EN 1090-2 Structural Steel Welding: Execution Classes EXC1-EXC4

Structural steel fabricators face a compliance obligation that intensifies at the contract award stage: every structural component bearing the CE mark under EN 1090-1 must be manufactured in accordance with EN 1090-2. The execution class assigned to a structure is the variable that determines which welding, NDT, and quality management requirements apply — and misassigning it, or failing to meet the requirements of the correct one, invalidates the CE marking declaration of performance and triggers liability exposure on the project. This guide covers the EN 1090-2 welding requirements that matter most for fabricators, quality managers, and welding coordinators taking on structural steelwork.

What EN 1090-2 Covers

EN 1090-2:2018 — Execution of steel structures and aluminium structures — Part 2: Technical requirements for steel structures — defines the technical requirements for the execution of structural steelwork across the European Union. It applies to building frames, bridges, industrial structures, crane runway girders, masts, towers, and any other load-bearing steel component falling under the Construction Products Regulation (CPR).

It does not govern pressure vessels (PED / ISO 3834), metallic industrial piping (EN 13480), or railway vehicles (EN 15085). It governs structural connections — from foundation base plates to roof-level moment frames — where fatigue, stability under load, and consequence of failure determine the rigor of execution requirements.

The standard operates in combination with EN 1090-1 (conformity assessment and CE marking), EN 1993 Eurocode 3 (design of steel structures), and EN 1994 Eurocode 4 (composite steel-concrete structures). Fabricators reading a project execution specification will find EN 1090-2 clause references embedded throughout — the structural engineer writes the specification, and EN 1090-2 defines what each referenced clause actually requires in production.

Execution Classes: EXC1 to EXC4

The execution class (EXC) is the central organising variable of EN 1090-2. It governs welding requirements, NDT scope, welder qualification, welding coordination responsibility, and documentation obligations. Four classes are defined, increasing in rigor:

The execution class is determined by the structural designer and owner on the basis of consequence class, service category, and production category as defined in EN 1090-2 Annex B. Fabricators cannot self-assign a lower class to reduce compliance burden — the class is fixed in the project execution specification and forms part of the Declaration of Performance.

Welding Procedure Requirements

WPS Qualification per EN ISO 15614-1

All welding processes used in EXC2 and above must be supported by qualified Welding Procedure Specifications (WPS) in accordance with EN ISO 15614-1 for arc welding of carbon and alloy steels, or the applicable process-specific standard (EN ISO 15614-11 for electron beam, EN ISO 15614-12 for laser, and so on). The WPS defines essential variables — base material group, filler metal classification, heat input range, preheat and maximum interpass temperature, PWHT conditions — within which every production weld must remain for the qualification to remain valid.

Pre-qualified procedures are permitted for EXC2 joints using standard structural steels in the S235–S355 range with listed consumables, provided the WPS specifies the standard geometry details per EN 1090-2 Table 4. For EXC3 and EXC4, or where higher-strength steels above S420 are used, full procedure qualification testing per EN ISO 15614-1 is mandatory.

Welder Qualification per EN ISO 9606-1

Welders must hold a current qualification per EN ISO 9606-1 covering the applicable welding process, base material group, and joint type. For EXC3 and EXC4 work, the qualification scope must cover the specific process and position combination used in production. Qualification continuity requires that the welder remains active in each qualified process — a six-month gap without use of a process requires requalification before returning to production welding on CE-marked structures.

Welding Coordination per EN ISO 14731

EN 1090-2 requires a responsible Welding Coordinator (RWC) for EXC2 and above. The minimum technical knowledge level required under EN ISO 14731 depends on execution class and the material group being welded:

The RWC is the single point of accountability for WPS compliance, welder qualification currency, NDT planning, and weld quality documentation. On a CE-marked project, the Declaration of Performance names the RWC’s qualification — a level of personal liability that makes the role operationally significant, not a paper function.

Weld Quality and Acceptance Criteria

EN 1090-2 references ISO 5817 for weld quality levels. The applicable level depends on execution class and the structural detail category assigned by the structural engineer:

• EXC2, static joints in secondary members: quality level D (permissive limits — undercut depth up to 1 mm, excess weld metal reinforcement without sharp notch)
• EXC2, fatigue-critical details (detail category 90 MPa and above): quality level C
• EXC3, standard welds: quality level C; transverse butt welds in the primary load path: level B
• EXC4: quality level B with additional finishing requirements — weld toe dressing by grinding or TIG remelting for fatigue-critical butt weld categories

NDT Requirements by Execution Class

EN 1090-2 Tables 24 and 25 define minimum NDT scope by weld type and execution class. Visual testing (VT) at 100% is the baseline for all classes. The incremental requirements above VT are:

NDT personnel must be qualified to EN ISO 9712 at minimum Level 2 in the applicable method. The choice between UT and RT for volumetric examination depends on joint geometry, material thickness, and access — UT is preferred for thicker sections and restricted access, RT remains standard for thin-material butt welds where film geometry is practical. NDT procedures must be documented and approved by the NDT coordinator before production begins.

Timing of NDT is specified in EN 1090-2 Clause 12.4: for steels with a specified minimum yield strength above 355 MPa, volumetric inspection must not begin less than 16 hours after completion of welding to allow hydrogen-induced cracking to manifest if the preheat or WPS was inadequate.

CE Marking and Factory Production Control

CE marking of structural steel products under EN 1090-1 requires a Factory Production Control (FPC) system assessed by a Notified Body. The FPC covers all EN 1090-2 activities: incoming material traceability and mill certificate review, WPS and WPQR library management, welder qualification record maintenance, calibration of measuring equipment (including contact thermometers and thermal cameras for preheat verification per EN ISO 13916), NDT procedures and reporting, and non-conformance management.

For EXC3 and EXC4 fabricators, Notified Body assessment typically includes annual surveillance audits and unannounced visits. Documentation retention requirements for CE-marked structural components on public infrastructure projects are typically a minimum of 10 years from supply.

Fabricators who also perform pressure equipment manufacture or pipeline work will find significant overlap between EN 1090-2 FPC requirements and ISO 3834-2 quality requirements for fusion welding. Particularly: preheat and interpass temperature monitoring, heat input traceability per weld, consumable traceability to batch certificate, and non-conformance disposition records.

In-Process Monitoring for EN 1090-2 Compliance

EN 1090-2 Clause 7 and Annex D require that production welding parameters remain within the limits defined in the approved WPS and are documented accordingly. For EXC3 and EXC4 structures, parameter records form part of the weld traveler reviewed by the Notified Body during surveillance. The two most common documentation failures in EN 1090-2 audits are preheat assumed rather than measured, and interpass temperature recorded from a remote point rather than the actual joint.

Thermal monitoring cameras positioned at the weld station generate per-weld records including:

• Preheat spatial map: quantitative temperature field across the full joint before arc ignition, not just a single thermocouple point near the arc
• Interpass temperature peak per pass: automatically compared against the WPS maximum, enabling intervention before the next pass begins
• Heat input distribution: arc energy per pass correlated to the WPS essential variable limits, traceable to welder and timestamp without manual recording

For high-volume structural steel fabrication — column base-plate fillet welds, beam splice butt welds, hollow section chord-to-brace connections — automated thermal records close the gap between what the WPS specifies and what was actually applied on each joint. The records are available for Notified Body review alongside NDT reports and the FPC weld register.