Large Diameter Welded Pipe Development And Application

Large Diameter Welded Pipe development and application

In the early days of the founding of the people's Republic of China, titanium was only used in the military industry, belonging to the national strategic control materials. It was not used in the chemical industry of civil industry until the 1970s. So far, it has a history of more than 40 years. Titanium, as an excellent corrosion-resistant structural material, has established its irreplaceable position, and as an ideal material in the chemical transmission pipeline of corrosive media, Large diameter titanium welded pipe has also attracted more and more attention and use of equipment and pipeline designers.

As we all know, large-diameter titanium welded pipe is mostly used in corrosive environment because of its excellent characteristics. When the liquid with corrosive medium flows through the pipe wall, the corrosive medium will slightly erode the inner wall of the welded pipe. The corrosion degree of titanium welded pipe varies with the medium and its concentration. Generally, the corrosion rate of high concentration medium in the same medium is greater than that of low concentration medium. When the medium is boiling, the corrosion rate of Cl containing medium is greater than that of other salt solutions. The corrosion rate of titanium material with high inner wall bearing pressure is greater than that of titanium material with low inner wall bearing pressure under the same wall thickness and medium.

Therefore, the service life of large-diameter titanium welded pipe mainly depends on the corrosive medium, service environment and bearing pressure.

Introduction of production process of large diameter welded pipe

The production of large-diameter titanium welded pipe in China is limited by the technical level and small market demand, and the production method is mostly intermittent production process. The forming method of most manufacturers is to use the bending machine, and the forming length is limited and the ovality is large. Baoji City Changsheng Titanium Company adopts special equipment and self-developed mold to press and shape, and the length of the pipe can be up to 6 meters, with small ovality and straightness. In terms of welding, most manufacturers use argon arc welding (TIG) manual welding, which has poor weld formation, general weld quality, and uneven weld reinforcement; But we company adopt plasma arc automatic welding (PAW) welding, which has beautiful weld formation, excellent weld quality, and uniform weld reinforcement, which is more recognized by customers.

The production process is implemented according to the following steps: 

(1) blanking: measure the size of the unfolding plane of the titanium pipe, and use the automatic cutting machine to blanking, and the raw material is wide titanium plate or tape;

(2) Pressing: on the lower die, press from both sides of the titanium plate with special bending equipment, and both sides are pressed into a circular arc; 

(3) Jointing: a customized special double column oil press is used. The side pressure column closes the welded junction, the upper pressure column is the welded junction is flat, and the conveyor belt is set at the bottom to push the welded pipe forward; 

(4) Spot welding: spot welding is carried out in the process of conveying pipeline with conveyor belt by using specially customized oil press while closing operation is carried out; 

(5) Welding: advanced plasma welding equipment is used for welding. The thickness of the welding plate of the welded pipe can reach 14mm-18mm. There is no need for beveling, one-time penetration, and the formation of the back of the weld is beautiful. The qualified rate of X-ray photography of the weld is as high as 98%; 

(6) Reshaping: round and straighten the welded pipe with a special oil press and a supporting shape correction mold; 

(7) Nondestructive testing: weld joints shall be tested as required。

Application of Large Diameter Welded Pipe

Titanium welded pipe was first used in the aerospace field because of its high specific strength. It can not only reduce the weight of aircraft, but also prolong the service life and reduce the maintenance time.

In the early 20th century, the civil market of titanium materials and products was formed. Large diameter titanium welded pipe was widely used in petrochemical, salt making, pharmaceutical and other industries because of its excellent corrosion resistance and thermal conductivity.

With the rapid development of modern industry, the natural environment and water resources have been greatly polluted, which makes copper and copper alloy pipes and stainless steel pipes, which were originally excellent in pure water and clean seawater, prone to serious corrosion leakage. As a substitute for other metal materials, high-efficiency, environmental protection and energy-saving large-diameter titanium welded pipes have been used in seawater desalination, sewage treatment and other equipment.

Although the price of large-diameter titanium welded pipe is slightly higher, the service life of the whole titanium pipe is greatly improved, the shutdown and maintenance costs are reduced, and the environmental pollution is small, which meets the overall requirements of the current national construction of an energy-saving and environment-friendly society.

In addition, the price of large-diameter titanium welded pipe is 40% - 60% lower than that of seamless titanium pipe of the same specification, which greatly reduces the input cost of end users.