Sumitomo Metals Develops Super 17 Chrome Steel Pipes, OCTGs with High Corrosion Resistance and High Strength for Use in Ultra-Deep Oil Wells
Sumitomo Metal Industries, Ltd. (Sumitomo Metals) has developed SM17CRS-125 (referred to as “Super 17 Cr steel”), martensitic stainless oil country tubular goods (OCTG) *1 with the world’s highest level of corrosion resistance and strength. This product will be used to meet increasing demand in ultra-deep oil well development and contribute to the world’s stable energy supply.
1. Development background
Seamless OCTGs are used in developing oil and natural gas wells because of their higher reliability compared with the welded pipes. Martensitic stainless steel 13 Chrome (Cr)*2 OCTG has been used in carbon dioxide oil and gas wells, as it withstands carbon dioxide (CO2) corrosion*3 and has high strength.
Seamless OCTGs are used in developing oil and natural gas wells because of their higher reliability compared with the welded pipes. Martensitic stainless steel 13 Chrome (Cr)*2 OCTG has been used in carbon dioxide oil and gas wells, as it withstands carbon dioxide (CO2) corrosion*3 and has high strength.
In recent years, the number of oil and gas well developments in depths of over 6,000 meters has increased. In such deep well development, steel pipes are required to have strength to withstand geopressure and sustain their own weight, as well as corrosion-resistance in an environment as high as 200℃ temperature. In such a corrosive environment, 13 Cr OCTG suffers stress corrosion cracking*4, therefore cannot be used. Thus, more expensive duplex stainless OCTGs*5 have been used instead.
Duplex stainless OCTGs contain chromium (22-25%), an alloy element that improves corrosion resistance. They withstand CO2 corrosion in high temperatures more than 200℃. However, they are expensive, as they contain a substantial amount of expensive alloy elements such as nickel and molybdenum and cold-working is required in order to enhance their strength*6.
To respond to the growing need for ultra-deep oil well development, Sumitomo Metals has developed Super 17 Cr steel that withstands tougher corrosion environment such as high temperature than Super 13 Cr, while not requiring cold working unlike duplex stainless steel and containing less alloy elements.
2. Characteristics of Super 17 Cr steel
(1) Corrosion resistance required for ultra-deep carbon dioxide oil wells
In order to prevent stress corrosion cracking in a high-temperature carbon dioxide environment, pipes are required to have high proportion of chromium, an alloy element that enhances corrosion resistance. Sumitomo Metals has found that a chemical composition of 17% chromium is optimal to ensure corrosion resistance needed for ultra-deep carbon dioxide oil wells.
(1) Corrosion resistance required for ultra-deep carbon dioxide oil wells
In order to prevent stress corrosion cracking in a high-temperature carbon dioxide environment, pipes are required to have high proportion of chromium, an alloy element that enhances corrosion resistance. Sumitomo Metals has found that a chemical composition of 17% chromium is optimal to ensure corrosion resistance needed for ultra-deep carbon dioxide oil wells.
(2) Strength required for ultra-deep oil wells
In the case of the chemical composition of 17% chromium, the metallic structure is duplex: containing soft ferrite, in addition to hard martensite (see chart 1). By adjusting the chemical composition, Sumitomo Metals has succeeded in ensuring yield strength of 125ksi (861MPa), which exceeds the general yield strength of 13 Cr steel of 80ksi-110ksi*7 (551-758MPa), even though soft ferrite is included.
(3) Product performance
Super 17 Cr steel was announced this September at the International Organization for Standardization (ISO) Committee concerning corrosion materials for OCTGs and the Society of Petroleum Engineers, and highly received by oil majors. We have begun to provide samples to our customers.
Super 17 Cr steel was announced this September at the International Organization for Standardization (ISO) Committee concerning corrosion materials for OCTGs and the Society of Petroleum Engineers, and highly received by oil majors. We have begun to provide samples to our customers.
3. Future development
Development of ultra-deep oil and gas wells is expected to increase, as easy-to-explore oil and gas wells have gradually become exhausted. Super 17 Cr steel pipes will be applied for the development of deep sea oil wells in Brazil’s offshore and the Gulf of Mexico, ultra-deep oil wells in South East Asia and the Indian Ocean, oilfields in Australia and other harsh corrosive environments.
