Coating challenges in cold environments

Many types of coatings have been used on pipelines around the world. Some older technologies are no longer used and new coatings are being developed to meet the demands of the changing environments in which pipelines are constructed. The environment considered in this discussion is that of extreme cold weather. When coating girth welds on plant coated pipelines during cold weather conditions, the applicator must consider many factors in selecting the type of coating to be applied. The extent of preparation and amount of money the contractor or owner is prepared to spend will be determining factors in the selection criteria.

Considerations for cold environments

Coatings systems must be carefully selected for the environment in which they are to be used. Environmental conditions are not specific to application, but also include the storage environment, service life conditions such as operating temperature, soil stress and backfill conditions. Successful coating performance also requires proper surface preparation and adequate cure time prior to backfill. Existing low temperature coating solutions all have limitations. Cold temperatures can be close to 0°F in the depth of the winter and reach extreme low temperatures below -50°F with average high temperatures staying below freezing. These extreme conditions demand products and processes able to withstand such conditions. Many coatings work well in cooler temperatures. But few work in these frigid conditions. Some coatings can be formulated for these harsh environmental conditions, but still require additional work process modifications. Even those materials designed to work at extreme low temperatures may require long cure times and may not cure at all if the temperature drops below the acceptable range. If the weather is too cold, the coatings may not cure or mix properly. If the substrate is too cold, curing and proper adhesion may not occur.

The procedure in general includes ensuring that the product is kept in a warm environment immediately prior to application. All coating materials must be stored in heated storage containers in the temperature ranges identified in the manufacturer’s recommendations. Even when transported to the job site, the coating materials must be properly stored in the proper temperature ranges as well being kept out of inclement weather such as snow, rain, wind blown debris and other things that may affect the coating performance. Once at the job site, the coating material must continue to be kept in the proper temperature range during surface preparation stage, mixing and application (wrapping, brushing, troweling, rolling, spraying, etc.). One of the most common mistakes is to throw the coating in the back of the construction truck early in the morning when the coating is warm and within a short time, the coating temperature is out of the required temperature range for proper application.

Cold weather curing considerations

The other issue is the temperature of the pipe. This relates to the cure of the coating, the primer, or the adhesion of the compound to the pipe. If the pipe is not heated to the proper temperature based on the manufacturer’s recommendations, the coating will not function as intended. Overheating the pipe can also cause the coating to fail by causing over cure or compound damage. If the pipe or air temperature cools too quickly, that will also affect the coating performance.

When air or pipe temperatures drop below 45°F, some coating types are not only difficult to apply, but may not cure properly. This has been the case with some two-part epoxies and other liquids coatings that are frequently used during the cold weather months. Even the cold weather cure varieties do not always provide acceptable service when applied in some of these extremely cold environments.

Two-part epoxies and other liquid applied coatings are good coating systems when used and applied properly. Surface preparation is a critical component of coating performance, and the pipe surface must be blasted for proper adhesion and the surface warmed for these epoxies to cure properly. Even if these coatings appear to cure, the cure may not be complete. When the pipe is handled during construction activities, the epoxy can crack because of the under cure. In some cases, even when cured properly, the extremely cold temperatures can cause these epoxies to crack during normal construction activities…

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