Baoji Taicheng Clad Metal Materials Co., Ltd is a titanium steel clad plates factory. In the previous article, we introduced the analysis of the causes of cracks in titanium steel clad plate equipment. So, how should we avoid them in daily use? What happens? And how to solve this situation?
1. Ensure a clean welding environment and do a good job of preparation before welding. Titanium is an active element. In the process of manufacturing titanium equipment, sufficient attention should be paid to the requirements for a clean environment to prevent pollution problems. Dust particles in the environment, especially iron ions in the manufacturing plant, are likely to pollute titanium materials, cause weld embrittlement, reduce the corrosion resistance of equipment titanium materials, and cause weld defects. And in the corrosive medium, when the content of these impurities such as iron ions is too high, it is easy to form a stable iron-rich phase region near the weld, which will produce chemical or electrochemical reactions with the titanium base layer, and further expand the defects in the weld, affecting The use of equipment is even scrapped. Therefore, the manufacturing environment of titanium equipment should be separated from other materials, and it should be manufactured in a clean and dry processing area; before welding, the surface cleaning process of degreasing, and removing oxide skin, and getter layer should be carried out. After surface cleaning, Welding parts should not be placed for a long time, and should be welded immediately; during the clamping process of the workpiece, the operator should wear clean gloves, and should not touch the welding joint and its vicinity. It is strictly forbidden to hit the welding joint with iron tools to avoid contamination of the welding joint; Contamination testing should be carried out throughout the manufacturing process.
2. Control the content of hydrogen and oxygen to ensure the quality of welding. During the design and manufacture of titanium equipment, requirements for hydrogen and oxygen in the gas must be put forward. If it is necessary to use welding wire with low hydrogen content or hydrogen removal treatment. During welding, shielding gas is also very important: argon gas with a purity of 99.99% should be used for argon protection; sufficient argon time should be filled before welding, and welding can only be carried out after the air around the welding joint is completely removed to prevent During the welding process, the titanium reacts with the hydrogen and oxygen in the air; the shielding gas needs to be kept until the weld temperature is lower than 370°C before it ends; during welding and cooling of the weld metal, the heat-affected zone must be protected from normal temperature Oxidation and water vapor evaporation make the weld and heat-affected zone brittle, and produce cold cracks under welding stress. In the heat treatment of equipment, specific requirements should also be put forward, such as using an electric heating furnace according to regulations, and the furnace should be in a weak oxygen environment.
3. Pay attention to testing such as hot gas cycle tests and anodizing treatments. Due to the high price of titanium materials, in order to reduce the cost of equipment, large and thick-walled pressure vessels are often designed and manufactured with titanium composite plates. However, due to the many longitudinal and circumferential welds of the equipment, the linear expansion coefficients of the titanium steel materials are inconsistent. The difference of difference becomes larger as the temperature rises, so when the equipment heats up, the titanium cladding is in a state of tensile stress. If there is a problem with the quality of the weld on the cladding titanium weld, it will cause cracks in the titanium weld, and eventually causing a leak. The hot gas cycle test is a test method that simulates the operating temperature and pressure of the equipment in the manufacturing plant, and keeps the temperature and pressure for a period of time. After the temperature drops to room temperature, it is a test method to further test the weld quality of the equipment in the operating environment. Therefore, it is necessary to conduct a hot air cycle test on the equipment after the equipment has passed the hydrostatic test.
At present, iron pollution cannot be completely avoided in the manufacturing process. During equipment operation, both titanium and iron can form compounds and enter titanium. The anodizing treatment uses titanium as the anode, stainless steel or other materials as the cathode, and under the action of a certain dielectric, the titanium presents a method of anode passivation. After the titanium surface is anodized, a stable oxide film will be formed, which can prevent the titanium material from directly contacting the medium, improve corrosion resistance, and prevent metal titanium from corroding. At the same time, anodizing can also dissolve the iron precipitate remaining on the titanium surface, and the formed oxide film covers the iron and titanium compound and the iron-rich β phase, which isolates the iron and titanium from contacting the electrolyte, and improves the hydrogen permeation resistance of the titanium material.
Due to the chemical characteristics of titanium, whether titanium equipment can operate efficiently and safely, the manufacture, inspection, and testing of titanium equipment are very important links, and sometimes even determine the length of equipment life. Therefore, the manufacturing inspection requirements of titanium equipment are more complicated and strict than those of general steel containers, and it is reasonable to a certain extent. Various pre-manufacturing preparations, equipment inspections, tests, hot gas cycle tests, anodizing treatment, etc., are complex but essential, and the order of each inspection and test must not be reversed, these are to ensure that the equipment can Long-term operation played a key role.
