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Horizontal Directional Drilling: Utility and Pipeline Applications

Chapter 7: HDD Pipe Stress Analysis for Plastic Pipe

7.1 General Information

When planning HDD crossings with plastic pipe, the primary concern for owners is usually whether the product pipe can safely handle the stresses and the required pullback loads. As discussed in Chapter 4, after selecting the required DR for the product pipe the next step is to determine if the DR selected can handle the installation loads. As with steel product pipe, plastic pipe, when installed by HDD, may experience high-tension loads, severe bending, and external fluid pressures. Usually these installation loads are more severe than the design service loads, and they are the primary factor in pipe material selection. It is quite common for the installation forces to be the deciding factor and to require the designer to specify a lower DR (stronger pipe) than would have been required for the other factors.

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 drag on 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. The equations provided in this chapter are guidelines only, and the pulling loads calculated are estimated values.

7.2 Bore-Path Profile

The procedures for designing the bore path for plastic pipe are basically the same as discussed for steel pipe in Chapter...

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