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500 series for Water Treatment Vessel

OVERVIEW:    Pinholes affected the ‘wash area’ in an 800‐1000mm wide band below the tank’s centerline. Osmosis blistering resulted in crevice corrosion which was invisible at the coating application stage. These pin-holes measured 3-4 mm in depth and .5-1mm wide. Previous coating failure had developed a concentration cell with a difference in aeration, depleted of oxygen, which led to a highly corrosive condition in deepening the pinhole.

ENVIRONMENT

Produced water environment (coalescing) at 95°C

SUBSTRATE

Lining on produced water treatment vessel

CHALLENGE

The original coating was failing with osmosis blistering and exposure of the substrate to the cargo which caused localised corrosion pitting. Remedial work for this job needed to be completed along side ongoing repairs to ensure that the vessel arrived in Singapore in 2 years time for a refit. Corrosion rates of 2-3 mm per year would have reduced vessel’s corrosion allowance to zero resulting in a vessel perforation.

SOLUTION

Chemcote recommended that the affected areas be abrasive blasted and treated with repeated high pressure hot washes. A steam lance would heat the vessel up with steam to 400°C to remove salt from the pin-holes. Measurement of pinholes would ensure glass-flake epoxy coating filling. During the application of the coatings, metallic salt, environment and high voltage spark testing would be carried out to guarantee long life protection.

SCOPE

Abrasive blasting to remove coating

Salt tests revealed metallic salts, contaminated areas

After water washing and drying, abrasive blast to whip surface back to class 2.5

Spigots were blasted using angle nozzle

Whip blasting of floor and spigots for salt test

Area carefully hand painted to fill pinholes

Coating inspected and declared fit for purpose

Vessel boxed and pressure tested

PRODUCTS

OUTCOME

The vessel’s internal lining was replaced with corrosion resistant glass-flake filled epoxy resin. This film will protect the substrate and prevent further metal loss. The Chemcote team carried out the job successfully despite many challenges and maintained final coating quality much to client’s satisfaction. The pin-holing challenge was resolved by pit-filling and is to be reviewed in future NFT programs.

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