Epoxy Coal-Tar Coating Steel Water Pipes

The epoxy coal-tar coating steel water pipe is a carbon steel welded or seamless pipe commonly used in water supply systems, where the base steel pipe has been protected with an epoxy coal-tar coating. These steel water pipes are widely used for water transmission and water distribution.

The epoxy coal-tar coating

The epoxy coal-tar externally coated spiral-weld steel water pipes, 16″ x 7 mm x 6m, made to AWWA C200, supplied to Morocco.

This coating primarily consists of epoxy resin and coal tar as the main film-forming substances, with various rust-inhibiting pigments, insulating fillers, toughening agents, and other additives. The paint can be viewed as an epoxy modified with coal tar and other additives. Its characteristics include excellent adhesion, toughness, resistance to moisture, water, and acids, alkalis, saltwater, volatile oils, salt spray, and other chemical substances, as well as the ability to expand and contract in sync with the substrate, ensuring the coating does not peel off or crack. Especially, the epoxy coal-tar coating is known for its excellent water resistance and ability to form a dense, impermeable barrier, making it suitable for underwater piping systems and underground water pipes.

Base Pipe Selection

The base pipes furnished with the epoxy coal-tar coating are typically steel water pipes manufactured in accordance with AWWA C200 standard specifications. It can be either a carbon steel seamless pipe, longitudinally electric-resistance-welded (ERW) pipe, or spirally submerged-arc-welding (SSAW) pipe. These steel water pipes usually have an outer diameter ranging from 100 mm to 4000 mm, a wall thickness from 5 mm to 16 mm, and pressure ratings ranging from PN6 to PN40. The steel grades include ASTM A283, ASTM A516, ASTM A36, ASTM A515, etc.

Production Process of the epoxy coal-tar coating

The coal-tar epoxy coated SSAW water pipes, 20″ x 10mm x 12m, supplied to Santiago, Chile.

The application of epoxy coal-tar coating to AWWA C200 steel water pipes involves several steps to ensure proper adhesion and corrosion protection. Generally, it shall be furnished in accordance with AWWA C210 standards. Here’s an overview of the production process:

• Surface Preparation: The steel water pipe surface shall be blast cleaned to remove oil, grease, mill scale, water, and any other contaminant,  creating a rough surface profile for better coating adhension.
• Holdback for field weld: When the steel water pipes are to be joined by field welding, a band that is free of lining and coating shall be left on the inside and outside surfaces at each pipe end. This band shall be of sufficient width to permit field welding without damage to the lining and coating.
• Primer Application: A primer, usually an inhibited epoxy, is applied to the prepared surface. This layer helps with the adhesion of the coal-tar epoxy and provides additional corrosion protection.
• Coal-Tar Epoxy Application: The coal-tar epoxy is then applied over the primer. This can be done using airless spray equipment, which ensures a uniform and thorough coating.
• Wrapping: In some cases, after the coal-tar epoxy application, a wrap of glass fiber mat may be applied, followed by another layer of epoxy coal-tar. An outer wrap of coal-tar impregnated glass fiber felt is then added to reinforce the coating.
• Curing: The coated pipe is left to cure, allowing the epoxy coal-tar to harden and form a durable protective layer.
• Inspection and Testing: After curing, the coating is inspected and tested to ensure it meets the required standards and specifications for thickness, adhesion, defect-free coverage, and required corrosion resistance.
• Handling and Storage: Proper handling and storage are crucial to prevent damage to the coating. Coated pipes should be stored in a way that avoids direct sunlight and extreme temperatures, which can affect the coating’s integrity.