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AutoPIPE Wiki 09. How to calculate the Hoop stress and Hoop allowable for ASME B31.8?
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              • -ASME B31.8 Piping Code Calculation Issues
                • 01. How to calculate B31.8 -2003 code allowable of per code equation:
                • 02. How to calculate the combined stress for a node point, equation used, and individual values being applied in the AutoPIPE equation?
                • 03. ASME B31.8, the hoop stress uses the D/t ratio to decide which formula to use, thin or thick, what is AutoPIPE doing?
                • 04. Using ASME B31.8 2012-2016, how is the hoop stress being calculated in AutoPIPE?
                • 05. ASME B31.8, AutoPIPE does not seem to consider the bending stresses in the pipe due to large diameter elastic bends ( 1200 m). it only reports the stresses due to pressure , temperature and gravity?
                • 06. Why are Hydrotest results different using AutoPIPE ASME B31.8 piping code?
                • 07. How can I set the RESTRAINED pipe option for B31.8 2007 onshore / underground piping
                • 08. Why are the Stress results for ASME B31.8 (2014) 0.00 in AutoPIPE's results Grids and output reports?
                • 09. How to calculate the Hoop stress and Hoop allowable for ASME B31.8?
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    09. How to calculate the Hoop stress and Hoop allowable for ASME B31.8?

    Applies To
    Product(s): AutoPIPE
    Version(s): ALL;
    Area: calculation
    Date Logged
    & Current Version
    July 2022
    12.08.01.010

    Problem:

    According to AutoPIPE help

    Stress

    Design pressure P = 6750psi
    Nominal outside diameter of the pipe D = 8.625in
    Nominal wall thickness t = 0.875in
    Hoop stress factor Y = 0
    Hoop stress Sh  = [P D / (2 x t)] - (P x Y)

    Hoop Stress = 33.268 ksi

    Allowable

    Specified minimum yield strength - API 5L X65 S = 65ksi
    Hoop stress design factor F = 0.72
    Longitudinal joint weld factor Ej = 1
    Temperature derating factor T = 1
    Allowable hoop stress Shallow = S x F x Ej x T

    Allowable Hoop Stress = 46.8 ksi

    Why are AutoPIPE results showing differently:

    Solution:

     In this case, the model was sent in and the following was found on the General Model Options dialog:

    Question: Are the correct piping code equations being used?

    Answer: No, the wrong equations are being used. Why?

    Again, look at the piping code selected on general model options dialog, the original screen image above of the calculations, and the actual definitions under the code compliance calculations description. 

    The key word is Offshore.

    Note, that the equations shown were for B31.8 onshore not B31.8 Offshore. There is a huge difference between these codes and one must be carful when selecting the piping code in the program. Therefore the correct equations to be referenced should have been :

    Stress = [P x (D-t)] / (2 x t)

    Stress = 29892.86 psi

    Allowable = F1 x S x T

    F1 = 0.5

    Note: as mentioned in the help, 

    Currently since Autopipe cannot assign a different design factor to different section of piping the Default values are conservatively based on risers. These values are be entered under hoop, longitudinal, and combined design factors in Tools> model options> Results dialog.

    Update these values manually as needed. 

    S = 65 ksi

    T = 1

    Allowable = 32500 psi

    See Also

    ASME B31.8 Piping Code Calculation Issues

    Bentley AutoPIPE

    • B31.8
    • AutoPIPE
    • allowable
    • stress
    • ASME
    • Hoop
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    • Mike Dattilio Created by Bentley Colleague Mike Dattilio
    • When: Tue, Jul 12 2022 1:21 PM
    • Mike Dattilio Last revision by Bentley Colleague Mike Dattilio
    • When: Wed, Jul 13 2022 12:50 PM
    • Revisions: 5
    • Comments: 0
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