How to vent a pipeline that doesn’t have a high-point vent for pipeline hydrotesting
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There is a 4.2-kilometer-long oil pipeline in the project (from the dock to the tank farm) that needs to undergo a hydrostatic test. Since it is a piggable line, to prevent residual welds from blocking pigging, sufficient high-point vent valves are not installed at the highest points of the pipeline. My question is: 1. What impact does incomplete exhaust of the pipes have on pressure testing? Are there any security implications? 2. How to remove air completely to ensure that the pressure test is accurate and valid? 3. Is there any risk in performing a single pressure test on a 4.2-kilometer-long pipeline? Thank you all, fellow sailors, for helping to clarify things.
If air is not released during the hydrostatic test, does it accumulate inside the pipes? I find it quite unsafe. . Are there no areas on the pipeline where instruments can be installed for measurement? The pressure gauge and such, remove that and vent from there?
It’s difficult to increase the pressure when there is no air release; and even if the pressure is achieved, it can’t be maintained. In that case, use air pressure!
The background you provided is not detailed enough, so it’s difficult to give accurate advice. If the pipeline is not under high temperature and pressure, you can try the following methods: 1. Drill a hole at a high point and weld an exhaust valve ； 2. Inject water slowly at a low flow rate to expel as much air as possible from within the pipeline ； 3. Try to conduct experiments in segments as much as possible ； 4. Insert a thin rubber tube into the end of the pipe to pour water in.
Thank you all for your replies. Adding an exhaust valve at the high point is not considered for now. For ball-passing pipelines, one method involves using a ball to remove air: a rubber ball with a slight interference fit is placed at the end of the pipeline where water is introduced (with water filled inside it), and then water is pumped into the pipeline under test. The pressure from this water pushes the rubber ball forward within the pipeline, driving all the air to the discharge point or the end of the pipeline. The disadvantage of this method is the concern about ball jamming. Air pressure is not taken into account; since the pipelines pass through docks and populated areas, there is a high risk related to air pressure.
Just thinking about this method is amazing; it seems the ball needs to be soft, otherwise what about pipes with weld beads and slight deformations? Personally, I think using segmented pressure testing is a viable approach (there should be no branch pipes, or rather no pipes that extend upward, otherwise how can one ball be sufficient?). Theoretically, this method works, but I’m not sure if it’s practical in reality. Has anyone actually succeeded in removing air and testing pressure using this method? Wishing the original poster success