In recent years, with the continuous improvement of smelting technology, the output of titanium materials has increased rapidly, and this non-ferrous metal with excellent performance has been increasingly used in the manufacture of chemical equipment (mostly used as lining). Titanium has a high specific strength, but it is more expensive. Most of the pressure vessels or pressure vessels are made of titanium steel clad plates. Due to the inconsistent linear expansion coefficients of the two materials, improper fixing of the titanium lining often leads to leakage.
1. The fixed relationship between titanium and carbon steel
Titanium material has excellent performance, the biggest feature is small mass, high strength, excellent corrosion resistance, good low-temperature performance, and excellent corrosion resistance in seawater and most acid, alkali, and salt media, so it is widely used in various It is a kind of chemical reaction vessel and heat exchanger material, but the disadvantage is that the cost is high, especially when it is used as a structural component, this problem is particularly prominent, and the effective solution is to use titanium steel composite plate.
Due to the poor weldability of titanium and carbon steel materials, silver brazing is generally used for sealing welding. Due to the high price of silver, welding is only performed under special circumstances such as air tightness testing. Currently, the commonly used connection forms are as follows two kinds.
1) Explosive composite form
This method uses explosives as the energy source and uses the impact force generated by the explosion to make the weldment violently collide, plastically deform, melt, and inter-diffusion between atoms to achieve a pressure welding method. First, keep a certain interval between the two metal plates to be crimped, and then put an appropriate amount of explosives on them. It is detonated from one end of the explosive, and the explosion speed is several thousand meters per second. With the explosive energy, the titanium plate collides with the base steel plate at an angle. At the collision point, the base steel plate and the titanium plate form a connection under ultra-high pressure due to the very large deformation speed. Joining is done in an instant.
2) Screw fixing form
First, drill holes and taps on the carbon steel substrate, and at the same time drill holes on the titanium plate, fix the titanium plate on the carbon steel substrate with titanium screws, and then perform sealing welding on the upper surface of the screws. The welding generally adopts argon arc welding. . In order to provide an inert gas passage to protect the back of the lining weld, inspect the welding quality of the lining, and discharge the air between the lining and the shell when welding the lining in the shell, the lining equipment should be equipped with a leak detection system. The leak detection system is usually composed of a semicircular leak detection groove with a radius of 1.5mm~3mm and a leak detection hole communicating with the atmosphere, which are connected to each other on the back of the lining.
2. Leak location and cause analysis
①Leakage location: the sealing surface of the head and the flange of the tube sheet leaks.
②On-site disposal: Use the tensioner to tighten the bolt according to the requirements of the bolt tensioning moment, but the tightening is invalid and the leakage point is not eliminated.
③ On-site dismantling inspection: Remove the head to check the sealing surface of the tube sheet and the tube box, and there are no obvious scratches and obvious deformation on the surface. The sealing surface of the pipe box (fixed by screws) was tapped lightly with a metal hammer, and there was a hollow sound in some positions, especially in the position where the leakage was serious. PT nondestructive testing was carried out, and no obvious defects were found, which proved that the titanium plate and the base material There are problems in between.
④Cause analysis: According to the above phenomenon, the cause of leakage is that the sealing surface of the flange of the pipe box and the sealing surface of the base material is not firmly attached. After tightening the bolts according to the torque, there is a virtual point in the contact position of the sealing surface, causing leakage.
3. Treatment and maintenance methods
To replace the original titanium ring sealing surface, the specific steps are as follows:
①Use a lathe to remove the sealing surface of the titanium ring.
②Repair the corrosion position of the carbon steel base material of the pipe box. The repair welding should be higher than the surface of the base material. Use a lathe to smooth the surface of the base material, and the roughness should reach 3.2 or more.
③One new titanium ring is made. Due to the large size, the whole circle prefabrication wastes a lot of material, so three arcs are used for splicing to save material.
④The titanium ring and the base material are equipped with drilled fixing screw holes. Originally, M8 screws were used for fixing, but M12 screws were used for fixing, and the number remained unchanged.
⑤Use the tooling to press and fix the sealing surface of the titanium ring around the entire circumference, and then tighten the titanium screws.
⑥ Weld the titanium screw and the titanium ring. Whether the welding surface is qualified or not can be judged according to the color of the heat-affected zone of the weld.
⑦ Remove the tooling after the temperature of the weldment drops to room temperature and check the spring back rate of the titanium plate, which is qualified within the range required by the drawing.
⑧ Process the sealing surface of the titanium plate to the drawing size.
⑨ All welds are tested by PT.
Baoji Taicheng Clad Metal Materials Co., Ltd is a metal clad plate manufacturer, which can provide customized titanium steel clad plate services for buyers at home and abroad, and we have professional customer service online 24 hours a day for you, and finally summarize the following two points for the above problems: (1) After the flange sealing surface is tightened, the distance deviation of the sealing surface should be measured, and the distance difference should generally be less than 0.5mm. (2) In the process of replacing the sealing surface of the titanium plate, special attention should be paid to the welding speed and the compactness of the tooling, which is the key to avoiding the deformation of the titanium plate. Hope it helps you!
