What is the difference between a prequalified weld and a procedure-qualified weld on a crane boom?

by | Sep 13, 2026 | Crane Repair

Welder in protective helmet joining a crane boom section, two parallel weld seams glowing amber on high-strength steel in an industrial workshop.

If you work with cranes professionally, you have probably come across the terms prequalified weld and procedure-qualified weld at some point. They sound similar, and both relate to welding procedure specifications, but they mean very different things in practice. Understanding the distinction matters a great deal when it comes to crane boom repair, especially on high-strength steel structures where the margin for error is essentially zero.

This article breaks down what each qualification route involves, how they compare, and why the choice between them directly affects the safety, compliance, and long-term value of your crane asset.

How welding standards are set for crane booms

Crane booms are not ordinary steel structures. They operate under dynamic loads, bending stresses, and fatigue cycles that place extreme demands on every weld joint. Because of this, the welding carried out on a crane boom must conform to recognized standards that govern how welds are designed, executed, and verified.

In Europe, the primary standard for structural welding is EN ISO 15614, which defines how welding procedures must be tested and qualified. For mobile crane booms specifically, manufacturers and repair specialists also reference guidelines from bodies such as the FEM (Federation Europeenne de la Manutention) and crane-specific OEM documentation. Together, these frameworks determine what qualifications a welder and a welding procedure must hold before any work begins on a crane boom. The result is a formal document called a Welding Procedure Specification (WPS), which sets out every relevant parameter: material grade, filler material, preheat temperature, heat input, and more.

What a prequalified weld means in practice

A prequalified weld is one where the welding procedure is accepted without the need for physical testing, because it falls within parameters that a recognized standard has already deemed proven safe. In other words, the standard itself acts as the qualification.

This route is common in general structural steelwork. If a joint design, base material, filler metal, and process all sit within the limits defined by the standard, the WPS can be written and used without conducting a separate qualification test. It saves time and cost, and for standard construction steels it works well.

The important limitation is this: prequalification is only valid within defined boundaries. The moment a variable falls outside those boundaries, the prequalified status no longer applies. For crane boom welding, where materials often include high-strength steels in the 690 to 1100 N/mm² range, those boundaries are frequently exceeded. High-strength steels behave differently under heat, are more sensitive to hydrogen cracking, and require tighter control of heat input. Standard prequalification tables were not built with these materials in mind.

What procedure qualification involves for crane steels

When a welding procedure cannot be prequalified, it must go through a full qualification process. This is where the Procedure Qualification Record (PQR) comes in.

The process works like this:

  1. A preliminary WPS is written, setting out the proposed welding parameters.
  2. A test weld is produced under controlled conditions using those exact parameters.
  3. The test weld is subjected to destructive and non-destructive testing: tensile tests, bend tests, impact tests, and hardness measurements.
  4. If the test weld passes all required tests, the results are recorded in the PQR, which then validates the WPS for production use.

For high-strength mobile crane boom steels, this process is not optional. Grades such as S960 and S1100 are not covered by prequalification tables in most standards. Any repair or fabrication on these materials requires a procedure-qualified WPS backed by a valid PQR. This is one reason why so few companies in Europe are equipped to carry out crane boom repair on 960 and 1100 grade booms. The qualification process is demanding, the testing is expensive, and the technical knowledge required to develop a reliable WPS for these steels takes years to accumulate.

Key differences that affect crane boom repair decisions

When you are evaluating a repair provider or assessing a repair plan, the distinction between these two qualification routes has real practical consequences.

  • Material grade: Prequalified procedures cover standard structural steels. High-strength steels used in modern crane booms almost always require a procedure-qualified WPS.
  • Testing evidence: A prequalified WPS relies on the standard as its evidence base. A procedure-qualified WPS is backed by physical test data from a real weld sample, documented in a PQR.
  • Scope of validity: Procedure qualification defines a specific range of variables within which the WPS is valid. Changing a significant variable, such as material grade or heat input, requires requalification.
  • Regulatory acceptance: For crane boom repairs, third-party notified bodies and certification authorities will expect to see a procedure-qualified WPS with a supporting PQR. A prequalified WPS alone will typically not satisfy these requirements on high-grade steel.
  • Welder qualification: Both routes require welders to hold valid qualifications, but procedure-qualified work often demands welder testing on the specific material and joint type involved.

In short, if a repair company tells you they are using a prequalified procedure on a high-strength crane boom, that is a signal worth investigating further.

Why the right weld qualification protects asset value

A correctly qualified welding procedure is not just a compliance checkbox. It is the foundation on which the entire repair stands, both technically and legally.

After a crane boom repair, the crane must return to service with its CE certification intact. In Europe, this means the repair must be traceable, documented, and verifiable. A valid WPS and PQR form part of that documentation trail. Without them, a notified body cannot sign off on the repair, and the crane cannot legally return to operation.

Beyond compliance, the right procedure protects the mechanical integrity of the boom itself. High-strength steels are sensitive to improper heat input. Too much heat causes the heat-affected zone to soften, reducing the strength of the base material around the weld. Too little preheat increases the risk of hydrogen cracking, which may not appear immediately but can propagate under load. A procedure-qualified WPS, developed and tested specifically for the steel in question, controls these variables and gives you confidence that the repaired boom performs as intended under real working conditions.

