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DIN 50021 Salt Spray Testing

DIN 50021 salt spray testing is a widely recognized standard for salt spray testing, a crucial method for evaluating the corrosion resistance of various materials and coatings. In this article, we will explore the significance of DIN 50021 and delve into the related terms, such as salt spray testing, salt fog testing, or salt mist test. We will also touch upon other relevant corrosion testing methods and industry standards, including ASTM salt spray test, cyclic corrosion test, and more. DIN 50021 salt spray testing is crucial for assessing the corrosion resistance of various materials and coatings.

Salt spray testing, as per DIN 50021, simulates corrosive environmental conditions that accelerate the corrosion process. It helps manufacturers assess the reliability and durability of materials, coatings, and products exposed to corrosive environments. Understanding the core concepts, such as salt spray testing, salt fog testing, ASTM salt spray test, and cyclic corrosion testing, enables manufacturers to ensure product durability and reliability. Adhering to industry standards like DIN 50021 and ASTM B117 ensures consistent and accurate evaluation of corrosion performance, making it an indispensable tool in product development and quality control.

DIN 50021 Salt Spray Testing
Type and Description WEW-YW-120D WEW-YW-130D WEW-YW-160D
Inner Dimension(mm) 1200*800*500 1300*850*600 1600*1000*600
Outer Dimension(mm) 1700*1150*1200 1800*1200*1300 2300*1250*1450
Test Room Size (Liters) 500 Liters 650 Liters 1000 Liters
Power Supply AC 220V, 50Hz AC 220V, 50Hz AC 380V, 50Hz
Power Current 1Phase, 2.9 kW 1Phase, 3.5 kW 3Phase, 5.0 kW
Lid Opening Method Manual Opening Pneumatic Air-Operated
Brine Tank Volume 30 Literes 35 Literes 40 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, 
Testing Type NSS, AASS,CASS NSS, CASS NSS, AASS,CASS
Safety Devices 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 Special Samples Support Customisation. Special Samples Support Customisation. Load Capacity According To Actual Situation
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
salt spray testing
For the purposes of this standard, spray tests are tests in which the corrosive agent is an aqueous sodium chlo-ride solution with a concentration by mass of 5 g/100 mt(main constituent) that is sprayed continuously by means of compressed air.  3 Principle
Note. Other methods of producing a spray may be employed provided that the equivalence of the corrosion effect has been recognized by a committee of experts of the Normenausschu8 Materialprufung (Materials Testing Standards Committee). 
There are three different spray tests as specified in Table 1:
a) salt spray test (SS test);
b) acetic acid salt spray test (DIN 50021 – ASS test);
c)copper-accelerated acetic acid salt spray test
(CASS test) (see Explanatory notes)
Table 1 Conditions for spray testing

The DIN 50021 test standard provides specifications for corrosion testing equipment and corrosive agents used in salt spray testing. Its objective is to ensure that identical conditions can be replicated in all spray tests conducted based on standards or agreements. The standard does not cover specimen preparation, testing duration, post-testing specimen treatment, or result evaluation. The selection of one of the three methods listed in clause 3 for a specific case should be agreed upon by the involved parties, unless otherwise specified in relevant standards (refer to Explanatory notes).

The tests outlined in the DIN 50021 test standard serve two purposes: characterizing the effectiveness of corrosion protection systems and quickly identifying any defects. However, they are not designed to specifically detect defects in cases where the coating on the substrate (e.g., zinc or aluminum on steel) is of a different base metal, as the defect would be cathodically protected by the adjacent coating.

These tests are classified as accelerated corrosion tests according to DIN 50 900 Part 3 and do not directly provide information on the performance of the tested parts during service. It is important to note that the corrosion effects observed in these tests may differ significantly from those encountered in actual service, potentially involving different corrosion processes. Therefore, a comparison of the protective properties of various corrosion protection systems is only valid when the similarity between them is sufficiently close.

