How To Maintain OCTG Pipes of Different Materials?

OCTG pipe mainly include casing pipe, tubing, drill pipe, etc. OCTG pipes are crucial in oil and gas production. Different materials have different chemical compositions and properties, and maintenance cannot be generalized. Each has its own key points, which are related to its own life and production efficiency. Due to their different chemical compositions and performance characteristics, OCTG pipes of different materials have different special requirements for maintenance, as follows:

Duplex stainless steel material

1. Prevent chloride ion stress corrosion

Duplex stainless steel is more sensitive to chloride ions, and high-concentration chloride solutions should be avoided during maintenance. If used in an environment where chloride ions may exist, the chloride ion content on the surface of the pipe needs to be regularly tested. If the chloride ion exceeds the standard, it should be rinsed with clean water and dried in time.

2. Control the temperature range

Duplex stainless steel may undergo phase transformation in certain temperature ranges, affecting its performance. Generally, it should be avoided from being in a temperature environment of about 475℃ for a long time. After being used in a high temperature environment, it should be cooled slowly to prevent stress caused by rapid temperature changes.

3. Special cleaning requirements

When cleaning duplex stainless steel OCTG pipes, a mild cleaning agent should be used, and fluorine-containing and sulfur-containing cleaning agents should be avoided to avoid damaging the passivation film on the surface of the pipe. A neutral water-based cleaning agent can be used for cleaning with soft tools to prevent damage to the surface of the pipe.

Austenitic alloy material

1. Avoid sensitization temperature range

Austenitic alloys are prone to sensitization when they stay in a certain temperature range (such as 450-850℃) for a long time, resulting in increased sensitivity to intergranular corrosion. During use and maintenance, its operating temperature should be controlled to avoid long-term operation in this temperature range. If it cannot be avoided, measures such as rapid cooling can be taken to reduce the residence time in the sensitization temperature range.

2. Prevent intergranular corrosion

To prevent intergranular corrosion, austenitic alloy OCTG pipes can be solution treated or stabilized. During maintenance, pay attention to check whether there are signs of intergranular corrosion on the surface of the pipe, such as microcracks, surface roughness, etc. If intergranular corrosion is found, pickling, passivation and other methods can be used to restore the passivation film on the surface of the pipe.

3. Pay attention to stress relief

Austenitic alloys have a greater tendency to work hardening, and residual stress is easily generated during processing and installation, increasing the risk of stress corrosion cracking. Therefore, after processing or installation, stress relief treatment should be carried out as needed, such as heat treatment or vibration aging.

High-alloy stainless steel material

1. Strengthen surface protection

Although high-alloy stainless steel has good corrosion resistance, the passivation film on the surface still needs to be protected. During storage and use, avoid contact with sharp objects to prevent scratches on the surface passivation film. If the passivation film is found to be damaged, it should be repaired in time. Chemical passivation or electrochemical passivation can be used to restore the integrity of the passivation film.

2. Adapt to special environmental maintenance

High-alloy stainless steel is often used in harsh environments such as high H₂S partial pressure and high chloride. During maintenance, targeted treatment should be carried out according to the specific environmental characteristics. For example, in an environment containing H₂S, the corrosion of the pipe should be regularly tested. Corrosion monitoring coupons and electrochemical monitoring can be used to detect potential corrosion problems in a timely manner.

3. Strictly control the welding process

High-alloy stainless steel is difficult to weld, and defects such as thermal cracks and pores are prone to occur during the welding process, which affects the performance and service life of the pipe. Therefore, when welding and repairing high-alloy stainless steel OCTG pipes, it is necessary to strictly control the welding process parameters, select appropriate welding materials and welding methods, and have experienced welders to operate, and perform necessary post-weld heat treatment and non-destructive testing.

Summary

In short, accurate maintenance of OCTG pipes of different materials is the key to smooth mining operations. Each material is carefully cared for at each stage according to requirements to keep it alive, help the energy industry, and drive the industry forward.