What is the standard GB3639?

    All of us must know the standards of seamless steel tube, such as DIN2391, En10305-1 and GB3639. We also know that they have different names, but the details are similar. Din 2391 is the standard from German, En10305-1 is of Britain, and GB3639 is of China. Then we will give a brief introduction about this standard.

    GB3639 specifies the classification and code, size, shape, weight and allowable deviation, technical requirements, test methods, inspection rules, packaging, marking, and quality certificates of cold-drawn and cold-rolled precision seamless steel tubes. In addition, this standard is suitable for cold-drawn and cold-rolled precision seamless steel tubes with special dimensional precision and high surface quality for mechanical structure, hydraulic equipment, and car tubes.

Classification and code：

Steel tube can be divided into cold finished(hard) BK, cold finished(cold)BKW, cold finished and stress-relleved BKS, annealed GBK, normalized NBK according to the delivery state. The tube in different state has different hardness and yield strength.

Dimensions and limit deviations:

There are two tables to stipulate limit deviations of steel tube in different delivery states. For steel tube of BK and BKW, the limit deviations must be must conform to the rules of the sheet 1. For steel tube of BKS, GBK, NBK, it must be conform to the rules of the sheet 2(for the form, PREFT the original standard)

For the length, the usual length of steel tube is 2000~7000mm. The fixed length and multiple length of steel tube should be controlled in the usual length range, and the permissible deviation of the full length should be in accordance with the following regulations:

Length≤5000mm +0~5mm

Length＞5000mm +0~10mm

Steel pipe with multiple length for delivery, each ruler shall keep the margin of incision according to the following regulations:

OD≤159mm 5~10mm

OD＞159mm 10~15mm

For the straightness, the straightness of steel tube in BK/BKW should be less than 3.00mm/m, the straightness of steel tube in BKS/GBK/NBK should be less than 5.0mm/m.

Technical requirements:

Steel tube is used of 10#/20#/35#/45# steel, whose chemical composition should satisfy the regulations of GB/T699. Steel tube is inspected according to the melting composition. Besides, GB3639 also stipulates the producing method, delivery state, mechanical properties, compactness, surface roughness, surface quality and other requirements.

Now, maybe you have a general understanding of this standard. Raymond steel tube will introduce more standards of steel tube. Whether we are suppliers or buyers, we all need know the details to avoid unnecessary complications.