ISO 7253 Paints and Varnishes – Determination of Resistance to Neutral Salt Spray Fog

ISO 7253 is a globally recognized standard for evaluating the resistance of paints and varnishes to neutral salt spray. By conducting corrosion tests according to this standard, manufacturers can ensure the durability and performance of their coatings. Utilizing salt spray chambers and testing equipment enables accurate assessment of a coating’s resistance to corrosion, leading to improved product quality and customer satisfaction. ISO 7253 is an international standard that specifies a test method for evaluating the resistance of paints and varnishes to neutral salt spray (fog).

ISO 7253 provides a standardized method for evaluating the performance of paints and varnishes when subjected to salt spray environments. It simulates the effects of long-term exposure to corrosion-inducing conditions such as saltwater, rain, and humidity. Compliance with ISO 7253 ensures that coatings meet the required standards, guaranteeing their performance and durability. This test is crucial in determining the corrosion resistance of coatings and ensuring their durability in various environments.

Mode and Description WEW-YW-60D WEW-YW-90D WEW-YW-110D
Inner Dimension(mm) 600*450*400 900*600*500 1000*750*500
Outer Dimension(mm) 1070*600*1180 1410*880*1280 1600*1050*1200
Test Room Size (Liters) 108 Liters 270 Liters 420 Liters
Power Supply AC 220V, 50Hz AC 220V, 50Hz AC 220V, 50Hz
Power Current 1Phase, 1.5 kW 1Phase, 2.0 kW 1Phase, 2.5 kW
Lid Opening Method Manual Opening Manual Opening Manual Opening
Brine Tank Volume 15 Literes 25 Literes 30 Literes
Test Room Temp Range Ambient Temperature +5℃ – +30℃, Ventilation is recommended, if the temperature exceeds +30℃, it is recommended to adjust the room temperature by suitable means. Ambient humidity should be controlled below 80%RH.
Test Room Temp Range RT+10℃ – +55℃ RT+10℃ – +55℃ RT+10℃ – +55℃
Saturated Barrel  RT+10℃ – +70℃ (Purpose: Heating and filtering of compressed air to reduce nozzle crystallisation.)
Temp Performance Temperature Uniformity: ≤2℃,  Temperature Fluctuation: ≤ ±0.5°C Temperature Uniformity: ≤2℃, 
Salt Mist Settling Rate 1~2 ml/80 cm2/h (Take 16 Hours To Test The Average Value)|1~2 ml/80 cm2/h
Spray Method Continuous, Intermittent,  Programmable Tests Continuous, Intermittent, 
Safety Devices Low Water Level Alarm|Over-Temperature Alarm (Mechanical Over-Temperature Protection + Electronic Over-Temperature Protection Double Over-Temperature Protection)
Air Requirements Inlet Pressure Above 0.4Mp. Two-Stage Pressure Regulation. Spray Pressure 0.07~0.17mp (Adjustable)
Sample Holder One Set Each Of V-Groove And O-Round Bar (Combined To Form An Angle Of 20°±5%).
Standard Configuration 1 Set Of V-Type/O-Type Shelves, 2 Bottles Of Test Drug Sodium Chloride (500g/Bottle), 1 Plastic Anti-Rust Bucket (5l Capacity), 1 Nozzle
ISO 7253 Paints and Varnishes - Determination of Resistance to Neutral Salt Spray (Fog)
5.1The test solution shall be prepared by dissolving sodium chloride in water of at least grade 3 purity as defined inISO 3696 to produce a concentration of (50±5) gl.The sodium chloride shall be white, of minimum assay 99,6 %(m/m), and substantially free from copper and nickel; it shall contain not more than 0,1 %(m m) of sodium iodide. lfthe pH of the solution is outside the range 6,0 to 7,0, the presence of undesirable impurities in the salt or the wateror both shall be investigated. 5 Test Solution
5.2 The pH of the test solution (5.1) shall be adjusted so that the pH of sprayed solution collected within the testcabinet (see clause 6) shall be between 6,5 and 7,2.Any necessary adjustment to the pH shall be made byadditions of solutions of either hydrochloric acid or sodium bicarbonate of analytical grade.
