May 26, 2026

Salt Spray Test Requirements by Product Type: Hours and Acceptance Criteria

Salt spray test requirements define how long a product or coating is exposed to a controlled corrosive environment and how its corrosion performance is evaluated after testing. Requirements can vary according to the product, material, coating system, intended environment, applicable standard, and customer specification.

A product may be tested for 24, 96, 240, 500, or more than 1,000 hours depending on the specified requirement. The exposure duration alone does not determine whether a product passes the test. Acceptance criteria, such as red rust, white corrosion, blistering, coating delamination, or corrosion around a scribe, must also be defined.

Common salt spray testing methods include ASTM B117 and ISO 9227. These standards establish controlled test procedures, while the required exposure duration and acceptance criteria generally come from the applicable product specification, coating specification, customer requirement, or other referenced standard.

What Are Salt Spray Test Requirements?

Salt spray test requirements usually define several important test conditions:

Applicable test method
Type of salt spray test
Exposure duration
Specimen preparation
Whether the coating must be scribed
Areas of the specimen to be evaluated
Corrosion evaluation method
Acceptance criteria

For example, a specification could require a coated steel component to undergo a defined period of neutral salt spray exposure, followed by evaluation for red rust, blistering, coating deterioration, or corrosion spread from a scribed area.

For this reason, specifying only a 500-hour salt spray test is often incomplete. The test specification should also state what condition the specimen must meet after 500 hours.

Do ASTM B117 and ISO 9227 Specify Pass or Fail Requirements?

ASTM B117 and ISO 9227 primarily define salt spray test methods and operating conditions. They do not establish one universal exposure duration or pass/fail requirement for every product.

ASTM B117 describes the operation of salt spray (fog) apparatus and controlled exposure conditions commonly used for corrosion testing.

ISO 9227 covers salt spray test methods including:

Neutral Salt Spray (NSS)
Acetic Acid Salt Spray (AASS)
Copper-Accelerated Acetic Acid Salt Spray (CASS)

The appropriate test method, duration, and acceptance criteria must therefore be determined from the applicable specification.

A buyer may specify, for example:

ASTM B117, 500 hours, no red rust on significant surfaces.

Another specification may require evaluation of coating blistering or corrosion creep after exposure.

This distinction is important when comparing salt spray test results. The number of hours has meaning only when considered together with the test method, specimen preparation, coating system, and acceptance criteria.

Common Salt Spray Test Durations

Salt spray exposure periods can range from several hours to thousands of hours.

Frequently specified durations include:

Test Duration	Examples of How the Duration May Be Used
24 hours	Short-duration screening or certain decorative finishes
48 hours	Short-duration coating or plating evaluations
72 hours	Certain plated components and hardware specifications
96 hours	Common intermediate corrosion-resistance requirement
168 hours	One-week exposure used in some coating specifications
240 hours	Longer-duration coated component evaluation
500 hours	Frequently specified for higher corrosion-resistance coatings
720 hours	Extended corrosion-resistance testing
1,000 hours	High-duration coating or component specifications
1,500+ hours	Specialized specifications requiring extended exposure

These durations should not be interpreted as universal requirements for particular products. A zinc-plated fastener, powder-coated enclosure, or automotive bracket can have very different requirements depending on its coating specification and application.

Salt Spray Test Requirements by Product Type

Different products require different corrosion-control strategies. The correct salt spray specification should therefore be established from the actual product and its applicable requirements.

Fasteners and Hardware

Fasteners are frequently subjected to salt spray testing because corrosion can affect appearance, threaded connections, assembly performance, and service life.

Products can include:

Screws
Bolts
Nuts
Washers
Hinges
Brackets
Clips
Locks
Door hardware

Corrosion resistance depends heavily on the surface treatment.

Common systems include:

Zinc electroplating
Zinc alloy coatings
Mechanical plating
Organic coatings
Conversion coatings
Hot-dip galvanizing

A fastener specification may define an exposure period and separately establish the permitted amount of white corrosion or red rust.

For zinc-coated products, this distinction can be particularly important because white corrosion and red rust represent different forms or stages of corrosion and may have separate acceptance criteria.

