Mobile Crane Boom Inspection — Pre-Purchase Checklist for UAE Buyers
Boom condition is the single biggest determinant of a used mobile crane's long-term value. Engine and hydraulics can be repaired; a structurally compromised boom usually can't. Here is the field inspection checklist we run on every unit before we list it for sale, written for buyers who want to do their own pre-purchase walk-through.
The pre-inspection setup
Park the unit on level ground. Cab off, ignition off, hydraulic pressure released. Boom retracted but extended on the outriggers if possible (raises the boom off rest pads for visibility). Bring a torch, a pair of latex gloves, a 150µm feeler gauge, and a magnet on a stick if you can. Plan 60–90 minutes for a full walk-around.
1. Boom external structure
Walk the length of each boom section. You're looking for:
- Welding repair scars — weld beads not on the original factory pattern. Factory welds are clean, repair welds tend to be lumpy or grind-marked. Photograph any you find. Repair scars on the upper boom section near the head sheaves are the worst sign — that's where overload bends happen.
- Dents on the side or top surfaces. Dents from impact (e.g. swung into a wall) are usually safe if shallow. Dents from twist or compression are not — they indicate the boom has been overloaded.
- Surface cracks — particularly at boom-pivot pin areas, lugs, and around the boom-base connection. A surface crack here is a major red flag.
- Paint condition — original factory paint with normal wear is fine. Fresh repaint is suspicious unless documented. Repainted boom sections often hide repair scars.
2. Wear pads — the easiest tell
Telescopic boom sections slide on plastic / polymer wear pads. As they wear, the boom sections start metal-on-metal contact, which scores the inside surfaces and is expensive to fix.
Look between the boom sections at the joint. New wear pads are typically 12–15mm thick. Pads worn to under 5mm = end of life. If you can see metal-on-metal scratching on the boom sections, the wear pads are gone and the boom has been operating with damage. Walk away from this unit unless the price reflects a full boom rebuild.
3. Slew bearing — the expensive failure
The slew bearing is the ring under the cab that lets the upper structure rotate. It's massive, sealed, and not user-serviceable. When it fails, replacement is AED 150,000–280,000 on a 50–100T crane.
Inspection method:
- With the boom fully extended forward, slowly rotate the upper structure 360 degrees and listen.
- Sound: clicking = inner-race damage; grinding = ball / roller damage; squealing = grease starvation.
- With the unit at rest, push hard on the boom tip laterally and watch the gap between upper and lower structure on the back side. Vertical play of more than 1–2mm = bearing is starting to fail.
- Check the slew-bearing grease points. Fresh grease present = recent service. Dry zerks = neglected service.
4. Hydraulic seals — cylinder-by-cylinder
Run the boom up, down, in, out. Watch each cylinder rod. A small wet-film of oil on the rod is normal — it's how the seal lubricates itself. Drips of oil running down the rod onto the boom = seal failing. Reseal cost is AED 8,000–25,000 per cylinder depending on size.
Check the boom for an oil-streaked underside. That's where boom-cylinder seal leaks land first.
5. Boom angle indicator & LMI
The Load Moment Indicator must be functional and uncalibrated. With the boom at known angles, the cab display should read those angles. Disconnect or "fault" indication on the LMI = the unit has been operating without the safety system. Will not pass UAE EIAC inspection — means project mobilisation is impossible.
6. Hook block & main winch
Easier checks. The hook itself shouldn't be deformed; the throat opening should match factory dimensions (gauge it if you have a hook gauge). The main winch wire rope should not have broken strands or kinks. End-fittings should not be loose.
Quick-summary inspection score
| Item | Pass | Conditional | Walk away |
|---|---|---|---|
| External structure | Original paint, no welds | Documented repair welds | Undocumented repair welds, fresh paint |
| Wear pads | >8mm visible | 5–8mm | <5mm or metal-on-metal |
| Slew bearing | Smooth rotation, no play | Slight clicking, <1mm play | Grinding, >2mm play |
| Cylinder seals | Wet-film only | Slow drip on one | Active leak on multiple |
| LMI | Working, calibrated | Working, needs calibration | Disconnected / fault |
| Hook & rope | OEM hook, clean rope | Aftermarket hook, minor rope | Hook deformed, broken strands |
Where we fit
We run this checklist on every unit before listing. Photos, video, and a written inspection note ship with each unit on our Sajaa yard. For sourcing, we run pre-shipment inspection in China through TUV / Bureau Veritas before the unit is loaded.
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