Sumitomo Metals contribute to the oil and natural gas development in the world, by providing to the customers our leading technologies and product line-up.
Development of ultra-deep oil and gas wells is expected to increase, as easy-to-explore oil and gas wells have gradually become exhausted. Super 17 Cr steel pipes will be applied for the development of deep sea oil wells in Brazil’s offshore and the Gulf of Mexico, ultra-deep oil wells in South East Asia and the Indian Ocean, oilfields in Australia and other harsh corrosive environments.
Sumitomo Metals contribute to the oil and natural gas development in the world, by providing to the customers our leading technologies and product line-up.
＜Terms＞
*1 Martensitic stainless steel pipes
They are made of stainless steel alloy that mainly composes of a high-strength martensitic structure. 13 Cr steel and Super 13 Cr steel are widely used among others. Martensite is formed by rapid cooling of austenite through the subsequent transformation of its crystal structure. It has high strength and toughness. In the case of higher alloy element content, rapid cooling does not transform the crystal structure and it stays in the form of austenite (becoming duplex stainless steel austenite.) Ferrite possesses the same but smaller crystal structure disturbances than martensite hence generally softer than martensite.
*1 Martensitic stainless steel pipes
They are made of stainless steel alloy that mainly composes of a high-strength martensitic structure. 13 Cr steel and Super 13 Cr steel are widely used among others. Martensite is formed by rapid cooling of austenite through the subsequent transformation of its crystal structure. It has high strength and toughness. In the case of higher alloy element content, rapid cooling does not transform the crystal structure and it stays in the form of austenite (becoming duplex stainless steel austenite.) Ferrite possesses the same but smaller crystal structure disturbances than martensite hence generally softer than martensite.
*2 13Cr steel pipe for pipelines
It contains chromium (13%) and possesses superior corrosion resistance than carbon steel. When the chrome content reaches 13%, the protective coating on the steel surface becomes tougher and greatly enhances corrosion resistance.
It contains chromium (13%) and possesses superior corrosion resistance than carbon steel. When the chrome content reaches 13%, the protective coating on the steel surface becomes tougher and greatly enhances corrosion resistance.
*3 CO2 corrosion
Corrosion caused by crude oil and natural gas that contain some level of carbon dioxide (CO2). High chromium content in materials restrains CO2 corrosion speed.
Corrosion caused by crude oil and natural gas that contain some level of carbon dioxide (CO2). High chromium content in materials restrains CO2 corrosion speed.
*4 Stress corrosion cracking
Stress corrosion cracking is caused when metals are subjected to a tensile stress in a corrosive environment, especially at elevated temperatures. In the case of OCTGs, the temperature to start stress corrosion cracks tends to be the temperature limit for their usage.
Stress corrosion cracking is caused when metals are subjected to a tensile stress in a corrosive environment, especially at elevated temperatures. In the case of OCTGs, the temperature to start stress corrosion cracks tends to be the temperature limit for their usage.
*5 Duplex stainless OCTGs
Duplex stainless steel pipes have a two-phase microstructure consisting of ferritic and austenitic stainless steel. They have high corrosion resistance due to their chromium, molybdenum and nitrogen content.
Duplex stainless steel pipes have a two-phase microstructure consisting of ferritic and austenitic stainless steel. They have high corrosion resistance due to their chromium, molybdenum and nitrogen content.
*6 Cold-working is required in order to enhance strength
Both the ferrite and austenite structures that constitute duplex stainless steel are soft metallic structures and cannot be hardened by heat treatment. Hence, the material is processed at normal temperature and work-hardened (strengthened by plastic deformation).
Both the ferrite and austenite structures that constitute duplex stainless steel are soft metallic structures and cannot be hardened by heat treatment. Hence, the material is processed at normal temperature and work-hardened (strengthened by plastic deformation).
*7 ksi
Short for kilo pound per square inch, It is a unit of pressure or stress on materials. For an example, 80 ksi means that the material withstands a force of 80,000 pounds (approx. 39,000 kg) applied to a section area of one square inch. 1 ksi = approximately 6.89 MPa/mm.
Short for kilo pound per square inch, It is a unit of pressure or stress on materials. For an example, 80 ksi means that the material withstands a force of 80,000 pounds (approx. 39,000 kg) applied to a section area of one square inch. 1 ksi = approximately 6.89 MPa/mm.
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