Polyurea Tank Lining

A 360m2 steel storage tank on a chemical dosing tank farm required a new long-lasting polyurea tank lining system installed. This particular tank had an epoxy tank lining that had done really well with 20 years service. Unfortunately an inspection showed signs that it had started to deteriorate.

Due to the sensitive location of the tank, and the fact it was a COMAH site, specialist precautions would need to be taken to prevent any risk of explosion during the re-lining process.

The works would take 2 weeks to complete, during which time we would have to work around methanol tanker offloading. This meant our teams would need to work flexible hours to complete the project on time.

This particular system would involve abrasive blasting the existing epoxy, and bringing the metal to an industry standard of SA2.5 cleanliness, with a surface profile of 75 microns.

Due to the storage of demineralised water, a polyurea lining system was chosen. Not only for ease of application, but for the 20+ year service the client required.

Abrasive Blasting – Preparation

The most important step to ensure any lining adheres to a substrate such as steel, is in the preparation. Abrasive blasting is the best form of preparation as it takes away a small amount of the surface of the steel. This leaves peaks and troughs for the new lining to bite into.

With polyurea, a sharp surface profile is required. The blasting process needs to comply with the COMAH legislation, meaning non-sparking. All our equipment was earthed, our blast hoses were anti-static, and our blast operatives wore anti-static ellingtons with flame retardant blast overalls. Atex lighting was used for the tank illumination, and there were no hot works allowed inside the tank.

Once the blasting was complete, all spent media was removed. The entire tank was dry vac to remove dust from the surface profile in preparation for the pure polyurea tank lining application. The blasting process for this particular tank took 5 days to complete, including both the blasting and cleaning.

Specialist Polyurea Application

When it comes to polyurea application, specialist equipment is required to apply the coatings. Polyurea is a 1:1 ration material consisting of amine resin and Isocyanate. Both materials when mixed together create a reaction which is an almost instant cure. Our polyurea application rig is completely mobile, and due to its size can be utilised in most areas. With up to a maximum of 100ft of hose, it can access most hard to reach areas such as vertical storage tanks and roofs.

When applying the material, both substances must be heated to 70 degrees centigrade to help with the atomisation and the viscosity of both fluids. Both substances are pumped from the machine to a specialist plural spray gun. As the trigger is pulled, it emits equal parts inthe a mixing chamber, causing the almost instant cure. The material itself can be built up to any thickness, which in turn offers fantastic structural integrity.

Once the entire tank was fully sprayed in polyurea at a nominal thickness of 2mm, the entire coated surface was to be quality control checked. This would involve the usage of a holiday detector. Even though the material is 2mm thick, there is every chance a pinhole may be present which would inhibit corrosion on the area affected. Whilst the rest of the tank would be protected, after a number of years that pinhole would corrode, causing the tank to leak.

Our operatives are trained to check, check, and check again.

Following completion of the quality control checks, the project was signed off and the quality control form filed in accordance with our ISO9001.