FFS on offshore equipment

FFS on offshore components (i.e. piping, pipelines, structures,….etc) is not simple as FFS on onshore components; as there are many parameters shall be considered during the assessment. Last job I was involved in, was FFS on platform riser; in order to check the remaining thickness against the operations conditions. There are many codes and standards you have to check against it during calculating the required thickness to accommodate the new operations conditions.

Usually for onshore FFS, you want to check mainly against the internal pressure for the piping, pipeline or pressure vessels, and calculate the remaining life time accordingly. Of course in some application you have to check against some other parameters. For example, in onshore pipeline, you have to check the required thickness for the buoyancy in case of buried pipeline in soil having a high level of water table.

For offshore, checking the reaming thickness against the internal pressure is just the first step in the FFS. Then, based on the item you calculate the FFS for, you will check the other related parameters. For example, in case of the offshore riser, after check the remaining thickness against the internal pressure using ASME on DNV codes, you shall check the fatigue requirement using the DNV codes in order to determine the actual SCF which will impact on the MSYS used in the first step of calculating the remaining thickness. Also, you have to check the met-ocean data against the planned remaining life time as it is important to decide for how long time the riser will withstand all of these parameters.

In conclusion, if you want to calculate the FFS for the Steel riser you will open ASME B31.4, ASME SECTION II-D, DNV RP-C203, DNV RP F-206, DNV OSS 302 and DNV SE 0476. It is not the matter of internal pressure only.