The required salt spray performance should therefore be taken from the relevant fastener, coating, OEM, engineering, or customer specification.

Salt Spray Requirements for Powder Coating

Powder-coated products are commonly evaluated using salt spray testing to assess the corrosion protection provided by the complete coating system.

Products may include:

Outdoor furniture
Metal cabinets
Electrical enclosures
Appliances
Architectural components
Machinery housings
Steel frames
Equipment panels

Performance is affected by several factors, including:

Substrate material
Surface preparation
Pretreatment system
Powder chemistry
Coating thickness
Curing conditions
Edge coverage
Coating defects

For coated panels, the test may require a scribe through the coating before salt spray exposure. Corrosion development around the scribe can then be measured after testing.

Other evaluation criteria may include:

Blistering
Rusting
Loss of adhesion
Corrosion creep
Delamination
Surface deterioration

A statement such as salt spray certified powder coating therefore provides limited technical information by itself. The underlying test method, exposure duration, substrate, coating system, specimen preparation, and acceptance criteria are needed to understand the claimed corrosion performance.

Salt Spray Requirements for Automotive Components

Automotive components may be exposed to water, humidity, road contaminants, deicing salts, and temperature changes during service.

Components commonly evaluated for corrosion resistance include:

Fasteners
Brackets
Clips
Retainers
Chassis components
Underbody components
Plated metal parts
Coated structural components

Automotive requirements are frequently established through OEM or component-specific specifications.

These specifications may define:

Test method
Exposure cycle
Number of cycles or test hours
Coating thickness
Preconditioning
Scribing requirements
Permitted corrosion
Evaluation areas

Some automotive specifications also use cyclic corrosion testing involving changing wet, dry, humidity, and salt conditions. Therefore, ASTM B117 or ISO 9227 should not automatically be assumed to be the required automotive corrosion test.

Salt Spray Requirements for Outdoor Furniture

Outdoor furniture contains numerous coated and plated components that may be exposed to rain, humidity, condensation, and airborne contaminants.

Products can include:

Metal chairs
Tables
Furniture frames
Hinges
Fasteners
Brackets
Furniture fittings

Powder-coated steel and aluminum are common materials in this category.

Salt spray testing may be used to evaluate whether the surface treatment provides the required level of corrosion protection. Particular attention may be given to:

Welded areas
Edges
Fastener locations
Scratches or coating damage
Coating adhesion
Rust development

Products intended for coastal or highly corrosive environments may require more demanding corrosion specifications.

Salt Spray Requirements for Construction and Architectural Hardware

Construction products can experience prolonged exposure to moisture and changing environmental conditions.

Examples include:

Brackets
Connectors
Railings
Fencing components
Door hardware
Architectural fittings
Coated steel components
Galvanized components

The required corrosion resistance depends on the product specification, coating system, installation environment, and applicable construction requirements.

A coating designed for an indoor fitting may have a substantially different specification from one intended for exterior or coastal use.

Salt Spray Requirements for Marine Components

Marine and coastal environments create demanding corrosion conditions because of frequent exposure to salt-containing moisture.

Components may include:

Marine fasteners
Fittings
Brackets
Hardware
Equipment housings
Coated metal assemblies

Salt spray testing can form part of a corrosion evaluation programme for these products.

However, salt spray testing should not automatically be interpreted as a direct simulation of years of marine exposure. Actual service environments can involve UV radiation, immersion, drying, temperature variation, mechanical wear, pollutants, and other conditions that a continuous salt spray test does not reproduce.

The applicable marine or product specification should determine the required testing programme.

Salt Spray Requirements for Electrical and Electronic Enclosures

Metal enclosures and housings may require corrosion testing when used in outdoor, industrial, marine, or high-humidity environments.

Typical products include:

Electrical cabinets
Junction boxes
Control panels
Lighting housings
Equipment enclosures
Communication equipment housings

Corrosion can affect appearance and may eventually compromise enclosure integrity.

Evaluation may focus on:

Coating blistering
Rust formation
Corrosion at edges
Corrosion around fasteners
Scribe creep
Coating adhesion

The relevant enclosure or product standard should be reviewed before selecting the salt spray conditions.

