How to replace the pipeline behind the safety valve during pipeline replacement?
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How to replace the pipeline behind the safety valve during pipeline replacement?
Safety valves usually come with a bypass pipeline that can be opened for replacement; if there is no bypass, then a short section must be used as a substitute for the safety valve. Additionally, the pipeline downstream of the safety valve is usually vented or sent to the flare; it’s not clear why replacement is necessary.
Is it possible to perform pressure relief and displacement by venting the main pipe?
In the case of low-pressure gas systems, they generally do not stop operating along with the shutdown of the equipment. Therefore, when steam is used to purge the system through the safety valve bypass line, we require that the safety valve bypass line be closed once the temperature reaches around 100 degrees. Subsequently, all safety valves are used together for purging until the valves leading out of the equipment become hot, after which the main valve leading out of the equipment is closed. Finally, the interior of the equipment is purged either in the forward or reverse direction, after which the gas supply is cut off and a blind flange is installed (or a blind flange is installed first before purging).
Our gas pipelines are equipped with low-pressure nitrogen behind the safety valves; simply turning on the nitrogen will do. If there is no nitrogen, with a manual valve located after the safety valve, it is possible to loosen the flange behind the safety valve and use the gas from the flare to displace the air
Even if there is nitrogen behind the safety valve, there is essentially a dead zone between the nitrogen interface and behind the safety valve; if purging cannot be carried out in the forward direction, residues will remain, right? So, for safety reasons, there is still a solution that allows for multiple pressure buildup and replacement cycles