Bimetal Clad Pipe

Bimetal Clad Pipe is cast with mold vanishing vacuum suction casting cladding process. Outer of straight pipe is common steel pipe, cladding realized by forming high chromium lining via centrifugal forming technique.

Bimetal wear resistant pipe, including: double metal wear-resisting straight pipe and double metal wear-resisting bend, double metal wear tee, double metal wear resistance reducer adopts the pipe fittings such as vacuum suction casting composite process, its advanced technology, effectively solve the problem of the bent pipe cannot be composite, bending and other various special-shaped pipe can do the whole compound, don’t change the material flow in the pipe bending trajectory, reduce resistance material conveying.

There are many kinds of names,Like Bi-metal Composite Steel Pipe,Corrosion Resistant Alloy (CRA) Clad or Lined Steel Pipes,CRA Mechanical or Metallurgical Composite Pipes,CRA Mechanical Lined Pipes etc.

Those special pipe composited by two different materials including inner(Lining) pipe and outer(backing)pipe.

Characteristics

Bi metal clad pipe with high carbon content, impact resistance, low thermal expansion, pressure, high temperature, mature, complete specifications; has many manufacturers of Bi metal clad pipe is widely used in oil, chemical, power and other industrial fields , Its scope of application more and more widely, brought about by the economic, environmental and social benefits are more obvious.

Bi metal clad pipe applicable areas

Bi metal clad pipe with high carbon content, impact resistance, low thermal expansion, pressure, high temperature, mature, complete specifications; has many manufacturers of Bi metal clad pipe is widely used in oil, chemical, power and other industrial fields , Its scope of application more and more widely, brought about by the economic, environmental and social benefits are more obvious.

Civil areas:

Cold, hot water pipes, direct drinking water pipes, heating, solar energy, ground source heat pump; civil construction water supply pipes, water distribution trunk; air conditioning circulation pipe, fine decoration high-grade commercial housing water pipes.

Industry:

Oil and gas pipeline, oil and gas wells casing, sewage return pipe; chemical heat exchanger tube bundle; power desalination water, desulfurization pipeline and other metallurgy, desalination, medicine and chemical industry, sewage treatment, new energy, food processing and other industries.

Bimetallic connection
Most of the outer tube is used galvanized pipe, followed by a galvanized pipe mature connection:

  • As shown in Figure 1, threaded connection (commonly known as thread connection), for DN15-DN100, the implementation of GB7306-2 and GB3287-1982 standards;
  • groove clamp connection, for more than DN100, the implementation of CJ / T156 standard;
  • flange connection, as the case may be, generally more than DN100, flange and so on by the manufacturers, and in the connection with a dedicated silicone layer;

As shown in Figure 4, welding connection, according to the actual working conditions using welding, the implementation of YB / T5092-2005 and JB / T4747-2002 standard, generally used three-layer welding, the first argon arc welding back cover, re-welding transition layer, the last manual arc Fill the filling surface.

Quality requirements
The inner and outer surface of bimetal wear-resistant elbow should be smooth and clean, without burrs, burrs, cracks, loose, pores or bubbles;The inner wall of the wear-resisting elbow should be smooth without accumulated powder.The bend should have good thermal shock resistance. When there is a sharp change in temperature or welding connection, the inner layer of the wear-resistant pipe will not break and spalling due to the expansion or contraction of the inner layer.The dimensional deviation shall meet the requirements of product drawings and order agreement, and shall meet the provisions of GB3092, GB8162 and GB8163 without special requirements.The thickness deviation of lining is + / – 1.2mm.

Welding process of bimetal wear-resistant composite pipe
Among the alloy materials for the bimetal wear resistant composite pipe lining, the best hardness and wear resistant properties are high chromium wear resistant white cast iron and high quality alloy wear resistant cast steel (collectively referred to as super hard wear resistant alloy).The hard phase of high chromium cast iron is M7C3 carbides, and its hardness reaches HV1500 ~ 1800, so it has good wear-resisting property, while the structure of Ka carbides is rod shape, so it has high toughness.On the basis of the traditional ingredients, rare metals and boron carbide hard mixture are added, which greatly increases the hardness and fatigue resistance of the traditional products, making them better than other products in wear resistance.

