Rigonomics: With Low Rates, HDD Rig Selection Is Critical

By Jeff Griffin, Senior Editor | June 2010 Vol. 65 No. 6

To share Rigomonics information with those unable to attend the UCT sessions, Underground Construction magazine will publish a series of reports on key topics covering HDD operations. The first is about selecting the right drill for the job.

“Once a drilling company is awarded a project, most of the time there will be several weeks to plan how to best execute it,” said Crumpton. “At this stage, you’re ahead of the game -- bid work should have provided information needed to make the installation.”

Selecting the right drill rig is an essential early step. Considering project specifications, such as pilot hole size, bore length, type of soil formation, size and type of product line to be pulled back and numerous other factors affect the decision of selecting the right machine for the job.

Important questions
Among questions that should be answered when selecting equipment for a job:

• Does the drill unit have sufficient push/pull and torque capability?
• Is the capacity of the mud pump enough to clean the hole and offer effective hydraulic horsepower?
• Is the drill pipe able to withstand the torsional and tensile forces that might occur on the job?

“The rig’s pumps must be able to handle the volume needed for the final reaming size,” said Crumpton. “If cuttings can’t be removed from the hole, there are going to be problems. Pressure is not the issue, volume is what is important. If necessary volume can only be achieved by running the pumps wide open, larger-capacity pumps should be used. Mud pumps cannot pump to engineering specifications because they are designed for actual efficiency ratings. For example: duplex pumps are rated at 85 percent efficiency. Triplex pumps have 90- to 95-percent efficiency ratings. If the pumps must be operated at maximum RPM, the efficiency is reduced. Either triplex or duplex pumps are very good to use in the HDD industry.”

Postponing starting a job because the right-size rig is not available is never an attractive option. A solution often used is to drill the pilot hole with a drill unit that may be too small to complete the installation.

“A smaller model can be transported to the job site, moved into position, rigged up and start the pilot hole faster and at less cost than a bigger machine,” Crumpton said. “Smaller rigs use less fluid, have smaller engines that burn less fuel and require fewer personnel on the job site.”