After a crane boom weld repair, the most commonly used non-destructive testing (NDT) methods are magnetic particle inspection (MPI), ultrasonic testing (UT), and radiographic testing (RT). Each method targets different flaw types and weld geometries, and they are often used in combination to ensure a complete structural assessment before the crane returns to service.
The choice of NDT method depends on the steel grade, weld geometry, and the specific defects that are most likely given the repair type. For high-grade steels up to 1100 N/mm², thorough weld inspection is not optional — it is a prerequisite for maintaining CE certification and operator safety. The sections below break down how each method works, what it detects, and when it applies.
Which NDT methods are most commonly used after a crane boom weld repair?
The three NDT methods most commonly applied after a crane boom weld repair are magnetic particle inspection (MPI), ultrasonic testing (UT), and radiographic testing (RT). MPI is almost universally applied as a baseline check on all new welds, while UT and RT are brought in for deeper subsurface analysis or when specific weld configurations demand it.
Each method has a defined role in the inspection sequence:
- Magnetic particle inspection (MPI): Detects surface and near-surface discontinuities such as cracks, lack of fusion, and inclusions. Fast to apply and highly sensitive to surface-breaking defects.
- Ultrasonic testing (UT): Uses high-frequency sound waves to detect internal flaws through the full thickness of the weld and surrounding heat-affected zone.
- Radiographic testing (RT): Uses X-ray or gamma-ray imaging to produce a visual record of internal weld structure, particularly useful for detecting porosity and inclusions in complex joint geometries.
In practice, a rigorous boom repair protocol applies MPI to 100% of new welds as standard, then supplements this with UT or RT based on the weld type, steel grade, and any risk factors identified during visual inspection. The combination approach ensures that neither surface nor subsurface defects are missed before the crane returns to load-bearing service.
How does ultrasonic testing detect flaws in a crane boom weld?
Ultrasonic testing detects flaws in a crane boom weld by transmitting high-frequency sound waves into the material and measuring how those waves reflect back. When a sound wave encounters a discontinuity — such as a crack, lack of fusion, or internal void — it reflects an echo back to the transducer. The time and amplitude of that echo reveal the location, depth, and approximate size of the flaw.
For crane boom welds, UT is particularly valuable because it can inspect the full cross-section of thick-walled steel without requiring access to both sides of the joint. The technician moves a probe across the weld surface in a defined pattern, and the resulting data is interpreted against acceptance criteria set out in applicable welding standards such as ISO 5817 or EN 1090.
One important consideration for high-grade crane steels is that the heat-affected zone (HAZ) surrounding the weld is often just as critical as the weld metal itself. Ultrasonic testing covers this zone as part of the standard scan pattern, making it effective for identifying hydrogen-induced cracking — a failure mode that can develop in the HAZ of 960 and 1100 grade steels after welding if preheat or post-weld procedures were not correctly applied.
Phased array ultrasonic testing (PAUT) is an advanced variant that uses multiple transducer elements to steer and focus the sound beam electronically. This gives inspectors a more detailed cross-sectional image of the weld and is increasingly used on complex crane boom geometries where conventional single-probe UT has coverage limitations.
What does magnetic particle testing reveal that other methods miss?
Magnetic particle inspection (MPI) is uniquely sensitive to surface-breaking and near-surface cracks — the category of defect most likely to initiate fatigue failure under cyclic loading. While ultrasonic and radiographic methods excel at subsurface detection, they can miss tight surface cracks that MPI reliably identifies through the visible clustering of magnetic particles at the defect location.
The process works by magnetising the weld area and applying fine ferromagnetic particles — either dry or suspended in a liquid carrier. Where a crack or discontinuity breaks or approaches the surface, it creates a leakage field that attracts and holds the particles, forming a visible indication directly over the defect. Under UV light with fluorescent particles, even very fine cracks become clearly visible.
For crane boom weld repairs, this matters because surface cracks are the most dangerous starting point for fatigue fractures under repeated loading cycles. A crack that is invisible to the naked eye and too tight to reflect a strong ultrasonic echo can still be clearly identified by MPI. This is why a 100% MPI check on all new welds is standard practice in quality-controlled boom repair operations — it acts as a final confirmation that no surface discontinuities remain before the boom is returned to service.
MPI does have one inherent limitation: it only works on ferromagnetic materials. For austenitic stainless steel or aluminium components, dye penetrant testing (DPT) serves a similar surface-crack detection function. However, the structural steels used in crane booms — including high-grade 960 and 1100 N/mm² variants — are ferromagnetic, making MPI the method of choice.
When is radiographic testing used on crane boom weld repairs?
