Operational Stress – Steel Pipe

Introduction

A pipeline is subjected to three primary loading conditions during installation by HDD: tension, bending, and external pressure. A thorough design process requires examination of the stresses that result from each individual loading condition as well as an examination of the combined stresses that result from the interaction of these loads.
Hence, the stresses imposed on steel pipe during both the HDD installation process and subsequent operation should be carefully evaluated.

Bending Stress (fb)

Bending stress resulting from a rigid steel pipe
being forced to conform to the drilled radius of curvature

f_b=\frac{ED}{2R}

f_b=\frac{ED}{2R}

E =modulus of elasticity for steel (psi)
D = outside diameter of the pipe (inch)
R = Shortest Radius of Curvature (ft)

Hoop Stress (fh)

Steel pipe will fail by buckling or collapse when under the influence of hoop stress. It’s important to calculate the wall thickness required to prevent collapse of round steel pipe under the influence of hoop stress.

f_h = \frac{\Delta P D}{2t}\~\\Delta P = P – (H – H_w)0.4333

f_h = \frac{\Delta P D}{2t}\\~\\\Delta P = P - (H - H_w)0.4333

P = Operating Pressure (psig)
H = Depth of the Pipe at Horizontal Section (ft)
H_w = Groundwater Table below Datum (ft)

Thermal Stress (fe)

Thermal stress resulting from changes in pipe temperature from the point in time at which the pipe is restrained by the surrounding soil to typical operating conditions.

f_e=E\alpha(T_2-T_1)

f_e=E\alpha(T_2-T_1)

𝐸 − Young′s Modulus of Elasticity 𝐸 = 29 x 10⁶
𝛼 − Coefficient of Thermal Expansion for steel α = 6.5 x 10⁶ [in/in℉]
T₁ = Installation Temperature (°F)
T₂ = Operating Temperature (°F)

Total Longitudinal Compressive Stress

f_1=f_b+f_h\theta+f_e

f_1=f_b+f_h\theta+f_e

f_l = Total Longitudinal Compressive Stress
𝜗 = Poisson′s Ratio = 0.3

Maximum Shear Stress (fv)

f_v=\frac{f_h-f_1}{2}

f_v=\frac{f_h-f_1}{2}

Maximum Allowable Shear Stress (fva)

f_{va}=0.45SMYS

f_{va}=0.45SMYS

SMYS – Specified minimum Yield Stress for Steel Pipe (psi)

Operating Conditions

\text{Operating Condition} =
\begin{cases}
\text{Pass: } f_{va} < f_v \ \text{Fail: } f_{va} > f_v
\end{cases}

\text{Operating Condition} =
\begin{cases}
\text{Pass: } f_{va} < f_v \\
\text{Fail: } f_{va} > f_v
\end{cases}

Input Parameters

1. To create a new case, click the “Add Case” button
2. Select the Operational Stresses – Steel Pipe application in the HDD Steel Pipe module
3. Enter Case Name, Location, Date, and any necessary notes
4. Fill out all required fields
5. Make sure the values you are inputting are in the correct units
6. Click the CALCULATE button

• Poisson’s Ratio
• Young’s Modulus of Elasticity [psi]
• Thermal Expansion Coefficient [in./in.°F]
• Operating Pressure [psig]
• Pipe Outside Diameter [in.]
• Pipe Wall Thickness [in.]
• Specified Minimum Yield Strength [psi]
• Installation Temperature [°F]
• Operating Temperature [°F]
• Depth of the Pipe at Horizontal Section [ft]
• Groundwater Table below Datum [ft]
• Shortest Radius of Curvature [ft]

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
• Bending Stress [psi]
• Hoop Stress [psi]
• Thermal Stress [psi]
• Total Longitudinal Compressive Stress [psi]
• Maximum Shear Stress [psi]
• Maximum Allowable Shear Stress (45% of SMYS)
• Operating Conditions

References

• Willoughby, David (2005). Horizontal Directional Drilling, McGraw-Hill, New York, ISBN 0-87814-395-5. v.
• Willoughby, David, Training – Horizontal Directional Drilling, TTI, November 2016
• HDD Consortium. (2001). Horizontal directional drilling, good practices guidelines, HDD Consortium.
• Horizontal Directional Drilling Training Manual, Horizontal Drilling International, February 1999
• Skonberg, Eric R. II. Muindi, Tennyson M. (2014). Pipeline Design for Installation by Horizontal Directional Drilling, American Society of Civil Engineers. Horizontal Directional Drilling Design Guideline Task Committee.
• “Installation of Pipelines by Horizontal Directional Drilling”, PRCI Report PR-227-9424
• Nayyar, Mohinder L. (1992). Piping Handbook, 6th Edition, McGraw-Hill, New York, NY.
• AWWA (2006), PE Pipe Design and Installation, M55, American Water Works Association, Denver, CO
• ASTM (1962), PPI Handbook

FAQ