Maintain and repair

Routine Maintenance

The housing must not be subjected to any impact; operations must be performed according to regulations. External valve fittings should be kept clean and intact, with valves that operate smoothly, and regular calibration should be conducted as required. Under normal operation, an annual inspection and maintenance of all valves, fittings, and instruments should be performed, and timely replacement of wearables (such as valve seals) should be carried out.

2. Insulation Performance Maintenance

One of the key requirements for low-temperature liquid storage tanks is excellent insulation performance, with the vacuum degree being a critical factor in determining this.

Once the vacuum of the storage tank is compromised, it cannot store low-temperature liquids. Therefore, special attention should be paid to protecting the vacuum integrity of the tank. The explosion-proof device on the tank shell and the vacuum valve are directly connected to the vacuum interlayer. The device must not be tampered with unless the interlayer vacuum is not damaged or it is not necessary to replenish and re-vacuum with mica sand. The vacuum valve is sealed with lead at the factory and must not be moved at will; otherwise, it will damage the tank's vacuum integrity.

The tank shell is an external pressure vessel, subjected to atmospheric pressure. It is strictly prohibited to strike or bump the shell to prevent damage and affect the vacuum level.

3. Inspect

(1) Routine inspection

1) Is the valve in the correct open/close position?

2) Accuracy and reliability of pressure gauges and differential pressure (level) meter measurements.

3) Check for any leaks or blockages in pipes and valves.

4) If the container pressure reaches the set pressure of the safety valve and the valve does not activate, the safety valve set pressure should be immediately adjusted to ensure the safety of the storage tank.

5) Are the turbocharger flange bolts loose, and is there any deformation in the pipes?

(2) Regular maintenance

1) The pressure gauge is calibrated annually.

2) The safety valve is calibrated annually.

3) Measure vacuum level annually.

4) Thermocouple vacuum gauges (purchased by the user, not within the supply scope) should be calibrated according to the instructions before each measurement.

5) Inspect the tank grounding resistance annually; a resistance less than 10Ω is considered acceptable. If greater than 10Ω, the connection status should be checked promptly.

(3) Vacuum Level Inspection and Re-evacuation

The tank's vacuum level is measured once a year. To measure, simply unscrew the protective cap of the metal thermocouple tube and insert the plug of the thermocouple vacuum gauge, then the interlayer vacuum level can be known.

After several years of use, the vacuum level in the tank may drop to 65Pa, requiring a re-evacuation to enhance insulation performance. Prior to re-evacuation, the liquid inside the tank should be drained first, and then heated with dry, oil-free air or nitrogen at 80-100℃ to blow out until it returns to normal temperature. Connect the vacuum piping, start the pump to remove the moist air from the pipe, and then open the vacuum valve to evacuate the tank.

To reduce the vacuuming time, the container can be heated with dry, oil-free air at temperatures below 100°C. The vacuum degree of the jacketed seal should be ≤3Pa. If necessary, the user may contact the manufacturer for vacuuming matters, and both parties can agree on the specific process for re-vacuuming.

4. Fault Handling

(1) Safety Valve Troubleshooting

1) Safety valve leakage

The valve disc and seat sealing surfaces may experience leakage beyond the allowable limit under operating pressure, and the possible causes may include:

There is debris on the sealed surface.

Before installation, if the cleaning with compressed air is not fully completed, or if solid impurities are mixed with the fluid during the trial operation, or if necessary actions are performed, debris may get trapped between the valve seat and the sealing surface. If it's easy to remove the debris manually, do so. However, if there's still leakage after removal, consider the following causes: it may be damage to the valve seat and the sealing surface; or the debris may be embedded between the valve seat and the sealing surface. If this situation is difficult for the user to handle, return it to the manufacturer for repair.

② Internal Pipeline Force

a) Human Factors

During the process of installing the safety valve on the pipeline, if it is forcibly rotated, the valve seat may rotate, which could change the position of the safety valve adjustment ring or cause the sealing surface to be worn down forcibly. A decrease in operational performance may occur. In such cases, depending on the situation, it can either be handled on-site by the user or returned to the factory for processing. However, it is necessary to fully grasp the situation and make a quick judgment.

b) Internal Force Factors

The adverse effects of welding residue's force within the pipeline on the safety valve are almost identical to the issue mentioned above. Therefore, it is crucial to thoroughly consider the absorption of internal pipeline forces during installation.

c) The setting pressure of the safety valve is too close to the normal operating pressure of the equipment, which results in an excessively low sealing ratio pressure on the sealing surface. This makes leakage more likely when the safety valve is subjected to vibration or fluctuations in the medium pressure. Under conditions of satisfying the strength requirements, the setting pressure of the safety valve should be appropriately increased during design.

③ Spring relaxation reduces the set pressure, causing the safety valve to leak.

The primary cause for spring relaxation may be that after the safety valve is calibrated, the adjustment screw of the safety valve is not securely tightened, leading to loosening during equipment operation, resulting in spring relaxation, decreased pre-tension, and premature opening of the safety valve. The safety valve should be recalibrated.

2) Inflexible safety valve operation

The reason may be:

Improper adjustment of the safety valve's regulating ring leads to an extended opening process or delayed return, which should be re-adjusted. By adjusting the lower regulating ring, increase the return seat pressure.

②The exhaust pipe of the safety valve has excessive resistance, resulting in significant back pressure during discharge, which causes the safety valve to open at an insufficient height. To normalize the operation of the safety valve, the exhaust pipe should be changed to a direct connection, eliminating the intermediate bend.

3) Safety valve frequent chatter or vibration

The reason may be:

The discharge of the safety valve is too high. The rated discharge of the selected safety valve should be as close as possible to the equipment's required discharge.

② The import pipeline diameter is too small or the resistance is too great.

③ Excessive resistance in the exhaust pipe causes excessive back pressure during discharge. The resistance of the exhaust pipe should be reduced.

④Improper adjustment of the adjusting ring leads to excessive return seat pressure. The position of the adjusting ring should be readjusted.

4) Operation of Three-way Valve A-5 when replacing the safety valve

① Two safety valves operate simultaneously during normal operation, with both channels open at the same time, as shown in Figure 1.

②When replacing the safety valve, rotate the handle 90 degrees (as shown in Figures 2 and 3), close the side channel to be replaced, and empty the remaining medium inside the channel, then replace the safety valve.