How to distinguish hot and cold seamless pipe?

A large number of seamless steel pipes are used for conveying fluid because of a hollow section, such as crude oil, nature gas or water. Under the same torsional strength, seamless steel tube is relatively light comparing with round steel or other solid steel. It’s an economical steel which is widely used in manufacture oil pipe and mechanical parts, such as drill pipes, automobile transmission shaft or steel ring parts.The reason why seamless pipe used widely is it can improve the utilization of materials, simplify the manufacturing process and save materials and processing time.
Seamless steel tubes are made by hot rolling or cold rolling with 10,20,30,35,45 high quality carbon steel and 16Mn, 5MnV low alloy structural steel or 30CrMnSi, 40Cr, 45Mn2, 40MnB alloy steel. Seamless pipe, made by 10,20 and other low carbon steel production, is mainly used for conveying pipe, while made by 45,40Cr medium carbon steel to manufacture mechanical parts.
The production process of seamless steel tube in general can be divided into hot rolling and cold rolling. 

Cold rolling seamless steel pipe

The production process of cold-rolled seamless steel pipe is generally more complicated than that of hot-rolled: tube is first to three roller skew rolling, then, to carry out a sizing test after extrusion. Round tube needs to cut through cutting machine and the length is about 1 meter. Entering the annealing process, annealing carry out pickling should pay attention to whether the surface has a large number of foaming, if there is a large number of bubbles produced that the quality of the steel pipe is not up to the corresponding standard. Cold-rolled seamless steel pipe is shorter than the hot rolled seamless steel pipe in appearance, but the surface looks brighter than the thick walled seamless steel tube.

• Advantage

  Forming fast, high yield, and no damage to the coating, it can be made into a variety of cross sectional form to meet the needs of the use of conditions; Cold rolling can cause great plastic deformation, so as to improve the yield of the steel.
  

• The technological process of cold-rolled seamless pipe

  round billet→heating→perforation→annealing→pickling→annoit→cold rolling→heating→straightening→hydrostatic test→signing→storage
  

Hot rolling seamless steel pipe

Hot rolling, as the name suggests, the temperature of rolled piece is high, so the deformation resistance is small to achieve large deformation. Take rolling of steel plate for example, the general thickness of continuous casting slab is about 230mm, and after roughing mill and finishing mill, the final thickness is 1~20mm. At the same time, due to the small thickness ratio of steel plate, the dimension accuracy is relatively low, it’s not easy to cause shape problem.

• Advantage

  It can destroy the microstructure of ingot casting, grain refinement of steel and eliminate microstructure defects, so that make steel structure compact and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel no longer is isotropic; Formation of bubbles, cracks and loose when pouring can also be welded under high temperature and pressure.
  

• The technological process of hot-rolled seamless pipe

  round billet→heating→perforation→extrusion→sizing→hot rolling→cooling→straightening→hydrostatic test→signing→storage