Regarding the issue with hydraulic pressure
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The new construction acceptance standards state that for design pressures greater than 0.6 MPa, a hydraulic test shall be conducted. However, the 25-kilogram steam main on the pipe tray has many branch pipes. According to the specifications, these steam branch pipes should be connected to the main pipe from above; in this way, when hydraulic pressure is applied to the main pipe, air will accumulate in each branch pipe, so it is not necessary to install a vent valve on every branch pipe. That seems unrealistic, doesn’t it? But when it was changed to a pressure test, the test pressure was too high, which was unsafe. For steam pipes under high pressure, how do people usually conduct pressure tests?
Under normal circumstances, an exhaust valve should be installed at the highest point of the pipeline; if none is available, it is recommended to introduce liquid into the pipe through the branch line that is at the highest installation position, so that the gas in the lower branch lines can be expelled (by opening the exhaust valve).
When testing steam pipes for pressure, the entire system is tested together. Each branch usually has a drain port or pressure gauge port before it connects to the equipment or other pipes; and even if such ports are not present, there are still valves available. The valve is closed, and air is vented from behind the flange. After venting, the connection is sealed before the pressure is increased to the test level.
Those that need to be suppressed must indeed be suppressed; in reality, there is no need for so much venting or exhaust. In many cases, the end result is a combination of water and air pressure (or at least air that cannot be expelled). Suppression is assessed by the pressure retention situation after stopping the suppression; the presence of air is also allowed.
“In this way, a vent valve is not required on every branch pipe. That seems unrealistic, doesn’t it? ” It’s very practical – that’s indeed the way it should be done. Additionally, cut-off valves are usually installed at the points where branch pipes emerge, so as to allow for the isolation of those branches from the main pipeline. If the design does not provide for this, temporary valves and blind flanges should still be installed during pressure testing, and removed after the testing is complete.
However, when using hydraulic pressure, if there is air present, the pressure will change. All the gas in the pipeline must be removed. The hydraulic test requires that all air be removed
The specifications require that the steam branch pipes be connected to the top of the main pipe, with valves installed on the branch pipes. There are high points between the branch pipe valves and the main pipe. Drain valves certainly won’t be installed in this section of pipe, as it remains at a high level whenever hydraulic pressure is applied to the main pipe. For hydraulic systems, I think it’s better to let water enter at a lower level, so that the air can move upward; this way, the exhaust effect will be better, right?
The branch pipe has a shut-off valve. What I mean is, when the supervisor operates the hydraulic system, how is the gas between the branch pipe shut-off valve and the main pipe released? For the supervisor, this branch pipe represents the high point.
During water filling, slightly open the branch pipe valve (the pipeline behind the branch pipe valve is removed before filling water), vent air, close it once water is seen, and then install a blind flange.
What’s said makes sense; it’s just a bit troublesome when suppressing it.
Water pressure test. It exceeds the design pressure by 0.1 Mpa. Hold the pressure for ten minutes to half an hour. Detect leakage points. . . . . It’s difficult to locate leaks using air pressure detection. Another issue is the low safety factor