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  1. pleckner

    Fire case for HC water mixtures

    A HC-water mixture is no different than any other mixture of differing boiling point components. The initial heat will boil off the lightest component first and so on. You can do a series of flashes, starting off with 1% to get the first HC and then continue from there. The response by Chance17...
  2. pleckner

    Negating A Relief Scenario

    Although the final conclusion of the above is correct if analyzing a system for a pressure vessel, I can easliy interpret the original post as one protecting piping and not a pressure vessel. In this case, ASME B31.3 is probably the Code that needs to be reviewed and there are considerations...
  3. pleckner

    Heat Exchanger's tube rupture two-thirds rule and location

    Unfortunately, it is a little more complicated than what has been discussed above. The rule given by API 521, 5th ed. January 2007 can be found in section 5.19.2. It does not say one can neglect tube rupture as a relief sizing case when the LPS test pressure is greater than or equal to the MAWP...
  4. pleckner

    PSV Set Pressure

    The difference between the maximum expected operating pressure and the PSV set pressure is not dictated by any Code or standard. The minimum difference should be the greater of, 10% of the maximum operating pressure or 25 psi to ensure you won't get simmering. But there is nothing that says you...
  5. pleckner

    CV Failure Philosophy

    chemsac2: I couldn't disagree with you more. Operations is not responsible for ensuring the PSV is designed correctly for any condition. That is the responsibility of the Process Design Engineer or the unit Process Engineer. Operations cannot just change the operating parameters without...
  6. pleckner

    CV Failure Philosophy

    Yes, Sheiko is even more correct. Upstream pressure should be 220 psig (unless relieving scenario is fire of course)... I wasn't thinking it all the way through; need to include the allowable overpressure during relief.
  7. pleckner

    CV Failure Philosophy

    You keep on talking about a failed-open control valve and this is indeed a credible scenario but I would like someone to justify that an operator cannot rationalize to manually open that control valve to depressure the upstream system going into relief?
  8. pleckner

    CV Failure Philosophy

    Who is to say that if the upstream side went into relief an operator wouldn't try to depressure that side by manually opening the control valve all the way? There is no engineering merit in just choosing an arbitrary upstream pressure like 180 psig. If anything, I can justify saying the...
  9. pleckner

    Independent Review

    There is no requirement in ASME (the Code) or API (the standard) that a review of the scenarios and calculations, internal or external, need to be performed. It only makes good engineering sense to do so as you would for any set of design calculations. A company will go "outside" only if they...
  10. pleckner

    Rupture Disk - Safety Valve Combinations

    ASME is Code, API is NOT. I always recommend using 2.4 from Code. However, you would be better off choosing a "conservative" combination from your company's (or client's) list of preferred vendors. If you still have none, then go with the 2.4 value.
  11. pleckner

    Setting pressure of safety device

    This is an update to my last post. I was only partially correct. After more digging and discussions I was reminded of the following in API 520, Part 1, 8th ed.: 5.4.3.4 Supplemental-device Installation 5.4.3.4.1 A supplemental-device installation provides relieving capacity for an additional...
  12. pleckner

    Filter vessel - Thermal relief valve or normal relief valve

    Do, if you have settled on the fact that thermal relief is the controlling scenario, don't be concerned about the flow rate. It will be so small that it won't matter. I hope you at least have a copy of Perry's Handbook because if you really want to calculate it, I believe you can find the...
  13. pleckner

    Filter vessel - Thermal relief valve or normal relief valve

    EngCutie: Please don't take this wrong but process safety calculations are too important to leave it up to the inexperienced. These must be done by someone who is a lot more experienced than you are. I'm not criticizing, just trying to emphasize the importance and danger involved in not getting...
  14. pleckner

    External Fire and Two Phase Flow

    There is nothing in current thinking and practices that would preclude you from using 21% overpressure for a fire case, all vapor or otherwise. The only exception to this would be if the fire caused a chemical reaction, then use 10% overpressure, otherwise 21% is OK. I also agree with the other...
  15. pleckner

    PSV vs Liquid Seal

    It will only qualify as a relief device if you can show the vent size will relieve against all credible scenarios and there is nothing in the seal pot that can ever create an obstruction against flow. I've heard of one case where some obstruction (don't have a clear definition of what it was) in...
  16. pleckner

    PSV vs Liquid Seal

    If the pressure in this vessel (appears not to be for water storage) can exceed 15 psig (as it appears to be able to do) then it falls within ASME Section VIII, Div. 1 scope. You either have to show the vessel is designed for containment against any credible overpressure scenarios or you will...
  17. pleckner

    ASME FIRE REQUIREMENTS FOR PSV

    Great question because I've been thinking of this myself. (a) Perhaps you can consider radiation heating from a fire that is normally outside the API fire zone, or from the atmospher. (b)Perhaps you have a jacketed vessel normally on cooling fluid but has a cross-over for whatever reason to a...
  18. pleckner

    Filter vessel - Thermal relief valve or normal relief valve

    What causes the large pressure increase in the confined space is the fact that the vessel is 100% liquid full and liquid, not being very compressible, has no where to expand. Once the relief valve pops, it spits out a small amount of liquid, dropping the liquid level in the vessel thereby...
  19. pleckner

    Filter vessel - Thermal relief valve or normal relief valve

    "Thermal" relief valves are not thermal at all but pressure relief valves. The industry calls them "thermal" because of the fact that the scenario is a liquid filled vessel that is heated (thermal effect). When the liquid heats it expands and puts enormous pressure on the vessel. The relief...
  20. pleckner

    Setting pressure of safety device

    There is no disagreemnt in the interpretation of those magic words, SHALL, SHOULD and MAY. We both agree that a supplemental valve can be set no higher than 105% of MAWP. Then in what instance do you acknowlege the use of UG-134(b), the allowance for a PRV to be set at 110% of MAWP? I contend...

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