Bending Stress-Caused by Fluid Flowing Around Pipeline – Gas

Introduction

This is the result of erosion that increase span length (exposed pipe) where the PLTB applications calculates the longitudinal stresses that estimates the forces on the pipe due to water flow. The same techniques can be used as spans.

Vortex shedding and the potential for fatigue failure of the pipe in flowing water, the apparent weight of the pipe will change because of buoyant forces. Flow velocity is sometime difficult to estimate at different depths i.e. drag and lift.

S=\frac{wD^2V^2L^2}{58.4(D^4-d^4)} \~\ L=\sqrt{ \frac{58.4S(D^4-d^4)}{wD^2V^2}}

S=\frac{wD^2V^2L^2}{58.4(D^4-d^4)} \\~\\ L=\sqrt{ \frac{58.4S(D^4-d^4)}{wD^2V^2}}

Where:
𝑆 − Bending stress (psi)
𝑤 − Unit weight of fluid (lb/ft³) @59℉ and 14.7 (psi): (air = 0.07651, water = 62.4)
𝐷 − Outside diameter of pipe (in)
𝑑 − Inside diameter of pipe (in)
𝑉 − Velocity of fluid (ft/sec)
𝐿 − Length of pipe (ft)
𝑑 − Deflection (in)

Bending Stress in Piling Caused By Fluid Flow Around Piling

S=\frac{wV^2L^2}{58.4D^2} \~\ L=\sqrt{ \frac{58.4D^2S}{wV^2}}

S=\frac{wV^2L^2}{58.4D^2} \\~\\ L=\sqrt{ \frac{58.4D^2S}{wV^2}}

𝐷 − Outside diameter of piling (in)

Case Guide

Part 1: Create Case

Input Parameters

• Nominal Pipe Size (in):(0.625” – 48”)
• Wall Thickness (in):(0.068”- >2”)
• Pipe grade: (24000psi-80000psi) (if unknown use Grade A 24000)
• Pipe Length (ft)
• Velocity of Fluid (ft/sec)
• Unit Weight of Fluid (default water) (lb/ft³)

Part 2: Outputs/Reports

Results

• Bending Stress (psi)

References

• ASME B31.8 – Gas Transmission and Distribution Piping Systems
• API 5L, API 5LS and API 5LX – Specification of Pipe Grade
• ASTM – Various – Weld Joint Factor
• CFR Code Part 192
• USDA-SCS Modified (Permissible Velocity of Water and Soil Erodibility)
• FHWA-HEC
• Pipeline Rules of Thumb Handbook
• Timoshenko, S – Theory of Elasticity Anchor Force

FAQ