Note 2: Attention is drawn to the possible changes in pH resulting from loss of carbon dioxide from the test solution where it is sprayed.Such changes may be avoided by reducing the carbon dioxide content of the solution by, for example, heating it to atemperature above 35 *C before it is placed in the apparatus or by making the solution from freshly boiled water.
5.3 The test solution shall be filtered before it is placed in the reservoir of the apparatus, in order to remove anysolid matter which might block the nozzle(s) of the spraying device.
Ordinary laboratory apparatus and glassware, together with the following: 6 Apparatus
6.1 A spray cabinet, made of,or lined with, material resistant to corrosion by the spray and with a roof whichprevents condensed moisture dripping on to the test panels. The cabinet shall have a capacity of not less than0,4 m3 since, with smaller volumes, difficulties are experienced in ensuring even distribution of spray.
The size and shape of the cabinet shall be such that the quantity of solution colected in the spray-collecting devices(6.4) is within the limits stated in 10.2.
Cabinets with a volume greater than 2 m3 will be difficult to operate unless careful consideration is given to theirdesign and construction. Factors which shall be taken into consideration are given in annex B.
6.2 Adjustable heater, adequate to maintain the cabinet and its contents at the specified temperature (see 10.1).The temperature shall be controlled by a thermostat element placed within the cabinet at least 100 mm from thewalls. A thermometer, capable of being read from the outside, shall be placed wholly within the cabinet at least100 mm from the walls, roof or floor.
6.3 Spraying device, comprising a supply of clean compressed air of constant pressure and humidity, a resevoir containing the solution to be sprayed and one or more spray nozzles made of material resistant to the solution.
The compressed air supply to each spray nozzle shall be passed through a flter to remove all traces of oil or solidmatter and shall be at a pressure of 70 kPa to 170 kPa2). in order to prevent evaporation of the spray droplets, theair shall be humidified before entering each nozzle by passage through a saturation column containing water of atleast grade 3 purity as defined in IS0 3696 at a temperature several degrees Celsius higher than that of the cabinet.The actual temperature of the water will depend on the pressure used and on the type of spray nozzle, and sha be adjusted so that the rate of collection of spray in the cabinet and the sodium chloride concentration of the spraycollected are kept within the specified limits (see 10.2).
The reservoir containing the test solution shall be made of material resistant to the solution and shall be providedwith a means of delivering a constant volume of solution to the spray nozzles at all times.
The spray nozzles shall be made of inert material, for example glass or plastic.
The cabinet shall be vented to ensure that there is no build up of pressure within the cabinet and in such a way thatthe environment outside the cabinet does not influence that inside the cabinet.
Note3 Baffies may be used to prevent direct impingement of spray on the test panels, and the use of adjustable baffies ishelpful in obtaining uniform distribution of spray throughout the cabinet.
6.4 Spray-collecting devices, of chemically inert material (see Note 4).The collecting devices shall be placed inthe zone of the cabinet where the test panels are placed, at least one close to a spray nozzle and one remote froma spray nozzle. They shall be placed so that only spray is colected, and not liquid dripping from test panels or partsof the holders or cabinet. The number of collecting devices shall be at least twice the number of spray nozzles.
Note 4: Glass or plastic funnels with their stems inserted into graduated cylinders have been found to be suitable collectingdevices.Funnels with a diameter of 100 mm have a collecting area of approximately 80 cm?.
6.5 Test panel holders, capable of supporting the test panels at an angle of between 15° and 25′ to the vertical, normally racks made of inert non-metallic material such as glass, plastic or suitably coated wood. Exceptionally , if itis necessary to suspend the test panels, the material used shall be synthetic fibre, cotton thread or another inertinsulating material, but on no account metalic material. The test panels may be located at different levels in thecabinet but they shall be positioned so that the solution cannot drip from panels or holders at one level on to otherpanels below.
