Seamless API OCTG Casing Pipe Steel 9" 5" 8" 5CT

Types of Alloy Grades
OCTG casing and tubing are designed to withstand the downhole conditions of a well. The alloy/grade of the OCTG describes the actual chemical composition and mechanical properties of the material. Different alloys or grades are better suited to various downhole environments, or are designed to withstand more extreme conditions, such as high pressure, corrosive environments, and varying temperatures.
It is important to note that the American Petroleum Institute (API) and the National Association of Corrosion Engineers (NACE) which is now called the Association for Materials Protection and Performance (AMPP), have set standards and specifications for OCTG casing and tubing to ensure their quality and performance. The specific alloy selection depends on factors such as well depth, pressure, temperature, corrosiveness of the formation, and other operational requirements.
The commonly used alloys and grades for OCTG casing and tubing can be categorized into five general groups based on their resistance to environmental factors. These groups, listed in order of increasing environmental resistance, are Carbon Steel, Chromium-molybdenum (Cr-Mo) Alloys, Martensitic Stainless Steel, Duplex Stainless Steel, and Nickel-Based Alloys.
Carbon Steel Grades
Carbon Steel grades are generally the most cost-effective option and are suitable in non-corrosive environments. They are often used in shallow wells with relatively low pressure, downhole conditions where the corrosive potential is minimal, and temporary applications where components may be removed after the initial phase or long-term production is not expected, therefore the long-term corrosion resistance of higher-grade materials may not be necessary. Carbon steel alloys include J55, K55, N80, L80, and P110.
Chromium-Molybdenum Alloys
Chromium-Molybdenum (Cr-Mo) Alloys have a higher tensile strength and resistance to sulfide stress cracking under certain conditions. They are commonly used in mildly sour and slightly deeper wells. These alloys include C95 and C110.
Martensitic Stainless Steels
Martensitic Stainless Steels are used extensively in sweet (CO2) environments where carbon and low alloy steels experience general corrosion, and are acceptable for moderate sour service conditions. They range in yield strength from 80 to 125 ksi, achieved by quench and temper heat treatment. 13 Chrome is the least alloyed of the stainless steels and most common for OCTG. These alloys include 13 Chrome, Modified 13 Chrome, Super 13 Chrome, 15 Chrome, and 17 Chrome.
Duplex Stainless Steels
Duplex Stainless Steels are required in sweet (CO2) environments containing chlorides or dissolved ocygen, where pitting and crevice corrosion are a concern. Cold-worked tubes are available with with yield strengths up to 140 ksi.
Super Duplex Stainless Steels
Super Duplex Stainless Steels extend the useful range of temperature and chlorides. Defined by Pitting Resistance Equivalent Number (PREN) greater than 40, they are recommended for conditions with high chlorides or dissolved oxygen, such as seawater and water injection wells. Duplex Stainless Steel alloys include 22 Chrome Duplex, 25 Chrome Duplex, and Super Duplex.
Nickel Based Alloys
Nickel Based Alloys are used primarily in sour environments where the partial pressure of H2S exceeds 3 psi. Their useful range of temperature, H2S, and chlorides is extended by increasing additions of nickel, molybdenum, and other elements. Solid solution nickel based alloys are available as cold worked tube with yield strengths up to 160 ksi. In addition to excellent resistance to chlories and H2S, they eliminate the risk of hydrogen embrittlement which may occur with heat treated alloys. Nickel based used in OCTG casing and tubing include 28 Chrome, 2535, 2035, 825, G3, G2, 2550, G50, C276, and C22.