Volume 26, Issue 5-6

ABSTRACT Coatings are the first line of defence against external corrosion of pipelines and, when they fail, cathodic protection (CP) acts as the backup. Because of their importance, a variety of coating properties are evaluated and standards developed. The standards used in North America for evaluating external pipeline coatings on pipelines are reviewed in this paper. These standards have been developed by the American Society of Testing and Materials (ASTM), the American Water Works Association (AWWA), the Canadian Standards Association (CSA), the National Association of Corrosion Engineers (NACE), and the Society of Protective Coating (SSPC). Limited information on standards used in Europe and elsewhere is also presented in this paper. There is good understanding in the industry of the important properties that have a detrimental effect on pipeline coating behavior, and several standards are available to test these properties. Some coating properties for which different standards have essentially the same requirements include blast cleaning, surface profile, penetration resistance, chemical resistance, dielectric strength, electrical conductivity, and impact resistance. Properties for which standards from different organizations have different requirements include cathodic disbondment, adhesion, cohesion, water permeation, flexibility, and abrasion resistance. These properties are also important for coating performance; thus harmonization of the standards used to evaluate these properties would be very useful. Properties for which no adequate standards have been developed include: quantification of visual and non-visual contaminations of steel surface, pH measurements at the disbonded coatings, blister formation, holiday detection using above-ground techniques, and compatibility and repairability of joint and mainline coatings. Properties for which adequate standards are available but are not utilised in the standards to evaluate pipeline coatings include: microbial resistance, weathering, gas permeation, and freeze-thaw stability. Correlation of performance of coatings in standard tests and in the field has not been well documented, nor is such a correlation a specified requirement in any of the standards. To date, no studies have been successful in establishing a correlation between field performance and performance in standard tests. Development of a capability to predict long-term coating performance from test data established in short-term standard tests is an industry priority.

ABSTRACT External surfaces of pipelines are protected from corrosion by polymeric coatings that have evolved in the industry over the past 60 years, beginning with asphalt and then coal tar coatings, followed by polyethylene, epoxy, and urethane coatings. When a coating degrades or fails, the type of coating has an effect on the generation of environments that can cause corrosion and stress-corrosion cracking (SCC). In this paper, the types of coatings, laboratory performance, field performance, and the state-of-the-art of various pipeline coatings are reviewed.