pipeline corrosion coating

Coating Types

There are many coating types that are employed in corrosion protection of steel pipes. This protection can be broken down into 2 areas. First, main line coating where this coating is applied to every pipe section with the exception of the last 6” of both ends and second, girth weld where the pipe ends are coated in the field and after the pipe joints are welded. Main line coating types include:

·         Cold applied tapes

·         Fused tapes

·         Fusion bonded epoxy

·         2 part Urethane

·         2 and 3 layer Polyethylene

Girth weld coating types include:

·         Shrink Sleeves

·         Cold applied tapes

·         2 part liquid epoxy

Tape Application to Pipe

The pipe coating process consists of the following steps, :

·         Drying and cleaning using a grit or sand blasting to remove mil scale

·         Phosphoric acid wash and drying, if required

·         Primer spray and drying

·         Inner-wrap application continuously and spirally using precision tension control

·         Outer-wrap application continuously and spirally using precision tension control

·         Holiday Detection

·         Cut backs at both pipe ends

The above steps are carried out using detailed specifics to conform to industry and tape manufacturer application standards under the watchful eyes of a certified inspector. For example, the sand blasting step requires achieving a well defined cleanliness and anchor pattern for the primer/inner-wrap to achieve expected adhesion, primer dryness and thickness, tape tension, temperature and overlap control are among many application conditions that are required to be practiced. Both tape layers are applied with recommended tension to insure good application to the pipe, to insure good conformability at the overlap and to achieve the mechanical and chemical adhesion of the coating system to the pipe. With machine application using tension the coating experiences tension and necking down of the coatings by < 2%. This tension effect creates a “gasket effect” or flow of the adhesive at the overlap sealing the adhesive to the overlap and further creating mechanical adhesion of the coatingto the substrate and to the multiple interfaces withinthe PE tape coating system.