The chassis is the foundation everything else stands on. It carries the slew bearing and the entire upper structure, it houses the mountings for outriggers or stabilisers, and it is the base that keeps the machine stable while a person works from the platform above. Damage to the chassis is therefore never local: a crack, a bent member or a distorted outrigger mount changes how the whole machine carries load and how reliably it stays upright. This guide covers how chassis damage happens, the symptoms that reveal it, why it is treated as a structural matter and how it is put right.
Symptoms of chassis damage
Damage to the base structure tends to show as:
- Cracks in the chassis members, welds or around high-stress points such as the slew mounting and outrigger boxes.
- Visible bending, buckling or distortion of a chassis rail or member, often from an impact or from being worked overloaded.
- A machine that no longer sits or sets up level, or that feels less stable than it should when the boom is out.
- Distorted or cracked outrigger and stabiliser mounts, or pads that no longer deploy squarely.
- Corrosion thinning chassis members, particularly on machines with a coastal or washdown history.
What causes chassis damage
- Impact — collisions, being struck on site, or heavy contact during transport and loading.
- Overloading and misuse, which put loads through the chassis and its mounts beyond what they were designed to carry.
- Setting up on inadequate ground, so outrigger loads are not properly supported and the mounts and members are overstressed.
- Fatigue at the high-stress connections around the slew and outrigger mountings after years of load cycles.
- Corrosion that thins members and seeds cracks, especially inside box sections where water collects.
How inspectors assess it
Chassis assessment starts with a careful visual inspection for cracks, distortion and corrosion, with particular focus on the high-stress connections — the slew bearing mounting and the outrigger and stabiliser boxes — where load concentrates. Distortion is checked against the machine sitting and setting up true, and suspect welds and members are crack tested rather than passed on appearance.
Because the chassis and its mountings are critical to stability and structural integrity, they are examined thoroughly during the major inspection, the AS 2550.10 check that some machine classes reach at 5 years and others at 10 years. That is when hidden corrosion and fatigue cracking around the mounts are most likely to be found.
How chassis damage is repaired
Chassis repair is engineered structural work. The base of the machine determines its stability, so a repair has to restore both the strength and the geometry — a chassis that is strong but no longer true is still a defect.
- Take the machine out of service and establish the full extent of the damage by inspection and crack testing.
- Where a member is cracked, remove the crack entirely and re-weld to a documented procedure with the correct materials.
- Where a member is bent or distorted, straighten or replace it so the chassis geometry is restored, verified against specification.
- Repair or renew damaged outrigger and slew mountings so loads are carried and reactions are supported as designed.
- Re-test the repaired welds, recoat, function test set-up and levelling, and record the engineering sign-off in the logbook.
Protecting the chassis
Much chassis damage is avoidable. Operating within capacity, setting up outriggers on adequate ground with the correct packing, and careful handling during transport and loading prevent the impacts and overloads that bend and crack the base structure.
Keeping the chassis clean and coated — and letting water drain out of box sections rather than sit in them — heads off the corrosion that quietly weakens members. Any crack or distortion in the chassis should stop the machine and be referred to a competent person for an engineered assessment.
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.