Horizontal directional drilling (HDD) rig

01

Pick the rig class for pipe size, length and depth

The Plastics Pipe Institute's Handbook of PE Pipe gives mini-HDD as pipes up to about 12 in diameter, distances of hundreds of feet and depths to about 15 ft (typ.), and distinguishes it from maxi (conventional) HDD, which installs pipes of 48 in or more in bores thousands of feet long at depths up to 200 ft, with midi-HDD in between. It notes that the pipe sees its highest lifetime loads during pullback and points to ASTM F1962 for maxi-HDD design. [1]

For planning, the chapter advises avoiding entry and exit elevation differences over 50 ft, locating buried structures within 10 ft of the path for mini-HDD and 25 ft for maxi-HDD, and allowing entry areas from about 100 × 150 ft for a 1,000 ft maxi crossing up to 200 × 300 ft for crossings of 3,000 ft or more, plus a pipe string lay-down area beyond the exit; it gives soil borings at 700 ft intervals (typ.) on long crossings and as few as three for crossings of 1,000 ft or less. Route bends increase pullback load through the capstan effect, so radii should be kept as large as possible. [1]

A utility (mini) rig shows the numbers behind the class. Vermeer's D24x40 S3 Navigator lists 124.6 kN (28,000 lb) of thrust and of pullback, spindle torque of 5,694 N·m (4,200 ft-lb) in low range, 4,745 N·m in medium and 2,712 N·m in high, a maximum spindle speed of 270 rpm, carriage speed up to 73.2 m/min, and a minimum bore diameter of 10.2 cm (4 in). Its drilling fluid pump delivers 189 L/min (50 gpm) at up to 72.4 bar (1,050 psi); a 93.2 kW (125 hp) John Deere 4045 engine drives it; it weighs 9,866 kg (10,092 kg with cab) and is 6.1 m long and 2.26 m wide for transport. Vermeer gives a sound power of 104 dB(A) and 83 dB(A) at the operator's ear, an automated rod loader, and Strike Alert and remote lockout as standard. [3]

Editorial calculation: 189 L/min of drilling fluid is about 11.4 m³ per hour (189 × 60 ÷ 1,000); ask how much fluid a reamed hole of your size and length needs per metre and whether the pump and a recycling unit can supply it at the pullback speed planned. [3]

Give the supplier the crossing length, depth and profile, product pipe material, diameter and wall, single pipe or bundle, ground conditions from borings (soil, gravel, cobbles, rock strength), groundwater, entry and exit site areas, required thrust, pullback and torque, mud system and recycling, drill pipe size and length, guidance system, transport and site access limits.

02

Plan reaming, drilling fluid and pullback

PPI describes reaming the pilot hole to a larger diameter, given as 1.2 to 1.5 times (typ.) the product pipe diameter depending on soil, stability, depth, drilling fluid and borehole pressure, which can be followed by a swab pass with the same reamer before pullback. Bentonite or polymer drilling fluid stabilises the hole, carries cuttings, reduces drilling torque and lubricates the pipe on pullback; loss of circulation can lock up and overstress the pipe. PPI gives pullback speeds of one to a few feet per minute (typ.), depending on size and local conditions, and too fast a pullback can cause hydrolock. [1]

PPI's back-ream guidance for mini-HDD recommends a final hole at least 50% larger than the pipe or bundle outside diameter, with no more than 12 in of clearance for pipes or bundles over 24 in and recommends pre-reaming in stages for pipes above about 4 in nominal size to reduce torque and thrust loads at the rig and the risk of voids, heave or fluid reaching the surface. [2]

Editorial calculation: for a 12 in pipe of 12.75 in outside diameter, a 1.2–1.5 times oversize gives a reamed hole of about 15.3 to 19.1 in; for a 30 in pipe, 1.5 times would be 45 in but the 12 in clearance limit caps it at about 42 in. Pipe sizes are assumed examples; the driller sets the final reamer size for the ground.

03

HDD rig ranges from Goodeng, Hanfa and SINOVO

Jiangsu Goodeng Heavy Machinery Technology Co., Ltd. lists G- and GS-series and electric horizontal directional drills; Hanfa Group lists fully automatic directional drilling rigs within a trenchless range; SINOVO Group lists horizontal directional drilling rigs alongside rotary and piling rigs. Ask each for thrust and pullback, torque, spindle speed, mud pump flow, drill pipe size and the class of crossing the rig is built for.

04

Compare a larger rig's pullback, fluid flow and drill-pipe bend radius

Ditch Witch's specification sheet for its JT100 horizontal directional drill shows how the figures scale on a larger rig. It lists pullback force of 445 kN (100,000 lb) and thrust force of 311 kN (70,000 lb), maximum spindle torque of 16,300 N·m (12,000 ft·lb) and spindle speed of 210 rpm, carriage thrust and pullback speeds of 46 m/min (150 fpm), and a drilling fluid system rated at 870 l/min (230 gpm) and 69 bar (1,000 psi). Power comes from a Cummins QSB6.7 diesel rated at 194 kW (260 hp) gross; operating mass is 21,668 kg and the entry angle 10–15°. [4]

Its drill pipe is 4.5 m long with a 102 mm tool-joint outside diameter and a minimum bend radius of 62.5 m (205 ft). The sheet states that the specifications are general and subject to change without notice, and that delivered equipment may differ with selected options. [4]

Editorial calculation: against the Vermeer D24x40 S3 above, the JT100's pullback is about 3.6 times higher (445 ÷ 124.6) and its fluid flow about 4.6 times (870 ÷ 189). PPI notes that route bends add pullback load and that radii should be kept as large as possible, so check that the planned bore path is no tighter than the drill pipe's minimum bend radius, and ask each supplier for these same fields. [3] [1]

05

Frame, rotary drive, mud system and guidance on an HDD rig

06

What to ask an HDD rig maker for, with Vermeer D24x40 S3 examples

The example values come from the Vermeer D24x40 S3 utility rig. Drill pipe size, track ground pressure, temperature range and IP rating are not given in the sources above and have to come from the maker.

07

Send the crossing, pipe and ground data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Crossing: [length; depth; profile; obstacles]
Pipe: [material; OD; wall; bundle]
Ground: [borings; soil; rock; groundwater]
Site: [entry and exit areas; lay-down]
Rig: [thrust; pullback; torque]
Fluid: [mud system; recycling]
Guidance: [system]

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