A welding procedure specification (WPS) is a formal, written document that defines the exact parameters a welder must follow to produce a weld that meets the required mechanical and safety standards for a specific material and application. For crane boom repair, a WPS is not optional documentation — it is the technical foundation that makes a structurally sound and certifiable repair possible. The sections below unpack the key questions operators and procurement managers ask when evaluating a repair contractor’s welding credentials.
What does a welding procedure specification actually contain?
A welding procedure specification is a structured technical document that prescribes every variable involved in producing a qualified weld. It covers the base material type and grade, the welding process, filler material, joint geometry, preheat and interpass temperature requirements, heat input limits, and post-weld treatment. Together, these variables define a repeatable, verifiable welding process.
The document is built around two categories of variables. Essential variables are those where any change would alter the mechanical properties of the weld — such as a switch in base metal grade or filler material. Non-essential variables, like electrode diameter within an approved range, can be adjusted without requiring requalification. A well-constructed WPS clearly distinguishes between the two.
For crane boom repair, the WPS will typically include:
- The exact steel grade being welded, including its yield strength in N/mm²
- Joint preparation requirements, including bevel angle and root gap tolerances
- Preheat temperature and the method used to achieve and verify it
- Maximum interpass temperature to prevent heat-affected zone degradation
- Approved filler materials and their classification
- Welding position and travel speed parameters
- Post-weld heat treatment, where required
- Required non-destructive testing (NDT) methods to verify the completed weld
A repair contractor who cannot produce a WPS for the specific steel grade of your crane boom is, in practical terms, working without a qualified process — regardless of how experienced their welders may be.
Why can’t standard welding procedures be used on high-grade crane boom steel?
Standard welding procedures are developed and qualified for common structural steels, typically in the S235 to S355 range. High-grade crane boom steels — particularly those in the 960 and 1100 N/mm² classes — behave fundamentally differently under heat, and applying a standard procedure to them will degrade their mechanical properties and introduce failure risk.
The core issue is heat sensitivity. High-strength steels achieve their properties through precise metallurgical processes during manufacturing, including controlled rolling and quenching. When heat is applied during welding, the steel in and around the heat-affected zone undergoes microstructural changes. If preheat temperatures are too low, hydrogen-induced cracking becomes a serious risk. If interpass temperatures are too high, the steel loses the tensile strength it was designed to deliver.
The filler material also requires specific matching. A filler rated for mild steel will not deliver the mechanical properties needed in a weld on 1100 N/mm² boom steel. Using an undermatched filler creates a weak point directly in the repair zone — exactly where stress concentrations are highest during crane operation.
This is why crane boom welding on high-grade steel requires a WPS that has been specifically developed and qualified for that material class. The procedure must account for the steel’s unique thermal behavior, its susceptibility to hydrogen embrittlement, and the mechanical performance the finished weld must deliver under load.
How is a welding procedure specification qualified and approved?
A welding procedure specification is qualified by executing a series of test welds under the exact conditions defined in the document, then subjecting those welds to destructive and non-destructive testing to prove the procedure produces joints with the required mechanical properties. This process produces a Procedure Qualification Record (PQR), which provides the documented evidence that the WPS is valid.
For high-grade steels used in crane booms, the qualification process typically follows international standards such as ISO 15614-1. The test welds must pass tensile testing, bend testing, impact testing at specified temperatures, and often hardness testing across the weld, heat-affected zone, and parent material. Only when all test results fall within the required limits is the WPS considered qualified.
Approval may also involve a third-party Notified Body or classification society, depending on the application and the certification framework under which the crane operates. For mobile crane boom repairs, the involvement of a Notified Body provides independent verification that the procedure meets the standards required for CE compliance.
A qualified WPS is not a permanent document that covers all future work. If the repair contractor changes a material, switches to a different welding process, or works on a steel grade outside the qualified range, a new qualification cycle is required.
What happens to CE certification after a crane boom is welded?
When a crane boom repair is carried out using a properly qualified welding procedure specification, and the repair is completed with full non-destructive testing and documented quality control, the CE certification of the crane remains valid. The repair does not automatically void the CE marking, provided the work meets the technical and documentation requirements that underpin the original certification.
