Part 2: Phases of Subsea Inspection

There are several phases of Subsea/Underwater Inspection, Repair & Maintenance (IRM) campaign throughout the lifetime of offshore structure:

1. Baseline Inspection

This shall be the first subsea inspection for the offshore structure and become the reference for the subsequent subsea inspection, hence the name “baseline”. It is also known as as-built or as-installed inspection. Many of the asset owner shall require the baseline inspection to be performed within one year of installation. The baseline inspection can be the most extensive inspection performed on the structure with various type of inspection and subsea Non-Destructive Testing (NDT) shall be performed depending on the type of structure. Besides obtaining baseline inspection data, it is also to ensure structural integrity after transportation & installation and fulfilling contractual requirement before handing over the structure from project team to asset owner.

2. Periodic Inspection

Usually once in every few years, the periodic subsea inspection of the offshore structure shall be performed. Like a car, it needs to be inspected from time to time to understand its current condition and to resolve any significant problem found. The project title’s varies according to type of structure, method of intervention or requirement by the asset owner – major platform inspection, ROV pipeline inspection, FPSO/FSO Underwater Inspection in lieu of Dry-docking (UWILD) – just to name a few. The extensiveness of the work shall depends on asset owner or Classification Society’s requirement (ever heard of ABS, DNV, BV or RINA? Those are among the Classification Society). Combination of several inspection technique and subsea NDT are common, using diver or ROV or both. Maintenance works such as cleaning blocked sump caisson’s termination or removing debris are not uncommon to be performed during the inspection project. Any damage or anomaly found during the inspection work shall be recorded & analyzed for future repair works if required.

3. Post Repair & Maintenance Inspection

It is very usual to perform some inspection after completing the underwater repair or maintenance work. Many project also require inspection at certain phases (pre and/or in-between) of the repair/maintenance work, to ensure the work process is done correctly and proper record is available. This can be part of the periodic inspection or as stand-alone project such as pipeline anode sled installation for multiple pipelines when issue with pipeline’s cathodic potential had been detected during previous ROV pipeline inspection. 

4.   Post Decommissioning Inspection

Offshore structure doesn’t last forever. When the time comes whether production had ceased due to depleted reservoir or it is no longer safe to use, the structure needs to be removed and decommissioned. If it is an offshore platform, the whole platform shall be removed, lifted and sent back to shore to be scrapped. The post decommissioning inspection shall be the last inspection to check that the seabed is clear from any debris or only the section determined by asset owner is left behind on seabed.

In the next article we shall explore some of the typical subsea inspection technique & NDT used during subsea IRM project. 

Note: All photos are from private collection with the exception of the jacket installation - credit to the originator.