This article tells you the causes of leakage and treatment measures Introduction to tubular heat exchanger
Tubular heat exchanger is a widely used heat transfer equipment. Compared with several other inter-wall heat exchangers, the unit volume of the equipment can provide a much larger heat transfer area, the heat transfer effect is also better.
The tube heat exchanger is composed of tubes, tube plates, folding plates, shells, end caps (tube boxes) and so on.
In the heat transfer, a fluid from the head of the connecting tube at the entry, in the tube flow, from the other end of the head of the exit tube out, which is called the tube process; the other - a fluid from the shell of the receiver into, from the shell of the other receiver out, which is called the shell process.
Tube heat exchanger leakage causes: tube heat exchanger internal tube system leakage is mainly divided into tube leakage itself and tube port leakage.
Heat exchanger tube port leakage causes: 1 excessive thermal stress The tube heat exchanger in operation, due to the cold, hot fluid temperature differences, so that the shell and tube wall temperature differences between each other. This difference makes the shell and tube thermal expansion is different, when the temperature difference between the two may twist and bend the tube, or make the tube from the flower plate pulled loose, or even destroy the entire heat exchanger. In this regard, it is necessary to structure to consider the impact of thermal expansion, the use of various methods of compensation. Heat exchanger in the process of starting and stopping the temperature rise rate, temperature drop rate exceeds the provisions, so that high plus the tube and tube plate is subject to greater thermal stress, so that the tube and tube plate connected to the weld or expansion joint damage occurs, causing port leakage.
2 tube plate deformation Mainly processing deformation of the tube plate and processing deformation, the tube and tube plate connected, tube plate deformation will make the port of the tube leakage.
3 plugging process is not appropriate Generally used conical plug welding plugging. Hit into the conical plug with moderate force; pounding force is too large, causing deformation of the pipe hole, affecting the neighboring tubes and pipe plate connected, will cause damage and make a new leak. Welding process, such as preheating, welding seam position and size is not appropriate, will cause damage to the neighboring tubes and tube plate connection. The use of other plugging methods, such as pipe expansion and plugging, such as improper process, can also cause leakage of the adjacent pipe mouth. Therefore, a strict plugging process should be followed.
Heat exchanger tube leakage itself causes: 1 scour erosion One reason is that when the steam flow rate is high and the steam flow contains large droplets of water, the outer wall of the tube by steam and water two-phase flow scouring, thinning, perforation occurs or by the pressure of the feed water and drum break. Another reason is the direct impact by steam or hydrophobic. Because the anti-scouring plate material and fixed way is not reasonable. Broken or fallen off in operation, the loss of anti-scouring protection; anti-scouring plate area is not large enough, water droplets with high-speed airflow movement, hit the anti-scouring plate outside the tube bundle; shell and the distance between the tube bundle is too small, so that the inlet at the high speed of the vapor flow.
2 tube vibration water temperature is too low or unit overload, etc., through the heat exchanger tube between the steam flow and flow rate more than the design value, with a certain degree of elasticity of the tube bundle in the shell side of the fluid disturbance force will produce vibration, when the frequency of the excitation force and the natural vibration frequency of the tube bundle or its multiples coincide, will cause the tube bundle resonance, so that the amplitude greatly increased, resulting in the connection between the tube and the tube plate is repeatedly The force causes damage to the tube bundle.
3 tube feed water erosion at the inlet end of the inlet tube erosion damage only occurs in the carbon steel heat exchanger, is a joint action of erosion and corrosion of the damage process: the mechanism is the tube wall metal in the surface of the oxide film formed by the high turbulence of the feed water damage and take away, the continuous loss of metal materials. The end result is the breakage of the tube.
4 corrosion when the low-pressure heat exchanger tube for copper, low plus copper tubes are often forced to replace because of serious leaks. pH 8.5 ~ 8.8 when the corrosion rate of copper is low. And carbon steel requires a pH value of not less than 9.5. boiler feedwater pH value is too high, resulting in the corrosion of copper tubes.
5 material, poor process tube material, uneven tube wall thickness, assembly before the tube has defects, expansion mouth over-expansion, the outer side of the tube has strain damage marks, etc., in the heat exchanger encounter abnormal working conditions, will lead to a large number of damage to the tube.
Tube heat exchanger leakage handling measures Leakage occurs after the handling measures Leakage occurs when the feed water pressure is reduced, the feed water sent to the boiler is reduced. Therefore, when a leak in the heat exchanger tube system is found, the heat exchanger should be immediately shut down to reduce the number of damaged tubes and mitigate the degree of damage. Unit shutdown, should check whether the high plus leaks, and find ways to eliminate. For port leakage, the original weld metal should be scraped and then welded, and appropriate heat treatment to eliminate thermal stress: for the tube itself leaks, you should first check the form and location of the tube bundle leakage, and choose the appropriate plugging process, plugging the two ports of the tube.
No matter what plugging process is used, to ensure the quality of the plugged pipe, the end part of the plugged pipe must be well treated to make the pipe plate, pipe hole round, clean, and have good contact surface with the plug. In case of cracks or erosion at the connection between the tube and the tube plate, the original tube material and weld metal at the end must be removed to make the plugging head in close contact with the tube plate.