6.6 lf the equipment has been used for a spray test, or for any other purpose, with a solution differing from thatspecified for this test, it shall be thoroughly cleaned before use.
6.7Calibration of the equipment shall be carried out as specified in annex C.

In addition to meeting the requirements of coating or product specifications, the determination of the resistance of coatings to neutral salt spray (fog) plays a crucial role in assessing the durability and quality of paints, varnishes, and related products. By subjecting these coatings to the intense corrosive and degrading effects of salt spray, this method enables manufacturers, suppliers, and customers to evaluate their performance and suitability for various applications and environments.

The neutral salt spray test serves as a valuable tool in predicting how coatings will withstand the challenges posed by harsh weather conditions, including coastal areas where high levels of salt and humidity prevail. This standardized procedure not only aids in comparing the performance of different coatings but also assists in identifying potential weaknesses, enabling further improvements in formulation and application techniques. By incorporating this method into the broader range of standards on sampling and testing, this International Standard enhances the reliability and consistency of assessments, contributing to the overall advancement of the paints, varnishes, and related industries.

salt spray testing
Corrosion testing is vital in industries dealing with the protection of materials against degradation. The ASTM (American Society for Testing and Materials) has developed several corrosion testing standards, including ASTM B117 for salt spray testing. ASTM standards provide guidelines for conducting tests, recording results, and interpreting data to determine the resistance of coatings to corrosion.
To perform corrosion tests according to ISO 7253 or ASTM standards, specialized equipment such as corrosion test chambers or salt spray chambers are used. These chambers create controlled environments that mimic the corrosive conditions a coating may encounter in real-world scenarios. Salt spray chambers allow for accurate monitoring and assessment of a coating’s resistance to corrosion.
The salt spray test involves subjecting coated specimens to a continuous salt-laden environment within the chamber. The duration of the test varies based on the requirements specified in ISO 7253 or other relevant standards. Typically, the test duration can range from a few hours to several weeks, depending on the intended application of the coating.
Take a representative sample of the product to be tested (or of each product in the case of a multi-coat system) as described in lSO 1512. 7 Sampling
Examine and prepare the sample for testing, as described in ISO 1513.
Unless otherwise specified or agreed, the test panels shall be of burnished steel complying with ISO 1514, and ofapproximate dimensions 150 mm x 100 mm x 1 mm. 8.1 Material and Dimensions 8 Test panels
Unless otherwise specified, prepare each test panel in accordance with lSO 1514 and then coat it by the specifiedmethod with the product or system under test. 8.2 Preparation and coating of panels
Uniess otherwise specified, the back and edges of the panel shall also be coated with the product or system undertest.
lf the coating on the back and edges of the panel differs from that of the product under test, it shall have a corrosionresistance greater than that of the product under test.
Dry (or stove) and age (if applicable) each coated test panel for the specified time under the specified conditions,and,unless otherwise specified, condition them at a temperature of (23 ±2)°C and a relative humidity of (50 ±5) %for at least 16 h, with free circulation of air and without exposing them to direct sunlight. The test procedure shallthen be carried out as soon as possible. 8.3 Drying and conditioning
Determine the thickness, in micrometres, of the dried coating by one of the non-destructive procedures described inISO 2808. 8.4 Thickness of coating
All scratches shall be at least 25 mm from each other and from any edge of the test panel.lf specified, make a straight scratch or scribed mark through the coating to the substrate. 8.5 Preparation of scratches
To apply the scratch, use a scratch instrument with a hard tip.The scratch shall have either parallel sides or anupwards-broadening cross-section which shows a width of 0,3 mm to 1,0 mm of the metallic substrate,unlessotherwise agreed.