The test apparatus, illustrated in the figure below , shaliessentially comprise the components described in subclauses 4.1 to 4.5.All parts of the test apparatus whichcome into contact with the spray or the test solutionsshall be made of a material that is resistant to the testsolutions and does not influence the corrosive action ofthe test solution or of the spray. If the test solution ischanged from CASS to ASs or Ss, or from ASS to ss,the apparatus shall be cleaned to ensure that copper saltor acetic acid cannot influence the results. 4 Apparatus
A cabinet that can be heated and in which the pressurecan be equalized is required, equipped with the measur-ing and control devices needed for setting and maintain-ing a test temperature of (35±2)C for the SS and ASStests, and of (50±2) C for the CASS test in the closedcabinet. 4.1 Spray Cabinet
The test chamber shall have a minimum capac-ity of 400 l (see Explanatory notes) and be designed toensure that drops of spray do not fall from the top cover,side walls and baffles on the specimens.After being sprayed, the testsolution shall not return to the reservoir.
Figure Iliustration of a test apparatus with two examples of nozzle arrangement
The useful space for test purposes is limited to that partof the cabinet which lies outside the spray jet and inwhich a uniform dispersion of the spray can be verifiedas described in subclause 7.2, third paragraph.
To produce the spray, nozzles of polyacrylate glass orstainless austenitic chromium-nickel-molybdenum steelshall be used; the use of other materials is permitted ifthey enable the conditions specified in subclause 7.2 and8.6 to be met.  4.2 Spray Nozzle(s)
Spray nozzles with an aperture diameterof 1 mm and an angle of dispersion of about 30° , operat-ing at a gauge pressure of about 0,7 to 1,4 bar and a suc-tion head of 200 to 500 mm, have proved effective.lt isexpedient to fit a metering and control device for moni-toring the flow rate (see figure).
Such dev ices allow theamount of test solution to be sprayed to be set andmonitored, so as to ensure that the amount of spraycollected in the cabinet each hour lies within the limitsspecified in subclause 7.2.
The operation of the spray nozzles can be monitored bymeans of the flow metering device.lf more than one noz-zle is used , each nozzle shall be assigned its own flow metering and control device.
The spray jet shall not beaimed directly at the specimens.That may require thespray jet to be directed against a baffle or a wall of theapparatus (see figure, example 
1). If the nozzle is locatedon the bottom of the chamber , a riser may be used (seefigure, example 2).The spraying arrangement shown inexample 1 should only be used in apparatus of largecapacity , to ensure that none of the specimens aremounted above the nozzles.
The number and arrangement of the spray nozzles shallbe chosen so as to ensure that the specifications of sub-clauses 7.2 and 8.6 for the useful space are met.
The reservoir for the test solution to be sprayed shall bedesigned to ensure that the suction head remains virtu-ally constant throughout the test. 4.3 Reservoir with Supply Pipe
Compressed air supply pipe and air humidifierThe air humidifier shall be designed to ensure that thecompressed air is saturated with water at the requiredtemperature (see table 2) throughout the test.The com-pressed air pipe between the humidifier and the nozzleshall be fitted with a pressure gauge for monitoring theair pressure at the nozzle. 4.4 Compressed Air Supply Pipe
Racks shall be used that allow the specimens (specimenpanels and product parts) to be arranged in the useful space of the spray cabinet so as not to touch one another,thus precluding contact corrosion.The specimens shall be arranged in such a way that drops accumulated onone specimen cannot fall on another. 4.5 Devices for Supporting the Specimen
Specimen panels shall be inclined by about 6o° to 75from the horizontal.The side to be tested shall be the side exposed to the spray. Product parts shall be mountedor suspended in the apparatus as a function of their size,shape and/or the corrosion to which they are exposed inservice.
This position may be agreed. Care shall be takento ensure that as little salt solution as possible can col-lect in any cavities.
The water to be used for preparing the test solutions asspecified in subclauses 5.1,5.2 and 5.3 shall be distilled or deionized , the electrical conductivity of the water notexceeding 2 mS/m at a temperature of (23± 2)°C.The sodium chloride used for making up the test solutionshall contain no more than 0,3 % of additives, the con-tent of sodium iodide shall not exceed 0,1 % and thetotal contents of copper and nickel shall not exceed 0,001%.In the case of NaCl , these requirements are metif it conforms to DAB 9 (German Pharmacopoeia). lf grades of sodium chloride which do not conform toDAB 9 are used, it may be necessary to filter the fin-ished solution. 5Test Solutions
The pH value of the sodium chloride solution shall beadjusted so that the solution collected has a pH value of6,5 to 7,2, measured at (23± 2)°C.Dilute , chemicailypure hydrochloric acid or chemically pure sodiumhydroxide solution shall be used for pH adjustment.The pH value shall be determined electrometrically at(23± 2) oC using a glass electrode (see also Explanatorynotes). 5.1 Test Solution For SS Test
