What is DIN2391 standard specifies for steel tube?

  Do you know what is steel tube standard specifies? Today I’d like to tell you DIN2391 standard specifies for steel tube.

  Firstly, from DIN2391 we know this is Germany standard. Such as SEA1020 is from USA standard, JIS G3429 is from Japan standard, and EN10305-1 is from United Kingdom.

  Secondly, DIN2391 is for cold finished which is the technical delivery conditions for steel tube precision seamless steel tube. As there are hot finished, such as hot rolled technology.

  Thirdly, which material is suitable for this standard. As below is a form which is chemical composition of steel grades show on ladle analysis. For example, St35, the C(max) is 0.17%, Si(max ) is 0.35%, Mn is more than and 0.4%, P(max) is 0.025%, S(max) is 0.025%. And this material is similar with 20# in China, SEA1020 in USA. 

  Fourthly, there are two kinds technology for production. The one is cold rolled which is high precision, has good smooth and slight surface such as stainless steel tube. The other is cold drawn which is matte color, a little rough surface.

  Fifthly, there are 5 types final supply conditions as the different application. They are cold finished (hard) also called BK, cold finished (soft) also called BKW, Cold finished and stress-relleved also BKS, Annealed also called GBK, Normalized also called NBK. These are different temperature, time and with or without oxygen when in the last process. So in the different environment, the mechanical properties of the tubes are also different. But we only focus on three items, those are tensile strength, yield strength and elongation. As below is the form as a reference.

  Sixth, the dimension and limited deviations. It shall be equal to 10% for outer diameter and wall thickness. For example the size is 27.1*3.55, the tolerance is 0-2.71mm for outer diameter and 0-0.355mm for wall thickness. But our standard is +/-0.05mm. So our steel tube is really have high precision.

  Seventh, the straightness, the outer diameter of the tube is more than 15mm, which shall not deviate of straightness by more than 0.25% for the total length that is random length. For example the tube is 18*2*6000mm, the tolerance just need less than 15mm/6m (6000*0.25%=15mm/6m). But for exact length tube, it shall not deviate of straightness by more than 0.3% for the total length.

  It means 18*2*6000mm, the tolerance just need less than 18mm/6m (6000*0.3%=18mm/6m).

And for a yield strength greater than 500N/mm2 tube shall not deviate of straightness by more than 0.3% for the total length.  

Those are total main point for DIN2391. Have you get it? If not, feel free to contact me. We are Changzhou RAYMOND steel tube company Ltd.