At present, the treatment of flue gas in China is mainly wet desulfurization. The flue gas produced by this method is significantly more corrosive than other processes, and the performance of concrete chimneys gradually cannot meet the needs of the current desulfurization process. Domestic concrete chimneys have gradually reached the design life, and more and more chimneys are facing demolition or renovation. The built-in titanium steel composite plate chimney can isolate the concrete cylinder from the flue gas, which can effectively slow down the corrosion rate and prolong the corrosion resistance period. The welding seam of the titanium surface is the weak link to the corrosion resistance of the titanium surface. The welding quality directly affects the service life of the product, so it is particularly important to ensure the welding quality of the titanium surface.
1. Principle of the welding process
(1) The overall strength of the titanium-steel composite chimney is borne by the carbon steel part, and the titanium layer part only plays the role of sealing and anti-corrosion. The welding of titanium steel clad plate cladding (titanium steel) adopts argon arc welding. In order to ensure that the titanium layer is not oxidized by heat when the carbon steel part of the substrate is welded, the titanium layer around the substrate welding is trimmed, and a titanium strip is attached to the welding and sealing.
(2) Titanium can quickly absorb hydrogen when the temperature is above 300 °C, oxygen can quickly absorb when it is above 450 °C, and nitrogen can be quickly absorbed when it is above 600 °C, that is, "oxidation". When these harmful gases are infiltrated into titanium, the plasticity and toughness of the welded joint will change significantly, especially above 882 °C, the grains of the joint are severely coarsened, and a martensite structure is formed during cooling, which makes the joint strength, hardness, and hardness. The plasticity and toughness decrease, the tendency to overheat is severe, and the joint is severely brittle. Therefore, the surface temperature of titanium should be strictly controlled within 300 ℃ during the formulation of process parameters and welding process.
2. Welding quality control measures
1) After the titanium steel-clad plate enters the site, it is necessary to protect the finished product to avoid contamination and damage to the titanium surface. When the titanium-steel composite plate is rolled, the roll will have direct contact with the titanium surface, and wrapping the plastic film on the roll can effectively protect the titanium surface.
2) Conventional steel plate clamps have teeth on one side and bosses on the other. Grind the side of the boss flat and weld a thin steel plate. When the titanium composite plate is hoisted, the toothed side is in contact with the carbon steel layer, and the new thin steel plate increases the contact surface between the plate clip and the titanium layer, reduces the pressure on the titanium layer, and ensures that the titanium layer is not damaged.
3) The deformation of the coil plate during transportation will increase the correction of the set-up. The titanium layer is on the inside of the steel chimney, and it will inevitably affect the titanium surface during the correction. Reducing transportation deformation can reduce the workload of correction, thereby reducing the impact on the titanium surface. Make a special transport trolley, and use a forklift for the short barge to reduce the deformation of the coil.
4) Before welding, it is necessary to carefully remove oxides, nitrides, oil stains, moisture, and other organic pollutants on the surface of the weldment and welding wire.
5) During the hot rolling process of the titanium-steel clad plate, the titanium surface is coated with a release agent, and the release agent is cured on the surface of the titanium layer after the finished product. After the test welding, the weld seam is oxidized and discolored seriously. In order to eliminate the solidified release agent on the titanium surface near the weld, through the test, manual grinding, chemical cleaning with carbon tetrachloride, banana water, and other chemical cleanings could not remove the dissolved release agent. And other common mechanical methods, the practical effect can be seen that shot peening can effectively remove the titanium surface curing release agent.
3. Welding environment
During CO2 gas-shielded welding and argon arc welding, the wind speed should be no more than 2m/s. Necessary wind and rain protection measures must be taken for on-site welding. Since the steel inner tube is constructed inside the concrete chimney, the top of the chimney and the lower manhole door should be installed. Closed, which can effectively ensure the welding environment requirements.
For the promotion of titanium-steel clad chimneys in China, Baoji Taicheng Clad Metal Materials Co., Ltd, as a titanium-steel clad plates manufacturer, can provide high-quality products and services for buyers at home and abroad. If you have related needs or questions, Welcome to consult!
