Long-Term Weathering Effects of Pipeline Coatings

Polyurethane coatings are selected as an external coating on welded steel pipelines for its properties as an excellent means to control corrosion, minimize cathodic protection requirements, and, in this case, help the pipe achieve a trouble-free, 100-year design life in the underground environment. For this cross country water transmission pipeline project, typical pipeline segment lengths approach 20 miles (32.2 km) and pipeline diameters range from 84 (213.4-cm) to 108 inches (274.3-cm). It is anticipated that pipe manufacturing and coating production will outpace the contractor’s field installation and subsequently lead to variable storage times of pipe strung along the alignment. During this time, the stored pipe will experience extended time above ground in extreme temperature and in the presence of solar light, including ultraviolet (UV) radiation. Construction and delays can result in pipe section exposure beyond the specified period of 180 days. Therefore, it is important to understand the expected magnitude of exposure deterioration beyond that limit. A previous study was conducted, and the results were presented at American Society of Civil Engineers (ASCE) Pipelines Conference 2014. Sample pieces of large diameter polyurethane coated steel pipe, exposed to elements for up to 2 years, were monitored for surface temperatures during the peak of summer. Darker-colored pipe surface temperatures exceeded 150 degrees F (65.6 degrees C). That presentation was a snap shot of the postexposure effects due to temperature and solar. This will illustrate and describe the periodic exposure results every 3 months, leading up to a total of 21 months of exposure. It will include discussion of the test set-up and procedures, laboratory measurement results, and polyurethane coatings response following each period’s weathering exposure.