Coatings Technology

Pipeline coatings and cathodic protection (CP) are the major defenses against external pipeline corrosion. The CP provides protection at coating holidays. Any change in the chemical, physical, or electrochemical properties of an external pipeline coating can be considered as a failure. Some failures can be catastrophic, when the protection is completely lost, whereas others have little or no effect on the coating performance.

The success of a coating greatly depends on its ability to provide a barrier against oxygen and water to work with the cathodic protection. The wetting, adhesion, cohesion and cathodic disbondment properties, which are interrelated, also dictate coating corrosion control ability. It has been calculated that an extremely small concentration of oxygen and water can start the corrosion process. Therefore, to minimize corrosion, material that has extremely low permeability have to be used in the formulation. For internal protection, however, success mainly depends on the coating’s ability to prevent corrosion causing ions from reaching the pipe surface. Although corrosion protection is the major factor in determining the type of pipeline coating, mechanical properties also influence this choice because of their role in controlling the economics of pipeline construction and the subsequent effect on pipeline safety.

Coating Options

There are many choices of coating and insulation products for onshore facilities and offshore pipelines, when considering external corrosion protection, flow assurance and efficiency at high temperature operating conditions and deepwater application. These include fusion bonded epoxy (FBE) single and dual layer, three layer FBE/polyolefin adhesive/polyolefin such as polyethylene or polypropylene and thermally sprayed aluminum (TSA) for external corrosion protection.

Selection of a product will depend on the service and environmental requirements, the required thermal properties, when used for insulating purposes, and an examination of economics. Considerations regarding the selection also include the handling, installation and operational constraints. The selection of the optimum coating or insulation system is as much an art as a science since prior successful use by the pipeline owner; knowledge of prior success by a similar pipeline owner or recommendations from a coating manufacturer or coating applicator are also used as selection criteria.

Coating Properties

The installation of offshore hydrocarbon pipeline systems is gradually approaching water depths of 10,000 feet for design lives of 30 years and more. As a consequence of these requirements external parent and field polymeric coating systems must have superior mechanical and physical properties that include the considerations below:

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