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  1. lizking

    Tailpipe losses not limited to 10%

    1. API 520 is now titled a "Standard." (Eighth Ed.) 2. Keep in mind that if your discharge dP meets your overpressure at values above 10%, it may not meet it at 10%. All the cases have to be checked. (has to do with the RV capacity being directly proportional to relieving pressure; but dP is...
  2. lizking

    Fire case thermal relief - Advantage of unheated fluid in a long pipe

    (Heat input) x (specific heat) / (mass of fluid) will give you temperature rise per time. You have your "allowable" temperature rise from the API formula. Now determine if the resulting time is sufficient enough for you to take mitigating action.
  3. lizking

    Fire case thermal relief - Advantage of unheated fluid in a long pipe

    1. You may take credit for the protection (insulation that meets certain criteria) with an appropriate factor per API 521. 2. If you can assume that the fluid is being heated somewhat uniformly, then yes you can look at how long the fluid would have to be heated to get to the design pressure of...
  4. lizking

    UG-125(g)(1) "External"

    JohnGP is correct. This clause is not referring to vacuum conditions.
  5. lizking

    PSV/ PRV Inspection Interval

    You may look into risk-based inspection methodologies. See API 580 & 581. Companies sell software to utilize the techniques.
  6. lizking

    Rupture disk-can it burst from the other side?

    Latexman is correct: it depends on the disk type. I would also add that there are "fail-safe" designs that actually will burst at lower that the specified burst pressure with "backward" flow. This type is used if you're worried about someone installing it backwards.
  7. lizking

    Challenging the common Bellows wisdom.

    Remember the bellows is protecting against built-up backpressure as well. If that valve opens, how will the additional backpressure affect the capacity? I would say, after a "short" time period, you're in "conventional" mode. I know, I know.... how short is short?
  8. lizking

    Relief valve maintenance philosophy

    Look into an API "risk based inspection" (RBI) methodology.
  9. lizking

    Rupture disc versus PSV for HEX Tube Rupture case

    That's what the transient analysis would tell you. Frequently, as you state, a PRV will not act fast enough. Also, the analysis will determine a required location of the relief device. Sometimes it must be right on the vessel (as opposed to the in/out piping).
  10. lizking

    Rupture disc versus PSV for HEX Tube Rupture case

    Depends largely on fluids. Gas on tubeside (high pressure side)and liquid on shellside with more than a 1000 psi differential warrants a transient analysis.
  11. lizking

    Fire case Overpressure in Europe

    Thanks, Morten. In my opinion, you could interpret the "1.1 PS restriction does not apply" two ways: 1. Take the overpressure higher, say to 21% like ASME; or, 2. Don't allow any overpressure (0%). However, I've seen blanket statements that ALL overpressure scenarios are to be restricted by...
  12. lizking

    Fire case Overpressure in Europe

    Does anyone know what the allowable overpressure is for the fire case per the European Pressure Equipment Directive (PED)? Their "Guideline 5/2" is clear as mud. Is it 0%, 10% or something greater than 10%?
  13. lizking

    why 21% for fire case

    I believe it's because a fire case is such a rare circumstance and even rarer that the RV discharges. Thus ASME allows 10% over the 10% = 21%.
  14. lizking

    ASME VIII front page

    maybe the tank was designed to Section VIII !!
  15. lizking

    SPRING SET PRESSURE

    For conventional RVs, a constant (stress CONSTANT) superimposed backpressure is subtracted from the set pressure to obtain "spring setting" or CDTP (cold differential test pressure). Built-up backpressure is NOT included. Note: caps used for emphasis.
  16. lizking

    water flow rate @ gauge pressure

    BigInch, FYI: Churchill is certainly acceptable, but there's an even more accurate method just published by Goudar in Hydrocarbon Processing Aug. 2008. A little more involved than Churchill, but still spreadsheetable.
  17. lizking

    Isothermal Tail Gas Calc - Darcy Friction Factor?

    There's no such thing as a "Darcy friction factor." Equation 25's variables are clearly explained below the equation: f= Moody friction factor. See Crane TP-410 for graphs of Moody friction factors.
  18. lizking

    Isothermal Tail Gas Calc - Darcy Friction Factor?

    API521 uses the Moody friction factor as used with the Darcy pressure drop formula (see Crane p. 1-6). See note after equation 33 in API521 for an example of Fanning friction factor usage.
  19. lizking

    Backpressure correction for balanced bellows

    If your backpressures are approximately equal, I guess the capacities are different. It may have something to do with the mechanical design of the valve internals. I'd give it the old "consult valve manufacturer" routine.
  20. lizking

    Backpressure correction for balanced bellows

    I assume your backpressure is built-up plus superimposed. The extra capacity for valve A will result in a higher backpressure and thus a lower Kb. It is somewhat of a trial-and-error procedure. (I'm not saying that they will equal out, but the Kb's should get close to each other.)

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