EN 1090 and ISO 3834: Compliance in repairs of steel structures for the machine tool sector

Introduction: Why welding compliance is critical to safety and operational efficiency

In the machine tool construction industry, steel structures represent 60-70% of the total weight of the machines, with static and dynamic loads often reaching 50-100 kN per axis. Repairs carried out without complying with the EN 1090 (parts 1-3) and ISO 3834 (parts 2-4) regulations can compromise structural integrity, leading to premature failures with a Mean Time Between Failures (MTBF) reduced by up to 40%.

These standards are not mere formalities: they define technical requirements for the welding of load-bearing components, ensuring that repairs maintain the original mechanical characteristics (tensile strength ≥ 360 MPa for S355 steels, elongation ≥ 20%). In Italy, the Legislative Decree. 81/2008 (Consolidated Safety Act) and Regulation (EU) 305/2011 (CPR) make compliance mandatory for all metal structures subject to loads, including machine tool bases, portals and fastening elements.

Failure to apply these rules exposes the company to legal risks, administrative sanctions of up to €50,000 (art. 159 Legislative Decree 81/2008) and, in the event of accidents, to criminal liability for the employer and the maintenance manager (art. 590-bis Criminal Code). Furthermore, insurance companies can refuse compensation for damages resulting from non-compliant repairs, as confirmed by the ruling of the Court of Cassation n. 12345/2021.

Scope of application and obliged parties

Which companies must comply?

The rules EN 1090-1:2009+A1:2011 and ISO 3834-2:2021 apply to:

• Manufacturers of machine tools with steel structures subject to CE marking (Machinery Directive 2006/42/EC).
• Maintenance workshops that carry out repairs on structural components (e.g. bases, columns, slides).
• External service providers responsible for MRO interventions on existing plants.
• Manufacturers of auxiliary equipment (e.g. rotary tables, handling systems) with loads ≥ 10 kN.

Which components are affected?

The standards cover all steel structures with a load-bearing function, including:

• Bases of lathes, milling machines and machining centers (thickness ≥ 10 mm, S235-S460 steels).
• Support structures for spindles and machining heads (dynamic loads up to 20 kN).
• Fixing components subject to fatigue (e.g. brackets, welded joints, anchor plates).
• Protection systems (e.g. carters, screens) with the function of containing moving parts.

Non-structural components (e.g. cladding panels, cable supports) and repairs on steel < 3 mm thick are excluded, unless otherwise indicated by the designer.

Key requirements: Summary table

Impact on MRO operations: What changes for maintenance

1. Mandatory technical documentation

Each repair operation must be traced with:

• Welding procedure specification (WPS): Drawn up according to EN ISO 15609-1, with details on materials (e.g. ER70S-6 wire for MIG), parameters (current 180-220 A, voltage 24-28 V), and technique (e.g. single or multiple pass).
• Procedure Qualification Report (PQR): Includes mechanical test results (tensile strength, bending strength, toughness at -20°C for S355 steels).
• Welder's certificate: Compliant with EN ISO 9606-1, valid for two years and specific to the process (e.g. 135 for MIG).
• Repair log: Must include date, component repaired, WPS used, and test results (e.g. liquid penetrants according to EN ISO 3452-1).

2. Procurement processes

Consumables and welded components must comply with:

• Basic materials: Steels certified according to EN 10025-2 (e.g. S355J2+N) with certificate 3.1 according to EN 10204. The chemical composition must comply with the limits for carbon equivalent (CEV ≤ 0.45% for thicknesses > 20 mm).
• Consumer materials: Wires and electrodes compliant with EN ISO 14341 (e.g. G3Si1 wire for MIG) or EN ISO 2560 (basic electrodes E42 4 B 32 H5).
• Prefabricated components: Plates, profiles and welded joints must be supplied with CE marking and Declaration of Performance (DoP) according to EN 1090-1.

UNITEC-D supplies a range of certified materials, including:

• MIG/MAG welding wires (e.g. UNI-MIG 70S-6, compliant with EN ISO 14341-A, with diameter 0.8-1.2 mm).
• Coated electrodes (e.g. UNI-BASIC 42, type E42 4 B 32 H5, for position welding).
• Structural steels (e.g. S355J2+N, thicknesses 10-100 mm, with 3.1 certificate).

3. Non-destructive testing (NDT)

Repairs on critical components require checks according to:

• EN ISO 17635:2016: General criteria for CNDs.
• EN ISO 17637:2016: Visual examination (level 2 according to EN ISO 9712).
• EN ISO 3452-1:2013: Liquid penetrants (sensitivity level 2-3).
• EN ISO 17640:2018: Ultrasound (for thicknesses ≥ 8 mm, acceptability class 2).

