EN 1090 and execution classes

What it governs

The standard series on the execution of steel structures sets the requirements for fabrication, welding, erection and inspection — everything that follows the design.

It covers traceability of materials, fabrication tolerances, qualification of welding procedures, the competence of welders, the extent of testing and the surface protection.

The execution classes

The standard defines execution classes (EXC). A higher class means stricter requirements: more testing, tighter tolerances, fuller documentation.

The class has to be chosen from the risk of the structure: how severe the consequence of a failure would be, what action the structure carries (static or fatigue), and how difficult the material and the fabrication are.

Who specifies it

The designer. The execution class is part of the design documentation — the fabricator does not decide it, and it cannot be left out.

If it is not specified, the fabricator either assumes the lowest or asks. Neither is good for the project.

What it means in practice

Qualification of the fabricator

A works fabricating structural steel components has to operate under the relevant system in order to fabricate in a given class.

The extent of inspection

The proportion of welds tested depends on the class.

Documentation

Material certificates, welding records, test reports.

Cost

A higher class is more expensive. So do not specify an unjustifiably high one — but not a low one either, because that is at the expense of safety.

The thin-walled side

Execution of a cold-formed, bolted frame follows a different logic: there is no welding there, and the quality comes from manufacturing accuracy and the quality of the screw fixing. In-process quality control.

Where the two technologies meet, the steelwork execution requirements apply to the welded members.

The point

The execution class is a design decision that affects price and quality directly. Leave it out of the drawings and it becomes a source of dispute later.