Case Study: Polyurethane (Solventless) Coating inside Mild Steel pipeline using Plural Component Airless Spray Equipment.
Project: Near Chennai.
About the project
The project was to protect sea water intake pipelines of Mild Steel to mitigate corrosion, and the designed dry film thickness was 1.5 mm (minimum).
Pipes were designed to carry saline water from Sea-intake to the Cooling Tower of the Thermal Power Plant.
Challenges
This thermal power station had sea water intake pipes of varying sizes ranging from 500mm to 4000 mm, which were prone to highly aggressive corrosive environment as it was designed to carry saline water alongwith sand particles, which added to the complexity of the project. Smaller diameter pipes required special rotary nozzle equipment for blasting and painting as human entry in the pipe was not feasible.
System Specification and Recommended Coating:
A durable high DFT (Dry Film Thickness) coating to withstand the aggressive environment called for Polyurethane or such hard and flexible coating. Coating required to dry fast on application without sagging. Cipy proposed its Branded 100% solid polyurethane product namely, Durathane 100EA which was already used in many saline water using structure in other similar Project and hence it was readily accepted. Minimum thickness of coating proposed was 1500 micron.
: 2 :
Conventional coatings applied by brush or single component airless spray could not deliver the desired thickness at one go. Hence, plural component airless spray equipment of Graco Make or equivalent was proposed. Also remote controlled rotary nozzle equipment was proposed for blasting and painting inside smaller diameter pipes.
Application procedure adopted at site:
On receipt of pipes for coating in the painting yard, pipes were first unloaded in the blasting yard. Pipes were blasted using dry compressed air using copper slag to SA 2.5 surface Profile. Immediately upon blasting, surface profile checked by Quality personnel of Cipy’ Applicator and Client and once approved, pipes were rolled to the painting section where polyurethane based primer (Cipy’s ACPC 60) mist coat was applied using single component airless spray equipment to stop flash corrosion on blasted steel surface. Within 24 hours from priming, final polyurethane coat was applied at a minimum thickness of 1500 micron using plural component airless spray equipment.
Final Checking and despatch:
After the application of Polyurethane coating, next day coated pipes were checked for holiday in coating by using suitable equipment. Any holiday detected were immediately attended as per approved procedure.
DFT were checked as per specification at number of locations in each pipe. If satisfactory, pipes were released. If not, those were again coated with surface preparation as per approved procedure till require DFT was achieved.
Metal coupons were made and prepared alongwith pipes in requisite numbers as per laid-down procedure. Coated metal coupons with Polyurethane over a coat of primer on properly blasted M.S coupons was tested for desired Pull-off test and shore “D” and finally on meeting all testing parameters, pipes were allowed for despatch to location where those were to be laid.
