API standard and cop steel
Be in early 1926, american oil learns (API) issue API-5L standard, include A25, A, B3 to plant only at first steel class, released several times again later, see a table 4. Express the cop steel class that 4 API issues
Note: API issued standard of U80, U100 1972, later instead X80, X100.
Before 2000, the whole world uses X70, be in about 40% , x65, X60 all is in 30% , line of vitta of small-bore finished product balances the amount chooses X52 steel course, and be in charge of continuously for resistance welding more (ERW steel tube) .
Industry of our country metallurgy paid huge pains to develop cop steel in more than 10 years, tackling key problem with all one's strength at present X70 is wide board, chemical composition of the X70 such as company of company of iron and steel of Shanghai treasure mountain, Wuhan iron and steel, X80, mechanical function parts rank expresses 5 ～ 9. Express 5 Wu Gang X80 to coil board the steel tube of class of 7 X70 of mechanical performance list of steel tube of class of performance list 6 X70 curves function to detect the Xia Bichong that the Xia Bichong that expresses steel tube of 8 X70 class as a result attacks tenacity to express duct of 9 high strenth attacks tenacity

Our country is current commonly used on pipe laying canal helix buries arc solder to be in charge of (SSAW) , seam the solder that bury arc to be in charge of continuously (LSAW) , resistance welding is in charge of (ERW) . Seamless steel tube is chosen when the diameter is less than 152mm.
60 time end reachs 20 centuries of our country 70 time, mill of helix solder pipe develops quickly, crude oil cop uses helix solder steel tube entirely almost, "Enrage on the west east be defeated " a kind of area of cop also chooses helix solder steel tube. The defect of helix solder steel tube is difference of precision of muscularity of a person operating from within in coordination with outside forces, dimension, the probability that produces limitation is high. According to the expert the analysis thinks, should use " walking on two legs " guiding principle, it is helix solder is in charge of a factory to undertake technical reformation actively pair now, there is an outlook greatly in returning; 2 it is to develop our country to seam control of the solder that bury arc to run line of business continuously energetically.
ERW steel tube has precision of outside and bright and clean, dimension tall, price is lower characteristic, in domestic and international wide already application.