A few words
ISO (International Organization for Standardization) is a worldwide standardization association. The development of international standards is usually carried out by ISO technical committees, and members who are interested in any subject developed by the Technical Committee are entitled to work closely with the Technical Committee (CIE) on all electrical technical standards.

Draft international standards are voted on by members, and publication as international standards requires approval by at least 75% of members.

International standard ISO7253 was developed by technical committee ISO/TC 35 “Paints and Finishes”, sub-committee SC9 “General test methods for paints and Finishes”.

This standard replaces the first version (ISO 7253:1984) with the following major changes:

a) Added correction methods for checking internal erosion of appliances;

b) More specifically describes the preparation of bottom plate scratches.

Appendices A, B, and C are the standard appendices.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

Brief introduction
There is little direct relationship between the salt spray effect of organic coatings and corrosion resistance in other environments. This is due to the fact that the influence of each factor in the erosion process can change at any time depending on the conditions encountered, such as the formation of protective films. Therefore, the results obtained from the tests should not be regarded as a direct guide to the corrosion resistance of the coating in all environments. Nor should the performance of the different coatings tested be taken as a direct guide to the corrosion resistance of the coatings in use, even under harsh conditions such as seawater. However, methods for checking the quality of the paint or paint system should be given.

Note 1: The instruments and operating conditions described in this standard shall comply with (but need not be identical to) the requirements of ISO 9927:1990 “Salt spray Corrosion Resistance Test in artificial atmosphere”. The minimum allowable size of the test chamber for paints, varices and related products is larger (see 6.1).

ISO 7253:1996(E)

Paints and varnishes — Neutral salt spray corrosion test

1 Scope
This standard is one of a series of standards for sampling and testing of coatings, varnishes and related products.

This standard specifies the method for determining the resistance of coatings to neutral salt spray corrosion according to coating requirements or product instructions.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

2 Reference standards
The FOLLOWING STANDARDS constitute THE provisions of THIS STANDARD by reference IN this STANDARD. At the time of publication, the versions shown shall be valid. The parties using them shall explore the use of new versions of each standard.

ISO 1512:1991 Paints and finishes – Sampling of liquid or paste products

ISO 1513:1992 Paints and finishes – Examination and preparation of specimens

ISO 1514:1993 Paints and varnishes — Standard base plates for testing purposes

ISO 2808:1) Paints and varnishes — Determination of coating thickness

ISO 3270:1984 Paints, varnishes and their raw materials – Temperature and humidity in condition and test

ISO 3574:1986 Cold rolled carbon steel sheets for industrial use and rolling quality

ISO 3696:1987 Description and test methods for water use in analytical laboratories

ISO 4628-1:1982 Paints and finishes – Determination of coating grades (strength, number and size of general defects)

Part 1: General principles and classification

ISO 4628-2:1982 Paints and finishes – Determination of coating grades (strength, number and size of general defects)

Part 2: Representation of foaming degree

ISO 4628-3:1982 Paints and finishes – Determination of coating grades (strength, number and size of general defects)

Part 3: Indication of corrosion degree

ISO 4628-4:1982 Paints and finishes – Determination of coating grades (strength, number and size of general defects)

Part 4: Representation of crack degree

ISO 4628-5:1982 Paints and finishes – Determination of coating grades (strength, number and size of general defects)

Part 5: Representation of the degree of shedding

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

3 Principles
A coating test floor was exposed to neutral salt spray and the effect of exposure was assessed according to standards agreed by the parties concerned.

4 Information to be explained
For some special coatings, the test methods specified in this standard shall be supplemented by other documents, Annex A.

5 Test solution
5.1 Dissolve Nacl in water with at least grade 3 purity conforming to ISO 3696 to make a solution with a concentration of (50±5) g/l. Nacl is white, pure at least 99.6%(m/m), free of copper and nickel, NaI content should not be more than 0.1% (m/m), if the PH value is not within the range of 6.0-7.0, salt, water or both should be checked for harmful impurities.

5.2 Adjust the above PH value so that the PH value of the spray in the test chamber is between 6.5 and 7.2 (see Clause 6). If necessary, the PH value can be adjusted by adding analytical sodium bicarbonate or hydrochloric acid solution.

Note 2: It should be noted that carbon dioxide spillage may cause PH changes during injection of test solution. This change can be avoided by reducing the carbon dioxide content of the solution. For example, heating it to above 35 ° C or preparing a solution with freshly boiling water before placing it in the instrument.

