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
  

What are delivery status of steel

Steel used in the oil tubular goods will pass through a complex process before leaving factory. According to the different characteristics and use of steel, the final delivery state of the steel is different. Common delivery conditions are: hot rolling treatment, cold stretching treatment, normalizing treatment, annealing state, high tempering state and solid treatment.

Hot rolling treatment

It’s known as hot rolling treatment when steel deliver directly after cooling without special heat treatment. The terminal temperature of hot rolling treatment is between 800℃ and 900℃, after that, it’s generally refrigerated in the air. As a result, the hot rolling treatment is similar to normalizing treatment. The difference is due to the hot rolling termination temperature fluctuated, which is different from strict normalizing temperature, fluctuations in steel microstructure and properties are more than that of normalizing treatment.

Currently, many steel companies apply controlled hot rolling. Because of strict termination temperature and forced cooling measures, delivered steel has higher comprehensive mechanical properties. Covered with a layer of iron oxide, delivered steel with hot rolling treatment has a certain degree of corrosion resistance. The storage requirements of hot rolling steel are unlike to cold stretching, medium-sized steel and thick steel plate can be stored in the open air yard.

Cold stretching treatment

The steel by cold stretching, which is without any heat treatment and direct delivery, is called cold stretching treatment. Compared with hot rolling treatment, cold stretching treatment steel has the features of good surface quality, low surface roughness and higher mechanical properties. However, the surface of steel staying cold-drawn state is not covered with oxide skin and there is internal stress result in corrosion and rusty. What’s more, the packaging and storage of that has higher strict requirements, that it’s generally stored in the warehouse and the temperature and humidity in warehouse should be controlled.

Normalizing treatment

Through normalizing before leaving factory, the steel is staying normalizing treatment. Since the normalizing heating temperature is stricter than hot rolling terminated temperature, the performance and organization of steel has stable performance. Compared with steel annealed condition, because of faster speed of normalizing cooling, pearlite in the steel is increasing and lamellar, therefore it has a higher comprehensive cooperation properties and it’s profitable to improve Widmanstaten of low carbon steel and make preparation for further heat treatment.
normalizing treatment

OCTG industry meet the opportunity because of the belt and road

What is "The Belt and Road"

Starting Central Asia and through South Asia, Southeast Asia, West Asia, Eastern Europe, "The Belt and Road" has been a longest world’s economic corridors. It is becoming the most development potential economic belt in the world. What’s more, countries along the fate become more and more close whether in the eyes of the economic development and improving people's livelihood or from the point of response to the financial crisis.


Currently, China is the world's largest energy consuming country and the second oil and gas consumption country. With the development of “The Belt and Road”, China will become the main resource exporting country.

A new opportunity to OCTG industry

In fact, countries alone “The Belt and Road” have a wealth of crude oil resources, but their infrastructure is relatively weak, which create a huge opportunity for China's OCTG industry. As we all know, influenced by the international market, not only steel pipes but also other export goods made in China were known as cheap in the past decades. We offer high-quality pipe with the lowest price. In other words, It’s a best time to buy cheap steel pipes from China if you need. "The Belt and Road" will help us develop new export markets, solve the dilemma of overcapacity and this will promote the economic and trade exchanges between China and the neighboring countries.

Some countries in Southeast Asia and South Asia develop slowly and have a large population, but the development of “The Belt and Road "must rely on the railway, highway, pipeline, shipping routes. Therefore, transportation, energy pipe network, manufacturing facilities, raw materials and equipment, high-end equipment, energy saving and environmental protection industry will usher a great opportunity. In the oil and gas industry, for example, with the completion of natural gas pipeline between China and Myanmar, a series of OCTG products in South Asia, Southeast Asia will have a good market prospects.


According to statistics in 2015, Chinese enterprises invest in 49 countries related to "The Belt and Road" directly and the investment grew 18.2%. Insiders have said that, under the stimulus of "The Belt and Road" policy, the next few years, the chemical industry is expected to recover.

CIPPE----an annual event in petrochemical industry

In petrochemical industry, there is an annual event, the Eighth China International Petrochemical Technology and Equipment Exhibition (CIPPE Shanghai Petrochemical Exhibition) will be held in Shanghai New International Expo Center on August 23-25. After eight years of development, CIPPE has developed into a communication and learning platform for trade cooperation, which is regarded as one of the highest quality in the petrochemical industry on businesses and professionals. Many companies will be unveiled this collective exhibition, to discuss "The Belt and Road" strategy for promote the petrochemical industry. We welcome you to attend and have a pleasant communication.