Over time, this translates directly into asset longevity. A boom repaired with a validated, documented procedure retains its structural value. One repaired without proper qualification may pass a visual inspection but carry hidden risks that surface later, often at the worst possible moment.

How Rusch Cranes helps with crane boom weld qualification

We specialize in boom repairs on high-strength steels up to 1100 N/mm², and we are one of only three companies in Europe qualified to repair the telescopic booms of 960 and 1100 grade mobile cranes. Every repair we carry out starts with a rigorous preparation process:

  • Material strength verification and full documentation of the repair scope
  • Development of a Welding Procedure Specification (WPS) and a detailed repair plan
  • 100% visual inspection and 100% magnetic particle inspection (MPI) on all new welds
  • Third-party ultrasonic or X-ray testing when required by a notified body
  • Full CE certification validity maintained after repair, with a 1-year guarantee

We offer crane boom repair services worldwide, so wherever your crane is operating, we can help. If you want to discuss a specific repair situation or find out whether your crane qualifies for repair rather than replacement, get in touch with our team and we will give you a straight answer.

Frequently Asked Questions

How do I know whether the steel in my crane boom requires a procedure-qualified WPS rather than a prequalified one?

The clearest indicator is the steel grade. If your crane boom is made from high-strength steel with a yield strength above approximately 460 N/mm² — such as S690, S960, or S1100 — it almost certainly falls outside the scope of standard prequalification tables and will require a procedure-qualified WPS backed by a PQR. If you are unsure of the material grade, a competent repair specialist should be able to verify this through material documentation, mill certificates, or on-site material testing before any repair work begins.

What should I ask a crane boom repair company to verify that their welding procedures are properly qualified?

Ask to see the actual WPS and the supporting PQR for the specific material grade and joint type involved in your repair. A legitimate procedure-qualified WPS will reference a PQR that contains real test data — tensile results, bend test results, impact values, and hardness measurements — from a physical test weld. You should also ask whether the qualification was carried out by an accredited testing body and whether the welders performing the work hold current qualifications on the relevant material and process. If a company cannot produce these documents on request, that is a serious concern.

Can a crane boom that has been improperly welded be re-repaired, or does it need to be replaced?

It depends on the extent of the damage caused by the improper weld and the structural condition of the surrounding base material. In some cases, a qualified specialist can assess the boom, remove the defective weld material, and carry out a correctly qualified repair — but this is only possible if the heat-affected zone has not been excessively compromised and the base material retains sufficient integrity. A thorough inspection using non-destructive testing methods such as ultrasonic testing or magnetic particle inspection is essential before any decision is made. In cases where the base material has been softened or cracking has propagated, replacement may be the only safe option.

How long does it typically take to develop a procedure-qualified WPS for a high-strength crane boom repair?

Developing a new WPS and PQR from scratch for high-strength steels like S960 or S1100 is a time-intensive process that can take several weeks, as it involves writing the preliminary WPS, producing a controlled test weld, and then conducting and documenting all required destructive and non-destructive tests through an accredited body. However, a specialist company that already holds validated WPS and PQR documentation for the relevant steel grades can proceed directly to your repair without this lead time. This is one of the key practical advantages of working with a repair provider that has invested in building a library of qualified procedures for high-grade crane steels.

Does a crane boom repair affect the original CE certification of the crane, and how is it reinstated?

Yes, any structural repair to a crane boom has the potential to affect the crane’s CE certification, which is why the repair process must be fully documented and verifiable. Reinstating CE certification after a boom repair requires the repair to be traceable — meaning the WPS, PQR, welder qualifications, inspection records, and material documentation must all be in order and available for review by a notified body. A qualified repair specialist will manage this documentation trail as part of the repair process and coordinate with the relevant certification authority to ensure the crane can legally return to service.

Are there situations where replacing a crane boom is a better decision than repairing it?

Yes, and an honest repair specialist should tell you when that is the case. Replacement tends to be the more appropriate choice when the boom has sustained extensive structural damage across multiple sections, when the base material has been severely compromised by improper previous repairs, or when the cost of a properly qualified repair approaches or exceeds the cost of a replacement boom. That said, for high-capacity mobile cranes where OEM replacement booms carry very long lead times or are no longer available, a qualified repair is often the only practical path to returning the crane to service — provided the structural assessment confirms it is viable.

What non-destructive testing methods are used to verify the quality of crane boom welds after repair?

The most commonly applied methods in crane boom repair are visual inspection (VT), magnetic particle inspection (MPI), ultrasonic testing (UT), and radiographic testing (X-ray or RT). Visual inspection and MPI are typically applied to 100% of new welds as a baseline, with MPI being particularly effective at detecting surface and near-surface cracks in ferromagnetic steels. Ultrasonic testing and radiography are used to detect internal discontinuities and are often required by notified bodies for certification purposes. The specific combination of methods required will depend on the joint type, material grade, and the requirements of the applicable standard and certifying authority.

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