5.3 Before placing in the sink of the instrument, the test solution should be filtered to remove solid material and avoid possible plugging of the nozzle.

6 Instruments
Ordinary laboratory instruments and glassware, as follows:

6.1 Spray box: made of anticorrosive material or lined, with a top cover, can prevent condensate gas to drop on the test floor. The volume of the test chamber should not be less than 0.4m3, because the space is too small to ensure uniform spraying.

The chamber shall be of such size and shape that the amount of solution in the spray collection device (6.4) shall be within the limits described in 10.2.

Test chambers larger than 2m3 are difficult to operate unless careful consideration is given to their design and construction, which should be considered in Appendix B.

6.2 Adjustable heater: fully maintain the temperature of the test chamber and its contents in accordance with the requirements (see 10.1), the temperature is controlled by a thermostatic unit placed at least 100mm away from the wall of the test chamber. The thermometer that can be read outside should be completely placed in the test box, and should be at least 100mm away from the wall, top and bottom.

6.3 Spraying device: including a supply device that can provide clean compressed air with continuous pressure and temperature, a tank for holding the test liquid to be sprayed, and one or more nozzles for erosion of the test liquid.

The air pressure supplied to each nozzle shall pass through a filter in order to remove oil or solid particles, and its pressure shall be 70kPa — 170kPa (1kPa=1kN/m2=0.01bar). In order to prevent the evaporation of spraying droplets, the air pressure air should be humidified through a water saturated column before entering each nozzle. The water contained should be at least grade 3 purity water stipulated by ISO3696. The temperature is several degrees Celsius higher than that in the test chamber. Adjust to keep the spray collection rate in the test chamber and the concentration of collected spray Nacl within specified limits (see 10.2).

The tank containing the test solution shall be made of a solution resistant material and shall be able to provide a certain amount of solution to the nozzle at any time.

Nozzles should be made of inert materials, such as glass, plastic.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

The test chamber should be breathable to ensure that there is no pressure accumulation inside the chamber, and the external environment of the test chamber should not affect the interior.

Note 3: BaffLES CAN BE USED TO AVOID DIRECT impact of spraying on the test floor. The use of adjustable baffles is helpful in obtaining uniform spraying throughout the test chamber.

6.4 Spray collection device: made of inert chemical materials (see Note 4). The device shall be placed in the test floor placement area of the test chamber, with at least one close to the nozzle and one away from the nozzle. It should be placed to collect only spray fluid and not droplets from the test floor, test chamber, or container components. The number of collecting devices is at least twice the number of nozzles.

Note 4: A glass or plastic funnel with a neck inserted into the measuring cylinder is a suitable collection device, and the collection area of a funnel with a diameter of 100mm is about 80cm2.

6.5 Test plate container: Can support the test board in the vertical direction deviation of 15° — 25°, usually by inert non-metallic materials such as glass, plastic or appropriate coated wood, in addition, if you need to lift the test board, the material should be synthetic fiber, cotton thread or other inert insulating materials, but never use metal material test board, can be placed in the test box at different heights, However, the test liquid dropped on the test plate or container of the same height cannot fall on the lower test plate.

6.6 If the equipment has been subjected to spraying test or other tests, and the test solution is different from that specified in the test, it should be effectively cleaned before use.

6.7 The calibration of the equipment shall be carried out according to Appendix C.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

7 Sampling
According to ISO1512 requirements, take a representative sample of the product for testing (take a sample of each product in the case of multi-coating).

Inspect and prepare samples according to ISO 1513 requirements.

8 Test plate
8.1 Materials and Dimensions

Unless otherwise stated or agreed, the test plate shall be a polished steel plate conforming to ISO1514, approximately 150mm x 100mm x 1mm.

8.2 Prepare and coat the test plate

Unless otherwise stated, prepare each test plate according to ISO1514 and apply the product to be tested in the specified method.

The back and edge of the test plate should also be painted unless otherwise stated.

If the coating on the back and edge of the test plate is different from the product to be tested, its corrosion resistance is greater than that of the product to be tested.

8.3 Drying and placing

Dried (or oven-dried) and hardened (if appropriate) coated test plates shall be carried out at the specified time and under the specified conditions. Unless otherwise stated, it should be placed in an environment of (23±2) ° C and relative humidity of (50±5) % for at least 16 hours, without air circulation and direct sunlight, and the test should be carried out as soon as possible.

8.4 Thickness of the coating

The thickness of the dry coating was determined in mm by one of the non-destructive methods described in ISO2808.

