Regarding the types of safety valves, when are they designed as safety valves for fire conditions, and when are they used as safety valves for blockage conditions?
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Every time I look at the PID diagrams, I have a question: for several containers connected in series in the process, some of their safety valves have relatively narrow inlets and outlets; they are labeled as safety valves for fire conditions, and their set pressure is the same as the design pressure of the pressure vessel； Some safety valves, on the other hand, have relatively thick inlets and outlets, and are labeled for blocked conditions. Question: Under what circumstances should it be designed for fire conditions, and under what circumstances should it be designed for blockage conditions? Don’t tell me that the fire condition is the one in which a fire could occur. What I want to ask is, what is the basis for this classification, and in which book can it be found?
There are more than a dozen operating conditions for safety valves. For containers, towers, etc. that can cause overpressure in case of a fire, fire conditions need to be taken into consideration. For outlet valves that, when closed, may cause overpressure in the upstream equipment, the condition of outlet blockage needs to be considered.
When designing a safety valve, the most important aspect is the calculation of its discharge capacity. When calculating this release volume, scenarios such as fire conditions, blockage conditions, other types of uncontrolled reactions, and overpressure/high temperature are considered; the scenario that results in the highest release volume is chosen. That’s how I understand it; I’m not sure what other sailors think
It seems that no specific information or book can provide a definite answer, after all, each manufacturing process is different. I generally calculate the safety discharge volume based on several possible operating conditions, and use the highest value as the basis for selecting the final safety valve.
First, it is necessary to determine whether the system is prone to overpressure or only experiences overpressure occasionally. Possible overpressure conditions include external fires, closed outlet valves, control valve failures, and excessive feeding into the pressure vessel ； Occasional overpressures such as reactor loss of control generally do not require a pressure relief safety analysis. 1. External fire: Regarding the possibility of an external fire, when the system is exposed to flames, the discharge capacity required of the safety valve is calculated based on the heat entering the container. Both the \"Regulations on Safety Inspection of Pressure Vessels\" issued by China’s Ministry of Labor and API Standard API-520 provide calculation methods for various external fire conditions. 2. Upstream control valve failure: Installing a control valve upstream in the system can result in the container pressure exceeding the maximum allowable value. For control valves, regardless of their position during an accident, it is recommended to analyze the discharge volume based on the fully open condition during the accident. 3. When the downstream outlet valve is closed and the inlet valve remains open, the discharge rate is the maximum normal flow rate of the closed pipeline. This operating condition is similar to some fault conditions in control valve failures and excessive feeding situations.
Not bad; although it’s not very detailed, I hope we can continue discussing the safety valves in fire conditions in the future.
I have the same question. As those of us who work on natural gas compressors, we notice that many foreign skid manufacturers design their PID systems such that the safety valves for air intake are considered for fire scenarios, while the others are designed for blockage scenarios. Is there any basis for this? ?
What is indicated on the P&ID represents only the most severe operating conditions; since the most severe conditions for each safety valve vary, the indications will differ accordingly.