EN 1090 governs the execution of steel and aluminium structures, and the execution class (EXC) sets how strict that execution must be. Classes run from EXC1 (lowest) to EXC4 (highest). For more demanding structures — bridges, load-bearing and safety-critical elements — EXC3 or EXC4 is often specified. Here is what that means and why it matters when choosing a welding contractor.
What EN 1090 and execution classes are
EN 1090-2 defines the technical requirements for executing steel structures — from material preparation and welding to inspection and traceability. The execution class (EXC1–EXC4) states how strict those requirements are. A higher class means more control, more documentation and stricter welding.
How the class is determined
The class is not arbitrary — it follows from the design. It is derived from the consequence class, the service category (static or fatigue loading) and the production category. The designer specifies it in the project documentation.
- Consequence class (how severe a failure would be)
- Service category (static or dynamic/fatigue loading)
- Production category (e.g. welding of higher-strength steels)
What EXC3 and EXC4 demand
For EXC3 and EXC4 the requirements are considerably stricter than for EXC1/EXC2:
- Full material and weld traceability
- A larger scope of non-destructive testing (NDT)
- Qualified welding procedure specifications (WPS/WPQR)
- A welding coordinator (e.g. IWE/IWT)
- More extensive documentation and acceptance
Why it matters when choosing a contractor
EXC4 is the highest class and applies to structures with the most severe consequences of a potential failure. A contractor experienced with EXC3/EXC4 has the quality systems, welding coordination and documentation needed to pass acceptance. If a contractor does not know these classes, you risk rejection at handover and rework.
At Save Consulting we have experience with steel structures to EN 1090, including execution classes EXC3 and EXC4.