ASME B31.8 Gas Pipeline Ripple And Dent Defect

Calculate ASME B31.8 metal pipe diameter and pressure design wall thickness from pipe schedule or user defined diameter and wall thickness (ASME B31.8 section 841.1). For ASME B31.8 the fabrication tolerance is accounted for in the design factor. The fabrication tolerance is ignored when calculating the pressure design thickness. The pressure design thickness equals the nominal thickness minus the corrosion allowance.

Select the pipe schedule (NPS or ISO), pipe diameter and wall thickness, or use the user defined option. Use the Result Table option to display the pipe schedule with nominal wall thickness and pressure design wall thickness for the selected diameter. Fabrication tolerance is ignored.

Tool Input

• schdtype : Line Pipe Schedule Type
• diamtype : Line Pipe Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Wall Thickness Type
  • tnu : User Defined Wall Thickness
• c : Wall Thickness Corrosion Allowance

Tool Output

• ID : Nominal Inside Diameter
• OD : Nominal Outside Diameter
• OD/tn : Diameter Over Wall Thickness Ratio
• tn : Nominal Wall Thickness
• tp : Pressure Design Wall Thickness

Calculate offshore pipe allowable ripple height from hoop stress (ASME B31.8 section 851.4.1).

For permanent operation the maximum ripple height should be calculated from the maximum allowable operating pressure (MAOP), and the pressure design wall thickness.

For temporary conditions the maximum ripple height can be calculated from the local operating pressure. For new condition pipe, the minimum wall thickness can be used. For corroded pipe the pressure design wall thickness should be used.

Tool Input

• schdtype : Line Pipe Schedule Type
• diamtype : Pipe Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Wall Thickness Type
  • tnu : User Defined Wall Thickness
• plitype : Internal Pressure Type
  • Priu : User Defined Reference Internal Pressure
  • Pliu : User Defined Local Internal Pressure
  • ρf : Internal Fluid Density
  • Zr : Reference Elevation
  • Zl : Local Elevation
• pletype : External Pressure Type
  • Pleu : User Defined Local External Pressure
  • ρe : External Fluid Density
  • Zs : Surface Elevation
• calctype : Hoop Stress Calculation Type
• walltype : Hoop Stress Wall Thickness Type
• ta : Corrosion Allowance

Tool Output

• ΔPl : Delta Pressure Across Pipe Wall
• ID : Pipe Inside Diameter
• OD : Pipe Outside Diameter
• OD/tn : Pipe Diameter Over Wall Thickness Ratio
• Ple : External Fluid Pressure
• Pli : Internal Fluid Pressure
• Sh : Hoop Stress
• h/D : Maximum Ripple Height Over Diameter Ratio
• hmax : Maximum Allowable Ripple Height
• t* : Wall Thickness For Hoop Stress Calculation
• th : Pipe Pressure Containment Wall Thickness
• tn : Pipe Nominal Wall Thickness

Estimate strain in pipeline dents from dent radius of curvature (ASME B31.8 appendix R and figure R-1).

Dent strain can be calculated according to ASME B31.8 2014, or ASME B31.8 2018. For re-entrant dents R1 is negative. R2 should always be negative.

Tool Input

• schdtype : Line Pipe Schedule Type
• diamtype : Pipe Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Wall Thickness Type
  • tnu : User Defined Wall Thickness
• R1 : Circumferential Radius Of Curvature (Re-entrant -ve)
• R2 : Axial Radius Of Curvature (Re-entrant -ve)
• d : Dent Depth
• L : Dent Length

Tool Output

• ε1 : Circumferential Bending Strain
• ε2 : Longitudinal Bending Strain
• ε3 : Longitudinal Extension Strain
• εi : Strain On Inside Pipe Surface
• εo : Strain On Outside Pipe Surface
• ID : Pipe Inside Diameter
• OD : Pipe Outside Diameter
• OD/tn : Pipe Diameter Over Wall Thickness Ratio
• R0 : Pipe Outside Radius
• tn : Pipe Nominal Wall Thickness