Welding of high efficiency tube sheet
In the manufacturing process of shell and tube heat exchanger, including vessel manufacturing, shell and tube heat exchanger’s tube and tube sheet connection, tube plate baffle manufacturing, these three aspects have high requirements for welding process.
Most of the shell and tube heat exchanger vessels are welded
Hydrogen elimination treatment and post weld heat treatment shall be carried out for welds. In the process of welding, hydrogen from welding rod, flux and air decomposes into atomic state and dissolves in liquid metal at high temperature. When the weld is cooled, the solubility of hydrogen in steel drops sharply. Because the weld is cooled very fast, the hydrogen can’t escape before it stays in the weld metal and forms delayed crack after a period of time. After welding, heat the weld to 200 ℃ for 16 hours, and then conduct hydrogen elimination treatment. Post weld heat treatment includes heating the whole or part of the weldment to a certain temperature below line a (phase change point) for heat preservation, and then furnace cooling or air cooling. As long as the purpose is to eliminate and reduce the stress produced in the welding process, to avoid cracks (hydrogen cracks) in the welding structure, and to restore the mechanical properties lost due to cold work. It should be noted that in order to ensure the sealing of the pipe box equipment flange, it is often required to process the sealing surface after the overall heat treatment.
Welding method of shell and tube heat exchanger
In the manufacturing process, the commonly used welding methods include manual arc welding, submerged arc automatic welding, gas shielded welding (argon arc welding, CO2 shielded welding), etc. According to different materials, different thicknesses, different bevels are made and different welding processes are adopted. Manual arc welding is a widely used welding method, which is flexible in operation, simple in equipment and can be used for all position welding, but the welding quality largely depends on the welder’s technical level; automatic submerged arc welding has high heat utilization rate, fast welding speed and high productivity, which can save metal and improve working conditions, but limited by it, it is generally only used for welding straight weld and large Circumferential girth weld. For example: when the cylinder (δ ≥ 18mm) is welded with longitudinal seam and circumferential seam, the manual arc welding can be used as the backing first, and then the submerged arc welding can be used after the test and inspection are qualified; because the heat exchange tube is relatively thin, the argon arc welding is used for the welding of tube plate and heat exchange tube, and then the tube expander is used for expanding.
The connection between tube and tube plate of shell and tube heat exchanger is generally as follows:
Strength welder pastes expansion B, strength expansion plus seal welding C, strength welding D, strength expansion. At present, expansion welding is widely used. This method can improve the fatigue resistance of the joint and eliminate stress corrosion and gap corrosion. At present, surface penetration or magnetic particle testing is widely used to control the quality of welded pipe joints, and there is no testing requirement for internal defects of welded joints.
The manufacturing of tube plate and baffle plate in shell and tube heat exchanger is a prominent problem in the manufacturing process.
The tubesheet is machined, and the hole diameter and the distance between holes have tolerance requirements according to different tube bundles. Drilling can be done by marking and drilling die, and one point can be done by numerical control machine tool. However, when using marking drilling, due to the poor accuracy, when drilling the pipe hole of baffle plate, the pipe plate and baffle plate shall be overlapped for drilling. After drilling, the baffle plate shall be numbered and oriented in order to facilitate assembly. The baffle plate shall be drilled according to the whole round plate, and cut into the required shape after drilling.
In the manufacturing of heat exchanger, the manufacturing process of cylinder, head and other parts is the same as that of general container manufacturing, but the requirements are different. Among them, the inspection of materials, drilling of tube plate and baffle hole, welding of cylinder, processing of flange, etc. Throughout its manufacturing process, most of the traditional processes are used, in which welding accounts for a higher proportion, so it is necessary to weld in strict accordance with the welding process, and to detect the weld.
Source: China Tube Sheet Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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