OREANDA-NEWS. December 7, 2011. 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.

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.