Execution classes under EN 1090-2: EXC1 to EXC4 explained

Anyone fabricating or procuring steel structures will encounter the execution classes of EN 1090-2. The execution class sets the severity of the requirements for welding, personnel qualifications, welding coordination, inspection scope and documentation. The range runs from EXC1 for simple structures to EXC4 for structures where failure would have extreme consequences.

In practice we regularly see the class determined incorrectly, or not recorded in the contract documents at all. That leads to disputes at handover, unnecessary cost, or a structure that falls short of the requirements. This article explains how the class is determined and what each class means for your workshop and your paperwork.

1. How the execution class is determined

The execution class follows from a risk assessment of the structure, based on three factors:

• Consequence class (CC1 to CC3) from EN 1990: the consequences of failure for people, the economy and the environment.
• Service category (SC1 or SC2): static loading or fatigue, as with crane runways and bridges.
• Production category (PC1 or PC2): covering aspects such as higher steel grades and site welding.

Since the 2018 edition of EN 1090-2, selecting the execution class formally rests with the structural designer or the client, through the execution specification. If nothing is specified, EXC2 applies by default. Always record the class explicitly in the specification and the contract.

2. EXC1 and EXC2: the baseline for most structures

EXC1 covers simple structures where failure has limited consequences, such as light canopies or fencing. Requirements are modest: welding procedure qualification is not mandatory and quality level D of ISO 5817 applies.

EXC2 is the standard class for the majority of building work: halls, platforms, stairs and common building structures. It requires qualified welding procedures to EN ISO 15614-1, welders qualified to ISO 9606-1, a welding coordinator, quality level C as the baseline and a quality system meeting at least ISO 3834-3.

3. EXC3 and EXC4: elevated and very strict requirements

EXC3 applies to structures with greater consequences of failure or fatigue loading: bridges, crane runways, heavily loaded industrial structures and much infrastructure work. The quality level rises to B, the scope of supplementary non-destructive testing increases, material traceability becomes stricter and ISO 3834-2 is required for the quality system.

EXC4 is reserved for structures where failure would have extreme consequences. The requirements equal EXC3, supplemented by project-specific requirements from the execution specification, such as quality level B with additional requirements and full traceability per component.

4. What the class means for welding and qualifications

The execution class feeds directly into the welding workshop:

• Welding procedures: from EXC2 onwards, qualified welding procedure specifications are mandatory, supported by qualification to EN ISO 15614-1 or another permitted route.
• Welders and operators: qualification to ISO 9606-1 and ISO 14732 respectively, valid for the process, material and position used.
• Quality level: D for EXC1, C for EXC2, B for EXC3 and B with additional requirements for EXC4, assessed to ISO 5817.
• NDT scope: beyond one hundred percent visual testing, the percentage of supplementary testing rises with the class and the joint type.

5. Welding coordination per execution class

From EXC2 onwards, EN 1090-2 requires a welding coordinator with tasks and responsibilities in line with ISO 14731. The required level of knowledge depends on the class, the steel grade and the material thickness. For EXC2 a coordinator with basic or specific technical knowledge often suffices; EXC3 and EXC4 almost always call for comprehensive technical knowledge, in practice usually an IWE or IWT. The tables in EN 1090-2 link steel group, thickness and class to the required level. Our article on the welding coordinator under ISO 14731 covers how to fill the role internally or externally.

6. Documentation and traceability

Each class carries its own documentation requirements. EXC2 calls for welding procedure specifications and qualification records, welder certificates, material certificates and NDT reports. From EXC3 onwards, stricter material traceability, recorded assignment of welds to welders and more extensive inspection and test plans are added. A quality dossier compiled only at handover almost always shows gaps, so set up the records from work preparation onwards, as part of your system under ISO 3834.

7. Common mistakes in practice

Three situations come up repeatedly. First, the class is not recorded anywhere, so fabricator and client each assume a different class. Second, EXC3 is specified as a matter of habit where EXC2 would structurally suffice, adding unnecessary cost for qualifications and testing. Third, a workshop certified for EXC2 accepts an EXC3 order without upgrading its system, coordination and testing regime. If you are unsure which class applies or what it means for your business, targeted EN 1090 support helps settle this before fabrication starts.