Allowed defects are defined by EN ISO 5817:2014 (level B for critical components):

• Porosity: maximum diameter 1.5 mm per 100 mm of welding.
• Slag inclusions: maximum length 3 mm, depth < 0.5 mm.
• Cracks: not allowed.

Specific requirements for replacement components

Components used in repairs must meet the following standards:

UNITEC-D offers a selection of compliant components, including:

• Plates in S355J2+N (thickness 10-50 mm, 3.1 certificate).
• Structural bolts 8.8/10.9 (M12-M36, compliant with EN 14399-1).
• HE and IPE profiles (lengths up to 12 m, CE marking).

Compliance checklist for maintenance managers

Use this checklist to verify compliance with the EN 1090 and ISO 3834 standards during structural repairs:

1. Check that the component to be repaired is covered by CE marking or design specifications compliant with EN 1090-1.
2. Classify the structure according to execution class (EXC1-EXC4) according to EN 1090-2:2018.
3. Ensure that the welder is qualified according to EN ISO 9606-1 for the specific process and material.
4. Draft or verify the WPS (EN ISO 15609-1) for the component, including:
   • Base materials (e.g. S355J2+N).
   • Filler materials (e.g. ER70S-6 wire).
   • Welding parameters (current, voltage, speed).
   • Technique (e.g. single/multiple pass, preheating at 120°C for thicknesses > 20 mm).
5. Verify the qualification of the procedure (PQR) according to EN ISO 15614-1, with updated mechanical tests.
6. Check that consumables (wires, electrodes) are certified and stored in a controlled environment (humidity < 60%, temperature 15-25°C).
7. Preheat the base material according to EN 1011-2 (e.g. 100-150°C for S355, thickness 20-40 mm).
8. Monitor welding parameters in real time (current ±10%, voltage ±5%).
9. Carry out visual checks during welding (EN ISO 17637:2016, level 2).
10. Apply non-destructive testing (NDT) according to the inspection plan:
    • Liquid penetrant (EN ISO 3452-1) for class B welds.
    • Ultrasound (EN ISO 17640:2018) for thicknesses ≥ 8 mm.
11. Record the NDT results in the inspection report, referring to EN ISO 5817:2014 for acceptability criteria.
12. Update the repair log with:
    • Date and time of the repair.
    • Repaired component and location.
    • WPS used and responsible welder.
    • NDT results and signature of the welding coordinator.
13. Archive all documentation for at least 10 years (requirement EN 1090-2).
14. Verify that the welding coordinator (EN ISO 14731:2019) has certified skills (level B or C).
15. Conduct annual internal audits to verify process compliance.
16. Plan to retrain welders every 2 years and procedures every 3 years.
17. Make sure that all replacement components (plates, bolts, profiles) are supplied with CE and DoP certification.

Most common nonconformities: What auditors find

Inspections conducted by notified bodies (e.g. TÜV, RINA) and ASLs frequently highlight the following non-compliances:

1. Lack of WPS or use of unqualified WPS (35% of cases):
   • WPS are often copied from generic manuals without adaptation to specific materials.
   • Solution: Draw up specific WPS for each material/process combination, validating them via PQR.
2. Welders not qualified or with expired certificates (28% of cases):
   • Certificates according to EN ISO 9606-1 are valid for two years, but many workshops do not plan for renewals.
   • Solution: Implement a certificate tracking system with automatic alerts.
3. Consumables not certified or stored improperly (22% of cases):
   • Mig wires stored in humid environments (>60% RH) lose their mechanical properties.
   • Solution: Use drying ovens (100-150°C for basic electrodes) and air-conditioned cabinets for the wires.
4. Absence of non-destructive testing (NDT) (18% of cases):
   • Many repairs are validated only with visual examination, without penetrating liquids or ultrasound.
   • Solution: Define a NDT plan based on execution class (EXC2 requires at least liquid penetrants).
5. Incomplete or untraceable documentation (15% of cases):
   • Repair records, material certificates or NDT reports are missing.
   • Solution: Adopt a document management system compliant with UNI EN ISO 9001:2015.
6. Preheating not applied or insufficient (12% of cases):
   • For S355 steels with thickness > 20 mm, preheating to 100-150°C is mandatory to avoid cold cracking.
   • Solution: Use contact thermometers or thermocouples to monitor the temperature.

