Oil drilling pipe is a geological drilling with steel made by hot or cold.Domestic steel with “geological” (DZ) said. Petroleum drill pipe steel gradeDZ40, DZ50, DZ55, DZ65 and DZ75 (DZ40 and DZ50 are eliminated).Geological drill pipe steel grade DZ50, DZ55, DZ60, DZ65, DZ75, DZ85and ...
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