Pull Force and Installation Stresses for PE Pipe

The procedures for designing the bore path for plastic pipe are basically the same as discussed for steel pipe. As with steel product pipe, plastic pipe, when installed by HDD, may experience high-tension loads, severe bending, and external fluid pressures. HDD installation subjects the pipe to axial tensile forces caused by the frictional drag between the pipe and the bore hole or drilling fluid, the frictional dragon the ground surface, the capstan effect around drill-path bends, and hydrokinetic drag. The pipe may also be subjected to external hoop pressures caused by the external fluid head and bending stresses. Estimating of pullback forces involves the assumption of many variables and installation techniques.

Estimated Average Radius of Curvature at Pipe Entry and Pipe Exit:

                           H – Depth of bore (ft)

Θin – Pipe entry angle (degree)

Θex – Pipe exit angle (degree)

L2 – Horizontal Distance to Achieve Desired Depth:

L4 – Horizontal Distance to Achieve Rise to the Surface:

L3 – Additional Distance Traversed at Desired Depth:

L_cross – Length of the Crossing

Weight of Empty Pipe:

D – Pipe Diameter (inch)
DR – Pipe Dimension Ratio
γa – Specific Gravity of Pipe Material

Average Weight of Empty Pipe:

Water Weight:

%water = Percentage of Pipe Filled with Water (percent)

ρw – Density of water (lb/ft3)

Net Upward Buoyant Force on Empty Pipe:

γb – Specific Gravity of the mud slurry

Hydrokinetic Force:

Pull Force at point A:

Pull Force at point B:

Pull Force at point C:

Pull Force at point D:

νa – Coefficient of Friction at the Surface
νb – Coefficient of Friction within Borehole

Bending Strain:

Bending Stress:

E24 = 24 hr.-Apparent Modulus of Elasticity

Allowable Tensile Stress:

δsp – Allowable/Safe Pull Stress (psi)

Tensile Stress at Point A:

Tensile Stress at Point B:

Tensile Stress at Point C:

Tensile Stress at Point D:

Breakaway Links Settings:

Static Head Pressure

Maximum Pressure During Pull back

Ovality Compensation Factor:

f0 – Ovality compensation factor based on % of Deflection (%Δ𝐷)

Tensile Reduction Factor:

Critical Collapse Pressure:

Safety Factor: