Can the hand valve upstream of the safety valve be omitted?
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Today I read an technical article posted online by a user named Haichuan on the ‘Process Industry’ account. The original text read as follows: When setting up safety valves, we often install a manual valve in front of them (safety valve, Bai Yunfan Jia); this is not allowed abroad, where factories use backup safety valves or stop production when the safety valve is removed. This is related to national conditions and culture. If a backup is to be set up, there must be a manual valve in front; otherwise, how can it serve as a backup? If no backup is provided, it’s indeed possible that no manual valve will be installed. I checked the design drawings for a Lanwanling crude oil processing plant that I have on hand, and found that there are manual valves upstream of the safety valves (at least in three or four locations I checked). Additionally, I looked into a set of WP wellhead treatment facilities. Indeed, as mentioned in the post, there are no manual valves upstream of the safety valve, because there’s no backup safety valve. Let’s discuss it together~~~~~
Is it because the quality of safety valve manufacturing abroad is high and there are fewer failures? The safety valves in our unit’s high-pressure system have failed to reseat several times. Depending on the pressure rating of the safety valve and its installation location (on rotating or stationary equipment), the impact on the equipment varies. Moving equipment can be switched, while stationary equipment can only be shut down. A malfunction of the high-pressure safety valve causes a rapid drop in system pressure; if the safety valve fails to activate, it would result in excessive damage to the system pressure, equipment, catalyst, etc. For rotating equipment that needs to be switched promptly, installing a upstream valve can be considered.
It should be set so that the safety valve, as required, is removed for calibration every year.
The safety valve must be calibrated once a year; without a manual valve, operations must be halted. During normal production, the manual valve should be locked in the normally open position and must not be closed at will.
Without a manual valve, how to maintain a constant pressure once a year?
There is reason for the gap between reality and ideals
In our country, it is necessary to have a bypass for control valves, while in other countries this is not required due to the high quality of the valves. I’ve seen that there is almost always a manual valve in front of the safety valve, except in cases of non-continuous production or for condensate water. There are no manual valves; whether it’s a backup safety valve or a bypass, how can you switch them? The main reason for not using hand valves is to control the pressure drop of the safety valve; therefore, valves with a low pressure drop are generally used, such as full-bore ball valves
Times are different, concepts are different, and there is a great difference in the way of thinking between Easterners and Westerners. It’s sufficient to draw on their ideas; there’s no need to copy them verbatim. Do things in the way that makes the most sense! I think domestic design is more flexible and easier to produce.
Manual valves should be installed; it’s one thing if they’re not needed, but they can be useful in emergency situations.
It is still better to install a manual valve, one for the safety valve inspection. The second is that a failure of the safety valve can be isolated, resulting in less impact on the system. The failure rate of valves in China is still relatively high; many important pipelines require the use of dual valves.