A mini-rig is a category of horizontal directional drilling (HDD) rigs used for shorter distances, lesser depths, and smaller-diameter pipes. The term is used in contrast to midi-rigs and maxi-rigs, which are names for larger categories. A mini-rig is used for mini HDD projects, which may be brief jobs dealing with utility installation or replacement.
Trenchlesspedia Explains Mini-Rig
In their Guidelines for Use of Mini-Horizontal Directional Drilling for Placement of High Density Polyethylene Pipe, the Plastics Pipe Institute laid out design and installation procedures for mini-HDD projects using HDPE, a preferred pipe material. The classification of drill rigs for this type of work would be considered a mini-rig.
The numbers that differentiate a mini-rig from a maxi-rig may vary depending on whom you ask. One drilling expert says that mini-rigs are rated at less than 40,000 pounds of thrust and less than 4,000 pounds of torque.