September 8, 2026

ASTM B117 Salt Spray Test: Standard and Requirements

ASTM B117 is the standard practice for operating salt spray (fog) apparatus used to expose metals and coated metal specimens to a controlled corrosive environment. The test is widely used to obtain relative corrosion resistance information for metallic materials, protective coatings, plated finishes, and painted surfaces.

As of 2026, the current active edition is ASTM B117-26, Standard Practice for Operating Salt Spray (Fog) Apparatus, last updated on January 19, 2026. ASTM B117 establishes the apparatus, procedure, and operating conditions required to create and maintain the salt spray environment. It does not specify a universal exposure duration, specimen type, or pass/fail requirement for individual products. Those requirements must come from the applicable product specification, coating specification, customer requirement, or other referenced standard.

What is ASTM B117?

ASTM B117 is a standardized laboratory practice published by ASTM International for conducting continuous salt spray testing.

During the test, specimens are placed inside a salt spray chamber and continuously exposed to a controlled salt fog. The environment accelerates corrosion processes and allows the condition of metals and protective coatings to be evaluated after a specified exposure period.

ASTM describes the practice as providing a controlled corrosive environment that can generate relative corrosion resistance information for metals and coated metals.

ASTM B117 is commonly associated with testing:

Zinc-plated steel
Galvanized components
Painted metal
Powder-coated metal
Electroplated components
Fasteners
Automotive components
Metal hardware
Electrical enclosures
Construction components
Coated steel products

The test is particularly useful when a specification requires products or coatings to withstand a defined number of hours of continuous salt spray exposure.

What is ASTM B117 Used For?

ASTM B117 provides a controlled method for exposing test specimens to a salt spray environment.

Testing may be specified to:

Evaluate the corrosion resistance of coated metal specimens
Identify defects or inconsistencies in protective coatings
Compare coating systems under defined conditions
Evaluate manufacturing consistency
Support coating qualification
Verify customer corrosion-resistance requirements
Compare different surface treatments
Support supplier quality control

The standard itself does not establish how many hours a particular product must survive.

For example, a customer specification may require a plated fastener to withstand a specified exposure period before unacceptable corrosion appears. ASTM B117 defines how the salt spray environment is operated, while the customer or applicable product specification defines the exposure duration and acceptance criteria.

How Does the ASTM B117 Salt Spray Test Work?

ASTM B117 testing exposes specimens to a continuous salt-containing fog inside a controlled chamber.

The basic process involves:

Preparing the specimens according to the applicable specification.
Positioning the specimens inside the salt spray chamber.
Preparing the required salt solution.
Establishing the specified chamber conditions.
Generating a continuous salt fog.
Monitoring operating conditions throughout exposure.
Maintaining exposure for the specified duration.
Removing and evaluating the specimens according to the applicable acceptance criteria.

ASTM B117 focuses heavily on controlling the test environment because changes in chamber conditions can influence corrosion results.

ASTM also notes that reproducibility depends on the specimens, evaluation criteria, operating variables, and other factors. Variation can occur between different salt fog chambers even when their operating conditions fall within the specified ranges.

ASTM B117 Test Conditions

ASTM B117 establishes operating requirements for the salt spray chamber and test environment.

Commonly referenced conditions include:

Parameter	ASTM B117 Salt Spray Condition
Test environment	Continuous salt spray (fog)
Salt	Sodium chloride
Salt solution concentration	Approximately 5%
Chamber temperature	Approximately 35°C
Solution pH	Neutral range
Exposure	Continuous unless otherwise specified
Test duration	Defined by product/customer specification
Acceptance criteria	Defined separately from ASTM B117

The current standard should always be consulted when establishing exact laboratory parameters and tolerances.

ASTM B117 provides the controlled environment. It does not assign a standard exposure time or universal corrosion limit to every product.

ASTM B117 Salt Solution

The salt solution used for ASTM B117 testing is prepared using sodium chloride and water meeting the requirements of the standard.

Maintaining the specified solution conditions is important because changes in:

Salt concentration
Water quality
Contamination
pH

can affect the corrosiveness of the test environment.

The solution is atomized inside the chamber to produce a continuous salt fog around the specimens.

Salt Spray Chamber Temperature

Temperature is another controlled variable during ASTM B117 testing.

The exposure zone of the salt spray chamber is maintained at approximately 35°C (95°F) under the specified conditions.

Stable temperature helps maintain consistent test conditions throughout the exposure period.

Temperature should therefore be monitored as part of routine chamber operation.

Salt Fog Collection

The amount of salt fog generated inside the chamber also needs to remain within the conditions established by ASTM B117.

Collection devices positioned inside the exposure zone are used to monitor the amount of fog being deposited.

This helps laboratories verify that specimens receive an appropriate and reasonably uniform salt fog exposure throughout the test.

Specimen Positioning

Correct specimen positioning is important during salt spray testing.