One or two scratches may be applied. The scratch(es) shall be parallel to the longer edge of the test panel, unlessotherwise agreed. Cutting the scratch with a knife is not allowed.
For aluminium panels,two scratches shall be made which are perpendicular to, but do not intersect, each other.One scratch shall be parallel to the rolling direction and the other at right angles.
Note 5: lf zinc- or zinc-alloy-coated steel is used as a test panel the intention is that the scratch should be to the zinc coating, and not further, to the steel, unless otherwise agreed.
salt spray fog apparatus
9.1 Place the panels in the cabinet such that they are not in the direct line of travel of spray from a spray nozzle. 9 Method of Exposure Of Test Panels
9.2 Each test surace shall be placed in the cabinet facing upwards at an angle of between 15° and 25° to thevertical.
Note6 The angle at which each panel is exposed in the cabinet is very important.
By agreement between the interested parties,it is sometimes necessary to expose painted components of differentshapes. When such tests are conducted, it is of particular importance to expose the shaped components in theirnormal attitude in use.Within this restriction the component shall be placed so as to minimize the disruption of flow.Furthermore, other test panels and components cannot be tested at the same time if the shape of the paintedcomponent interferes with the general direction of flow.
The degree of film breakdown at different angles of orientation may vary, and due consideration shall be given tothis in the interpretation of the results.
9.3 Arrange the panels so that they do not come into contact with one another or with the cabinet and so that thesurfaces to be tested are exposed to the spray only where it is settling freely.
10.1 The measured temperature inside the spray cabinet shall be (35±2) ℃. 10 Operating Conditions
10.2 The average rate of collection of spray solution, measured over a minimum period of 24 h, shall be 1 ml/h to2,5 ml/h for a horizontal spray-collecting device of area 80 cm2.
This solution collected shall have a sodium chloride concentration of (50±10) g/l and a pH of 6,5 to 7,2(see 5.2).
10.3 Test solution which has been sprayed shall not be re-used.
Carry out the determination in duplicate, unless otherwise agreed. 11 Procedure
11.1 Set up the apparatus and adjust it to meet the conditions specified in clause 10.
11.2 Arrange the test panels in the cabinet as described in clause 9.
11.3 Close the cabinet and start the flow of the test solution through the spray nozzle(s). Continuously spraythroughout the prescribed test period, except for a short daily interruption (see clause 12) to inspect, re-arrange orremove test panels, to check and replenish the solution in the reservoir and to check that the conditions specified inclause 10 are still being met.
Make periodic examinations of the panels, taking care not to damage the surfaces under test. The panels shall beassessed as quickly as possible and the cabinet shall be turned off for no more than 30 min in any 24 h. Do notallow the panels to dry. 12 Examination of Test Panels
Whenever possible, the examination shall be made at the same time of day.
At the end of the specified test period, remove the panels from the apparatus and rinse with clean, warm water toremove residues of test solution from the surface. Immediately dry the panel and examine the test surfaces forsigns of deterioration, for example blistering, rusting or creep of corrosion from the scratch(es), in accordance withlSO 4628, parts 1 to 5 [see annex A, item g)].
lf required, keep the panels in the standard conditions defined in IS0 3270 for the specified period and then re-examine the test surfaces for deterioration.
lf it is required to examine the substrate for signs of attack, remove the coating by the specified method.
No relevant precision data are currently available. 13 Precision
ISO/TC 35 intends to obtain precision data for all relevant standards, including IS0 7253. When precision data areavailable these will be incorporated in the standard.
Users of this standard should be aware that, because of the subjective nature of the assessment of the deterioration of the coating,precision will depend upon a number of factors.These include the evaluation method, the preparation of the test panels, the thickness of the coating, the drying and conditioning of the test panels and the preparation of the scratch(es).
However, the method has been found to be useful in comparing the salt spray resistance of different coatings. lt ismost useful in providing relative ratings for a series of coated panels exhibiting significant differences in salt sprayresistance.
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