A cracked weld is the defect that keeps engineers awake, because the joint that holds a boom together is only as good as the metal fused across it. On an elevating work platform the welds along boom sections, at lugs and around the turntable carry loads that reverse and cycle thousands of times, and a hairline crack in the wrong place can grow silently until the day it lets go. This guide explains where weld cracks come from, what an operator might notice, why a visual check is never the final word, and what a sound repair actually involves.
Symptoms you might actually see
Most weld cracks give little away in their early life, which is exactly what makes them dangerous. By the time one is visible to the naked eye it has often been growing for a long time under paint, grease or a factory coating.
The signs worth treating as a stop-work trigger include:
- A fine dark line tracking along the toe of a weld, sometimes weeping rust from beneath the paint where moisture has entered the crack.
- Flaking, cracked or lifted paint following the run of a weld, which frequently marks movement in the metal underneath.
- A weld or joint that has begun to feel or sound different — a knock, a click or a small amount of play that was not there before.
- Rust staining running from a joint on an otherwise clean machine, a classic tell of a crack drawing water in and out under load.
What causes welds to crack
Weld cracks on an EWP are rarely a single event. They are usually the end result of stress meeting a weakness in the joint over time.
- Fatigue from repeated load cycles — the boom lifting, slewing and lowering puts the same welds through millions of small stress reversals across a working life.
- Overloading or shock loading, such as dropping the platform onto a structure or working the machine beyond its rated capacity.
- Original weld quality — porosity, lack of fusion or undercut left from manufacture or a past repair becomes the point a fatigue crack starts.
- Corrosion at the weld toe, which both removes metal and creates the sharp notch that concentrates stress.
- Poorly executed field repairs that introduce residual stress or a mismatch in weld metal.
How an inspection confirms a crack
A visual walk-around is where a crack is first suspected, but it is not where it is confirmed. Because the most dangerous cracks are sub-surface or hidden under coatings, a competent inspector relies on non-destructive testing to turn suspicion into fact.
On steel structure, magnetic particle testing is the usual method for surface and near-surface cracks in critical welds, while ultrasonic testing can probe deeper into thick sections. The weld is normally cleaned back to bare metal first, because paint and grease will mask an indication. This kind of testing is standard practice within a major inspection — the deep check that AS 2550.10 sets at the 5-year mark for some equipment classes and the 10-year mark for others — and it is also how a suspect crack is investigated at any point in between.
How a weld crack is repaired
Repairing a cracked structural weld is engineering work, not a quick tack-up. The crack must be fully removed, not just welded over, or it will simply grow again beneath the new bead.
- Take the machine out of service and confirm the extent of the crack by testing, so the full length and depth are known before any grinding starts.
- Gouge or grind the crack out completely back to sound parent metal, verifying with a follow-up test that no defect remains.
- Re-weld to a documented procedure using the correct filler and technique for the parent material and joint.
- Re-test the completed weld with non-destructive testing to prove the repair is sound.
- Recoat the area and record the repair, its testing results and the engineering sign-off in the machine's logbook.
Preventing the next crack
You cannot stop a boom being cycled, but you can stop small problems becoming cracked welds. Keeping structure clean and painted denies corrosion the notch it needs to start a crack, and operating within the rated capacity avoids the overloads that seed fatigue.
Prompt, competent repair of any structural damage matters just as much — a botched field weld is a future crack waiting to happen. If you suspect a cracked weld on a machine, stop using it and have a competent person assess it; you can reach EWP Australia on 0416 689 689 to arrange testing rather than risk running a compromised structure.
This guide is general information prepared by EWP Australia and is grounded in publicly available Australian Standards and Safe Work Australia material. It is not a substitute for the current published edition of the relevant standard or for site-specific engineering advice. Always work from the current standard and consult a competent person for your specific equipment and application.