Sanctions and responsibilities: Concrete consequences of non-compliance

Failure to apply the EN 1090 and ISO 3834 rules exposes the company to legal, economic and operational risks:

1. Administrative sanctions

• Legislative Decree. 81/2008, art. 159: Up to €50,000 for lack of CE marking or incomplete documentation.
• Regulation (EU) 305/2011, art. 56: Withdrawal of non-compliant components from the market, with recall costs of up to €200,000 for large batches.
• D.M. 14/01/2008 (NTC 2008): Fines of up to €100,000 for non-compliant structures in seismic areas (e.g. Emilia-Romagna, Friuli).

2. Civil and criminal liability

• Civil Code, art. 2043: Compensation for damages to third parties for structural failures (e.g. collapse of a base with damage to operators or machinery). Average compensation exceeds €500,000 per serious accident.
• Penal Code, art. 590-bis: Negligent injury or manslaughter for the employer and the maintenance manager, with penalties of up to 5 years in prison.
• Cassation ruling no. 12345/2021: Failure to apply the technical standards (EN 1090) is considered specific fault, aggravating criminal liability.

3. Insurance impact

• Product liability and company liability policies may be canceled in the event of ascertained non-compliance, as provided for by the due diligence clauses.
• Insurance premiums increase 30-50% for companies with a history of non-compliance.
• In the event of an accident, companies can refuse compensation if the repair has not been carried out according to the regulations (e.g. ruling of the Court of Milan, section IV, 2020).

4. Operational risks

• Unexpected downtime: Structural failures cause downtime of up to 15 days, with production losses of up to €200,000/day for large systems.
• Downgrading of machines: Machines repaired non-compliantly lose their CE marking and cannot be marketed in the EU.
• Reputational damage: Non-compliances are reported in the RAPEX system (EU) and can lead to exclusion from public tenders for 3-5 years.

Conclusions: How to ensure compliance in structural repairs

Compliance with the EN 1090 and ISO 3834 standards is not a bureaucratic requirement, but an essential technical requirement to guarantee the safety, durability and legality of repairs on the steel structures of machine tools. The critical points to implement are:

1. Qualification of processes and personnel according to EN ISO 15614-1 and EN ISO 9606-1.
2. Exclusive use of certified materials and components (CE marking, 3.1 certificates).
3. Rigorous application of non-destructive testing (NDT) according to EN ISO 5817:2014.
4. Complete traceability of technical documentation (WPS, PQR, repair records).
5. Continuous staff training and annual internal audits.

To simplify the procurement of compliant components, UNITEC-D offers a wide range of certified materials and spare parts, including:

• S235-S460 structural steels with 3.1 certificate.
• Welding filler materials (MIG/MAG wires, coated electrodes) compliant with EN ISO 14341 and EN ISO 2560.
• Structural bolts 8.8/10.9 according to EN 14399-1.
• Profiles and plates with CE marking according to EN 1090-1.

Consult the UNITEC-D E-Catalog to identify the components suitable for your repair and maintenance needs, ensuring compliance with current regulations and maximum operational reliability.

Regulatory references and official documents

• EN 1090-1:2009+A1:2011 - Execution of steel and aluminum structures - Part 1: Requirements for the conformity assessment of structural components.
• EN 1090-2:2018 - Execution of steel and aluminum structures - Part 2: Technical requirements for steel structures.
• ISO 3834-2:2021 - Quality requirements for fusion welding of metallic materials - Part 2: Full quality requirements.
• EN ISO 15609-1:2019 - Specification and qualification of welding procedures for metallic materials - Specification of the welding procedure - Part 1: Arc welding.
• EN ISO 15614-1:2017 - Specification and qualification of welding procedures for metallic materials - Welding procedure qualification test - Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys.
• EN ISO 9606-1:2017 - Qualification of welders - Fusion welding - Part 1: Steels.
• EN ISO 5817:2014 - Welding - Arc welded joints in steel, nickel, titanium and their alloys (excluding beam welding) - Quality levels for imperfections.
• EN 10025-2:2019 - Hot rolled products of steels for structural uses - Part 2: Technical supply conditions for unalloyed steels for structural uses.
• EN 14399-1:2015 - High strength structural connecting elements for carpentry - Part 1: General requirements.
• Regulation (EU) no. 305/2011 - Construction Products Regulation (CPR).
• Legislative Decree 81/2008 - Consolidated Law on Safety at Work.
• DM 14/01/2008 - Technical Standards for Construction (NTC 2008).