Bresle method

The Bresle method is a method used to determine the concentration on soluble salts on surfaces prior to coating applications. These salts can cause serious adhesion problems after time. The Bresle method is the industry's standard for determining if a surface can be coated.

Importance

Salt is almost omnipresent in the coastal area’s. You can taste it on your lips after a walk on the beach. Salt is in a concentration of about 3.5% w/w present in sea water. With spray from waves and other means this salt gets into the air as an aerosol, and eventually as a dust like particle. This salt dust can be found everywhere near the coast. Salt has the property of being hygroscopic. This hygroscopic property makes it so dangerous at coating applications.

Coating adhesion is heavily influenced by the presence of salt between the steel and coating. The hygroscopic property draws water trough the coating to the salt causing poor adhesion and corrosion. Herewith reducing the life expectancy of the coating by many years. Shot blasting is often seen as an good method to clean surfaces, however when it comes to salts shot blasting will only increase the problem. When shot blasting the salt pollution will only be forced further into the surface.

Origin of the Bresle method

The Bresle method was first launched in 1995 in the ISO 8502-6 and ISO8502-9 standards. The test was developed to measure soluble salt concentration on surfaces prior to blasting and coating. Not only the ISO but also the US Navy, IMO, NAVSEA and ASTM adopted this method as their standard. The method developed is even at present still the primary and most flexible test method for soluble salts on surfaces.

Principle

The Bresle Method is based on the use of the difference of conductivity of salts in water. Each salt has a different conductivity in water. This correlation between concentration and conductivity can be found in for example “Handbook of chemistry and physics”. This relationship between concentration and conductivity only applies when the dissolved salt is known. Fortunately not every salt causes the same increase in conductivity. Sodium chloride causes an big increase in conductivity.

Salt residue is First dissolved after applying an special patch. This Patch has an hollow opening, that is after being applied to the test surface injected with deionized water. Soluble salts that are present on the surface will be dissolved in the deionized water. The extracted fluid is filled up to a specified volume and the conductivity is measured. From this conductivity the amount of soluble salts measured as Sodium Chloride can be determined.

Different calculation factors

Through the years multiple factors developed to determine the salt concentration on the surface. The factors are influenced by multiple causes. Some of these causes are:

- Difference in determined salt type.

- Difference in volume of measurement sulotion.

- Different work or reference temperature.

- Different read out value of the used meter.

The two biggest causes for errors in field application are deviations in the salt solutions to be determined and the used conductivity meter.

The mostly used calculation factors are:Factor 6 For the determination of soluble salts measured as Sodium ChlorideFactor 5 For the determination of soluble salts measured as mixed salts.Factor 3.6 For the determination of soluble salts measured as Cloride

{| class="wikitable"
-! Conductivity µS/cm! Conductivity mS/m! As Chloride µg/cm2! As Chloride mg/m2! As Sodium Chloride µg/cm2! As Sodium Chloride mg/m2! As mixed salts µg/cm2! As mixed salts mg/m2
-! 1! 0,1
0,36
3,6
0,6
6
0,5
5
-
5
0,5
1,8
18
3
30
2,5
25
-
10
1
3,6
36
6
60
5
50
-
20
2
7,2
72
12
120
10
100
-

The results

The maximum amount of salt that is allowed on the surface is determined by the coating supplier and the yard. No clear standard values can be given.

Measurement tools

One of the first suppliers to provide a complete test kit according to the Bresle Method was TQC. At present there are multiple suppliers with all slight differentiations in the test kit. These variations often result in misunderstandings of the inspectors and contractors.

References

1. Handbook of Chemistry and Physics

2. ISO 8502-6, “Extraction for soluble contaminants for analysis – The Bresle Method ”

3. ISO 8502-9, “Field method for soluble salts by conductometric measurement”

4. Bresle-method site by TQC [http://www.bresle.nl]

Bresle comparison / calculation table. Courtesy of TQC