Booms, chassis rails and pins are the primary load path on excavators, cranes, trucks and loaders, and they fail by fatigue. A crack at a weld toe on a boom foot may be a few millimetres long and invisible under paint for months before it becomes critical. Magnetic particle testing finds surface cracks; ultrasonic and phased array testing size them, find subsurface defects in repair welds, and inspect pins in place without removal.
This page covers NDT of structural welds and pins as a targeted service, applied to any asset class. Machine-specific inspection scopes are described on the individual equipment pages.
Inspection checklist areas
- Surface preparation and visual
- Paint and scale removal at weld toes and pin bosses, visual inspection for cracks, deformation, prior repairs and paint cracking that indicates movement.
- Magnetic particle testing of welds
- Wet fluorescent or visible MT to AS 1171 at boom feet, cylinder mounts, box-section corner welds, frame rail splices, cross-members and pin bosses; indication length and orientation recorded.
- Ultrasonic testing of welds
- UT to AS 2207 or PAUT of full-penetration and repair welds to detect lack of fusion, porosity and subsurface cracking; indication location, depth and length sized.
- In-situ pin inspection
- Straight-beam and angle-beam UT from pin ends to detect cracking in the pin body and at bore transitions without pin removal; bore wear and ovality measurement where accessible.
- Thickness and section loss
- UT thickness survey of box sections, chassis rails and plates where corrosion or wear is suspected.
- Reporting against acceptance criteria
- Each indication assessed against AS/NZS 1554.5 for fatigue-loaded structures, AS/NZS 1554.1 for static structures or the OEM criteria, with a repair, monitor or engineering assessment recommendation.
Known failure modes
Weld toe fatigue cracking
Cracks initiating at the toe of fillet and butt welds where stress concentration is highest, growing under cyclic load.
Lack of fusion in repair welds
Subsurface planar defects in field repairs made without a qualified procedure, invisible to surface methods.
Pin fatigue fracture
Cracks at the shoulder or retaining groove of pins, often preceded by bore wear that changes the load distribution.
Box-section corner cracking
Cracks at longitudinal corner welds of boom and frame box sections under torsion and bending.
Crack growth from arc strikes and gouges
Cracks initiating at unrepaired arc strikes, gouges and hard-facing on primary structure.
Applicable standards and regulations
| Reference | Title | Relevance |
|---|---|---|
| AS 1171 | Non-destructive testing — Magnetic particle testing of ferromagnetic products, components and structures | Technique and sensitivity requirements for MT. |
| AS 2207 | Non-destructive testing — Ultrasonic testing of fusion welded joints in carbon and low alloy steel | Technique and acceptance basis for UT of welds. |
| AS/NZS 1554.5 | Structural steel welding — Welding of steel structures subject to high levels of fatigue loading | Weld quality and acceptance criteria for dynamically loaded structures such as booms and frames. |
| AS/NZS 1554.1 | Structural steel welding — Welding of steel structures | Acceptance criteria for statically loaded structures and general weld quality categories. |
| ISO 9712 / AINDT | Qualification and certification of NDT personnel | Technician certification requirements for each method. |
| AS 1418.1 and AS 2550.1 | Cranes — General requirements; Safe use | Context for NDT scope in crane periodic and major inspections. |
When to inspect
- Scheduled structural inspection intervals for high-hours plant
- Visible cracking, paint disturbance, oil weeping from a weld or unusual noise
- Verification of a repair weld before return to service
- Crane and EWP ten-year major inspections
- Pre-purchase assessment of second-hand plant with unknown repair history
Frequently asked questions
Why is paint removed before MT?
Magnetic particle testing needs the particles to reach the surface at the crack. Thick paint, mud and scale reduce sensitivity or hide indications entirely, so weld toes are cleaned to bare metal at each test location and recoated afterwards.
Can pins be inspected without removing them?
Usually. Ultrasonic testing from an accessible pin end can detect cracks along the pin body and at shoulder transitions. Where both ends are inaccessible or the geometry is unsuitable, pin removal is recommended and stated in the report.
What happens when an indication is found?
It is sized, photographed and located on a sketch, then compared with the acceptance criteria of the governing standard or OEM. Rejectable indications are reported with a recommendation: repair to a qualified procedure and re-test, monitor at a defined interval, or refer for engineering assessment.
Is phased array better than conventional UT?
Phased array gives better coverage and a permanent electronic record, and is preferred for critical full-penetration welds and complex geometry. Conventional UT remains adequate for thickness surveys and many pin inspections. The method is selected for the joint, not by default.