Case Study: ROV-deployed inspection of firewater pumps on a North Sea platform

Graham Marshall

July 16, 2013

Fig. 3: Corrosion mapFirewater pumps are crucial to the safe operation of platforms. Caissons protect the pumps from the harsh offshore environment and provide the transport route for firewater. Degradation of the caisson can render pumps ineffective; so it is necessary to demonstrate caisson integrity for the safe platform operation. This relies on inspection to determine caisson condition.

A recent inspection of a firewater caisson by the MAG-Rover found degradation. The inspection included 0° corrosion mapping to quantify the condition of the material. Degradation was found on the internal surface of the caisson, therefore the damage was not visible to external inspection.

This corrosion map defines the nature, depth and extent of the wall loss. A further representation of the condition of the material is provided in the wall thickness distribution shown in Figure 4.

Fig. 4: Wall thickness DistributionThis distribution shows the proportion of the area inspected as a function of thickness. It shows that about 60% of the area is below nominal thickness and is clearly suffering wall loss. About 10% of the area is below 76% of nominal and about 1% of the area is below 68% of nominal. About 0.2% of the area is below 60% of nominal and the minimum thickness is near 52% of nominal. The detailed information obtained provided the basis for understanding caisson integrity of the and ensured sound decisions.