Pipeline Combined Stress Check

Calculate axial load, combined stress, hoop stress, longitudinal stress, bending stress and torsion stress for onshore and offshore pipelines.

The axial load is calculated using the thick wall formula (API RP 1111 and DNVGL ST F101). Loads are positive in tension, and negative in compression. The external pressure is assumed constant for installation and operation (submerged pipeline). The internal pressure is assumed zero for installation.

The combined stress may be calculated using either Tresca's or Von Mises' formula. Generally, the combined stress should be less than or equal to 90% of yield. The stress check can be calculated for either the nominal wall thickness, or the corroded wall thickness (nominal wall thickness minus corrosion allowance).

Tool Input

• pletype : External Pressure Type
  • Peu : User Defined External Pressure
• syutype : Stress Table Type
• mattype : Yield Stress Type
  • SMYSu : User Defined Specified Minimum Yield Stress
• schdtype : 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
• corrtype : Pipe Wall Corrosion Type
• modptype : Pipe Material Type
  • νu : User Defined Pipe Poisson's Ratio
  • αu : User Defined Pipe Thermal Expansion Coefficient
  • Eu : User Defined Pipe Elastic Modulus
• sectype : Pipe Section Properties Type
  • Asu : User Defined Steel Cross Section Area
  • EAαu : User Defined Pipe E x A x alpha
  • Zu : User Defined Pipe Z Modulus
• walltype : Hoop Stress Calculation Type
  • Yu : User Defined ASME Y Factor
• loadtype : Axial Load Type
  • Fgu : User Defined Global Axial Load
  • Fwu : User Defined Pipe Wall Axial Load
• ifactype : Stress Factor Type
  • iiu : User Defined In Plane Bending Stress factor
  • iou : User Defined Out Of Plane Bending Stress Factor
  • itu : User Defined Torsion Shear Stress Factor
• sbtype : Bending Stress Type
• sttype : Torsion Shear Stress Type
• checktype : Stress Check Type
• momtype : Bending Stress Type
• tc : Corrosion Allowance
• Fd : Design Factor
• Td : Design Temperature
• Pi : Internal Pressure
• Tin : Installation Temperature
• Fin : Installation Load
• M : Design Moment

Tool Output

• α : Pipe Thermal Expansion Coefficient
• ν : Pipe Poisson's Ratio
• Ax : Pipe Cross Section Area
• E : Pipe Elastic Modulus
• EAα : Pipe E x A x alpha
• Fg : Global Or External Axial Load
• Fw : Pipe Wall Axial Load
• ID : Pipe Inside Diameter
• OD : Pipe Outside Diameter
• OD/t : Pipe Diameter Over Wall Thickness Ratio
• PΔ : Pressure Difference
• Pe : External Pressure
• SMYS : Specified Minimum Yield Stress
• Sb : Bending Stress
• Schk : Check Stress
• Schk/Sd : Hoop Stress Over Allowable Stress Ratio
• Sd : Design Stress
• Sh : Hoop Stress
• St : Torsion Stress
• Sx : Pipe Wall Axial Stress
• Z : Z Section Modulus
• ii : In Plane Bending Stress Factor
• io : Out Of Plane Bending Stress Factor
• it : Torsion Shear Stress Factor
• t : Stress Check Wall Thickness
• tn : Pipe Nominal Wall Thickness

Calculate pipeline SMYS, SMTS, SMTS over SMYS ratio and SMYS over SMTS ratio from pipe stress tables.

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

Tool Output

• SMTS : Specified Minimum Tensile Stress
• SMTS/SMYS : Tensile Stress Over Yield Stress Ratio
• SMYS : Specified Minimum Yield Stress
• SMYS/SMTS : Yield Stress Over Tensile Stress Ratio

Calculate pipeline diameter, pressure design wall thickness (nominal wall thickness minus fabrication allowance and corrosion allowance), and minimum wall thickness (nominal wall thickness minus fabrication allowance) from nominal wall 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, minimum wall thickness and pressure design wall thickness for the selected diameter.

Tool Input

• schdtype : Schedule Type
• diamtype : Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Wall Thickness Type
  • tnu : User Defined Wall Thickness
• ttoltype : Wall Thickness Fabrication Tolerance Type
  • txu : User Defined Negative Wall Thickness Fraction
  • tfu : User Defined Negative Wall Thickness Allowance
• c : Wall Thickness Corrosion Allowance

Tool Output

• ID : Nominal Inside Diameter
• OD : Nominal Outside Diameter
• OD/tn : Diameter Over Wall Thickness Ratio
• tf : Wall Thickness Fabrication Allowance
• tm : Minimum Wall Thickness
• tn : Nominal Wall Thickness
• tp : Pressure Design Wall Thickness
• tx : Wall Thickness Fabrication Fraction

Calculate typical line pipe elastic modulus, shear modulus, bulk modulus, density, and thermal expansion coefficient.

