Lame's Equation Compound Cylinder Or Pipe

Calculate the interference fit and stress distribution in compound pipes or cylinders using Lame's equation. The interference fit (during fittup) can be defined by either the contact interference, or the contact pressure. The internal and external pressure are assumed equal to zero during fittup. The two cylinders are assumed to be the same material.

The contact pressure during operation is calculated so that the change in radial strain at the contact point is equal for both cylinders. The calculation is by iteration. Check that the convergence is close to or equal to one.

The stress distribution can be calculated during operation for internal pressure and or external pressure. Use the no pressure option to calculate the stress distribution during fittup. Use the Result Plot option to plot the stress across the combined radius.

Tool Input

• modptype : Pipe Material Type
  • νu : User Defined Pipe Poisson's Ratio
  • Eu : User Defined Pipe Elastic Modulus
• loadtype : Interference Fit Type (Fittup)
  • dcfu : User Defined Contact Interference (Fittup)
  • Pcfu : User Defined Contact Pressure (Fittup)
• presstype : Pressure Type
  • Peu : User Defined External Pressure
  • Peu : User Defined Internal Pressure
• OD : Pipe Outside Diameter
• CD : Pipe Contact Diameter
• ID : Pipe Inside Diameter
• r : Radius

Tool Output

• ΔPw : Local Pressure Difference Across Pipe Wall
• ν : Pipe Poisson's Ratio
• A : Lame Constant A
• B : Lame Constant B
• E : Pipe Elastic Modulus
• Pcf : Contact Pressure (Fittup)
• Pco : Contact Pressure (Operation)
• Pe : External Pressure
• Pi : Internal Pressure
• Sa : Axial Stress
• Sc : Tresca Combined Stress |St - Sr|
• Sr : Radial Stress
• St : Tangential Or Hoop Stress
• cvg : Convergence Check
• dc : Contact Interference (Fittup)

Calculate pipeline SMYS, SMTS and allowable stress SE and SEF from pipe stress tables.

The allowable stress is calculated by multiplying the SMYS times the quality factor E and the design factor F. The quality factor is used to account for casting quality, or longitudinal weld joint quality. The design factor is used to account for design risks (for pipelines requiring a high level of safety use a low design factor). Temperature derating is not included.

Select one of the API, ASME or DNV stress table options. The API stress values are taken from API 5L tables 6 and 7 (note the API 5L X series is superseded). The ASME stress values are taken from ASME B31.3 process piping table A-1M. The DNV stress values are taken from DNVGL ST F101 submarine pipelines, tables 7-5 and 7-11.

Use the Result Table option to display the stress values for the selected stress table (click the Result Table button, and then click the make table button).

Tool Input

• syutype : Stress Table Type
• mattype : Material Type
  • SMYSu : User Defined Specified Minimum Yield Stress
  • SMTSu : User Defined Specified Minimum Tensile Stress
• efactype : Quality Factor Type
  • Eu : User Defined Quality Factor
• ffactype : Design Factor Type
  • Fu : User Defined Design Factor

Tool Output

• E : Quality Factor Or Joint Factor
• EF : Design Factor (E x F)
• F : Stress Factor
• SEF : Allowable Stress
• SMTS : Specified Minimum Tensile Stress
• SMYS : Specified Minimum Yield Stress

Calculate pipeline diameter, pressure design wall thickness (nominal wall thickness minus corrosion allowance) from nominal wall thickness.

For ASME B31.4 (oil pipelines), ASME B31.8 (gas pipelines) and AS 2885 (oil and gas pipelines) the fabrication allowance is accounted for in the design factor. Fabrication allowance is not included when calculating the pressure design thickness.

Select the pipe schedule (NPS or ISO etc), 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.

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