Best practice for FPSO maintenance, repair and inspection is a procedure that should be ongoing. The cycle of inspection, repair and maintenance for FPSO vessels is known as IRM for short. And FPSO, of course, is also an acronym for floating, production, storage and offloading. These are floating vessels used in the oil and gas industry as they are more cost effective than employing pipelines to get the oil or gas ashore.
Pipelines are rigid and stay in place, while an FPSO can release its riser turret and moorings and be towed away, or if the vessel has its own power source, it can move away under by itself. This is a considerable benefit in places where weather condition might threaten the FPSO. In some countries it may be a typhoon or hurricane, or in colder countries it might be icebergs, for example. By being mobile the FPSO can avoid danger and thereby save the company money in the long term.
One of the greatest dangers to an FPSO in the North Sea, and in other places where storms are common, is green water. This is where heavy, driven quantities of sea swell hit the FPSO with force. In the North Sea, four out of five FPSO’s are affected adversely by green water, especially in winter. Damage occurs to almost anything that is exposed to the seas, and it now appears that testing with models was not effective enough to predict the actual consequences. This means that most FPSO’s are not built to an adequate standard to fully withstand the immense forces that the North Sea can deliver.
This of course has a direct effect on FPSO maintenance. While the fitting of side panels to strengthen the structure, and the fitting of raised bow walls to limit the ingress of green water have had a positive effect on lessening the damage, FPSO maintenance still means regular repairs due to a lot of green water damage on an ongoing basis. Green water damage is mainly responsible for damage above the waterline.
Damage below the waterline can also happen. This can be as a result of vessel collision. The collision may not be severe, and only be little more than a bum in bad weather, but if the FPSO is carry a lot of oil or gas, what seems as a small bump can create serious problems. Divers are used to inspect the vessels below the waterline. Their reports will determine the maintenance and repair routines subsequently required.
In the North Sea around three out of every five FPSO’s have been aware of internal cracks between tanks. Inspection and maintenance routines usually discover the cracks through evidence of small leaks, usually not too big to be a serious problem in themselves, but indicative of something else that is more serious. FPSO maintenance and repair routines in these cases can be expensive as the tanks have to be taken out of service, cleaned and then have strengthening stiffeners welded in place.
FPSO maintenance is a never ending task. In the North Sea corrosion is rife and all installations require regular inspection and maintenance routines with repairs where necessary.