Introduction

The performance of protective coatings of paint and related products applied to steel is significantly affected by the state of the steel surface immediately prior to painting. The principal factors that are known to influence this performance are:

a) the presence of rust and mill scale;
b) the presence of surface contaminants, including salts, dust, oils and greases;
c) the surface profile.

The ISO 8501, ISO 8502 and ISO 8503 series have been prepared to provide methods of assessing these factors, while the ISO 8504 series provides guidance on the preparation methods that are available for cleaning steel substrates, indicating the capabilities of each in attaining specified levels of cleanliness.

These international standards do not contain recommendations for the protective coating systems to be applied to the steel surface. Neither do they contain recommendations for the surface quality requirements for specific situations, even though surface quality can have a direct influence on the choice of protective coating to be applied and on its performance. Such recommendations are found in other documents such as national standards and codes of practice. It is necessary for the users of these international standards to ensure that the qualities specified are:

— compatible and appropriate both for the environmental conditions to which the steel will be exposed and for the protective coating system to be used;
— within the capability of the cleaning procedure specified.

The four series of international standards referred to above deal with the following aspects of preparation of steel substrates:

— visual assessment of surface cleanliness (see ISO 8501 series);
— tests for the assessment of surface cleanliness (see ISO 8502 series);
— surface roughness characteristics of blast-cleaned steel substrates (see ISO 8503 series);
— surface preparation methods (see ISO 8504 series).

Each of these series of international standards is in turn divided into separate parts.

This document, along with the other parts of the ISO 8502 series, specifies tests for the assessment of surface cleanliness. In connection with such tests, there are several methods for the extraction, for analysis, of soluble contaminants on surfaces to be painted. Some of these methods are based on the swabbing of comparatively large test surfaces. This technique provides average values of the contamination present, but it might conceal localized concentrations of contaminants. Swabbing might not ensure sufficient penetration to dissolve all of the deep-seated contamination such as ferrous salts. Furthermore, the solvent used affects the dissolution rate and what contaminants are dissolved. This document covers sampling with a weak acid as solvent.

There are other methods, however, which use small cells for the liquid to remove and collect the surface contaminants. The cells (rigid or flexible) are attached to test surfaces where soluble contaminants could be expected, for example where pitting has occurred. This technique usually provides more accurate point values of the contamination present.

BS EN ISO 8502-15:2024

Preparation of steel substrates before application of paints and related products. Tests for the assessment of surface cleanliness - Extraction of soluble contaminants for analysis by acid extraction

Current

Published:

31 Jan 2025