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:

— the presence of rust and mill scale;
— the presence of surface contaminants, including salts, dust, oils and greases;
— the surface profile.

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

This document describes acid pickling, which is an effective method for surface preparation. It is widely applicable because this method of surface preparation has a number of versatile features listed below.

a) In general, the equipment is stationary but can be mobile.
b) The method is applicable to most types and forms of steel surface, especially those that would deform by abrasive blast-cleaning.
c) It is possible to remove rust or mill scale and non-steel metal traces from internal, external and complex structures surfaces.
d) Acid pickling can be performed for decorative and or aesthetic purposes.

There are several items that should be included in the purchaser's procurement documents to supplement this document. Surface imperfections should be considered before surface preparation and coating application. The ISO 8504 series does not contain recommendations for surface cleaning of equipment and cleaning of pipelines (such as chemical pipelines, petroleum pipelines).

The ISO 8504 series does not contain recommendations for the protective coating system to be applied to the steel surface. The ISO 8504 series does not contain recommendations on surface quality requirements for specific situations even though surface quality can have a direct influence on the choice of protective coating and on its performance. Such recommendations are found in other documents such as national standards and codes of practice. The ISO 8504 series is used to ensure that the specified qualities are:

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

BS EN ISO 8504-4:2024

Preparation of steel substrates before application of paints and related products. Surface preparation methods - Acid pickling

Current

Published:

31 Dec 2024