Severe rust and deterioration on sub-sea drilling risers in Nigeria for pipes used in offshore oil drilling operations. Due to cycles of immersion underwater and storage on deck pipes had severe corrosion problems. Very tough environment and very tough life cycle (salt water, salt spray, sun, impacts, abrasion, and temperatures ranging from 4°C to 85°C). The original coating system, applied four years ago, had badly deteriorated.
Due to pitting, drilling risers were commercially blasted to SSPC-SP6 /NACE 3 standard. After surface cleaning and salt removal with CHLOR-RID , RUST GRIP was applied at 300 micron wet/150 micron DFT to encapsulate the surface metal, additional coatings included MOIST METAL GRIP (2 part water repelling epoxy), and 3 coats of ENAMO GRIP (2 part aliphatic urethane enamel top coat).
Generally speaking, submerged applications are taken care of by epoxies. Polyurethane is used on top to prevent UV degradation. Since these oil pipes are subject to immersion / UV exposure cycles, the polyurethane topcoat is needed. If the pipes were permanently used for deep water application, a polyurethane would not be used. Furthermore, as a rule of thumb, for submerged applications one needs a final DFT not less than 350 microns.
Note: Water/sun cycles are much more severe than permanent immersion.
The result was a rust free, air- and waterproof, ultra-durable surface to withstand the harsh underwater environments.
reference: products we used
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