Steel Grades of OCTG Casing Pipe

What are the steel grades of OCTG casing?

Oil Country Tubing Goods (OCTG) is a range of steel tubing used in oil and gas exploration and production. OCTG casing is a structural component of the well structure. It helps maintain the integrity of the wellbore and helps prevent formation fluids, such as water and natural gas, from entering. OCTG casing is also important for cementing wells and preventing pressure build-up in the well. Therefore, selecting the correct grade of oil well casing is critical to the successful and safe operation of an oil and gas well. OCTG casing follows API 5CT standard.

What is API 5CT standard?
‌API 5CT is a standard issued by the American Petroleum Institute (API), which is mainly used to specify the technical requirements and quality standards of oil casing used in the oil and gas industry. It has been recognized and used by the world. The API 5CT standard applies to various types of oil casing, including seamless steel pipes and welded steel pipes (mainly ERW welded pipes).

The API 5CT standard specifies the delivery technical conditions of steel pipes (including casing, tubing, plain end casing liner and short joints), covering the requirements of size, shape, chemical composition, heat treatment system and mechanical properties.

Grades of OCTG Casing Pipe:

OCTG casing is manufactured in various grades, each with its own unique characteristics, in order to meet the needs of specific applications. The API 5CT standard divides oil casing into different steel grades. Common OCTG casing pipe steel grades include API J55, API K55, API L80, API N80, API P110, API Q125, API S135 and API V150. These steel grades have different tensile strength and yield strength to meet different usage requirements. Let’s look at these grades in more detail. 

API J55 
API J55 casing is a general-purpose grade that is the most commonly used grade for oil and gas wells. It is known for its affordability and versatile nature. It is usually selected when cost is the main consideration. J55 casing has relatively low yield and tensile strength properties, ranging from 73,000 psi to 92,000 psi respectively. It is often used in shallow wells that require only modest pressure containment or when there is little risk of hydrogen sulfide corrosion.

API K55 

K55 casing is slightly stronger than J55 and is classified as a medium-strength grade. It is best suited for use in shallow wells with less stringent containment and corrosion requirements. It is also more durable and can withstand greater pressure than J55. It has an average yield strength of 82,000 psi and an average tensile strength of 110,000 psi. It is often used in onshore wells requiring medium tensile and yield strength.

API L80 

L80 casing is a higher-strength grade than J55 and K55. It combines good strength and toughness in one grade. It is particularly suited for sour service operations and is often used offshore. It has an average yield strength of 83,500 psi and an average tensile strength of 95,000 psi. It provides superior corrosion resistance, making it ideal for deeper wells with higher pressure loads.

L80 is divided into L80-1, L80-9Cr, and L80-13Cr. They have the same mechanical properties and delivery condition. The differences lie in their applications, production difficulty, and price. L80-1 is the standard type, while L80-9Cr and L80-13Cr are both high-corrosion-resistant tubing, which are difficult to produce and expensive, typically used in heavily corroded oil wells.

API N80 

N80 casing is a higher grade than L80 and offers superior strength and performance in depths of up to 20,000 ft. It is most commonly used offshore and has an average yield strength of 85,000 psi and an average tensile strength of 100,000 psi. It provides superior protection against corrosion making it an ideal choice for deep, high-pressure wells.

N80 is divided into N80-1 and N80Q. N80-1 means that in addition to meeting all the basic requirements of N80 steel grade, it must also pass the Charpy impact test to prove that it has sufficient toughness. N80Q means that it must undergo quenching and tempering treatment, and its impact energy should meet the API 5CT requirements and should be subject to non-destructive testing.

API P110 
P110 casing is the highest grade of OCTG casing available. It combines exceptional strength and ductility, with an average yield strength of 105,000 psi and an average tensile strength of 125,000 psi. It is most commonly used offshore and is suitable for depths of up to 30,000 ft. It is also highly resistant to corrosion and offers superior pressure containment capabilities.

API Q125 
Q125 casing is a premium-grade product with exceptional strength and ductility. It is often selected for demanding applications, such as extreme depths and high pressures. It has an average yield strength of 115,000 psi and an average tensile strength of 140,000 psi. It is most commonly used in offshore wells, but can also be found in some onshore wells.

API S135 
S135 casing is the preferred material for extreme-depth applications, such as ultra-deepwater wells. It is known for its superior strength and ductility and is able to withstand extremely high pressures. It has an average yield strength of 125,000 psi and an average tensile strength of 155,000 psi. It is also highly resistant to corrosion and is therefore ideal for the most extreme conditions.

API V150 
V150 casing is the strongest grade of OCTG casing available. It has an average yield strength of 135,000 psi and an average tensile strength of 165,000 psi. It is designed to withstand the highest pressures and depths, and is most often used in ultra-deepwater wells. Its superior strength and durability make it an excellent choice for challenging drilling operations.

Conclusion 

By understanding the grades of OCTG casing available, you will be able to make an informed decision when selecting a casing grade for your well. Choosing the wrong grade for a project can cause problems, so carefully consider your well's needs and choose the grade that best suits your application.

Read more: Casing Pipe Material Types and Selection or OCTG Casing Pipe Size Chart