Radiographic testing is used on crane boom weld repairs when a permanent visual record of internal weld quality is required, when the weld geometry makes ultrasonic scanning difficult, or when a Notified Body or client specification explicitly calls for it as part of CE certification documentation. RT is not applied to every repair as standard — it is typically brought in for specific welds where its imaging capability adds something that UT alone cannot provide.
The method involves directing X-ray or gamma radiation through the weld onto a film or digital detector on the opposite side. Variations in material density — caused by porosity, slag inclusions, or incomplete penetration — appear as darker areas on the resulting radiograph. The image becomes a traceable quality record that can be reviewed independently and archived alongside the repair documentation.
RT is particularly well-suited to detecting volumetric defects such as gas porosity and slag inclusions in fillet and butt welds. It is less effective than UT for detecting planar defects like cracks oriented parallel to the radiation beam, which is one reason the two methods complement each other rather than substitute for one another.
In a regulated repair environment, the decision to include RT is typically made during the preparation of the Welding Procedure Specification (WPS) and Repair Plan, based on the weld joint type, material thickness, and the applicable inspection standard. When a third-party Notified Body is involved in validating the repair, they may specify RT as part of their independent verification scope.
How do NDT results affect CE certification after a crane repair?
NDT results are a direct input into the CE certification process after a crane boom repair. For the CE marking to remain valid following a structural repair, the operator and repair provider must demonstrate that the repaired boom meets the original design specification — and documented NDT results are the primary technical evidence used to support that claim.
Under the Machinery Directive and applicable harmonised standards, a repaired crane boom that returns to service must be shown to be structurally equivalent to its pre-damage condition. NDT reports — covering MPI, UT, or RT as applicable — form part of the technical file that accompanies this demonstration. If a Notified Body is involved, they will review the NDT findings alongside the WPS, repair plan, and material certificates before issuing or reconfirming the CE documentation.
Critically, a failed NDT result does not automatically invalidate the repair — it identifies a specific location that requires remediation before re-inspection. The process is iterative: repair, inspect, document, and repeat if necessary until all welds meet the acceptance criteria. Only once all NDT results fall within the required acceptance levels can the CE certification process proceed.
For operators, this means that the quality of the NDT process directly determines whether the crane can legally return to work. Inadequate inspection coverage or poorly documented results can delay certification, create liability exposure, and in some jurisdictions, constitute a regulatory breach if the crane is operated without valid certification.
Who is qualified to carry out NDT on a crane boom weld repair?
NDT on a crane boom weld repair must be carried out by personnel certified to a recognised qualification scheme — in Europe, this is typically PCN (Personnel Certification in Non-Destructive Testing) or EN ISO 9712, both of which define three certification levels based on the technician’s training, examination results, and practical experience. Level 2 is the standard operating qualification for conducting and interpreting inspections; Level 3 is required for setting procedures and approving results.
The specific method determines the required certification. An MPI Level 2 technician is qualified to perform and interpret magnetic particle inspections; a UT Level 2 holds an equivalent qualification for ultrasonic work. For radiographic testing, additional radiation safety licensing is required under national regulations, and the work environment must meet legal requirements for controlled radiation zones.
For repairs involving high-grade steels such as 960 or 1100 N/mm², the qualifications of the NDT personnel are often scrutinised more closely, because the acceptance criteria for these materials are tighter and the consequences of a missed defect are more severe. In practice, this means that the NDT provider should have demonstrable experience with structural crane steels specifically — not just general industrial weld inspection.
When a third-party Notified Body is required as part of the CE certification process, they will typically deploy their own qualified NDT personnel or review and accept results produced by a certified independent inspection body. In either case, the inspection records must be traceable to named, certified individuals — anonymous inspection reports are not acceptable under most quality management frameworks.
How Rusch Cranes approaches NDT in crane boom weld repairs
Rusch Cranes integrates NDT directly into every crane boom repair rather than treating it as an afterthought. Their process begins before the first weld is laid — with material strength verification, a formal Welding Procedure Specification, and a structured Repair Plan — and concludes with a documented inspection sequence that supports CE certification.
- 100% visual inspection on all new welds as a baseline quality check
- 100% MPI on all new welds to confirm the absence of surface and near-surface cracks
- Third-party UT or RT conducted by a Notified Body when the repair scope, steel grade, or client specification requires it
- Full photographic documentation of every repair, supporting traceability and the CE technical file
- CE certification remains valid after repair, backed by a 1-year guarantee on all work performed
Rusch is one of only three companies in Europe qualified to repair telescopic booms made from 960 and 1100 grade steel, and their worldwide welding services mean that this level of inspection rigour is available whether the boom is brought to their workshop in the Netherlands or the repair team is deployed to your site internationally. If you need a crane boom repair with full NDT documentation and CE certification support, contact Rusch Cranes to discuss your requirements.
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