A SEMINAR REPORT

ON

‘Salt spray test’

Prepared by:

Shashank Agrawal (06BMTR002)

Achit Gautam (06BMTR012)

Vishal Soni (06BMTR056)

Contents

1. Introduction

2. Testing equipment

2.1 Salt Spray Testing Equipment

3. Standardization

4. Salt Spray Test Procedure

5. Uses & Application

6. References

Abstract

Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment.

Corrosion tests have been conducted for a long time but there are only a few cases of corrosion data quality assessment or inter laboratory comparisons for such measurements. Each test method when used in different laboratories gives different results, as it is impossible to perform the whole procedure exactly in the same manner. Therefore, a very essential parameter of the method is its robustness. A proper validation of the corrosion test method means the evaluation of the impact of various environmental features and performance variations on the uncertainty of the test result.

Our aim was to present an experimental evaluation of the corrosivity of the salt spray corrosion test cabinet, to indicate the gaps in the description of the corrosion test method according to ISO 9227 and to estimate the main components of the uncertainty of the corrosivity measurement.

The validation results require changes in the salt spray test method description and maybe in the performance.

History

The basic salt spray test reportedly dates back to 1914, with roots in the National Bureau of Standards (NBS) in the United States (now known as NIST). The neutral salt spray procedure was formalized as an ASTM B117 specification in 1939. (ASTM itself was founded in 1898.)

This specification reportedly changed considerably in the early years, compared with its present form. Concerning the early years of changes, Thomas Doppke has commented: "Even the salt concentration varied from 20% to as low as 3.5%."

F.D. Timmins reportedly was one of the pioneers in shifting salt spray tests away from the simplistic ASTM B117 approach, to accelerated cyclical (wet/dry) testing. The solution used in the ASTM G85 Annex A5 and ASTM D5894 cyclical test procedures is still referred to as "Timmins solution".

1. Introduction

The salt spray test is a standardized test method used to

check corrosion resistance of coated samples. Coatings provide corrosion

resistance to metallic parts made of steel, zamak or brass. Since coatings can

provide a high corrosion resistance through the intended life of the part in use, it

is necessary to check corrosion resistance by other means. Salt spray test is an

accelerated corrosion test that produces a corrosive attack to the coated

samples in order to predict its suitability in use as a protective finish. The

appearance of corrosion products (oxides) is evaluated after a period of time.

Test duration depends on

the corrosion resistance

of the coating; the more

corrosion resistant the

coating is, the longer the

period in testing without

showing signs of

corrosion.

Salt spray testing is

popular because it is

cheap, quick, well

standardized and

reasonably repeatable.

There is, however, only a

weak correlation between the duration in salt spray test and the expected life of

a coating, since corrosion is a very complicated process and can be influenced

by many external factors.

( a salt spray cabinet )

Nevertheless, salt spray test is widely used in the industrial sector for the

evaluation of corrosion resistance of finished surfaces or parts.

2. Testing equipment

The apparatus for testing consists of a closed testing chamber, where a salted

solution (mainly, a solution of sodium chloride) is atomized by means of a

nozzle. This produces a corrosive environment of dense saline fog in the

chamber so that parts exposed in it are attacked under this severe corroding

atmosphere. Typical volumes of these chambers are of 15 cubic feet (420 L)

because the smallest volume accepted by ASTM-B-117, ISO 9927 (400 litres)

and now discontinued DIN 50021 (400 litres). It has been found very difficult to

attain constancy of corrosivity in exposure regions within the test chambers

below 400 litres. Chambers are available from sizes as small as 9.3 cu ft (260 L)

up to 2,058 cubic feet (58,300 L), most common machines range from 15 to 160

cubic feet (420–4,500 L).

Tests performed with a standardized 5% solution of NaCl are known as NSS

(neutral salt spray). Results are represented generally as testing hours in NSS

without appearance of corrosion products (e.g. 720 h in NSS acc. to ISO 9227).

Other solutions are acetic acid (ASS test) and acetic acid with copper

chloride (CASS test), each one chosen for the evaluation of decorative coatings,

such as electroplated copper-nickel-chromium, electroplated copper-nickel or

anodizedaluminium.

Some sources do not recommended to use ASS or CASS test cabinets

interchangeably for NSS tests, as it is claimed that a thorough cleaning of the

cabinet after ASS or CASS test is very difficult. ASTM does not address this

issue, but ISO 9227 does not recommend it and if it is to be done, advocates a

thorough cleaning.

2.1 Salt Spray Testing Equipment

The Salt Spray cabinet is made of acrylic or PVC top cover acrylic with removable lid and handle. It is a complete standard unit together with atomizing nozzle, air pressure indicator, solution inlet and drain outlet, etc.

The Salt Spray Test Chamber comes with accessories:

Digital temp controller: 1

Glass holder: 1

Pt. 100 Ss 316L Sensor: 1

Time tantalizer range 9999.9hrs: 1

The Salt Spray Test Chamber has sizes: 450x250x250 mm approx and 910x510x310 mm approx.

