Fatigue is the damage a machine accumulates simply by being used. Every lift, slew and lower puts the structure through a stress cycle, and metal that survives a single heavy load without complaint can still fail after enough repetitions at loads well below its limit. On an EWP this matters because the whole point of the machine is to put a person in the air, so the structure that keeps them there is exactly the part that quietly ages with every shift. This article looks at how fatigue behaves, where it appears first, and why an ageing machine deserves closer scrutiny than a new one.
How fatigue shows itself
Fatigue rarely announces itself. It works away invisibly at the material until a crack initiates, and only then does it produce symptoms an operator can notice — by which point the damage is already advanced.
On an ageing machine, watch for:
- Hairline cracks appearing at the same stress-raising points where the design concentrates load, such as weld toes, holes and section changes.
- Small, repeatable amounts of play developing at joints and connections that were previously tight.
- Localised paint distress that keeps returning at one spot even after touch-up, hinting at metal moving beneath it.
- A machine that has simply done a lot of duty cycles — a hire unit or a production machine will have aged faster than its calendar age suggests.
What drives fatigue damage
Fatigue is fundamentally about the number and severity of stress cycles, not the age printed on a plate. Two machines built the same year can be in very different condition depending on how hard they have worked.
- The sheer count of load cycles — how many times the machine has been raised, slewed and lowered under working loads.
- The magnitude of each cycle, so machines routinely worked near capacity fatigue faster than lightly loaded ones.
- Shock and vibration, including travel over rough ground and abrupt control inputs that spike the stress in a cycle.
- Stress concentrators built into or introduced onto the structure — sharp corners, weld defects, corrosion pits and drilled holes.
How inspectors track fatigue
Because fatigue is cumulative and invisible until late, the inspection regime is designed to catch it before it becomes a crack that matters. Routine and periodic inspections look for the early signs, while the deeper checks go after what the eye cannot see.
The major inspection is the key defence. AS 2550.10 sets that deep check at 5 years for some machine classes and at 10 years for others, and it involves disassembly and non-destructive testing of critical welds and members precisely so that fatigue cracking can be found and measured before it propagates. This is also why an older machine, having accumulated more cycles, warrants enhanced scrutiny as it approaches the end of its service life.
Repair, and knowing when not to
Where fatigue has produced a discrete crack in a repairable location, the crack is removed, the joint re-welded to procedure and the repair re-tested — the same disciplined process any structural weld demands. That restores the local area.
What repair cannot do is reset the fatigue clock on the rest of the structure. Widespread fatigue across an old, hard-worked machine is a different problem: at some point the honest engineering answer is that the structure has reached the end of its useful life and continued patching is neither safe nor economic. This is where the findings of a major inspection feed directly into a keep-versus-replace decision.
Slowing fatigue down
You cannot eliminate fatigue, but good practice extends the life you get:
- Operate within the rated capacity and avoid the shock loads that put oversized cycles into the structure.
- Drive smoothly and keep travel over rough ground gentle to reduce vibration-driven cycling.
- Keep the structure clean and coated so corrosion never creates the notch a fatigue crack needs to start.
- Address any structural damage or repair promptly and competently, so nothing left in the metal becomes a crack initiation site.
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.