This is the modified Salt Spray Test

Introduction

The ASTM G85 standard consists of a set of 5 modifications to the ASTM B117 continuous salt spray test.These modifications are referred to in ASTM G85 as annexes A1 to A5 and are applicable to ferrous and nonferrous metals, and also to organic and inorganic coatings.

ASTM G85 annex A1 - Acetic acid salt spray test, continuous

This was orginally published as ASTM B287

ASTM G85 annex A2 – cyclic acidified salt spray test

This test was developed for exfoliation testing on certain aluminium alloys and was originally known as the MASTMAASIS test

ASTM G85 annex A3 – seawater acidified test, cyclic

This test was originally published as ASTM G43, and is used to determine corrosion resistance in a severe marine atmosphere. It is widely referred to as the SWAAT test.

ASTM G85 annex A4 – Sulphur dioxide (SO2 ) salt spray test, cyclic

The test was originally developed by the U S Navy to simulate exfoliation corrosion on aircraft carriers.

ASTM G85 annex A5 – dilute electrolyte cyclic fog /dry test.

This test was developed by F.D. Timmins in conjunction with Mebon Paints, a UK manufacturer of surface coatings, during the 1970's and became widely known as the PROHESION

These tests have evolved to address the need for a corrosion test capable of replicating the effects of naturally occurring corrosion and accelerate these effects.

This acceleration arises through the use of chemically altered salt spray solutions, often combined with other test climates and in most cases, the relatively rapid cycling of these test climates over time.

The type of test chambers used for modified salt spray testing to ASTM G85 are generally similar to the chambers used for testing to ASTM B117, but will often have some additional features, such as an automatic climate cycling control system.

Test Conditions

ASTM G85 annex A1 – acetic acid salt spray test, continuous

Test specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of acidified (pH 3.1to 3.3) salt water solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour, in a chamber temperature of +35oC. This climate is maintained under constant steady state conditions. The test duration is variable.

ASTM G85 annex A2 – cyclic acidified salt spray test

Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises of the following 3 part repeating cycle. 0.75 hours exposure to a continuous indirect spray of acidified (pH 2.8 to 3.0) salt water solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour. This is followed by 2.0 hours exposure to an air drying (purge) climate. This is followed by 3.25 hours exposure to a high humidity climate of 95%RH. The entire test cycle is at a constant chamber temperature of +49oC. The number of cycle repeats and therefore the test duration is variable.

ASTM G85 annex A3 – seawater acidified test, cyclic

Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises of the following 2 part repeating cycle. 30 minutes exposure to a continuous indirect spray of acidified (pH 2.8 to 3.0) synthetic seawater solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour. This is followed by 90 minutes exposure to a high humidity climate of above 98%RH. The entire test cycle is at a constant chamber temperature of +49oC (may be reduced to +24 to +35oC for organically coated specimens). The number of cycle repeats and therefore the test duration is variable. 

 

ASTM G85 annex A4 – Sulphur dioxide (SO2 ) salt spray test, cyclic

Test specimens are placed in an enclosed chamber, and exposed to 1 of 2 possible changing climate cycles. In either case, the exposure to salt spray may be salt water spray or synthetic sea water spray. The most appropriate test cycle and spray solutions are to be agreed between purchaser and seller.

The first climate cycle comprises of a continuous indirect spray of neutral (pH 6.5 to 7.2) salt water/synthetic seawater solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour. During this spraying, the chamber is dosed with SO2 gas at a rate of 35cm³/minute/m³ of chamber volume, for 1 hour in every 6 hours of spraying. The entire test cycle is at a constant chamber temperature of +35oC. The number of cycle repeats and therefore the test duration is variable.

The second climate cycle comprises of 0.5 hours of continuous indirect spray of neutral (pH 6.5 to 7.2) salt water/synthetic seawater solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour. This is followed by 0.5 hours of dosing with SO2 gas at a rate of 35cm³/minute/m³ of chamber volume. This is followed by 2.0 hours of high humidity soak. The entire test cycle is at a constant chamber temperature of +35oC. The number of cycle repeats and therefore the test duration is variable.

ASTM G85 annex A5 – dilute electrolyte cyclic fog /dry test

Test specimens are placed in an enclosed chamber, and exposed to a changing climate that comprises of the following 2 part repeating cycle. 1.0 hours exposure to a continuous indirect spray of dilute acidified (pH 5.0 to 5.4) salt water solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour, in an ambient chamber temperature (21 to 27oC). This is followed by 1.0 hours exposure to an air drying (purge) climate, in a chamber temperature of +35C. The number of cycle repeats and therefore the test duration is variable.

Typical Applications

ASTM G85 annex A1 - acetic acid salt spray test, continuous

Can be used to test the relative resistance to corrosion of decorative chromium plating on steel and zinc based die castings, when exposed to an acetic acid salt spray climate at an elevated temperature.

ASTM G85 annex A2 - cyclic acidified salt spray test

Can be used to test the relative resistance to corrosion of aluminium alloys when exposed to a changing climate of acetic acid salt spray, followed by air drying, followed by high humidity, all at an elevated temperature. This test was developed for exfoliation testing on certain aluminum alloys. Exfoliation testing determines the rate at which corrosion products form and fall away from the body of the test sample.

ASTM G85 annex A3 - seawater acidified test, cyclic

Can be used to test the relative resistance to corrosion of coated or uncoated aluminium alloys and other metals, when exposed to an changing climate of acidified synthetic seawater spray, followed by a high humidity, both at an elevated temperature.

ASTM G85 annex A4 - Sulphur dioxide (SO2 ) salt spray test, cyclic

Can be used to test the relative resistance to corrosion of product samples that are likely to encounter a combined SO2/salt spray/acid rain environment during their usual service life.

ASTM G85-Annex 5– dilute electrolyte cyclic fog /dry test 

Can be used to test the relative resistance to corrosion of paints on steel, and is a useful tool for the evaluation of prefinished steel building products. 

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