The table values of Poisson ratio and bulk modulus are calculated from the elastic modulus and shear modulus. Project specific data should be used if it is available. Use the Result Table option to display a table of properties versus material type.

Tool Input

• modptype : Material Type
  • Eu : User Defined Elastic Modulus
  • Gu : User Defined Shear Modulus
  • Ku : User Defined Bulk Modulus
  • νu : User Defined Poisson Ratio
  • ρu : User Defined Density
  • αu : User Defined Thermal Expansion Coefficient

Tool Output

• α : Thermal Expansion Coefficient
• ν : Poisson Ratio
• ρ : Density
• E : Elastic Modulus
• G : Shear Modulus
• K : Bulk Modulus

Calculate pipeline bending shear force, bending moment, slope, deflection and stress check from combined loads for single layer pipeline sections (file data - a modern browser is required).

Section end types include free fixed (cantilever), guided fixed, pinned fixed, fixed fixed (built in or fixed), pinned pinned (simply supported), and guided pinned section ends.

Combined loads can include axial load, point loads, distributed loads, weight loads, concentrated moments, angular displacements, lateral displacements, and uniform temperature differential.

For compressive axial loads, the bending moment, slope and deflection tend to infinity as the axial load tends to the buckling load (load controlled conditions). For tension loads, the bending moment, slope and deflection decrease with increasing tension. The buckling load can be calculated using either the Euler equation (suitable for long sections), the Johnson equation (suitable for short sections), or the buckling load equation can be determined from the transition length. The axial load can either be calculated from temperature and pressure or user defined. The effective length factor should be used for sections on a soft foundation such as soil, where the section ends are poorly defined. For defined section ends, such as structures, the effective length factor should be set to one (fe = 1).

The stress check includes longitudinal stress, Tresca combined stress, and von Mises equivalent stress. The bending stress is calculated at the pipe mid wall. The hoop stress is calculated using the Barlow mid wall equation with the nominal wall thickness.

:

`Sh = (P - Pe) (OD - tn) / (2 tn) `

where :

Sh = hoop stress
P = internal pressure
Pe = external pressure
OD = pipe outside diameter
tn = pipe nominal thickness

Use the Result Plot option to display the bending moment, shear force, slope, deflection and stress versus position x. Refer to the figures and help pages for more details. Refer to the example text file in resources.

Tool Input

• pletype : External Pressure Type
  • Peu : User Defined External Pressure
• schdtype : Schedule Type
• diamtype : Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Wall Thickness Type
  • tnu : User Defined Wall Thickness
• syutype : Line Pipe Stress Type
• mattype : Material Type
  • Syu : User Defined Yield Stress
• modptype : Material Property Type
  • αu : User Defined Thermal Expansion Coefficient
  • Eu : User Defined Elastic Modulus
  • ρpu : User Defined Density
  • νpu : User Defined Poisson Ratio
• sectype : Section Properties Type
  • EIu : User Defined E x I
  • EAαu : User Defined E x A x alpha
• wltype : Weight Type
  • wu : User Defined Unit Weight
• loadtype : Axial Load Type
  • Fau : User Defined Axial Load
• fbtype : Buckling Load Type
  • Fbu : User Defined Buckling Load
• endtype : End Type
• leftype : Effective Length Type
  • feu : User Defined Effective Length Factor
• sstype : Stress Type
• chktype : Stress Check Type
• btype : Location On Beam
• ρc : Internal Fluid Density
• ρb : External Fluid Density
• Lo : Nominal Length
• x : Length From End
• Pi : Internal Pressure
• Td : Design Temperature
• Tin : Installation Temperature
• Fin : Installation Load

Tool Output

• α : Thermal Expansion Coefficient
• θ : Slope Or Angle
• ν : Poisson Ratio
• ρp : Density
• AX : Cross Section Area
• E : Elastic Modulus
• EAα : E x A x alpha
• EI : E x I
• Fa : Axial Load
• Fa/Fb : Axial Load Over Buckling Load Ratio (> -1)
• Fb : Buckling Load
• Fw : Pipe Wall Load
• I : Moment Of Inertia
• ID : Inside Diameter
• Le : Effective Length
• Lt : Transition Length (Short to Long Beam)
• M : Bending Moment
• OD : Outside Diameter
• Pe : External Pressure
• R : Reaction Or Shear Load
• SG : Specific Gravity
• Sb : Bending Stress
• Schk : Check Stress
• Schk/Sd : Check Stress Over Yield Stress Ratio
• Sh : Hoop Stress
• Sx : Axial Stress
• Sy : Yield Stress
• Y : Distance To Outer Fiber
• Zs : Section Modulus
• h : Beam Height In Plane Of Bending
• mc : Contents Unit Mass
• md : Displaced Unit Mass
• mp : Line Pipe Unit Mass
• tn : Wall Thickness
• w : Weight Per Unit Length
• y : Deflection

Calculate pipeline bending shear force, bending moment, slope, deflection and stress check from combined loads for single layer pipeline sections (file data - a modern browser is required).

