In many Horizontal Directional Drill (HDD) installations the height of the weld cap results in the coating on the weld being damaged by the mechanical forces of pull back. When pulling pipe through an engineered hole, all of the coating is subjected to gouge, impact, and abrasion forces, but the height of the weld cap focuses those forces so that they are particularly damaging.
In November 2020, DTE Energy ran a trial application of a novel composite outer wrap for girth weld protection on HDD. An 880 foot, 8 inch diameter pipe was pulled to a maximum depth of 10 feet under a creek in Canton, Michigan. The soil was mostly loam, mixed in with cobble. The pipe was coated with factory-applied FBE and ARO. The girth welds were coated with a two part epoxy. The composite outer wrap was applied to two girth welds connecting the pull head to the carrier pipe.
This paper discusses the results of the trial: a composite-outer-wrapped girth weld was pulled through a real-world HDD, cut out from the pipe, and then examined in a laboratory. The results from the testing show significant added protection for gouge, impact, and abrasion resistance without inhibiting the future effectiveness of cathodic protection.
Horizontal directional drills (HDD) have become an essential pipeline construction tool for crossing spans of the right of way with obstructions such as wetlands, rivers and streams, railroads, roads, businesses, and high consequence areas (HCA). This trenchless technology allows a pipeline to be installed without open cutting the ground. Prior to any construction, geological surveys with core samples are performed to determine the optimum route for the HDD (Figure 1).
A pilot hole is dug from one side of the span (called the entry point) and bores under the earth to the exit hole. Once the pilot hole is drilled, one or more reaming passes are made to enlarge the hole to a size larger than the pipe to be installed. Usually, a sweep pass is then performed to clear any debris from the hole. The pipe to be pulled is already strung out, welded, and coated on the exit side of the pilot hole. The pipe is attached to a pull head and pulled through the hole by the drilling rig (Figure 2).