The solution collected shall have a concentration by .mass of (50±5 g) of sodium chloride per litre. 
The pH value of the sodium chloride solution shall beadjusted using acetic acid complying with the purityrequirements specified in DAB 9 so that both the solu-tion to be sprayed and the solution collected have a pHvalue of 3,1 to 3,3 at (23 ± 2)°C,1 to 3g of acetic acidper litre being required for this purpose.The pH valueshall be measured electrometrically using a glass electrode.The solution collected shall have a concentration by mass of (50 ±5) g of sodium chloride per litre.  5.2 Test Solution for ASS Test
First,(0,26± 0,02) g of analytical grade copper《II)chloride, Cucl2· 2H2O , shall be added per litre to thesodium chloride solution.Then, the pH value shall beadjusted using acetic acid as in subclause 5.2 so thatboth the solution to be sprayed and the solution col-lected have a pH value of 3,1 to 3,3 at (23± 2)°C.ThepH value shall be measured electrometrically using aglass electrode. 5.3 Test Solution for CASS Test
The solution collected shall have a concentration bymass of (50±5) g of sodium chloride per litre.
salt spray fog apparatus
The temperature in the useful space of the closed spraycabinet shall be (35 ±2) ℃ during the Ss and ASS tests,but (50 ±2)℃ during the CASS test, a brief drop in temperature when the cabinet is opened being permitted(see subclause 7.3). Note.The variation in temperature over time should be registered by a temperature recorder. 7.1 Test Temperature 7 Procedure
The quantity of test solution, as specified in subclauses5.1,5.2 and 5.3, to be sprayed per unit of time in thespray cabinet shall be adjusted so that the average rateof sprayed solution collected in each of the collector ves-sels provided in the cabinet, assuming for each device ahorizontat collecting area of about 80 cm2 and a mini-mum collection period of 16 h,is (1,5±0.5)ml perhour.  7.2 Quantity and Distribution Of The Spray
For tests taking less than 16 h, the minimumperiod for determining the average shall be 8 h. when the nozzle descrpeh test solution spraying rate,. given a predetermined, constant pressure and a constant To check that the spray is uniformly dispersed, at leasttwo collector vessels shall be provided at representative points in the useful space. 
Suitable as collector vessels are, for example, glass or lecting area of 78,5 cm2) , which are passed through a medoefes on no account shall drops that have formed on the topcover and walls of the spray cabinet, on any baffles provided , on the racks or on the specimens fall into acollector vessel.
Spray tests shall be interrupted and the spray cabinetopened only briefly to enable specimens to be removedand introduced and to carry out interim assessments. 7.3 Test Interruptions
To check the repeatability of the test results obtained with a test apparatus, or the reproducibility of test results from different test apparatuses, functional checks are to be made. 8 Functional Check On Test Apparatus
The functional check described in this clause applies to the SS test. Functional checks for the ASS and CASS tests may be made analogously. The type of specimens, duration of tests and the permissible losses in mass per unit area shall be agreed accordingly.
Five specimens are required, each measuring 50 mm inwidth,100 mm in length and 0,6 to 1,5 mm in thicknessand made of St 14 05 as specified in DIN 1623 Part 1(bright). 8.1 Specimens
Prior to the functional check , the specimens as specifiedin subclause 8.1 shall be degreased with white spirit oranother suitable solvent using a soft, non-fibrous cloth ora brush and subsequently weighed to the nearest ± 0,1 mg.lf they cannot be weighed immediately after degreasing,the specimens shall be kept in a desiccator until weighing.After weighing, the specimens shall be coated on one side with a strippable protection (e.g. self-adhesive filmsor strippable varnishes). 8.2 Preparation of Specimens
The specimens shall be set up on edge, inclined at anangle of 60° to 75~ to the horizontal, in the test appara-tus with the test surface upwards and exposed for 96 hunder the conditions specified for the ss test. 8.3 Exposure
Before the corrosion products are removed, the coatingsapplied before exposure shall be stripped off.The corro-sion products shall be removed from the specimens bypickling at a temperature of 18°C to 28°C.A hydro-chloric acid inhibited with 3,5 g of hexamethylene-tetramine per litre, with 9= 1,10 g/ml , may be used forthis purpose, e.g. 500 ml of HCl , with 9= 1,19 g/ml,chemically pure, made up to 1 litre with deionized water.Solutions as specified in lSO/DIS 8407- 1987 may alsobe used. 8.4 Removal of Corrosion Products
After the removal of corrosion products, the specimensshall be thoroughly rinsed in water , dried and subse-quently kept until weighing in a desiccator at tempera-tures of 18°C to 28°c. 8.5 Weighing of specimens The specimens shall be weighed to the nearest ± 1 mg.8.6Evaluation of functional check results The loss in mass shall be related to the surface areaexposed to corrosion and expressed in g/m2.The aver-age loss shall be (140± 20)g/m2.
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