How to Buy a Used Foundation Drilling Rig

Start with the pile, not the rig

Work backwards from the piles you actually build. The diameter and depth you need, in the ground you typically work in, set the torque and crowd force required — not the other way round. A rig comfortably rated for 1,200 mm piles in sand may stall at 900 mm in stiff clay or weathered rock.

Ask what the rig has been drilling and to what depth. A machine that has spent its life on shallow CFA work has been loaded very differently from one doing deep kelly bores with rock augers, even if the hour meters match.

Site constraints matter as much as capacity. Headroom, working radius, ground bearing pressure and transport width regularly disqualify a rig that is otherwise ideal. Establish the transport dimensions and weight, in the configuration you would actually move it in, before anything else.

Torque, depth and crowd are a set

Rotary torque is quoted as a maximum, usually at low speed. What matters in practice is the torque available at the speed you drill at, and whether the rig can sustain it without the hydraulics overheating. Ask for the torque curve if the seller has it.

Maximum drilling depth is quoted with a specific kelly bar. Change the bar and the figure changes with it, so a depth rating is meaningless without knowing which kelly it assumes and whether that kelly is included in the sale.

Crowd force is the one buyers most often skip. It is what pushes the tool into the ground, and an underpowered crowd shows up as slow progress in exactly the conditions where you needed the rig to earn its keep.

The kelly bar is half the machine

Kelly bars wear, and replacing one is a serious cost — often a substantial fraction of a used rig’s price. Establish the type (friction or interlocking), the number of sections, the outer section diameter and the total length, and confirm each of those against what the rig is rated for.

Interlocking bars transmit crowd force positively down the whole string and are the norm for deep or hard drilling; friction bars are simpler and lighter but rely on the weight of the string and the tool. A rig sold with the wrong type for your work is a rig you will be re-equipping.

Inspect the bar itself for twist, for wear on the drive keys and stops, and for weld repairs. Ask when it was last crack-tested and whether a certificate exists.

Mast, undercarriage and hours

The mast carries every load the rig generates. Look along it for straightness, check the pivot pins and the parallelogram or slew linkage for play, and look closely at any repaired welds — a repaired mast is not automatically a problem, but it is always a question.

Undercarriage is the most predictable large cost on a used rig and the easiest to assess. Measure or ask for the percentage remaining on chains, sprockets, idlers and rollers. A machine at 20% undercarriage is carrying a bill you should be subtracting from the asking price, not discovering later.

Hours tell you less than buyers expect. A rig with 8,000 hours of steady CFA work in sand may be in better condition than one with 4,000 hours of rock drilling. Use hours to sense-check the seller’s account of the machine’s life rather than as a score on its own.

Engine, hydraulics and emissions compliance

Confirm the engine make, model and emissions tier, and check that tier against where the rig will work. Emissions rules can prevent an otherwise sound machine from being used or registered in some jurisdictions, and this is discovered far too late far too often.

Run the rig up to working temperature if you can. Watch for hydraulic oil temperature climbing under sustained load, listen to the rotary head under torque, and look for leaks at the rotary drive, the crowd cylinder and the winch motors.

Ask for recent oil sample analyses. A seller who has been sampling the hydraulics and the rotary gearbox usually has other habits worth inheriting; a seller who has never sampled is asking you to take the drivetrain on trust.

Paperwork, tooling and what is actually included

Establish in writing what comes with the rig. Augers, buckets, cleaning buckets, casing drivers and the kelly bar are routinely assumed by the buyer and excluded by the seller, and the gap between the two is expensive.

Ask for the service history, the original manuals, the CE or equivalent conformity documentation, and any inspection or thorough-examination certificates. For a cross-border purchase, confirm who is responsible for export documentation and what the rig is being declared as.

Finally, confirm ownership and that the machine is free of finance. On a machine at this value it is worth the cost of a formal check.

Inspection checklist

• Rotary torque and crowd force confirmed against your typical pile diameter, depth and ground
• Kelly bar type, sections, diameter and length confirmed — and confirmed as included
• Mast checked for straightness, pin wear and repaired welds
• Undercarriage percentage remaining recorded and priced in
• Engine emissions tier checked against every jurisdiction the rig will work in
• Hydraulic and gearbox oil samples reviewed, or taken before purchase
• Rig run under load to working temperature
• Tooling, service history and conformity documentation listed in writing
• Ownership and outstanding finance verified

Frequently asked questions