Standards for oil and gas pipeline coatings
Oil and gas pipelines are an essential part of the energy infrastructure, and their coatings must meet a multitude of standards: Preserve the equipment, protect from corrosion, follow federal regulations — and be quick to apply for fast-moving pipeline owners.
For the three major types of pipeline locations — below-ground buried systems, above-ground pump stations and underwater pipelines — there are tried-and-true coating systems used for their ease and efficiency. Outlined below are the preferred coating system for each pipeline environment and how they meet the high standards of pipeline owners and inspectors.
Regulations for pipeline coatings
Depending on the materials a pipeline is transporting (process oil, crude oil, dry gas, wet gas, or sour gas), there are various requirements required for corrosion protection. In the U.S., the Department of Transportation’s Pipelines and Hazardous Materials Safety Administration (PHMSA) issues minimum standards that pipeline owners are required to meet. In Canada, pipelines are regulated by provincial jurisdiction, or by the National Energy Board (NEB) if they cross provincial borders. Pipeline owners and coatings contractors are both responsible for selecting pipeline coatings that meet the necessary regulations.
Surface preparation and application method
The minimum surface preparation standard for the oil and gas pipeline body is SSPC-SP 10 Near-White Blast Cleaning with SSPC-SP 11 Bare Metal Power Tool Cleaning for the ends of the pipeline where the joint coatings are applied. All coatings for the body of the pipeline are shop-applied by automation. The same goes for field-applied joint coatings, except when rough terrain or close quarters prevents the use of automatic units and manual spray coating must be used.
External coating systems based on pipeline location
For buried systems (the majority of most oil and gas pipelines), the almost-universal standard pipeline coating is fusion bond epoxy (FBE) powder systems. FBE has become the standard because it is easy to apply, is affordable, works well with cathodic protection and is tough enough to withstand transportation from the shop to the truck to the field. A section at each end of the pipe is left for the field-applied joint coatings: Either a three-layer shrink wrap or a high performance 100% solids liquid-applied epoxy. The drawback of the epoxy is the cure time, which isn’t ideal for fast-moving pipeline projects.
As buried systems are in an immersive environment (i.e. surrounded by water), cathodic protection is a must and is always used in conjunction with the FBE system. You wouldn’t be able to license a pipeline without cathodic protection. The coating system and the cathodic protection have a synergistic relationship: As the coating deteriorates with age and develops holidays, the cathodic protection takes over and ensures continued corrosion protection for the pipeline.
Pump stations and compressor stations
For the above-ground pump stations and compressor stations where pressure is reintroduced into the pipeline to maintain flow, pipeline coatings that protect against atmospheric conditions (wind, rain, UV, infrared) are the standard. This is typically an inorganic zinc primer, an intermediate coat of epoxy, then a topcoat of polyurethane for color and gloss retention. Joint coatings are field applied with the same coating system as the body of the pipeline. Cathodic protection isn’t used on the above-ground sections of the pipeline.
Though seemingly different from buried pipeline systems, underwater pipelines are actually in quite a similar environment, as they are both immersive. These pipelines are either pre-coated with three layers of FBE or applied with coal tar urethane on site. The choice between these two is based on the personal preference of the pipeline owner, though coal tar urethane’s health and safety concerns have seen it fall out of favor in recent years.
As with buried pipelines, underwater pipeline coatings are used in conjunction with sacrificial cathodic protection. One additional element that’s added to underwater pipelines is concrete weight coatings — some poured and laid on site, some pre-cast — to ensure the pipeline stays at the desired depth and doesn’t float out of the water.
A note on internal coatings
As with the exterior of most pipelines, corrosion is a risk factor for the interior of oil and gas pipelines. Robotic internal field joint coating companies exist all around the world. Their processes may be slightly different; however, each company is able to perform a quality product. When the owner and the welding contractor are aligned with the coating company, the highest quality coating outcome is achievable for the pipeline owner.
Other methods for preventing internal corrosion exist, such as engaging with a metallurgist to select a type of steel pipe that best interacts with the material. Each has their own advantages and disadvantages that should be discussed between the pipeline owner and the coatings contractor.
This article just begins to scratch the surface on the complex topic of oil and gas pipeline coatings. The be best way to deepen knowledge in this area is through AMPP pipeline educational offerings.