Application of composite steel pipe technology

Composite steel pipe is composed of two (or more) materials combined into one through specific technological means so that it has comprehensive characteristics

Sex's new steel pipe. Since the 1960s, Japan, the United States, Germany, the United Kingdom and other countries have attached great importance to the development of composite steel pipe, composite steel pipe products in energy, shipbuilding, chemical, petroleum and machinery and other fields have been widely used. Composite steel tube processing technology mainly includes rolling, casting, extrusion, brazing, welding and so on.

1.     Application range of composite steel pipe

The combination mode of two kinds of single layer materials of composite steel pipe completely depends on the application requirements and environmental characteristics. The basic steel pipe has high strength and rigidity, low price and good process performance. The covered steel pipe shall be of high hardness and have the ability to resist the corrosion of environmental medium. This layer can be in the inner layer of composite steel pipe (inner composite pipe) or in the outer layer (outer composite pipe).According to the nature of use can be divided into chemical use liquid gas pipe, oil and gas pipeline and oil well pipe, boiler, waste incinerator with multiple tube, pipe for heat exchanger, with wear resistance, corrosion resistance structure with multiple tube and architectural decoration pipe, etc., with the continuous development of composite pipe technology application, the application range of the composite pipe will be extended to more wide application fields.

2.     Production method of composite steel pipe

Composite steel pipes can be divided into two types, bimetallic and double-layer, according to the combined state of the contact interfaces of the two kinds of steel pipes. The composite steel pipe with the contact interface of inner and outer layer connected to metallurgical bonding degree is called bimetallic pipe, while the contact interface of inner and outer layer only reaches mechanical connection, and the composite steel pipe with longitudinal section layer and layer freely separated is called double layer pipe. There are many different process methods to produce composite steel pipes, each of which has its own characteristics and application scope.

2.1  Hot working process

In this method, ordinary carbon steel billet is used as outer base metal, center hole is drilled, and stainless steel or nickel alloy rod is used as inner layer. Outer guarantee the physical properties of the composite pipe, the inner pipe corrosion requirements, when the bar and billet surface after the inner hole surface is clean, will bar embedded billet hole of the pipe, welding seal the ends of the tube billet, use level of low frequency induction coil to control the heating, after being heated to set temperature, in 1 600 t hot punch on the vertical hydraulic punching machine, pipe billet in circular perforation mode and axial compressed gauge circle perforation, after thermal perforated tube billet, bar and the base material to metallurgical combination. This process is used by Tubacex, a Spanish extruded steel pipe company, to produce composite steel pipes with external diameters of 60· 3 and 219 · Imm. The thickness of the corrosion resistant lining pipe is usually 10% to 0% of the total thickness of the composite pipe, usually between 2 cm and 1 cm at the minimum.

2.2  Composite steel plate welding method

This method can be used to manufacture composite steel pipes for oil and gas transmission pipelines with diameters larger than 300mm.The composite steel plate was rolled into tube billet by UO process, and then welded into longitudinal seam. The process flow of composite steel pipe produced by this method is as follows: longitudinal seam welding -- pipe expanding -- heat treatment of steel sheet i-jo forming billet.

2.3  Cold process diffusion annealing

The tube billets of different materials are made into cold-rolled or cold-drawn seamless tubes respectively. A special low-melting intermediate layer thin belt is wound around the outer side of the inner layer of tube billets. After cold drawing, high-temperature diffusion annealing is carried out. The characteristic of composite steel pipe produced by this process is that the joint boundary is very obvious and even. Due to the addition of a low melting point metal layer between the two bonding interfaces, its binding strength is relatively high, usually greater than 300MPao. The low melting point metal gasket material is usually Ni - P alloy, and its melting point temperature decreases with the increase of the content of P. The other gaskets are B (1, 4Wt%), Si (up to 9Wt %), cr(up to 30Wt%) iron - or ni-based alloys. The melting point of the gasket material must be lower than that of the outer base tube and the inner tube. The composite steel tube produced by this process can withstand bending forming, and its dimensional accuracy and surface quality can meet the standard requirements.