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Drilling Dirty
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| HDD rigs offer a host of options to fit any soil type that might lurk under that hard concrete. Drill bits range from fl at end bits for use in sandy-type soils to carbide bits for rock-type drilling. |
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To snake through the complex web of infrastructure residing under our feet, homes and public institutions, HDD has to be able to make its way through cluttered, subterrestrial worksites. Enter the most important and overlooked aspect of the HDD rig — the mud system.
“The mud system is the heart of the drilling system. It not only provides the lubrication to the tooling and product being installed, but also serves as the conveyance system for removing the spoils from the borehole making room for the product to be installed,” says Levings.
Required for medium-duty (20,000 to 100,000 lbs of pullback force) to heavy-duty (100,000 lbs or higher of pullback force) rigs, the proper mud mix allows the tool to pierce the soil and covertly make its way to its destination. The systems are generally comprised of the mud mixing and storage system, the mud pressure pump for pumping the drilling fluid down the hole, the hoses and piping system, trash pump and power unit. On larger units, a mud-cleaning or recycling system is available for recirculating the drilling fluid.
While water would seem sufficient for creating mud, the drilling fluid is the key component to the mix. Using a combination of water and bentonite or polymer, the drilling fluid mix flows to the cutting head to help remove the spoils, stabilize the bore hole, cool the cutting head and lubricate the passage of product to
the pipe.
Most medium-duty units already have a mud pump integrated into the drilling unit. On larger units, the mud system will be sized depending on the job requirements. Contractors who buy larger units are well versed in the needs of large HDD projects and know what the requirements will be.
While larger HDD and corresponding mud systems offer a more specialized approach to a job, medium rigs can offer more flexibility than meets the eye. For the more advanced HDD contractor, bypassing the onboard mud pump on a medium-duty rig and using a larger, oversized pump has allowed contractors to bore longer and faster. With a larger pump pushing out more fluid comes higher fluid horsepower — allowing the contractor to make a larger pilot hole with a larger mud motor and use a larger reamer, eliminating one to two reamer passes (compared with a smaller, standard reamer).
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