Extra include:

Air compressor

Auto dosing pumps

Humidity chamber

3. Standardization

Chamber construction, testing procedure and testing parameters are standardized under national and international standards, such as ASTM B 117 and ISO 9227. These standards describe the necessary information to carry out this test; testing parameters such as temperature, air pressure of the sprayed solution, preparation of the spraying solution, concentration, pH, etc. Daily checking of testing parameters is necessary to show compliance with the standards, so records shall be maintained accordingly. ASTM B 117 and ISO 9227 are widely used as reference standards. Testing cabinets are manufactured according to the specified requirements here. However, these testing standards neither provide information of testing periods for the coatings to be evaluated, nor the appearance of corrosion products in form of salts. Requirements shall be agreed between customer and manufacturer. In the automotive industry requirements are specified under material specifications. Different coatings have different behaviour in salt spray test and consequently, test duration will differ from one type of coating to another. For example, a typical electroplated zinc and yellow passivated steel part lasts 96 hours in salt spray test without white rust. Electroplated zinc-nickel steel parts can last more than 720 hours in NSS test without red rust (or 48 hours in CASS test without red rust) Requirements are established in test duration (hours) and coatings shall comply with minimum testing periods.

3.1 International Standards

ASTM B 117: Standard practice for operating salt spray (fog) apparatus

ASTM B 368: Standard Test Method for Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test)

ASTM B 380: Standard Method of Corrosion Testing of Decorative Electrodeposited Coatings by the Corrodkote Procedure

ASTM D 1735: Standard Practice for Testing Water Resistance of Coatings Using Water Fog Apparatus

ASTM D 2247: Standard Practice for Testing Water Resistance of Coatings in 100 % Relative Humidity

ASTM D 870: Standard Practice for Testing Water Resistance of Coatings Using Water Immersion

ASTM G 85 A1-5: Standard Practice for Modified Salt Spray (Fog) Testing

ASTM G 87: Standard Practice for Conducting Moist SO2 Tests

JIS Z 2371: Methods of salt spray testing (Foreign—Japanese standard)

 

3.2 Telecom Standards (NEBS GR-CORE)

GR-487-CORE: General Requirements for Electrical Equipment Cabinets

GR-950-CORE: Generic Requirements for Optical Network Unit (ONU) Closures

GR-3108-CORE: Generic Requirements for Network Equipment in the Outside Plant (OSP)

GR-1209-CORE: General Requirements for Fiber Optic Branching Components

GR-326-CORE: Generic Requirements for Singlemode Optical Connectors and Jumper Assemblies

GR-2834-CORE: Generic Requirements for Basic Electrical, Mechanical & Environmental Criteria for Outside Plant Equipment

GR-2836-CORE: Generic Requirements for Assuring Corrosion Resistance of Telecommunication Equipment in the Outside Plant

3.3 Enclosure Standards

NEMA 250: Enclosures for Electrical Equipment (1000 Volts Maximum)

UL 50: Enclosures for Electrical Equipment

3.4 Military Standards

MIL-STD-810 method 509: Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests

MIL-STD-883 method 1009: Department of Defense Test Method Standard – Microcircuits

MIL-STD-202 method 101: Test Method – Standard Electronic and Electrical Component Parts

3.5 Automotive Standards

DIN 50017: Atmospheres and their Technical Application

DIN 50018: Testing in a saturated atmosphere in the presence of sulfur dioxide

DIN 50021: Salt Spray Testing

FORD BI 104-04: Adhesion /Immersion TestFORD BJ7-2:

GM 4298P: Salt Spray Test

GM 4465P: Water Fog Humidity Test

GM 4476P: CASS Test Copper – Accelerated Acetic Acid Salat Spray Test (Fog)

GM 9103P: Standard for Automotive Relays

GM 9110P: Procedure for Testing Switches

GM 9505P: Automotive Environmental Cycles

GM 9540P: Accelerated Corrosion Test

ASTM B117:

THE standard in salt spray testing:

The American Society of Testing and Materials (ASTM) test B117 is one of the most widely adopted continuous salt spray test specifications. Its use is internationally widespread and its provisions have been frequently re-written into the national standards of other countries, and also appear in other industry specific corrosion test standards.

ASTM B117 has always been and excellent reference document for the salt spray practitioner, with many helpful hints and tips contained in its useful appendixes. But since it is also regularly updated, by an active and broad based ASTM sub-committee, it is a standard that is always evolving and becoming ever more ‘user friendly’. The suffix to the main standard number indicates the year of publication. For example, ASTM B117 – 03 indicates a 2003 publication date (which was the latest version available at the time of writing). Please check you are using the most up to date edition available for your application.

History of ASTM B117:Continuous salt spray testing first became widely adopted as a corrosion test in 1939 when the American Society of Testing and Materials (ASTM) first published their salt spray test standard, known under its reference number: ASTM B117. In subsequent years, the use of ASTM B117 spread internationally and its provisions have frequently been re-written into national standards such as the UK's BSI, Germany's DIN etc., underpinning the widespread use of the standard today. The terms salt spray, salt fog and salt mist are all in widespread use for this type of testing and are generally interchangeable terms, as is the term cabinet or chamber, which is used to describe the equipment in which the test is conducted.