Specimens should be arranged so that they receive suitable exposure to the fog without interfering with one another.

Poor positioning can create:

Uneven salt deposition
Shielded areas
Dripping between specimens
Inconsistent exposure

The applicable standard and product specification should be followed when determining specimen orientation and preparation.

How Many Hours is an ASTM B117 Salt Spray Test?

There is no universal ASTM B117 test duration.

ASTM explicitly states that B117 does not prescribe exposure periods for specific products.

The required duration should be established by the relevant:

Product standard
Material specification
Coating specification
Engineering drawing
OEM specification
Purchase specification
Customer requirement

Commonly specified exposure periods can include:

24 hours
48 hours
72 hours
96 hours
168 hours
240 hours
500 hours
720 hours
1,000 hours

These values are examples of exposure periods that may appear in product or coating specifications. They are not ASTM B117 pass/fail requirements.

A requirement such as ASTM B117, 500 hours means the specimen is exposed using the ASTM B117 salt spray environment for 500 hours and then evaluated according to separately defined acceptance criteria.

Does More ASTM B117 Hours Mean Better Corrosion Resistance?

Within a properly defined product or coating specification, a longer required exposure period can represent a more demanding corrosion-resistance requirement.

However, salt spray hours should not automatically be treated as a universal ranking system between unrelated materials or coating technologies.

For example, it would be misleading to conclude that a product surviving 1,000 hours of ASTM B117 exposure will necessarily last twice as long outdoors as one surviving 500 hours.

The relationship between salt spray exposure and actual service life is much more complex.

How Are ASTM B117 Results Evaluated?

ASTM B117 creates the salt spray environment, but it does not establish universal interpretation or pass/fail criteria for test results.

After the specified exposure period, specimens may be evaluated for characteristics such as:

Red rust
White corrosion products
Blistering
Peeling
Flaking
Coating deterioration
Corrosion around defects
Corrosion creep from a scribe
Percentage of corroded area

The actual evaluation method depends on the product, coating system, and referenced specification.

A specification might state, for example:

ASTM B117 exposure for 240 hours with no red rust on specified significant surfaces.

In this case, 240 hours and the corrosion acceptance criterion come from the product or customer specification, while ASTM B117 defines the salt spray exposure environment.

Red Rust vs White Corrosion in Salt Spray Testing

Understanding the difference between red rust and white corrosion is useful when interpreting salt spray results on zinc-coated steel.

White Corrosion

White corrosion products are commonly associated with corrosion of zinc or zinc-containing protective layers.

Their appearance may indicate that the protective zinc coating is reacting with the corrosive environment.

Red Rust

Red rust generally indicates corrosion of the underlying iron or steel substrate.

For zinc-coated steel, specifications may therefore establish separate requirements for:

Appearance of white corrosion
Appearance of red rust

The permitted amount and timing depend on the applicable specification.

What Products Are Commonly Tested to ASTM B117?

ASTM B117 can be referenced for many metallic products and coated components.

Fasteners

Bolts, screws, nuts, washers, clips, and other fasteners frequently use protective metallic coatings.

Salt spray testing may be specified to evaluate the corrosion resistance of coatings such as zinc-based finishes.

Automotive Components

Automotive applications can include:

Brackets
Fasteners
Clips
Metal housings
Plated components
Coated parts

The applicable automotive specification determines the required test method, duration, and acceptance criteria.

Construction Hardware

Products may include:

Hinges
Brackets
Connectors
Fasteners
Door hardware
Window hardware

Corrosion testing can be particularly relevant where metal components may encounter moisture during use.

Powder-Coated Products

ASTM B117 can be used as part of an evaluation of powder-coated metal specimens.

Salt spray exposure can reveal problems associated with:

Surface preparation
Coating defects
Inadequate coverage
Coating damage
Pretreatment quality

The test is performed on the coated metal system, not on loose powder coating material.

Painted Metal Products

Painted metal panels and finished products can also be subjected to ASTM B117 exposure when required by the applicable coating or product specification.

Electrical and Electronic Hardware

Metal enclosures, brackets, connectors, and hardware may require corrosion-resistance testing where environmental exposure is relevant to the product specification.

ASTM B117 for Galvanized Steel

Galvanized steel uses a zinc coating to protect the underlying steel substrate from corrosion.

ASTM B117 may be referenced to evaluate the behavior of galvanized or zinc-coated specimens under continuous salt fog exposure.

During testing, evaluators may monitor the development of:

White corrosion products on zinc
Red rust indicating corrosion of the steel substrate
Localized corrosion
Coating deterioration

The required exposure time and allowable corrosion must be defined by the applicable galvanized product or coating specification.

ASTM B117 alone cannot determine how many years a galvanized component will last outdoors.

ASTM B117 for Powder Coating

Powder-coated steel and aluminum components can also be evaluated using ASTM B117 where the relevant specification requires it.