8.5 Preparation of scratches

All scratch spacing and edge spacing from the test plate should be at least 25mm. If indicated, scratch or scratch marks should be made to the substrate.

Scratch with a hard-pointed scratching instrument, unless otherwise agreed, in parallel or upwardly widened sections, exposed to a metal substrate of 0.3mm — 1mm.

One or two scratches should be made and, unless otherwise agreed, should be parallel to the long sides of the test plate.

Do not cut scratches with a knife.

For aluminum test plates, the two scratches should be vertical but not intersecting, one parallel to the rolling direction, the other vertical.

Note 5: If zinc or zinc alloy coated steel plate is used as a test plate, unless otherwise stated, the scratch should reach the zinc coating and not the steel plate.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

9 Test plate exposure method
9.1 The test plate placed in the test chamber shall not be in the straight direction of the nozzle injection.

9.2 The orientation of each test surface is placed in the test chamber and the vertical direction is between 15℃ and 25℃.

Note 6: The Angle at which each test plate is placed in the test chamber is important.

Depending on the agreement of the parties, it is sometimes necessary to expose coated parts of different shapes. When doing such tests, it is important to expose the shape of the part in the usual condition at the time of use. Such limitations facilitate the placement of components with minimal damage from fluid flow.

If the coated part is impacted in the direction of the coating, other test plates and specimens cannot be tested at the same time.

The degree of breakage of the coating in different directions may vary and should be given as appropriate in the conclusion.

9.3 The test plates should not be placed in contact with each other or with the test chamber, so that the specimens are exposed when spraying where they are placed independently.

10 Operating Conditions
10.1 The temperature in the spraying test chamber should be (35±2) ℃.

10.2 At least once every 24 hours, the measured average spray collection speed should be 1ml/h — 2.5ml/h (for 80cm2 horizontal spray collection device). The Nacl concentration in the collected test solution was (50±10) g/l, and the PH value was 6.5-7.2 (see 5.2).

10.3 The sprayed test solution cannot be used again.

11 Procedures
It should be measured twice unless otherwise stated.

11.1 Install the instrument and adjust it to meet the requirements of Clause 10.

11.2 Place the test plate in the test chamber as required by Clause 9.

11.3 Close the test chamber, start spraying with the nozzle, and spray continuously within the specified time (except for inspection, replay or removal of the test plate, short interruption every day, see Clause 12). Check and replenish the tank pilot test liquid to make it still meet the requirements of Clause 10.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

12 Test board inspection
Periodically check the test plate, pay attention not to damage the test surface, the test plate should be evaluated as soon as possible, the test box stop every 24 hours not more than 30 minutes. Don’t let the test board dry. If possible, inspections should be carried out at the same time each day.

At the end of the test, take out the test plate from the instrument and flush the residue left on the test surface with clean hot water. Dry the test plate quickly, check the surface of the test plate for corrosion, such as blisters, rust spots, creep (all from scratches), in accordance with the requirements of parts 1 to 5 of ISO4628 (see Appendix A and Clause 9). If necessary, place the test plate for a specified time (see conditions specified in ISO3270), and then check the corrosion of the test plate.

If it is necessary to check the substrate for corrosion, remove the coating by the specified method.

13 Accuracy
The timing of the accuracy has not yet been determined.

The ISO/TC 35 committee is preparing to develop precision for all relevant standards (including ISO7253), which will be included in the standard when developed.

Users of this standard should note that due to the objective nature of coating corrosion assessment, accuracy should depend on a number of factors, including assessment method, preparation of the test plate, thickness of the coating, drying and placement of the test plate, and preparation of scratches.

However, the method is useful in comparing different coatings against neutral salt spray corrosion and in relative grading for a series of coated test plates that exhibit significant differences in salt spray.

ISO 7253-1996 – Determination of neutral salt spray resistance of paints and varnishes

14 Test Report

The test report shall at least include the following:

a) identifying the necessary details of the product;

b) Reference to the international standard (ISO 7253);

c) Supplementary information relating to Appendix A;

d) can provide reference to international or national standards, product descriptions or other materials for the information in c);

e) The duration of the test;

f) whether one or more scratches were made prior to exposure, and if so, their characteristics and location (see 8.5);

g) Whether the position of the test plate has been changed;

h) test results regarding the stated requirements;

i) errors in the prescribed test process;

j) Test date.

Appendix A (Standard Appendix)
Additional information required

This appendix sets out the supplementary terms suitable for the test method.

The required information is better recognized by the relevant parties and may be obtained in part or in whole from international standards, national standards or other information related to the test product.

a) Office