Internal corrosion of oilfield tubulars is a prevalent risk in the oil field. This common problem can be caused by many sources, including hydrogen sulfide (H2S), CO2, dissolved oxygen, brinish disposal water, highly acidic soil conditions and more. Damage from corrosion can cause significant setbacks such as reduced productivity, maintenance downtime and even equipment replacement.

The costs of corrosion add up to billions of dollars per year in lost revenue and reduced operating profit for oil and gas companies.

Oil and gas operating companies must follow safe and timely production schedules, and therefore it is important to prevent the setbacks of corrosion damage. Without some form of internal protection, most tubulars will have a significantly diminished life cycle due to corrosion.

There are options available for protecting tubulars and minimizing internal corrosion. Two of the most common choices are internal coatings and liners. However, before a specification can be made, it is important to have a basic knowledge of the characteristics and capabilities of both coatings and liners to know which option will offer reliable protection in the application.

Internal coatings 
Internal coatings were originally composed of an organic solvent-based solution, which was changed in the 1970s. Due to the Clean Air Act, the industry cut the use of solvents and began making powder coatings to reduce emissions. However, coating with powder often is unsuccessful for a number of reasons. 

Powder coatings are thin, not very durable and easily damaged by impact. Powder coatings do not have a guaranteed consistent thickness. Chipping usually begins in thin areas first, allowing imperfections to grow easily and cause enough corrosion damage to prematurely shut down a system due to piping failure.

Many powder coatings have improved over the years, but it is essential to understand that coatings can only perform reliably under certain environmental and operational parameters. Adhesion failure is more likely to happen in higher temperature applications. Exposure to wireline tools or coiled tubing operations will very likely cause damage to coatings.

Qualification tests should be conducted for each coating option before selecting a powder coating. Care must be taken during the selection process that the coating standards are not confused with one another and that the testing during fit-for-purpose trials is relevant to the system in question since some standards might not be suitable for internal coatings.

Internal tubular polymer liners
The two most common liner options are thermoset glass-reinforced epoxy (GRE) liners and polyvinyl chloride (PVC) liners. GRE liners perform well in high-temperature and high-strength applications, while PVC liners operate in low-temperature applications. Recent developments include a family of liners that vary in chemical resistance but share a primary distinguishing feature—the allowable service temperature of each liner material.

The unique features and durability of GRE liners have made them a more efficient and reliable solution to many common challenges. Even in high-temperature applications, GRE liners resist deterioration due to their consistent strength and stability. GRE liners have proven to provide reliable long-lasting protection against corrosive fluids in a wide range of applications, including water injection, CO2 injection, gas production, gas-lifted oil production, environments containing H2S, and onshore and offshore chemical disposal wells (Table 1).

The manufacturing process for GRE liners used by Duoline Technologies is different from others in that the wound, epoxy-reinforced fibers undergo an advanced high-temperature cure process that cures liners from the inside out. This prevents the entrapment of air pockets in liner walls, guaranteeing consistent strength and stability throughout the entire liner. The curing technique produces the smoothest internal lining option available on the market.

Internal lining installation 
An internal lining system is made by inserting a rigid GRE tube into a steel tubular and filling the annular space with a special mortar. After the special mortar sets and the liner is firmly positioned in the steel pipe, the GRE liner is cut flush with the end of the steel tubular.

A molded flange called a “flare” protects the end of the GRE liner and mortar. The flare is bonded to the inside diameter of the liner with an adhesive, and a specially designed and reinforced corrosion barrier ring (CBR) is compressed in the connection by the opposing flares. These components effectively and reliably protect entire tubulars from exposure to corrosive fluids.

For American Petroleum Institute (API) connections, decision-makers need to choose one that provides an oil-resistant nitrile CBR with spring steel wire reinforcements to hold the ring in place during pressure cycles. For premium or proprietary threaded connections, Duoline provides a glass-reinforced teflon CBR that is designed exclusively for the DL-Ring.

The liner-flare-CBR combination along with the grout provides corrosion protection for the steel pipe and coupling. The liner and grout transfer internal pressure loads directly to the steel pipe that is the load-bearing member in the design. 

These GRE liners are being installed in oilfield tubulars. (Source: Duoline Technologies)

Case study
A GRE liner was installed on a well in the Gulf of Mexico (GoM) due to the harsh environmental conditions. Initial installation of the liner for the customer presented challenges. The staff overcame these obstacles by providing technical support and maintaining constant contact throughout the installation. Duoline provided its customer with onsite field technicians to oversee all aspects of the liner installation and ensure proper running and handling procedures were followed.

The first completed installation and operation of injector wells in the GoM were such a success that it has resulted in the installation of eight total additional wells. All were completed with GRE liners coupled with the VAM connection. The success of these eight completed wells demonstrates that the GRE liner is an ideal option for companies seeking to overcome the corrosive and rigid conditions in the GoM.

A little extra knowledge goes a long way when choosing the proper corrosion protection option in oilfield tubulars. Operators need to know basic characteristics and capabilities of coatings and liners and perform a complete assessment of the environment in which the liner will have to perform. GRE liners are a reliable choice that will bring long-lasting, effective corrosion protection to investments in a wide range of applications.

This GRE liner survived years longer than the oilfield tubular it was installed in. (Source: Duoline Technologies)