| CALC : Pipe : Wall Thickness 031 : ASME B31G Defect Assessment And Pressure Derating For Corroded Pipelines : Calculator
Description : Calculate the ASME B31.G allowable defect length and derated pressure (if applicable) for pipeline corrosion defects.
Discussion : For axial corrosino defects. Do not use this calculator to evaluate defects in the weld zone or the heat affected zone.
References :
Calculation Steps :
- Allowable defect length
- Derated Pressure if applicable
Input Variables :
- D = Pipe Nominal Diameter
- L = Defect Longitudinal Length
- P = Pipeline Design Gauge Pressure
- c = Defect Depth
- tn = Pipe Nominal Wall Thickness
Output Variables :
- A = ASME B31G A Value
- B = ASME B31G B Value
- Ba = ASME B31G Allowable B Value
- La = Allowable Defect Length
- Pd = Pipeline Derated Gauge Pressure
- cot = Pipeline Defect Depth Over Wall Thickness Ratio
Calculation :
cot = c / tn
B = L / ( 1.12 √( D tn ) )
If cot < 0.1749344
Ba = 4
else if cot > 0.8
Ba = 0
Otherwise
Ba = √( cot / ( 1.1 cot - 0.15 ) 2 - 1 )
End of If Block
La = 1.12 Ba √( D tn )
If cot > 0.1 AND L > La
A = 0.893 L / √( D tn )
If A > 4
Pd = 1.1 P ( 1 - cot )
Otherwise
Pd = 1.1 P ( ( 1 - 2 / 3 cot ) / ( 1 - 2 / 3 cot / √( A 2 + 1 ) ) )
End of If Block
Otherwise
A = B
Pd = P
End of If Block
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