How Are Salt Spray Test Acceptance Criteria Determined?

Salt spray test acceptance criteria define the condition a specimen must meet after the required exposure period.

The appropriate criteria depend on the specification being followed.

Red Rust

Red rust generally indicates corrosion of an exposed ferrous substrate.

A specification may define:

No visible red rust
Maximum percentage of rusted area
No red rust on significant surfaces
A defined rust rating

White Corrosion

White corrosion is commonly associated with corrosion products on zinc and zinc-coated surfaces.

Specifications may establish separate limits for white corrosion and red rust.

Blistering

Coated surfaces may be inspected for blister formation after salt spray exposure.

The size, frequency, and distribution of blisters can be evaluated according to the referenced assessment method.

Corrosion Creep From a Scribe

Coated test specimens may be deliberately scribed before exposure.

After testing, the distance that corrosion has progressed from the scribe can be measured and compared with the specified maximum.

Coating Delamination

Salt spray exposure may reveal loss of adhesion between the coating and substrate.

A specification may limit the amount of coating separation permitted around damaged or scribed areas.

Percentage of Surface Corrosion

Some requirements establish a maximum percentage of the evaluated surface that may show corrosion after testing.

Consequently, a salt spray test result should include both the exposure duration and the observed condition of the specimen according to the specified evaluation criteria.

How Many Hours of Salt Spray Testing Does a Product Need?

There is no single salt spray duration that applies to all products.

The required duration should be determined from:

Applicable product standard
Engineering drawing
Coating specification
OEM requirement
Customer specification
Purchase order
Approved sample or technical agreement

Where no requirement has been specified, the appropriate test duration should be established before testing begins.

Choosing an arbitrary number of hours can produce a test result that has little value for product acceptance.

For example, successfully completing 500 hours of exposure does not automatically mean that a coating satisfies every specification requiring 500 hours. The acceptance criteria may differ substantially.

ASTM B117 vs ISO 9227 Requirements

ASTM B117 and ISO 9227 are among the most widely referenced salt spray test standards.

Area	ASTM B117	ISO 9227
Main purpose	Salt spray/fog test practice	Salt spray corrosion test methods
Neutral salt spray	Yes	Yes
AASS	Different practices/specifications may apply	Included
CASS	Different practices/specifications may apply	Included
Universal product duration	No	No
Universal pass/fail criteria	No	No

For ISO-based specifications, the applicable salt spray method may be identified as NSS, AASS, or CASS.

The test method should always be confirmed before testing because different methods use different test solutions and conditions.

How to Specify a Salt Spray Test

A complete testing request should provide enough information for the laboratory to conduct and evaluate the test correctly.

Important information includes:

Product or specimen identification
Applicable standard
Salt spray method
Exposure duration
Substrate material
Coating or plating type
Coating thickness where applicable
Specimen preparation requirements
Scribing requirements
Evaluation method
Acceptance criteria

For example, a complete requirement might specify a test method, 500-hour exposure, defined specimen preparation, and a maximum permitted level of corrosion after testing.

This provides a much clearer basis for evaluation than simply requesting a 500-hour salt spray test.

Common Salt Spray Test Specification Mistakes

Several problems can make corrosion test results difficult to interpret.

Common examples include:

Specifying test hours without acceptance criteria
Failing to identify the applicable test standard
Assuming ASTM B117 establishes the required exposure duration
Assuming ISO 9227 establishes universal pass/fail criteria
Comparing results obtained using different salt spray methods
Ignoring coating thickness and surface preparation
Using test duration alone as a corrosion-resistance rating
Applying a general requirement when an OEM specification exists

Clear test specifications help ensure that laboratories, suppliers, and buyers evaluate corrosion performance using the same criteria.

Salt spray test requirements should define the test method, exposure duration, specimen preparation, evaluation procedure, and acceptance criteria. Test hours alone provide an incomplete basis for determining corrosion performance.

Before testing begins, the applicable product standard, coating specification, engineering requirement, or customer specification should be reviewed to establish clear pass/fail criteria.