Sea Water Tank Inspection

Challenge

Inspectahire were tasked with carrying out a sea water tank inspection on Shell’s Brent Charlie Platform in 2013 located in the North Sea. The scope included checking Column 3 SW tank riser section for blockages and restrictions, checking pump nozzles (P4010,P4020 and P7250) from inside the tank for blockages and restrictions, and checking the plug on a blocked riser to confirm its current condition.


Solution

Access to the Sea Water Tank was from within column 3. Normal leg entry procedures applied to gain access to the gas tight floor and tank access point. A temporary scaffold was erected for protecting the open riser hole and for supporting the lowering system. The scaffolding boards covering the access point prior to starting work were removed after the boxing ring scaffold was erected, allowing full access to the tank. All work was carried out according to Shell permit to work system. All electrical equipment was tested by the platform electrician. Gas testing was carried out prior to entry into the column and energising of camera equipment. The camera system was energised and tested. The pan and tilt camera was lowered into the tank in 0.5 meter increments and manoeuvred around until as much of the tank was covered as possible. The smaller Pearpoing P455 pipe camera was deployed in to the Sea Water Intake Riser using the pan and tilt camera for guidance. The length of the riser was covered down to 50 meters from the tank floor. Once the camera systems were removed from the tank, an ROV was deployed to cover the remainder of the tank towards the rear and behind the pumps, which could not be seen using the other cameras.

Result

The Sea Water Intake Riser was found to have a covering of marine growth along its length. A considerable amount of marine growth was found to be present on the cross bars at the end of the Intake Riser covering approximately 80% of the opening and continuing back up the riser for 2 meters. The Sea Water Intake Riser measured 50 meters from the base of the Sea Water Tank. It was not possible to inspect the riser blank repair work done previously or the lower tank section as the base of the tank had a covering of marine growth and debris. Four hessian style sacks/bags and a barrier label were removed prior to the ROV survey. A small piece of debris proved too awkward to remove with the ROV on one of the strainers. The supporting cross members of the tank were showing signs corrosion along with other smaller metal supports/brackets. The Fire Pump strainer looks to be in clean condition.