corrosion on pipes

What Is Decarburization and Precaution of OCTG Casing and Tubing?

OCTG stands for Oil Country Tubular Goods, mainly referring to the various piping products extensively used in oil & gas production and drilling activities. Equipment such as drill pipes, steel casing pipes, tubing pipes, couplings, connections, and accessories majorly form the OCTG group.

OCTG casing and tubing, in particular, is a popular type of steel pipe used in the oil and gas industries. However, they may encounter decarburization, which reduces the pipes’ performance and lifespan. Let’s look at the three main types of OCTG pipes, the decarburization process, and how to avoid it.

OCTG Drill Pipe

Drill pipes are heavy equipment involved in the drill bit’s rotation and are responsible for circulating the drilling fluid. The fluid is pumped through the bit and backs up the annulus. As a result, the pipe comes under extreme axial tension, large amounts of torque, and intense internal pressure. This is why drill pipes are extremely tough and robust.

Steel Casing Pipe

The steel casing pipe is an essential component in drilling operations and is used to line the borehole dug into the area for extraction. It is also subject to extreme levels of axial tension. The large diameter pipe is strategically placed inside the borehole and is held in place with cement.

The casing, in particular, is subject to heavy axial tension due to its dead weight and extreme external pressure by the rock surrounding the pipe. It also experiences internal pressure due to extreme fluid purging.

Standard steel casing pipes include API 5CT, Common Grades in J55/K55, L80, N80, C90, P110, and T95. Casing pipes usually have end connection types in BTC, LTC, and STC.

OCTG Tubing Pipe

The OCTG tubing pipe is responsible for extracting oil from the drilled area. It goes inside the casing pipe and is generally found in 30ft (9m) with a robust threaded connection at both sides. The tubing should always be sturdy enough to withstand extreme pressure during extraction and resist heavy loads and deformations.

Decarburization and Prevention

Decarburization is a process that reduces the carbon content in steel. It occurs when the steel used in pipes is heated above the lower limit or its recrystallization temperature, usually around 700 degrees Celsius. Decarburization can be detrimental to your oil & gas drilling, excavation, and transportation operations because you need the OCTG and steel pipes to work in optimal conditions and withstand varying temperatures.  

An offshore oil rig

Excess decarburization affects the production and follow-up process. It reduces the efficacy of operations. Therefore, OCTG manufacturers usually take several steps to ensure the minimization or decarburization to protect casing and tubing.

There are two effective ways to eliminate or avoid decarburization. First is to fully utilize nitrogen protection to sustain the pressure inside your application, typically an oil well. The neutral nitrogen prevents outside air from decomposing into oxygen and water vapors, dispersing the application’s oxidation gas.

Another way to avoid decarburization is to balance the carbon dioxide levels. If the carbon dioxide level in the oil well is higher than the content of carbon dioxide and other gases outside, it will help avoid decarburization and oxidation. Therefore, it is important to calculate the balance point relevant to the application’s internal temperature and carbon content.

An oil drilling rig in the ocean

Importance of Regular Inspections

As mentioned earlier, OTCG casting and tubing are the foundation of gas and oil wells and pipeline design. They provide the conduit for efficient and safe transportation of oil and gas products to the market. Regular inspections and preventive maintenance are integral to your oil & gas pipeline operations because they can reveal how these equipment are holding up during various operations.

Identifying minor issues early can help fix them before they escalate into a full-blown-out crisis. Besides averting worker injuries and costly damages, inspections also help prevent leakages from damaged OCTG and their negative effect on the environment.

Damaged or cracked pipe thread can have a catastrophic impact on drilling projects, increasing repair costs and causing the loss of valuable revenue and unnecessary downtime. That’s why thorough inspections are crucial to keeping drilling operations up and running in the long term.   

Get Started with CNPS

If you’re looking for world-class OCTG pipe solutions and oilfield service equipment for your operations without excessive decarburization, check out the products at CNPS.

Our cutting-edge EOR technology solutions, oil and gas equipment and services, fiberglass pipe systems, composite pipes, fiberglass tanks, and mud logging equipment are designed to provide optimal utility and meet API standards and ISO certification requirements.

Our Fiberglass piping systems are more flexible, versatile, durable, non-conductive, and economical in the long run. The material is highly tensile and offers the ultimate vibration resistance, helping ensure that mechanical vibrations or winds don’t hinder operations. Such properties make them ideal for applications prone to decarburization. Get in touch to learn more about our premium products and offerings.

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