MITRE
BEND Calculation Work Procedure for Internal Pressure (ASME B 31.3)
Step1: Select the Pipe Material
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Step2: List Down
Ø Pipe Outside Diameter, (mm) = D
Ø Internal Design
Pressure,(Kg/cm²) = P
Ø Design Temperature,
(C°) = T°
For the material under consideration.
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Step 3: List down
Ø Allowable Stress, (Kg/cm²) = S
ASME B 31.3 @ Design Temperature.
(TABLE A-1)
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Step 4: Select
Ø Joint Efficiency factor = E (TABLE A-1A)
ASME B 31.3 (TABLE-1A)
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Step 5: Select
Ø Corrosion Allowance, (mm) = c
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Step 6: Formula @ ASME B 31.3
S*E*(T-c) (T-c)
Pm1 = -------------- [---------------------------------------------]
+ c ……….Eq.-I
r2 (T-c) + 0.643*TAN θ * √r2*(T-c)
S*E*(T-c) (R1-r2)
Pm2 = -------------- [---------------------]
+ c ……….Eq.-II
r2 (R1-0.5*r2)
Pm1 = Max. Allowable Internal Pressure for Mitre Bend, (Kg/cm²) @ Eq.-I
Pm2 = Max. Allowable Internal Pressure for Mitre Bend, (Kg/cm²) @
Eq.-II
P = Internal Design Pressure, (Kg/cm²)
θ = Angle of mitre cut
r2 =
Mean Radius of pipe, mm (D-T)/2
R1 = Effective radius of mitre bend, mm
T = Available
thickness,(mm) ( after deducting Mill Tol. & Corrosion Allowance)
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Step 7: Compare values of Pm1 & Pm2
Min (Pm1, Pm2) = Pm
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Step 8: Compare values of Pm & P
If (Pm < P)
Pipe Thickness (T) is OK.
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Pm should be greater than P write.
ReplyDeleteas far as i concern, Pm should be greater than P so it would not derate the pipe system. If Pm lower than P, then miter bend angle should decrease or increase the thickness.
ReplyDeleteOur existing pipe systems design P= 50psi The calculated welder miter Pm= 12psi. We have been in operation for 30 years without incident, perhaps our calculation for the miter is an error.
ReplyDeleteWhich one is correct If (Pm < P) or (Pm > P)
ReplyDelete