Overview
SIST EN ISO 8504-4:2025 provides comprehensive guidance for the preparation of steel substrates prior to the application of paints and related products, with a specific focus on acid pickling. This European and international standard, developed by SIST and based on ISO 8504-4:2022, specifies acid pickling as a typical shop floor method for removing rust and mill scale from new steelwork. Acid pickling is particularly effective for steel surfaces that may be easily deformed by abrasive blasting and is generally used when a high degree of surface cleanliness is required before coating.
Key Topics
- Acid Pickling Process: Details the use of acidic solutions, such as inorganic or organic acids, alongside inhibitors and surfactants, for the removal of rust and mill scale.
- Surface Cleanliness: Emphasizes assessment in alignment with ISO 8502 series to ensure suitability of the steel surface prior to coating application.
- Method Sequence:
- Initial degreasing (may remove slight oil residues)
- Rinsing with fresh water
- Acid pickling (full immersion recommended)
- Post-treatment, such as conversion coatings and drying
- Equipment and Safety:
- Recommends anti-corrosion materials for tanks and pipes
- Highlights the need for healthy and safe work practices due to the hazards of acids and other materials used
Applications
Acid pickling is primarily applied in the following situations:
- Preparation of New Steelwork: Used before applying protective paint systems in industrial, construction, or manufacturing settings.
- Delicate or Thin Steel Surfaces: Especially valuable when abrasive blasting might distort or damage the substrate.
- Complex Structures: Suitable for internal and external areas, including parts with intricate geometries that are challenging to clean with mechanical methods.
- Quality-critical Environments: Ensures optimal adhesion and performance of paints and related products by effectively removing corrosion products and contaminants.
Key practical benefits include:
- Achieving a clean, chemically active surface to maximize coating adhesion
- Reducing the risk of coating failure caused by embedded contaminants or incomplete rust removal
- Compatibility with subsequent conversion coatings (e.g., phosphatising) or alternative treatments to enhance corrosion protection
Related Standards
To ensure optimal steel surface preparation and paint performance, the following related standards are frequently referenced alongside SIST EN ISO 8504-4:
- ISO 8501 (all parts): Visual assessment of surface cleanliness of steel substrates
- ISO 8502 (all parts): Tests for the assessment of surface cleanliness, providing methods for verifying the effectiveness of acid pickling
- ISO 8503 (all parts): Surface roughness characteristics of blasted steel substrates
- ISO 9717: Metallic and other inorganic coatings - Phosphate conversion coating of metals, referenced for post-pickling treatment options
- ISO 12944-4: Corrosion protection of steel structures by protective paint systems - Types of surface and surface preparation
Using SIST EN ISO 8504-4:2025 together with these standards supports a holistic, standardized approach to steel substrate preparation, ensuring durability and long-term performance of protective coatings in industrial and construction sectors.
Keywords: steel substrate preparation, acid pickling, surface preparation methods, rust removal, mill scale removal, steel surface cleanliness, paint adhesion, ISO 8504-4, protective coating performance, conversion coating, surface treatment standard, SIST standards.