Test Conditions:Can be used to test the relative resistance to corrosion of coated and uncoated metallic specimens, when exposed to a salt spray climate at an elevated temperature. Test specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of neutral (pH 6.5 to 7.2) 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 +35C. This climate is maintained under constant steady state conditions. The test duration is variable.

Method:Salt fog testing is performed by placing samples in a test cabinet that has been designed in accordance with Paragraph 4 (Apparatus) of ASTM B117 and operated in accordance with Paragraph 10 (Conditions) of ASTM B117.

A 5% salt solution, prepared by dissolving sodium chloride into water that meets the requirements of ASTM D1193 Specification for Reagent Water, Type IV is supplied to the chamber. At the time the samples are placed into test, the cabinet should be pre-conditioned to the operating temperature of 35ºC and fogging a 5% salt solution at the specified rate. The fog collection rate is determined by placing a minimum of two 80 sq. cm. funnels inserted into measuring cylinders graduated in ml. inside the chamber. One collection device is located nearest the nozzle and one in the farthest corner.

Orientation:Unless otherwise agreed upon, the samples are placed at a 15-30 degree angle from vertical (automotive components, however, are often tested in the "in-car" position). This orientation allows the condensation to run down the specimens and minimises condensation pooling. Overcrowding of samples within the cabinet should be avoided. An important aspect of the test is the utilization of a free-falling mist, which uniformly settles on the test samples. Samples should be placed in the chamber so that condensation does not drip from one to another.

Test durations:Test durations are typically in 24-hour increments and can range from 24 hours to 5000 hours (where salt fog exposure is a part of a more complex test method, exposure time can be as little as 15 minutes.) Except for sample rotation and daily monitoring of collection rates, the cabinet should remain closed for the duration of the test.

4 Salt Spray Test Procedure

Basically, the salt spray test procedure involves the spraying of a salt solution onto the samples being tested. This is done inside a temperature-controlled chamber. The solution is a 5% salt (sodium chloride – NaCl) solution. The samples under test are inserted into the chamber, following which the salt-containing solution is sprayed as a very fine fog mist over the samples. The temperature within the chamber is maintained at a constant level. Since the spray is continuous, the samples are constantly wet, and therefore, constantly subject to corrosion. Through the years, there have been some new twists added to better simulate special environmental conditions, but the most common procedure by far in North Americais the test as described in ASTM B 117 Standard Practice for Operating Salt Spray (Fog) Apparatus.

(Drawing of the tank)

The Procedure:

Wooden racks are contained in the salt fog chamber (3’ high, 3’ deep, 5’ wide) Place samples on a the wooden rack at a small tilt angle 5% NaCl in tap water pumped from a reservoir to spray nozzles Solution mixed with humidified compressed air at nozzles Compressed air atomizes NaCl solution into a fog at the nozzles Heaters maintain a 95°F cabinet temperature Test duration can be from 24 hours to 1000 hours and more for some materials

Within the chamber, the samples are rotated frequently so that all samples are exposed as uniformly as possible to the salt spray mist.

When the salt spray test is used for testing metallic-coated steel sheet, the corrosion performance is rated in the following ways:

• Number of hours until rusting of the steel is first evident• Number of hours until 5% of the surface area is rusted• Number of hours until 10% of the surface area is rusted, etc.

5 Uses & Application

Typical coatings that can be evaluated with this method are:

Phosphated surfaces (with subsequent paint/primer/lacquer/rust preventive)

Zinc and zinc-alloy plating (see also electroplating). See ISO 4042 for guidance

Electroplated  chromium, nickel, copper, tin

Coatings not applied electrolytically, such as  zinc flake coatings acc. to ISO

10683

Organic coatings

Hot-dip galvanized surfaces are not generally tested in salt spray test (see ISO 1461 or

ISO 10684). Hot-dip galvanizing  produces zinc carbonates when exposed to the

environment, thus protecting the coating metal and reducing the corrosion rate. These

by-products are not produced when a hot-dip galvanized specimen is exposed to a salt

spray fog. Hence, hot-dip galvanized steel is not normally tested according to this test

method and corrosion resistance is expressed as years of corrosion protection in

different environments. See ISO 9223 for guidance.

Painted surfaces with an underlying hot-dip galvanized coating can be tested according

to this method. See ISO 12944-6.

Testing periods range from a few hours (e.g. 8 or 24 hours of phosphated steel) to more

than a month (e.g. 720 hours of zinc-nickel coatings, 1000 hours of certain zinc flake

coatings).

Examples of application of this test as an acceptance method for coated surfaces are

the automotive, construction and aerospace industries.

Application:

This test has its origins in the early 1900s. In the United States, it was well defined by

1939 with the release of the initial edition of the ASTM B117 standard. Since that time, it

has found its way into the environmental requirements of many different organizations in

such areas as general mechanical testing, automotive specifications, military

requirements, electrical enclosures, and the telecommunications NEBS (Network

Equipment Building System) requirements. The following list gives a sampling of

standards incorporating a salt fog test.