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Api 526 Psv Flange Ratings And Pressure Limits

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#1 SawsanAli311


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Posted 22 May 2019 - 11:42 AM

Looking at API 526 tabulations for the effective orifice area designations, I am looking into the key basis for setting the inlet and outlet flange limitations for the different PSV sizes and for two types (conventional and pilot operated) for the same size. I have the following queries, appreciate your kind support and feedback:

  1. Looking at the attached API 526 extract for orifice E spring loaded PSV,I would like to ask about the main driver for API 526 setting the outlet flange rating, is it mainly driven by the set pressure. I can see they refer to ASMEB16.32, I would like to understand the main parameters playing role in specifying inlet flange 2500# always with an outlet of 300#,why not 2500# inlet with 600# outlet flange, for example?
  2. For the same PSV body material and same relieving temperature range and set pressure, same P orifice size, if we compare P spring loaded versus P pilot operated, we can see that pilot operated PSV tends to accept higher inlet flange rating and higher outlet rating.For example, inlet flange 900#/150# for spring loaded and 900#/300# for pilot operated. Can we say this is driven by the fact that pilot operated valves accept less margin between the maximum operating pressure and set pressure as well as higher PSV ?
  3. Similar to point 2,if we look at the P orifice we can see that for the same body material and set pressure with relieving temperature range, an inlet flange of 900# is coupled with 150# outlet flange for conventional spring loaded while the same PSV has an inlet flange of 900# coupled with 300# if its pilot operated, can anyone agree on the reasoning that the higher outlet flange rating is driven by higher built up backpressure allowed by pilot operated?
  4. What is the significance of the column for the outlet pressure limits for the conventional and the bellows. Why bellows have less pressure tolerance than conventional PSV?
  5. I would like to know the basis of specifying the inlet and outlet PSV nozzle sizes, are these based on 3% inlet pressure loss criteria for multiple corresponding flow rates and set pressures?
  6. What is the significance of the center to center distance? Where it is actually playing a role from process perspectives?  
  7. Why note 4 in the table is stating that 300# inlet flange is preferred over 150# inlet flange for low pressure applications?

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Edited by SawsanAli311, 24 May 2019 - 01:48 AM.

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