The critical factors that preserve CE validity are:
- A qualified WPS specific to the steel grade — demonstrating the welding process was controlled and appropriate
- Certified welders — operators must hold current welder qualification certificates aligned with the procedure used
- Full NDT of all new welds — typically 100% visual inspection and magnetic particle inspection (MPI), with ultrasonic or radiographic testing where required
- A documented repair plan — outlining the scope, method, and material specifications for the repair
- Involvement of a Notified Body — for repairs on safety-critical components, third-party verification provides the documented evidence required by certification authorities
Where these conditions are not met — for example, where a repair is carried out without a qualified WPS or without adequate NDT — the CE certification is compromised, and the crane operator carries significant legal and safety exposure.
How does a WPS affect the cost and timeline of boom repair?
A qualified welding procedure specification adds preparation time and cost to a boom repair, but it substantially reduces the total cost and timeline compared to the alternatives. The WPS-driven preparation process — material strength verification, joint preparation, controlled preheat, and post-weld testing — prevents the need for rework and ensures the repair does not need to be repeated.
The cost comparison that matters most for B2B operators is not WPS repair versus no-WPS repair. It is WPS-qualified repair versus sourcing a new boom section from the original manufacturer. New OEM boom sections for high-grade mobile cranes carry significant lead times — often measured in months rather than weeks — and procurement costs that far exceed the cost of a qualified repair. A repair carried out under a proper WPS restores the boom to its original mechanical value, including in high-tension areas, at a fraction of the replacement cost.
The timeline is also a function of preparation quality. Contractors who invest in a proper WPS and repair plan before work begins encounter fewer unexpected complications during the repair itself. The controlled process reduces the likelihood of post-weld defects that would require additional NDT cycles or remedial work, both of which extend downtime.
Who should verify that a repair contractor holds an approved WPS?
The responsibility for verifying that a repair contractor holds a qualified welding procedure specification lies with the crane owner or operator, their HSE officer, and the procurement lead responsible for selecting the repair partner. This verification should happen before any repair work begins, not after.
The verification process should include:
- Requesting the WPS document itself, along with the supporting Procedure Qualification Record (PQR)
- Confirming the qualified steel grade range covers the specific boom material being repaired
- Checking that the welding process, filler material, and joint type in the WPS match the planned repair
- Verifying that the welders assigned to the repair hold current qualification certificates aligned with the WPS
- Confirming the contractor’s NDT capability and whether third-party Notified Body involvement is included in the scope
For operators working with cranes built from 960 or 1100 N/mm² steel, this verification step is especially important. Very few repair contractors in Europe hold qualified procedures for these steel grades, and the consequences of an unqualified repair on ultra-high-strength material are severe — both mechanically and legally.
Insurers and certification bodies may also request evidence of a qualified WPS when a repaired crane undergoes re-inspection. Operators who cannot produce this documentation after a repair face potential certification issues that are far more disruptive and costly than the original damage.
How Rusch Cranes approaches WPS-qualified boom repair
Rusch Cranes applies a structured, WPS-driven repair process to every crane boom that enters their workshop or is repaired on-site. As one of only three companies in Europe qualified to repair telescopic booms made from 960 and 1100 N/mm² steel, their approach directly addresses the technical and certification challenges outlined above.
Every repair begins with material strength verification and the preparation of a dedicated Welding Procedure Specification and Repair Plan before any welding takes place. The full repair process includes:
- Precise measurement and photographic documentation of all damage prior to work
- Controlled preheat and interpass temperature management throughout welding
- 100% visual inspection and 100% magnetic particle inspection (MPI) on all new welds
- Third-party Notified Body involvement for ultrasonic or X-ray testing where required
- CE certification validity preserved after completion of the repair
- A 1-year guarantee on all performed repairs
Rusch repairs both telescopic and lattice booms, with lattice boom repairs carried out at the client’s location anywhere in the world or at their workshop in the Netherlands. Onshore inspection services are offered within the Netherlands. If your crane boom has sustained damage or you need to verify whether a repair is viable before committing to replacement costs, contact Rusch Cranes directly to discuss the scope and receive a qualified assessment.
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