Jis G3459 Seamless Steel Heat Exchanger Pipe Thermal Conductivity Material

Heat exchanger tubes are used to cool, heat, or reheat fluids, gases, and air. Heat exchanger tubes play a vital role in facilitating the heat transfer process by enabling the exchange of thermal energy between the process fluid and the shell-side fluid.

In order to be able to transfer heat well, the pipe should have good thermal conductivity. Because heat is transferred through the tube from the hot side to the cold side, there is a temperature difference across the width of the tube. Because pipe materials have different tendencies to thermally expand at different temperatures, thermal stresses occur during operation. This does not include any stresses caused by the high pressure generated by the fluid itself. The tube material should also be compatible with the shell-tube side fluid over the long term under operating conditions (temperature, pressure, pH, etc.) to minimize deterioration such as corrosion.

Improper tube material selection can result in tube leakage between the shell and tube sides, resulting in to fluid cross-contamination and possible pressure loss. Of course, since the pipe is under pressure for a long time, fatigue will occur over time, resulting in leakage. When this happens, how to repair the heat exchange tubes in the heat exchanger?

Leakage of heat exchange tubes in pressure vessels generally occurs in two places, one is the connection of the tubes, and the other is the leakage of the tube itself.

(1) Leakage at stainless steel heat exchanger tube connections

There are three main methods for connecting pipes and tube sheets: expansion joints, welding, welding, and expansion joints. Due to the fluctuation of temperature and pressure and the uneven deformation of the temperature difference, the expansion pipe causes the pipe to pull off, loosen, and leak from the tube sheet. Complementary expansion can be used to eliminate the leakage. If it is ineffective, it can be done again. The supplementary expansion cannot be more than three times, otherwise This will cause the material at the tube plate hole to harden due to cold work and become less tight.

If the expansion is ineffective, the pipe must be replaced or welded. It should be noted that after welding, the surrounding tubes need to be expanded again because the thermal expansion and contraction of the tube sheet after welding will cause leakage in the expansion joints of other surrounding tubes. If the weld between the pipe and the tube sheet is leaking, it can be repaired by grinding and repairing the weld.

(2) The pipe itself is leaking

Due to corrosion, abrasion, erosion, sedimentation corrosion, and other reasons, heat exchange tubes often cause cracks, perforations, and leaks in the tubes. The leakage of the pipe itself cannot be repaired under normal circumstances. If the number of leaking pipes is not large, you can use conical metal plugs to block both ends of the pipe mouth. If the pressure on the pipe side is high, plug it tightly and then weld more for reliability. The length of the metal plug is generally twice the inner diameter of the pipe, the diameter of the small end should be equal to 85% of the inner diameter, and the taper is 1:10.

The hardness of the plug material should be less than or equal to the hardness of the pipe. When plugging pipes to eliminate leaks, the number of pipes plugged should not exceed 10%. When one end of the stainless steel heat exchange tube is damaged, the drawn tube repair method can also be used. This is because the elongation rate of the stainless steel tube is 40%~45%. When the total elongation of the drawn tube does not exceed 12%, the tube can be drawn multiple times.