Sumitomo Metal Industries Limited has developed SM17CRS-125 (referred to as Super 17 Cr steel), martensitic stainless oil country tubular goods 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 OCTG has been used in carbon dioxide oil and gas wells, as it withstands carbon dioxide corrosion 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 geo pressure and sustain their own weight, as well as corrosion resistance in an environment as high as 200 degree temperature. In such a corrosive environment, 13 Cr OCTG suffers stress corrosion cracking, therefore cannot be used. Thus, more expensive duplex stainless OCTGs have been used instead.
Duplex stainless OCTGs contain chromium (22% to 25%), an alloy element that improves corrosion resistance. They withstand CO2 corrosion in high temperatures more than 200 degree. 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.
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
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.
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.
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.
