FOR VACUUM JACKETED PIPING SYSTEM
VACUUM BAYONET CONNECTION TYPE WITH FLANGES AND BOLTS
The Installation Precautions
The VJP (vacuum jacketed piping) should be placed in a dry place without wind before installation. The outer packaging layer of VJP cannot be opened, to prevent the tube into foreign bodies (sand, small organisms, etc.). In rainy or long-term wet weather, also need to pay special attention to the inside of the pipeline waterproof.
It is forbidden to use VJP directly as welding electrode, strike arc or welding on VJP.
The VJP packaging layer cannot be removed until the pipe is installed to prevent the breakdown of welding in other positions.
During the whole installation process, VJP should be carefully handled. Protect both ends of VJP, do not use the vacuum joint on the VJP (figure 1 and 3) as the point of force to prevent leakage of vacuum.
When installing, pay attention to the reliability of hoisting, do not fall and damage or injury.
The Installation Steps of VJP
1. Check the drawings, whether the quantity and dimension of pipes on the drawings are the same with the field pipes. Before installation, find out each VJP according to the drawing and number. Example: HL2018GLN-59-02-01, which means the project code is 59, liquid nitrogen medium, pipe No. 01 of line No. 02. An iron nameplate with this number is attached to the VJP at the site (figure 1), and an electric corrosion nameplate is attached near the vacuum joint on the VJP (figure 2).
Note: the quantity and No. of pipes in the drawing must be the same as the quantity and No. of VJPs on site. If there is any discrepancy in the checking, be sure to contact our personnel on site.
2. After checking the VJP quantity and No., according to the drawings, move the VJPs on the corresponding brackets/supports or place VJPs on the ground next to the corresponding brackets/supports.
3. Before the flanges are connected, first check whether the seal rings and cold seal unit are properly installed
4. Clean the joints of female & male extension pipe, seal rings and cold seal unit with oil-free and water-free reagent.
5. Insert the male and female extension pipe horizontally and slowly. Then pull the two flanges together and press, and install all the bolts on the flanges (don't tighten them right now).
6. After ensuring the correct position of the two flanges, tighten the bolts step by step. Ensure that the flange is kept level during installation
7. Check whether the flange tightening is qualified.
8. The interval of two support is 3m, PTFE plate should be installed between the support point and outer pipe.
Details for Operation & Maintenance
1. Operators should be familiar with the workflows between the equipment in the system. It should be known that liquid oxygen, liquid nitrogen and liquid argon are cryogenic liquids. When the ambient temperature is higher than the boiling point, they will be naturally gasify and pressurized, resulting in a gradual increase in the pressure in the VJP and related equipment.
2. Precooling of VJP before Use
Since the unused VJP is at ambient temperature, the pipe is filled with air which contains moisture. Therefore, the purpose of pre-cooling is: firstly, to gradually reduce the temperature of the VJP to the temperature of the cryogenic liquid, so as to avoid the direct contact of a large amount of cryogenic liquid with the normal temperature pipe, producing rapid and huge amount of gasification, resulting in rapid pressurization of the VJP, thus causing damage to the VJP and terminal liquid equipment. The Secondly, is to gradually remove the air inside the VJP and to avoid a large number of cryogenic liquid directly contact with the air, resulting in freezing and blockage inside the VJP.
Prior to the re-use of the vacuum adiabatic pipe after the first use or stop production, precooling shall be carried out so that the vacuum adiabatic pipe can operate normally only after it reaches the working state.
3. The Precooling Method of VJP
First, check whether the valves, pressure gauges and safety valves etc. in the VJP system are in the corresponding normal state. After the above check is completed, slowly open the inlet valve of VJP system and vaporize/gasify the low-flow liquid into cool air to pre-cool the VJP for about 30 minutes. The pressure in the VJP fluctuates greatly at this time. When the pressure in the VJP becomes stable, the infusion volume can be gradually increased until it meets the requirements. (Note: during the pre-cooling process, if the pressure in the VJP is higher than the corresponding design pressure, it must be immediately stopped to infusion into VJP system. Meanwhile, completely open the vent valves on the line to release pressure.)
4. Shut Down the VJP
When stopping infusion, it is strictly prohibited to close the valves of both ends of the VJP system at the same time, so as to form a closed state in the VJP system, resulting in overpressure of residual liquid in the VJP due to gasification.
5. Periodic Discharge of Cryogenic Liquids (Liquid Oxygen Only)
Because hydrocarbons and residues exist in VJP of the liquid oxygen, these substances will be deposited in the inner pipeline for a long time when transported through the VJP. Once hydrocarbons are deposited in the tube in large quantities and for a long period of time, as the weather heats up or the production of liquid oxygen is stopped, the concentration of hydrocarbons in the VJP increases, and the reaction with remaining oxygen can cause an explosion.
6. Safety Device of VJP
In each of the VJP system should be set up safety discharge system (including the relief valve and vent valve), When the pressure of the VJP reaches the opening pressure of the safety valves which will automatically open and release the pressure in time. At the same time, the vent valves can also be opened manually to release the pressure to ensure the safety of the whole VJP system.
Malfunction and Disposal
|
Possible Breakdowns |
Reason |
Handling |
| The rising pressure causes the safety valve to start continuously. | Valves at both ends of the VJP are closed at the same time, Cause pressure to rise. | Immediately open the valves at both ends of the VJP for pressure relief, and open the vent valves at the same time. |
| Blocked pipeline infusion. | There's something blocking in the VJP. | Blow the VJP with nitrogen gas. (Ice blocking: Blow with 100 oC nitrogen gas) |
Post time: Dec-02-2021
