Marine & Offshore Gaskets & Seals

Challenge

A bulk carrier experienced severe flange face corrosion on 316L stainless steel seawater cooling system flanges within 18 months of gasket replacement. Spiral wound gaskets with flexible graphite filler had been installed during a drydock in Asia, sourced as a lower-cost alternative.

Solution

Root cause analysis identified graphite as the cathode in a galvanic cell with the 316L flange faces. In warm seawater (above 25 °C), the critical crevice temperature (CCT) of 316L was exceeded. The crew replaced all seawater system gaskets with aramid fibre compressed sheet material. The operator updated the vessel's planned maintenance system (PMS) to specify 'no graphite or PTFE fillers for seawater service' in procurement specifications.

Result

Zero flange corrosion at the next drydock inspection (30 months later). Material substitution cost was negligible; the aramid fibre gaskets cost less than the graphite originals. Flange face machining avoided on 14 flanges.

Challenge

A super duplex stainless steel (2507) flange on a production line from a subsea manifold to an FPSO failed by crevice corrosion in the gasket region. External environment was seawater at 6–17 °C with 19,345 ppm chloride. Despite super duplex having a PREN above 40, crevice corrosion developed in the confined gasket-to-flange gap.

Solution

Even super duplex is vulnerable when the gasket material creates a tight crevice that concentrates corrosive media. Replacement used non-conductive vermiculite-based filler gaskets (Corriculite-type) that prevent galvanic coupling and reduce crevice severity. Protective flange coatings were applied to the seating face.

Result

Elimination of gasket-region corrosion. The non-conductive filler broke the galvanic circuit between the gasket and flange, and the open filler structure reduced crevice aggressiveness. This approach is now standard for Australian offshore platforms with ageing flange infrastructure, particularly relevant to Bass Strait and North West Shelf installations.

Challenge

During a planned shutdown at a Bass Strait offshore platform, maintenance crews discovered that gaskets for several large-diameter separator flanges (ASME B16.47 Series A) were missing from the pre-staged shutdown kit. The gaskets were non-standard sizes in 316L spiral wound with flexible graphite filler, appropriate here because separator internals handle produced hydrocarbons, not seawater. The shutdown window was 72 hours; any extension would cost hundreds of thousands of dollars per day in lost production.

Solution

Emergency manufacture of the required gaskets at our facility, with helicopter delivery to the Longford supply base and boat transfer to the platform. Total turnaround from order to platform delivery: 36 hours. Material traceability documentation was provided electronically before the gaskets arrived.

Result

Shutdown completed within the original 72-hour window. No production extension required. The operator now pre-stages gasket kits with us before every planned shutdown, with backup inventory held at Longford.