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What does API x70 steel grade mean?

Api stands for API gravity standard.

X70 I think your name is all, which should be X70 pipeline steel.

It refers to the production of high toughness pipeline steel hot rolled wide strip steel for oil pipeline by spiral welding.

At the end of 1960s and the beginning of 1970s, American petroleum organization put forward X56, X60 and X65 microalloyed controlled steel rolling in API 5LX and API 5LS standards. This kind of steel breaks through the traditional concept of steel, and the carbon content is 0. 1-0. 14%. By adding Nb, V and Ti ≤0.2% alloy elements to the steel, the mechanical properties of the steel are significantly improved by controlling the rolling process. Up to 1973 and 1985, X70 and X80 steels were successively added to API standards, and then X 100 pipeline steel was developed, and the carbon content decreased to 0.0 1-0.04%.