Direct Pipe® is a proprietary trenchless construction method of Herrenknecht AG, which enables borehole excavation and installation of a pipeline in one single step, by combining Microtunneling with Horizontal Directional Drilling (HDD). The system uses a conventional slurry microtunneling machine to excavate the hole.
The difference from microtunneling is the use of a Pipe Thruster in place of a jacking frame used in traditional pipe jacking applications. The Direct Pipe® method typically uses prefabricated steel pipe, pushed into the hole behind the microtunneling machine (in contrast to HDD, in which the pipe string is pulled into place).
This process results in expeditious and economic installation of pipelines of lengths of more than 5000-ft, and diameters ranging between 30-inch and 60-inch. Direct Pipe® provides higher alignment accuracy compared to HDD, and involves no back-reaming. Using the microtunneling cutter head, it is possible to cut through a wide variety of geological conditions, with minimal overburden. This process also minimizes the risk of frac-outs, commonly associated with traditional HDD.
When Permalok® steel casing pipe is used for Direct Pipe® installations, it eliminates the time spent on field welding joints in the launch pit, essentially doing away with the need to lay out an entire string of traditional butt-welded steel pipe prior to installation. On a recent project, Permalok® pipe was purposefully installed in a vertical curve alignment using Direct Pipe®.