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  1. arbor

    Over sized relief valve with reduced discharge piping

    Thanks so much for the suggestions. I used the downstream pressure and the pressure drop is 12 psi now. Can this 12 psi be considered as the backpressure to the valve? What would be my upstream pressure, 235 or 26 psi? 12 psi sounds much better than 0.7 psi. But does it make sense for 350...
  2. arbor

    Over sized relief valve with reduced discharge piping

    Thank you all for the advices. The equation I used is the simplified form for isothermal compressible gas flow. Both Crane book and Perry book has similar equations. I used 200 psi as the upstream pressure and I only got a pressure drop of 0.7 psi. However, the Darcy equation gives about 150...
  3. arbor

    Over sized relief valve with reduced discharge piping

    Latexman - thank you for your reply. I calculated the pressure drop through the discharge line use simplified equation for gas flow, P1^2-P2^2=25.2*(S*Q^2*Z*T*f*L)/D^5. p1: upstream pressure psia P2: downstream pressure psia S: Specific gravity Q: gas flow MMSCFD Z: compressibility factor T...
  4. arbor

    Over sized relief valve with reduced discharge piping

    Yes, the outlet is piped to a vent stack vented to atmosphere.
  5. arbor

    Over sized relief valve with reduced discharge piping

    I am new to the pressure relief valve world and having an issue on a relief valve that has already been installed. The valve is a conventional relief valve for pipe thermal relief of vapor and the outlet is piped to a vent. The capacity of installed valve is about 4 times of the flow rate...
  6. arbor

    Compress foundation bearing stress calculation

    The equation in compress is fc = Cc / (((tc - ts) + n*ts)*(d / 2)*K2) However, in the referred book is fc = Cc / ((ts + n*tc)*(d / 2)*K2) Thank you, Arbor
  7. arbor

    Compress foundation bearing stress calculation

    I noticed that the equation for foundation bearing stress calculation for the skirt base ring design is different from the referenced book by Jawad & Farr. Is this an error or there is some reason behind the change? Thank you,
  8. arbor

    Buckling and local stress in a leg supported vessel

    TGS4, thank you for a very clear procedure for using Part 5 of Div.2. I still have a couple of things unclear. 1. The buckling approach in Part 5 still does not cover my original questions. It has the minimum design factors for shell under axial compression and under external pressure...
  9. arbor

    Buckling and local stress in a leg supported vessel

    TGS4, thank you for your explanation. First I need to apologize that I didn't give enough background of my analysis and mixed all my questions together. The stress analysis is for a pressure vessel designed to Div.1. FEA is mainly used for the local stresses. Section II Part D allowable stress...
  10. arbor

    Buckling and local stress in a leg supported vessel

    Thank you all for the valuable comments. I have learned a lot from this forum. Regarding the local area in the circumferential direction, it was from the stress analysis for nozzle loads or localized loads. Depends on the geometry and loads, there could be a relatively large area in the...
  11. arbor

    Buckling and local stress in a leg supported vessel

    I am working on a stress analysis for a leg supported vessel with vacuum and seismic load. Due to the vacuum and the bending moment resulted from the seismic load, the area above the leg sees axial and hoop compressive stress. I am having a hard time for the buckling check and I hope I can get...
  12. arbor

    Compress Nozzle FEA occasional load

    I am trying to use Compress nozzle FEA for nozzle analysis. The nozzle loads are given as due to weight, thermal, and seismic. In compress nozzle FEA, there are input conditions for weight, operating, occasional and thermal. My understanding is that nozzle loads due to weight will be input...
  13. arbor

    Negative eigenvalues

    johnhors, You are right about my model and the eigenvalues. I have several approaches to check different failure modes of a pressure vessel based on ASME code. The approaches include linear elastic and non-linear plastic analysis. The code also requires to check buckling when there is...
  14. arbor

    Negative eigenvalues

    johnhors, I am trying to model the buckling of a pressure vessel head knuckle under internal pressure (there will be tangential compressive stress in the knuckle due to internal pressure). However, the model kept giving me negative values for the shell and head buckling which would be due to...
  15. arbor

    Negative eigenvalues

    hi bassmanjax, I am interested in positive eigenvalues only in my analysis. However the analysis hasn't been able to give me the first positive eigenvalue after many negative values. I don't know how long it needs to run to find the positive value. Is there anyway to get positive eigenvalues...
  16. arbor

    Manway burst test/pressure rating

    More information. The manway has no standard flange. For the manways I am working on, there are lugs welded onto the cover and trunnion tubes welded onto the collar. The lugs and tubes are connected by bolts and rods. The o-ring is between the contact surfaces of cover and collar. The o-ring...
  17. arbor

    Manway burst test/pressure rating

    Thanks again for the inputs. I got many valuable information. We are a manufacturing company and we have designed and made standard prefabricated manways to ASME VIII-1 Code for more than 20 years as I know of. Most of them are stainless steel manways. The manways are similar to these...
  18. arbor

    Manway burst test/pressure rating

    jehan and jt, thank you for the replies. Sometimes, the pressure at which the test was stopped due to leaking is much higher than the desired maximum allowable pressure, maybe two or three times of it. So the hydrostatic test (1.3x) will pass if we could rate the vessel at the desired pressure...
  19. arbor

    Manway burst test/pressure rating

    We are doing some burst tests for manway pressure rating. The maximum test pressure is usually limited by leaking from gasket before reaching the desired pressure. As a result, we will get a lower rating pressure for the manway although the steel components may be able to stand much higher...
  20. arbor

    Material properties for Section VIII Div 2 elastic-plastic analysis

    I wish some expert here can shed my some light on using stress-strain curve for elastic-plastic analysis in Section VIII, Div 2. 2007. Div.2 Part 3 provides the true stress-strain curves for materials. Part 5 requires to use the curve up to the true ultimate stress. Does this mean I need to...

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