Section end types include free fixed (cantilever), guided fixed, pinned fixed, fixed fixed (built in or fixed), pinned pinned (simply supported), and guided pinned section ends.

Combined loads can include axial load, point loads, distributed loads, weight loads, concentrated moments, angular displacements, lateral displacements, and uniform temperature differential.

For compressive axial loads, the bending moment, slope and deflection tend to infinity as the axial load tends to the buckling load (load controlled conditions). For tension loads, the bending moment, slope and deflection decrease with increasing tension. The buckling load can be calculated using either the Euler equation (suitable for long sections), the Johnson equation (suitable for short sections), or the buckling load equation can be determined from the transition length. The axial load can either be calculated from temperature and pressure or user defined. The effective length factor should be used for sections on a soft foundation such as soil, where the section ends are poorly defined. For defined section ends, such as structures, the effective length factor should be set to one (fe = 1).

Pipe unit weight and EI are calculated for a circular pipe with coatings and or internal liners. Enter the wall thickness and density for all layers. Only enter the elastic modulus for layers which will contribute to EI (including the concrete layer if applicable). Change the number of layers on the setup page. The bending stiffness can be calculated with the concrete stiffness factor (CSF). The CSF accounts for the additional stiffness provided by the external concrete coating.

The stress check includes longitudinal stress, Tresca combined stress, and von Mises equivalent stress. The bending stress is calculated at the pipe mid wall. The bending stress can be calculated either in the pipe body with no concrete stiffness effect, or at the field joint which includes the effect of concrete stiffness. For general calculations where the location of the field joint is not known, the field joint option should be used as a worst case. The hoop stress is calculated using the Barlow mid wall equation with the nominal wall thickness.

:

`Sh = (P - Pe) (OD - tn) / (2 tn) `

where :

Sh = hoop stress
P = internal pressure
Pe = external pressure
OD = pipe outside diameter
tn = pipe nominal thickness

Use the Result Plot option to display the bending moment, shear force, slope, deflection and stress versus position x. Refer to the figures and help pages for more details. Refer to the example text file in resources.

Tool Input

• pletype : External Pressure Type
  • Peu : User Defined External Pressure
• schdtype : Line Pipe Schedule Type
• diamtype : Line Pipe Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Line Pipe Wall Thickness Type
  • tnu : User Defined Wall Thickness
• syutype : Line Pipe Stress Type
• mattype : Material Type
  • Syu : User Defined Yield Stress
• sectype : Section Properties Type
  • EAαu : User Defined E x A x alpha
  • νu : User Defined Pipe Poisson's Ratio
• eitype : E x I Type
  • Kcu : User Defined Coating Factor
  • CSFu : User Defined Concrete Stiffness Factor
  • EIu : User Defined Pipe E x I
• wltype : Weight Type
  • wu : User Defined Unit Weight
• loadtype : Axial Load Type
  • Fau : User Defined Axial Load
• fbtype : Buckling Load Type
  • Fbu : User Defined Buckling Load
• endtype : End Type
• leftype : Effective Length Type
  • feu : User Defined Effective Length Factor
• sbtype : Bending Stress Type
• sstype : Stress Type
• chktype : Stress Check Type
• btype : Location On Beam
• WTi : Pipe Liner Wall Thickness
• ρi : Pipe And Liner Density
• Ei : Pipe And Liner Elastic Modulus
• αi : Pipe And Liner Thermal Expansion Coefficient
• νi : Pipe And Liner Poisson's Ratio
• WTo : Pipe Coating Wall Thickness
• ρo : Pipe Coating Density
• Eo : Pipe Coating Elastic Modulus
• ρc : Internal Fluid Density
• ρb : External Fluid Density
• Lo : Nominal Length
• x : Length From End
• Pi : Internal Pressure
• Td : Design Temperature
• Tin : Installation Temperature
• Fin : Installation Load