Performance depends on the complete coating system, including:

Substrate
Surface preparation
Pretreatment
Coating thickness
Curing
Coating coverage
Defects or damage

For this reason, coating thickness testing and salt spray testing can provide complementary information.

Thickness measurement confirms whether the coating meets specified dimensional requirements, while salt spray exposure evaluates corrosion behavior under the defined corrosive environment.

Can ASTM B117 Predict Real-World Corrosion Life?

ASTM B117 should not be used by itself to predict the actual service life of a product.

ASTM states that prediction of performance in natural environments has seldom correlated with salt spray results when those results are used as stand-alone data. Correlation and extrapolation are not always predictable.

Real-world corrosion can be influenced by:

Wet and dry cycles
Temperature
Humidity
Pollution
UV exposure
Chloride concentration
Rainfall
Material design
Surface damage
Installation conditions
Maintenance

Continuous salt fog exposure does not reproduce every environmental condition encountered during actual product use.

Therefore:

500 hours of ASTM B117 does not equal a specific number of years outdoors.

Salt spray results should be interpreted according to the applicable specification and intended evaluation purpose.

ASTM B117 vs ISO 9227

ASTM B117 and ISO 9227 are both widely used standards associated with salt spray corrosion testing, but their scope and structure are different.

Feature	ASTM B117	ISO 9227
Organization	ASTM International	International Organization for Standardization
Test	Salt Spray (Fog)	NSS, AASS and CASS
Main Purpose	Defines salt spray apparatus and operating conditions	Defines standardized salt spray test methods
Test Duration	Defined separately	Defined separately
Universal Pass/Fail Criteria	No	No
Real-World Service Life Prediction	Not intended as a direct predictor	Not intended as a direct predictor

ASTM B117 focuses on operating a continuous salt spray environment. More aggressive or modified ASTM salt fog procedures are addressed separately, including methods under ASTM G85. ASTM describes G85 as providing modified salt spray environments where a different or more corrosive environment than B117 is required.

The required standard should be determined from the applicable product, coating, customer, or engineering specification.

ASTM B117 vs ASTM G85

ASTM B117 and ASTM G85 should not be treated as interchangeable test methods.

ASTM B117 covers the apparatus, procedure, and conditions for the conventional continuous salt spray environment.

ASTM G85 covers several modified salt spray procedures, including continuous and cyclic acidified environments. ASTM identifies these modifications for applications requiring conditions different from, or more corrosive than, the B117 environment.

The correct method depends on the referenced specification and the corrosion environment being evaluated.

Common Reasons Products Fail ASTM B117 Testing

Salt spray failures often indicate weaknesses somewhere in the material or coating system.

Common causes include:

Insufficient Coating Thickness

A coating below the required thickness may provide insufficient protection to the underlying metal.

Poor Surface Preparation

Oil, rust, scale, dirt, or other contaminants can interfere with coating adhesion and corrosion protection.

Inadequate Pretreatment

Pretreatment quality can significantly affect the corrosion performance of painted and powder-coated metal systems.

Coating Damage

Scratches, chips, exposed edges, and handling damage can create locations where corrosion begins.

Poor Coating Coverage

Complex geometries, recesses, edges, welds, and corners may receive inadequate coating coverage.

Process Variation

Changes in plating chemistry, curing, cleaning, pretreatment, or coating application can result in inconsistent corrosion performance between production batches.

When a product fails salt spray testing, the investigation should consider the entire coating system and manufacturing process, rather than focusing only on the exposure chamber.

How to Prepare Samples for ASTM B117 Testing

Before testing, the required test scope should be clearly defined.

Important information includes:

Product or specimen type
Material
Coating system
Required ASTM B117 edition
Exposure duration
Number of specimens
Sample preparation requirements
Whether specimens require scribing
Acceptance criteria
Evaluation method
Required reporting information

Providing only the instruction such as test according to ASTM B117 is usually insufficient because ASTM B117 does not establish the exposure duration or product-specific acceptance criteria.

What Should an ASTM B117 Test Report Include?

A salt spray test report should document enough information to identify the specimens, test conditions, exposure duration, and evaluation results.

Depending on the testing program, the report may include:

Test standard and edition
Sample identification
Specimen description
Coating or finish information
Exposure duration
Test conditions
Observations
Corrosion results
Photographs
Deviations from specified procedures, where applicable
Final evaluation against provided acceptance criteria

Clear reporting is particularly important when salt spray results are used for supplier qualification or product approval.

ASTM B117 provides a controlled and standardized salt spray environment for evaluating the relative corrosion resistance of metals and coated metals. Reliable testing begins with a clearly defined exposure duration, specimen preparation method, and acceptance criteria from the applicable product or coating specification.

Results should be evaluated within that defined specification and should not be converted directly into expected years of real-world service life. This keeps ASTM B117 testing useful for coating evaluation, product qualification, supplier control, and production quality verification.