Maximum Allowable Pipe Span Length

API 1117 Movement of In-Service Pipelines using the free span between pipe supports. PLTB predicts stresses due to pipe movement of in-service and out of service lines as well as operating pipelines having unintended free spans.

This calculation is based on a four-span loaded beam. Because there are many variables during the construction movement of the pipe to the new lowered bedding position, this puts limits on the stresses that can be calculated.

Step 1: Variables Definition
𝐷 − Pipe Outside Diameter [in]
𝑊 − Weight [lb/ft], includes water weight if hydrostatic testing is specified
MOAP − Maximum Allowable Operating Pressure [psi]
SMYS − Specified Minimum Yield Strength or Grade of Steel [psi]
OP − Operating Pressure [psi]
𝑡 − Pipe Wall Thickness [in]
𝑆−Section Modulus [in2]
𝐼−Moment of Inertia[in4]
𝑒− Modulus of Elasticity (29000 ksi)
𝐻 − Hoop Stress [psi]
𝐵 − Bending Stress [psi]
𝑀 − Bending Moment [ft−lb]
𝐿 − Span Length [ft]
𝑑 − Deflection [in]

Step 2: Calculate Hoop Stress

PTLB Design & Stress Analysis_2.14 Intro 2.pngWhere 𝑃 = MOP

Step 3: Calculate Maximum Allowable Bending Stress
Solve Von Mises Equation through Quadratic Equation, and then solve for Bending Stress B

PLTB Liquid_DesignStress_2.14 Step 3.png

Step 4: Calculate Maximum Allowable Bending Moment

PLTB Liquid_DesignStress_2.14 Step 4.png

Step 5: Calculate Maximum Span Length L, due to Bending
PTLB Design & Stress Analysis_2.14 Intro 5.png

Step 6: Calculate Maximum Span Length L, due to Deflection

PTLB Design & Stress Analysis_2.14 Intro 6.png

Input Parameters
To create a new case, click the “Add Case” button
Select the Maximum Allowable Pipe Span Length (G) module.
Enter Case Name, Location, Date and any necessary notes.
Fill out all required fields.
Make sure the values you are inputting are in the correct units.
Click the CALCULATE button.
Nominal Pipe Size
Wall Thickness (in.)
Grade
Pipe Class
Youngs Modulus of Steel (psi)
Poisson’s Ratio for Steel
Average Unit Weight of Steel (Calculated)
Pipe installed after November 11, 1970 (Y/N)
PLTB Liquid_DesignStress_2.14 Input Rev_092420.png

PLTB Liquid_DesignStress_2.14 Input 2 Rev_092420.png

Outputs/Reports
View the results.
If an input parameter needs to be edited be sure to hit the CALCULATE button after the change.
To SAVE, fill out all required case details then click the SAVE button.
To rename an existing file, click the SAVE As button. Provide all case info then click SAVE.
To generate a REPORT, click the REPORT button.
The user may export the Case/Report by clicking the Export to Excel/PowerPoint icon.
To delete a case, click the DELETE icon near the top of the widget.
PLTB Liquid_DesignStress_2.14 Output Rev_092420.png

Related Links
Pipeline Design & Stress Analysis

Pipeline HUB — User Resources

Maximum Allowable Pipe Span Length

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