This process is suitable for the welding requirements of bimetal composite pipe castings:

  1. When installing the bimetal composite pipe, the pipe shall be aligned with the center line of the pipe to ensure that both ends of the pipe are facing and connected accurately.Due to the high hardness of chromium alloy lining, only the outer wall of the ordinary steel pipe for welding, must be welded through.In the field cutting, according to the thickness of the composite pipe, plasma cutting machine must be used for the field cutting.
  2. Select J507 ordinary electrode with diameter of 4.0mm.

3, generally use direct current welding machine welding, can also use ac welding machine welding.

  1. After the groove welding of both ends is completed, the reinforcing hoop shall be used in the middle of the weld, and the outer wall of the composite pipe shall be welded to ensure the solidity of the weld.
  2. Welding under tuyere with low temperature and humidity should be avoided.
  3. Spot welding, symmetrical welding and integral welding should be adopted for welding parts to avoid cracking of stress concentrated casting.
  4. In order to ensure the welding quality of the bimetal composite pipe, the welding surface shall be cleaned to avoid oil stains, slag inclusion and other defects.

Extrusion production process of bimetal clad pipe
The hot extrusion technology is a kind of pressure processing method to put pressure on one end of the billet in the container (extrusion barrel) and make it form through the die hole to get the pipe with the die hole shape and section.During the whole process of hot extrusion, the metal can exert the maximum plasticity by having a stronger three-direction compressive stress state than rolling.Therefore, it can be used for rolling or forging metal materials that are difficult or even impossible to process.The extrusion method can produce not only simple shaped tubes, rods and wires on one device, but also bimetallic composite tubes and profiles.

The forming principle of bimetal composite pipe billet is to make use of centrifugal casting technology to cast metal liquid with different components in layers, so that the fusion layer of internal and external metal can be controlled within a certain thickness range to form a complete metallurgical fusion.Horizontal centrifugal production process of bimetal composite tube blank is as follows: tube mold cleaning → preheat → spray paint → drying → top end cap → start centrifuge → (outer metal liquid melting) casting outer layer → (inner metal liquid melting) casting inner layer → blank → processing into composite tube blank.

After centrifugally casting the billet into a bimetal composite tube, the billet needs to be machined on the inside and outside surface.Main differences with single metal billet processing: before bimetal billet processing, it is necessary to verify the middle diameter, according to the actual size of the middle diameter to determine the processing size of the outer diameter and inner diameter;The roughness of the surface is required by different materials. Generally, it is carbon steel and alloy steel Ra≤6.3 m, stainless steel Ra≤3.2 m, and nickel-based alloy Ra≤1.6 m.

Control points of extrusion process:

Heating. Since the high temperature plastic deformation of the two layers of metal is different, the heating temperature setting principle is difficult to avoid. For example, the heating temperature of 10/GH600 bimetal composite pipe only considers the best high temperature plastic zone of GH600;
Lubrication. The selection of glass powder should consider not only the temperature of the inner and outer layers, but also the properties of different materials.
Extrusion speed. Because the high temperature flow characteristics of the two layers of metal are not the same, the extrusion speed will compromise to make the metal flow speed of the two materials close, reduce the tensile stress of the two layers of metal, to avoid causing tension crack.
Because of its unique function and economy, bimetal composite pipe will be widely used.Since 2004, the use of “centrifugal casting and extrusion process” double metal composite tube, after hundreds of billet and tube manufacture, conquer the billet casting and extrusion of various technical difficulties, successfully developed more than 30 different specifications, different steel grade combination is metallurgical combination of double metal composite tube, and has been applied to various industries.The application results show that the centrifugal casting pipe blank extruded composite pipe has super metal bonding force of inner and outer layers, which is convenient for making various pipe fittings, and can realize the complementary strength and toughness of inner and outer layers of metal, avoid stress concentration, and improve the safety performance of pipeline.The product can be used in boiler, oil, wear-resistant transport environment, Marine liquid transport and other fields.

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