Tool Output

• α : Effective Thermal Expansion Coefficient
• θ : Slope Or Angle
• ν : Effective Poisson Ratio
• AX : Effective Cross Section Area
• CSF : Concrete Stiffness factor
• EAα : E x A x alpha
• EI : Effective E x I
• EIc : Concrete E x I
• EIp : Pipe E x I
• Fa : Axial Load
• Fa/Fb : Axial Load Over Buckling Load Ratio (> -1)
• Fb : Buckling Load
• Fw : Pipe Wall Load
• I : Moment Of Inertia
• IID : Pipe Inside Diameter Including Liner
• Kc : Coating Factor
• Le : Effective Length
• Lt : Transition Length (Short to Long Beam)
• M : Bending Moment
• OD : Line Pipe Diameter
• OOD : Pipe Outer Diameter Including Coatings
• Pe : External Pressure
• R : Reaction Or Shear Load
• SG : Specific Gravity
• Sb : Bending Stress
• Schk : Check Stress
• Schk/Sy : Check Stress Over Yield Stress Ratio
• Sh : Hoop Stress
• Sx : Axial Stress
• Sy : Yield Stress
• Y : Distance To Outer Fiber
• Zs : Section Modulus
• h : Beam Height In Plane Of Bending
• md : Displaced Unit Mass
• mlc : Contents Unit Mass
• mlp : Pipe Unit Mass Including Liner And Coating
• tn : Line Pipe Thickness
• w : Weight Per Unit Length
• y : Maximum Deflection

Calculate pipeline EI (ExI), unit mass and unit weight for multi layer pipelines.

The concrete stiffness factor is used to account for the effect of the concrete layer. The concrete stiffness factor is calculated from the ratio of concrete EI over pipeline EI. The concrete stiffness factor is calculated in accordance with DNVGL RP F105. Only include the Young's modulus value for the layers which will contribute to EI. The unit weight can be calculated for dry empty, dry full, wet empty and wet full pipe.

Tool Input

• schdtype : Line Pipe Schedule Type
• diamtype : Line Pipe Diameter Type
  • ODu : User Defined Outside Diameter
  • IDu : User Defined Inside Diameter
• wtntype : Line Pipe Wall Thickness Type
  • tnu : User Defined Wall Thickness
• eitype : E x I Type
  • Kcu : User Defined Coating Factor
  • CSFu : User Defined Concrete Stiffness Factor
• wltype : Pipe Weight Type
• WTi : Pipe Liner Wall Thickness
• Ei : Pipe And Liner Elastic Modulus
• ρi : Pipe And Liner Density
• WTo : Pipe Coating Wall Thickness
• Eo : Pipe Coating Elastic Modulus
• ρo : Pipe Coating Density
• ρf : Contents Fluid Density
• ρb : Displaced Fluid Density

Tool Output

• CSF : Concrete Stiffness Factor (DNVGL)
• EIi : Inside Layers E x I
• EIo : Outside Layers E x I
• EIp : Total E x I
• IID : Pipe Inner Diameter Including Liners
• Kc : Coating Factor (DNVGL)
• OD : Line Pipe Nominal Diameter
• OOD : Pipe Outer Diameter Including Coatings
• SG : Pipe Specific Gravity Relative To Displaced Fluid
• mb : Displaced Fluid Mass Per Length
• mc : Contents Fluid Mass Per Length
• mi : Inner Layers Total Unit Mass
• mo : Outer Layers Total Unit Mass
• mp : Pipe Mass Per Length Including Liner And Coating
• tn : Line Pipe Nominal Wall Thickness
• w : Pipe Total Weight Per Length Including Contents and Buoyancy

Calculate pipeline concrete stiffness factor and effective EI from the concrete pipeline EI ratio for a general pipeline.

The concrete stiffness factor is used to account for the effect of the concrete layer on the bending modulus EI and the natural frequency. The concrete stiffness factor is calculated from the ratio of concrete EI over pipeline EI.

`CSF= A ((EIc) / (EIp))^0.75 `
`EI = EIp (1 + CSF) `

where :

CSF = concrete stiffness factor
EIc = concrete EI
EIp = pipe EI
EI = effective EI
A = 0.33 for asphalt coating and 0.25 for PP/PE coating

The concrete stiffness factor is calculated in accordance with DNVGL RP F105. Use the Result Plot option to plot the concrete stiffness factor (CSF) versus EI ratio and CSF type, or effective EI versus EI ratio and CSF type. Refer to the help pages for more details.

Reference : DNVGL RP F105 Free Spanning Pipelines (Download From DNVGL website)

Tool Input

• coptype : Cross Section Type
  • EIcu : User Defined Concrete E x I
  • EIC/EIPu : User Defined E x I Ratio
• csftype : Concrete Stiffness Factor Type
  • Kcu : User Defined Coating Factor
  • CSFu : User Defined Concrete Stiffness Factor
• EIp : Beam E x I

Tool Output

• CSF : Concrete Stiffness Factor
• EI : Effective E x I
• EIC/EIP : E x I Ratio