Deformation analysis of hot water tanks
Thread Content
During the drainage for maintenance of the hot water tank, when the liquid level was reduced to zero, there were two loud bangs and the hot water tank deformed. What could be the reason? Please help analyze it. Equipment factors: At the top of the hot water tank, there is a vent pipe with a diameter of DN100 ； Overflow pipe DN100; bottom drain outlet DN 80. Operating conditions: temperature of the hot water being discharged is 60°C. Environmental factors: air temperature of -10°C. Other factors: internal leakage in the heating steam valve. During drainage, the gas phase temperature of the hot water tank gradually rises to 98℃
Immediate cause: A negative pressure was created inside the tank. 1. Temperature difference ； 2. Insufficient qi replenishment.
That’s right; perhaps the drain valve isn’t open, causing water to be released and creating negative pressure.
Check the drawing of the hot water tank to see whether it is a atmospheric pressure tank or a pressure vessel. If it is a pressure vessel, then the vent valve is not open; if it is an atmospheric pressure tank, check whether the operating temperature range of the equipment exceeds 100 degrees. The most likely possibility is that the vent wasn’t turned on. Another reason is that steam instantly condenses into water, creating a negative pressure. What’s the approximate time for your DCS curves?
This is called negative pressure instability. Reasons for it: 1. The level gauge is inaccurate. 2. There may be blockages due to freezing in the vent pipe and overflow pipe, or the valves may not be open. 3. What is the height of the steam coil? If it is too high, there may be a large temperature difference between the top and bottom as mentioned above, as well as instantaneous condensation due to drainage
The vent and overflow ports have no valves and are directly connected to the atmosphere; checks show that they are not frozen. Judging from the DCS record curves, the most likely possibility is instantaneous condensation.
It is not heated by coils; instead, a Venturi mixer directly heats the water. The heating location is in the middle of the hot water tank
The temperature difference is too large, causing a phase change; the volume of the steam decreases rapidly, which leads to a drop in pressure below atmospheric pressure. As a result, the structure of the tank changes, which is what is referred to as structural instability mentioned earlier.
Find a mineral water bottle, cover it with a little hot water, then place it outside to freeze for a while to see if the effect is the same.
What are the diameters of the overflow pipe and the vent pipe? What is the diameter of the drainage pipe?
I quite agree with this analysis: handshake