Overview - EN ISO 8504-4:2024 (Acid pickling for steel substrates)
EN ISO 8504-4:2024 (identical to ISO 8504-4:2022) specifies the common method of acid pickling used in shop facilities for preparing steel substrates prior to the application of paints and related products. The standard is primarily applicable to new steelwork and describes a chemical cleaning process intended to remove rust and mill scale, with limited capability to remove light oil residues. It is particularly suited to steel surfaces that would be damaged or deformed by abrasive blasting.
Key topics and technical requirements
- Scope and applicability: Use on internal, external and complex steel structures where abrasive methods are unsuitable; typically used in stationary or mobile shop setups.
- Pickling liquids: Requirements for chemical materials, recommended formulations and process conditions; examples and an informative annex provide typical formulations.
- Bath equipment and analysis: Materials for bath construction, monitoring and bath analysis practices to maintain process control.
- Process steps: Defined procedure covering preparation, degreasing (components, immersion methods, time and temperature), fresh water rinsing/washing, acid pickling (immersion requirements, part placement, process temperature and time) and post‑treatment.
- Post‑treatment and surface conditioning: Conversion layer formation, surface neutralization, ways to improve phosphate layers, drying, and documented quality checks.
- Assessment of cleaned surface: Guidance on inspection and acceptance criteria tied to coating performance.
- Health, safety and environmental consideration: Emphasis on safe handling, disposal and regulatory compliance for pickling chemicals and effluents.
Practical applications
- Preparing structural steel, fabricated components and complex assemblies before painting or coating
- Situations where abrasive blasting risks distortion or cannot fully reach internal/complex surfaces
- Industrial coating shops, fabrication plants, and refurbishment projects requiring controlled chemical cleaning
- Generating a clean, etch‑conditioned surface for improved adhesion of primers and paint systems
Who should use this standard
- Coating specifiers and engineers
- Surface preparation contractors and shop managers
- Quality assurance/inspection personnel and production planners
- Asset owners, fabricators and paint manufacturers developing surface‑treatment procedures
Related standards
- ISO 8501 series - visual assessment of surface cleanliness
- ISO 8502 series - laboratory and field test methods for surface contaminants
- ISO 8503 series - surface profile measurement methods
- Other parts of the ISO 8504 series - guidance on alternative surface preparation methods
This standard is essential for professionals seeking a validated, repeatable acid‑pickling process to achieve reliable surface cleanliness and coating performance. Keywords: acid pickling, surface preparation, steel substrates, EN ISO 8504-4:2024, rust removal, mill scale removal, pickling liquid, degreasing, post‑treatment.
