Assessment of Surface Cleanliness by Soluble Salts Measurement

When the steel is passed over the surface, harmful substances can be removed from the steel surface, and the primer has good adhesion, helping to reduce the content of contaminants that cause corrosion. Because of its practical usage and simplicity, electrical conductivity method is becoming widely used in the quality control of steel substrates before application of paints and related products.

The EC500T and EC510T conductivity meter could test electrical conductivity of extraction to access various water-soluble salts on steel surfaces .

Standard Reference

ISO 8502-9:2020 

Preparation of steel substrates before application of paints and related products — Tests for the assessment of surface cleanliness — Part 9: Field method for the conductometric determination of water-soluble salts

The Principle

This document specifies a field method for the assessment of the surface density of various water-soluble salts on steel surfaces, before and/or after surface preparation, by conductometric determination. The individual surface densities of the salt composition like chlorides, sulphates, sodium, etc, cannot be determined by this method.

This method assesses only contaminants that forms an electrolyte (ions) when in contact with water. These represent the greater part of the contaminants.

Sampling

ISO 8502-6

Preparation of steel substrates before application of paints and related products -- Tests for the assessment of surface cleanliness - Part 6: Extraction of soluble contaminants for analysis using adhesive cells The Bresle method

The Measurement

The conductometer shall be compensated to 25 ºC.

Conductometer with temperature compensation and the most accurate range possible, from 0 mS/m(0 uS/cm) to 20 mS/m (200 uS/cm) with a resolution of 0,01 mS/m (0,1 uS/cm), 20 mS/m (200 pS/cmto 200 mS/m (2 000 pS/cm) with a resolution of 0,1 mS/m (1 uS/cm) and an accuracy of 2 %.

It allows to use a direct measuring type electrode or a submerged measuring type electrode.

Either being an immersion type instrument, where the electrode is submerged in the liquid under test, or a direct measuring type instrument where the liquid under test is injected in the measurement cell of the instrument.

The EC500T and EC510T conductivity meter could test electrical conductivity of a extract obtained by Bresle method.

∆γ=γ₂-γ₁

γ₁，Blank Conductivity: It needs to measure the equipment blank, including the beaker, syringe and the EC electrode.

γ₂, Electrical Conductivity of the extraction.

It needs to calculation the total amount of salt on the surface.

The relationship between mass of salts and conductivity can be expressed as

m=C·V·∆γ

where

C is a constant for the salts on the surface，is a constant for the salts on the surface, approximately equal to 5 kg·m^-2·s^-1 at 25 ºC.

V is the volume of water used for extraction.

∆γ is the change in conductivity, ie. the difference between the blank conductivity measured and the conductivity of the extraction.

Recommended Configuration

EC510T Conductivity Meter

EC500T 

50. Conductivity Range: 0.000 μS/cm～2000mS/cm
50. Conductivity Resolution: 0.001 μS/cm, automatic switching according to the range
50. Conductivity Accuracy: ±0.5% (FS)

EC510T 

50. Conductivity Range: 0.000 μS/cm～3000mS/cm
50. Conductivity Resolution: 0.001 μS/cm, automatic switching according to the range
50. Conductivity Accuracy: ±0.5% (FS)

Electrodes

1. DJS-0.1VTG Conductivity Electrode, apply to test the condcutivity of sample.