspections or close visual inspections, usually using ROVs (see B.3.2 for further information). Chain links are cleaned if this is necessary for inspection.
During inspection, ROVs visually inspect the whole chain lengths, especially at critical points such as touch down points which receive the most wear. They use callipers to take measurements of link diameters and link touch points. The data is then compared to measurements taken during manufacturing.
ROVs can also conduct photogrammetry to build a digital model of the chain to use in fatigue assessments and to monitor wear with time.
Synthetic mooring lines are inspected visually to check for wear and tear, especially at attachment points for buoyancy devices and clump masses.
The frequency of inspections depends on what is being inspected. Chain in the high-load environments like the touch down points may be inspected every six months, or even more frequently, initially. Chain in lower-load environments can be inspected annually or even less frequently. Frequency of inspection also depends on observed failure rates.
Mooring lines are replaced when observed wear breaches limits.
Jewellery such as links are inspected in a similar way to chains (see B.3.3 for further information), whereas jewellery such as buoyancy devices and load reduction devices are inspected visually.
In-line tensioners are inspected visually, but there is little else that can be done to ensure their condition, and their long-term performance has not been proven.
If an anchor or section of mooring line fails, then it is replaced as rapidly as possible.
Early floating offshore wind farms may install load monitoring on mooring lines to understand how actual loads compare with calculated loads and with observed degradation.