The Basics of OCTG Steel

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Published: 06th November 2012
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OCTG stands for oil country tubular goods, and the designation refers to seamless rolled products such as casing, tubing, and drill pipe subjected to various loading conditions depending on their specific application. Drill pipe is heavy tubing that circulates drilling fluid and rotates the drill bit on a drilling rig. It is subject to axial tension due to its weight, high torque due to the drilling rotation, and internal pressure from drilling fluid. It may also be subject to bending loads. Casing is the product that lines the bore hole, and it too is subject to axial tension as well as internal pressure, plus external pressure when drilling through rock formations. Tubing is the pipe that through which the product is transported from the well, and it must be highly corrosion resistant for OCTG applications.

Manufacturing Processes for OCTG Steel

OCTG line pipe and other OCTG products are typically manufactured using continuous mandrel-rolling processes and push bench processes for the smallest diameter products. Plug mill rolling is used to make larger diameter products, while cross-roll piercing and pilger rolling is used for yet larger diameter products. Because these processes do not allow for the customary thermo-mechanical processing used for welded pipe, alloying content must be increased to ensure high strength.

Ensuring Stress Cracking Resistance

Chromium and manganese are the main alloying elements that are used for sufficient hardenability of OCTG products. However, manganese is limited in its usefulness against sulfide stress cracking. Additionally, too much chromium can lead to formation of precipitates that can actually initiate cracks. Molybdenum can be used to overcome the limitations of manganese and chromium alloying because it is a much stronger hardener. For higher strength materials necessary for deep well drilling, highly tempered martensite is used due to its resistance to sulfide stress cracking. Adding molybdenum results in a product with optimum yield strength and sulfide stress crack resistance.

High-Chromium OCTG Products

In environments that exceed 100 degrees C, or with high partial pressures of carbon dioxide, steel grades with reduced carbon content and increased chromium in solid solution are more resistant to corrosion. Because sulfide stress cracking originates in pits, molybdenum is used due to its ability to improve steel's pitting resistance. Newer steels, with 15% chromium have even greater strength while being highly resistant to carbon dioxide corrosion at temperatures up to 200 degrees C.

Casings, Couplings, and Coatings

Numerous types of casings and couplings are used in OCTG applications. Internal coatings for tubing and casing are made from epoxy phenolic resins that are resistant to both impact and high temperatures. These coatings offer the same torque and bend resistance as the tubing itself and are suitable for high temperature and corrosive environments. Because these coatings resist scaling, pitch, and paraffin, they also promote efficient flow. If you are in the market for OCTG line pipe, drill pipe, or tubing, look for a steel tubing supplier with a long history of working with petroleum projects that involve hostile drilling environments. You will be able to get the required products in the sizes you need, and with the appropriate coatings so that you get the best possible results.

If your project depends on OCTG line pipe or other OCTG steel products, then you’ll want a supplier you can trust. The best suppliers, like the one you’ll find at, will ensure that your materials arrive on time and according to your specifications. Do you need a steel supplier that you can rely on? Go to Corpac Steel now.

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