Question: A steam pipeline does not have a drain valve, and it takes a long time to drain water
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This post was last edited by FORREST_GUMP on 2016-9-23 at 10:36. Dear everyone, something puzzling happened today, and I would like to ask for your advice: Phenomenon: Steam from the steam distribution cylinder enters the main pipe with a diameter of DN200 and a pressure of 0.5 MPa. The cylinder has 4 steam outlets, but only one outlet with a diameter of DN150 is currently in use. The distance from the outlet’s shut-off valve to the equipment that uses the steam is about 30 meters. No drain valves have been installed along the entire steam pipeline; drainage can only be done through the cylinder’s own drain valve, which has a diameter of DN25. The equipment uses steam indirectly; after the steam was used up the day before yesterday, the DN200 main steam pipeline valve of the steam distribution cylinder was closed, and the DN150 steam usage valve was also closed. This morning, steam was needed, but when the shut-off valve at the equipment was opened, severe water hammer occurred (which was expected). As a result, the main DN200 valve was closed, and the DN150 steam supply valve as well as the DN25 vent valve of the steam distribution cylinder were opened; it took almost half an hour to empty the system. Question: After shutting off the steam using the steam pipeline, it was forgotten to drain the steam; as a result, the steam cooled down and turned into condensed water. The volume of this condensed water is approximately 【(0.785*0.15*0.15*30*) m3*3.2 kg/m3】 = 1.7 kg ； And in reality, after waiting for half an hour, there should be at least 300 kg. Where does this extra water come from? (Prevent water from other pipelines from entering the steam pipe)
There’s no doubt it’s steam condensate; there is some steam condensate remaining in the pipes, but the amount is limited； There will also be cases where steam and condensate leak through because the valves are not closed properly ； It is more likely to be the condensate remaining in the main pipe and steam distribution panel when the main valve is opened. It can be checked.
Thank you~ When draining through the branch pipes, the main pipe valve is closed, and the volume of the steam distribution cylinder is not large either. The valve cannot be closed completely, resulting in internal leakage; steam gradually leaks through until the branch pipe is filled with condensed water. This might be an acceptable situation ； But we checked by closing the main pipe valve and the branch pipe valve, and opening the steam cylinder drain valve, and no steam leaked out.
This post was last edited by Engineering-Industrial Angry Youth on 2016-9-23 at 11:17. May I ask the OP how this calculation formula should be interpreted? For an inner diameter of 150, the volume should be 3.14*0.075*0.075*30 = 0.53 cubic meters, which is the volume of a 30-meter long pipe. The density of saturated water vapor at 0.5 MPA is 2.667 kg/m³ (as per tables); 0.53*2.667=1.4 kg
My volume is 0.53; we’re the same in that regard. The specific volume of saturated steam at 0.5 MPa(G) is 0.31 m3/kg, so its density is 3.2 kg/m3.
I looked at the wrong row in the table. It’s been modified; it’s almost done. . . Are all the pipelines sealed? Is it an internal leak in the valve on the equipment side, which is causing the circulating water or other fluids from that side to flow back into the steam pipes?
This can be ruled out, as it is a renovation project; the steam inlet pipe at the equipment side has been resized to DN50, and the valves are new, so the possibility of internal leakage is very low； Even if there is internal leakage, a DN50 valve won’t leak that much water.
Regarding the third point I mentioned, you let the condensate water in the pipes in front of the main valve and the steam distribution panel drain away for half a day; it was roughly 300 kg. Because, as you said, even if the volume of the pipeline behind the main valve is completely filled with water, it still won’t reach 300 kg.
The volume of the branch pipe is 0.53 cubic meters; if it is completely filled, it can hold 500 kg of water.
If that end of the steam pipe is connected to circulating water, backflow is also possible. Because after the main valve is closed, the steam in the steam pipeline condenses, creating a vacuum that directly leads to backflow.
It only shows that there was water in this cylinder from the start; it wasn’t used before, and the water kept accumulating until this amount was reached