As part of the 660,000 sq. feet Cooling Tower coating project for a  2 X 500 MW Thermal Power Plant, Amchem had to internally line several large diameter steel pipes carrying sea water with 2,000 Microns Purethane® 386/9000.

The steel pipes carry approx. 60,000 M³ / Hour (60 Million Litres / Hour) of Seawater and range from 7.8 feet (2.4 meters) to 10.5 feet (3.2 meters) in diameter. Amchem deployed special automation tools to ensure high quality blast cleaning and lining. Steel substrate was blast cleaned to SSPC SP-10. The specification allowed use of silica sand as blasting media and asked for an anchor profile of 50-100 Microns. However based on experience, Amchem opted to use  Granulated Copper Slag which provided a cleaner, sharper edge, profile of 100+ microns.

Amchem deployed its 10 MT bulk blasting pot for high output blasting. The compressed air / abrasive stream was fed into a special automated blast cleaning rig. This rig is motorized for linear travel and contains special rotary blast nozzles. Travel and rotation speeds are controlled by precision variable speed AC drives. This allows setting of optimum speeds for travel and rotation in accordance with available blast rates and pipe condition to endure blast cleaning of the highest quality. Blast finish obtained approximated a "White Finish : SP-5" compared to the "Near White : SP-10 " specified.

High quality blast cleaning is essential for high adhesion levels. This in turn provides better corrosion resistance and prevents de-lamination and damage to the applied coating.

After blast cleaning, the pipes were primed using Purethane® P-24 Primer. Graco Hydra Cat plural component airless spray system supplied mixed Purethane^® 386/9000, 100% Solids Polyurethane Coating, to the coating Rig. This rig is motorized for linear travel and contains a special rotary spray head. Travel and rotation speeds are controlled by precision variable speed AC drives. This allows setting of optimum speeds for travel and rotation in accordance with required coating thickness and tip spray rates.

Coating thickness was very even using the automated system with spot variation of not more than 100 Microns.

Field tests conducted on adhesion reported results of up to 16 N/mm² ( 2,300 Psi ) against the 8 N/mm² minimum specified. The pipe lining was holiday tested at 6,000 V and a pinhole free coating was provided.

Samples were also drawn and sent to the Indian Institute of Chemical Technology (CSIR), Hyderabad for testing coating parameters like Tensile Strength, Recoverable Elongation, Water Vapour Transmission, Flexibility, Impact and Abrasion Resistance.

100% of tests exceeded the specified parameters.