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  1. gocougs1

    Periodic Review of Unchanged Relief Systems

    Every 15 years is the general consensus for a full unit-wide PSV re-evaluation for the refinery I work for. There is no real basis for this other than what people think is appropriate. In a 15 year period there will typically be significant changes to the code and larger plant-wide changes may...
  2. gocougs1

    Applicability of the Fire Overpressure Scenario

    I came off a bit terse in my earlier post, sorry about that. For the client I am currently working with our guidelines suggest fire case overpressure protection is not required for vessels of less than 500 L and are not classed "very toxic". I think this is a well accepted practice in general...
  3. gocougs1

    Safety Relief Valve Chattering due to oversized valve

    There is no standard saying "thou shall not oversize PSVs", but API 521 has an excerpt saying: sect. 5.8.2.2 "These studies verified that vapors released from PRVs through their individual stacks are safely dispersed even when the valves were operating at only 25 % of their full capacity, which...
  4. gocougs1

    Applicability of the Fire Overpressure Scenario

    Fire calculation for a small vessel only takes a couple hours for an engineering contractor that has a fire PSV sizing template ready to go. Not worth trying to work around it. Just send them the vessel outline and fluid properties and they can size a fire PSV for it same day. Also, what if a...
  5. gocougs1

    Relief valves and Deficiencies

    From my 5 years of experience with refinery PSVs, I see three levels of priority for PSV audit deficiencies: High/Emergency Resulting overpressure > 3x MAWP (if you ever find one of these, triple check your calculations, and make sure it is a single jeopardy scenario. I have yet to find a PSV...
  6. gocougs1

    Can a Thermal Relief Valve be Discharged Into the Pump Suction Line

    Excellent question. In general it is not wise to have a TERV discharge to a pump's suction, as these systems may be isolated together. Ideally there should be no valves the process line it discharges into, to an upstream tank or downstream vessel. If operating pressure is greater than 70% of...
  7. gocougs1

    Latent Heat of Vaporization

    Usually PSV sizing is given to chemical engineers, but for a mixture of fluids the standard approach is to consider each distinct fluid phase separately. So you would need to calculate the latent heat (Hvap) of water, then the oil mixture. For the oil mixture we typically consider the latent...
  8. gocougs1

    Pressure Relief Valve For Fire Water System

    Fire water piping is exempt from API 520 as it is not considered a coded pressure vessel. I would highly recommend consulting an engineering consultant firm that specializes in PSVs. Installing a PSV willy nilly can lead to more problem than benefit.
  9. gocougs1

    PSV Set Pressure 10% Above Piping MAP?

    Hello, I seem to remember reading somewhere that PSVs may be set 10% above piping MAP, as ASME B31.1 allows up to 20% overpressure of flanged piping for short durations. Has anyone else read this somewhere or did I just imagine this? Anyone have a code reference on this? I am interested in...
  10. gocougs1

    Reduce operating pressure in residue coker unit

    Coke drums normally operate 15-25 PSIG, and what you have is 14 PSIG (0.4 kg/cm^2), so you probably will not be able to go much lower due to the main frac gas compressor suction limitations. Lowering pressure further can cause other issues like the formation of shot coke.
  11. gocougs1

    Bypassing Amine Filters HELPS foaming issues in Amine Contactor, WHY?

    It seems to me you are probably filtering out too fine, and need coarser filters. Perhaps you are filtering out the anti-foam agent that is left over from upstream process units? I believe anti-foam agents are silicon based, so maybe some of the contaminants contain silicon.
  12. gocougs1

    Heat exchanger duty in upset case

    When estimating the exchanger duty be aware, at least in the refinery world, that design exchanger duty uses the DIRTY service U factor. For PSV sizing the clean U must be calculated and used. I've never seen an abnormal heat input case for an exchanger like you are describing... usually we...
  13. gocougs1

    Clogging of Relief Valve Inlet Spool

    For slurry PSV service we recommend a nitrogen/fuel gas/inert gas pilot operated PSV. Sometimes a large dome, low pressure drop, filter is placed over the inlet to the PSV to extend the life before shutdown.
  14. gocougs1

    Storage Tank - Set Pressure

    Best practice is to set the PSV at MAWP, and if two PSVs are installed, one at MAWP and the 2nd at 105% of MAWP, per API 520. MAWP is already such a conservative number (about 1/3 of yield point) that lowering your set pressure by 5-10% below MAWP won't help the process, but now you run the risk...
  15. gocougs1

    Fire Relief for a Centrifugal Pump

    Pump casings contain a small amount of liquid volume, so even if one was isolated and engulfed in flame, the explosion radius would be small. PSV is not needed for fire protection. However, if it is in LNG service, sometimes a TERV will be installed on the piping for over pressure due to...
  16. gocougs1

    Relief Valve Inlet Hydraulics

    Inlet line losses are calculated with the vessel at MAWP + accumulation. Inlet line losses must then be less than 3% of set pressure per API 520 guidelines, however, some clients allow up to 5% of set pressure for existing relief valves.
  17. gocougs1

    Maintenance and Inspection of Tank Vent Devices

    I believe the tank would typically be placed out of service to perform work on the vent valve. Usually there is a way to temporarily divert flow to another tank while maintenance is being performed.
  18. gocougs1

    Inlet piping pressure drop for two phase flow

    For an equivalent mass flux, 100% or maximum vapor will require the greatest PSV orifice area and have the greatest line losses. However, if you are starting with 100% hot liquid water, then you should size for two phase flow through the piping using the highest expected inlet water temperature...
  19. gocougs1

    Vapour pressure question

    1) Small amounts of CO2, N2, O2, CO, C2's may be accumulating in the tank, although probably very little and more of a long term problem. 2) As the gas in the tank is compressed to smaller volume it will increase in temperature and pressure simultaneously. The vent line would ideally be sized to...
  20. gocougs1

    What Correlation To Be Used In Hysys Pipe Segments For Steam?

    I typically use the PRO/II default Beggs-Brill-Moody correlation and had good results. The other methods were either way off or practically identical to BBM and are not really worth exploring. The correlation does well at normal velocity but at near choke conditions it can deviate substantially...

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