Prohesion Testi — ASTM G85 Annex A5

What Is Prohesion?

The Prohesion test, defined in ASTM G85 Annex A5, is a cyclic corrosion test in which wetting and drying stages with a dilute ammonium sulfate and sodium chloride solution are cycled. It was developed specifically for paint systems.

Purpose of Prohesion

The purpose is to assess the performance of paint and coating systems against atmospheric corrosion in a manner closer to real conditions.

Which Products Is Prohesion Applied To?

Industrial paint systems
Structural steel coatings
Powder-coated surfaces
Outdoor metal components

In Which Sectors Is Prohesion Used?

AutomotiveMetalSteelConstructionMaritime

Standards Related to Prohesion

ASTM G85 Annex A5
ASTM D5894
ASTM B117tuz sisi (salt spray) korozyon testi test
ISO 9227tuz sisi korozyon testi test
ASTM G85modified salt fog (cyclic) test test
ASTM G48pitting and crevice corrosion in stainless steels test
ISO 16701cyclic corrosion test test
ISO 6270strength in condensation environment test
SAE J2334cyclic laboratory corrosion testing test
VDA 233-102cyclic corrosion testing in automotive test

Prohesion Conditions

Solution: Dilute solution of ammonium sulfate and sodium chloride (defined in ASTM G85 A5)
Cycle: Duration of wetting and drying stages defined in the specification
Temperature: Defined in the standard according to the stage
Time: Total cycles or hours defined in the specification

Equipment for Prohesion

Programmable cyclic corrosion chamber
Dilute electrolyte preparation setup
Temperature and humidity control
Data logging

Sample Requirements for Prohesion

Generally at least three specimens
Scribe pre-damage is applied per the specification
Coating system and dry film thickness should be recorded
Edges must be masked

Duration of Prohesion

Depends on the total duration defined in the specification; typical programmes take weeks.

Prohesion Procedure

1The dilute electrolyte is prepared.
2Samples are prepared and scribed.
3Wetting and drying cycles are run according to the programme.
4Interim observations are recorded.
5At the end of the exposure, samples are evaluated.

Prohesion Acceptance Criteria

The acceptance criterion is given in the specification as maximum corrosion spread around the scribe and blistering grade.

Evaluation of Results

Scribe spread, blistering and loss of adhesion are assessed. For paint systems it gives more discriminating results than salt spray.

Prohesion Report

Applied standard and annex number
Solution composition and cycle programme
Total duration and interim observations
Spread measurements and photographs

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Industrial paint specifications

Corrosion Tests — What Does This Testing Field Cover?

The section below describes the field that the Prohesion test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Corrosion testing assesses under accelerated conditions how long metals and coatings last in a corrosive environment. The family contains two approaches, and the difference between them is the most important knowledge in the field: constant-condition tests and cyclic tests.

Constant-condition salt spray (ASTM B117, ISO 9227) maintains the same environment in the chamber throughout: the same salt concentration, the same temperature, a continuously wet surface. The strength of this approach is its REPEATABILITY; because the conditions are tightly defined, results from different laboratories come out close to one another. That is exactly the property wanted when monitoring production consistency and comparing suppliers.

But the real atmosphere is not constant. A surface gets wet, dries, warms, cools, takes UV and becomes soiled. The wet-dry cycle changes the corrosion mechanism: during drying the salt concentrates, oxygen access increases and corrosion accelerates. The form of damage on a continuously wet surface differs from that on a cyclically wetted one.

Cyclic tests (SAE J2334, VDA 233-102, ASTM G85, ISO 16701) imitate this variability and give results closer to the damage patterns seen in the field. The automotive sector has largely moved to this approach. The practical consequence is this: the same two coatings may RANK DIFFERENTLY in constant and cyclic tests; which test was applied determines the result.

No test in this family defines a DURATION OR ACCEPTANCE CRITERION. How many hours it is applied for and what level of damage is acceptable come from the product standard or the customer specification. The assessment scales are defined in separate standards: different scales are used for degree of rusting, blistering, creep from a scribe and loss of adhesion.

The damage looked for varies with the coating type. For metallic coatings, white rust (corrosion of the coating itself) and red rust (corrosion reaching the base metal) are reported separately, and specifications usually give a separate duration for each. On painted surfaces, creep from a scribe and blistering come to the fore.

Electrochemical methods are a separate body of work and answer a different question. Potentiodynamic polarisation, electrochemical impedance spectroscopy and pitting potential measurements reveal the MECHANISM and rate of corrosion within hours; chamber tests give the result visually over weeks. The two are complementary rather than alternatives.

Stainless steels have a special sub-body in the field: pitting and crevice corrosion and intergranular corrosion tests indicate the quality of the heat treatment and the condition after welding.

Method groups in this field

Constant-condition salt spray
ASTM B117 and ISO 9227 (NSS); for repeatable comparison and process control.
Acidified and accelerated
The AASS and CASS conditions of ISO 9227; preferred for decorative chromium-nickel coatings.
Cyclic corrosion
SAE J2334, VDA 233-102, ASTM G85 and ISO 16701; approaches field behaviour through wet-dry cycles.
Humidity and condensation
Steady damp heat, condensation and cyclic humidity tests; these reveal coating blistering.
Electrochemical
Polarisation, impedance spectroscopy, pitting and crevice corrosion potential measurements.
Stainless steel specific tests
Pitting and crevice corrosion, intergranular corrosion; indicators of heat treatment and weld quality.
Assessment scales
Scales for degree of rusting, blistering, creep from a scribe and loss of adhesion; the ratings come from these standards.

Commonly confused in this field

Chamber hours cannot be converted into field life; there is no reliable conversion factor.
Constant and cyclic tests can produce different rankings; whichever the specification states is the one applied.
A corrosion report without a stated duration and acceptance criterion cannot be interpreted.
If the coating thickness is not reported, the result cannot be compared; thickness directly affects durability.
White rust and red rust say different things; the two must be reported separately.
The position and angle of the specimen in the chamber affect the result; standards govern this and the report must document it.

Which decisions these results support

Selection of the coating system and supplier approval
Process control of the coating line and lot acceptance
Evidence of durability for automotive and outdoor products
Assessment of field corrosion damage and warranty decisions
Verification of heat treatment and weld quality in stainless steel

Related Tests

Frequently Asked Questions About Prohesion

According to which standard is Prohesion made?

Prohesion is executed in scope ASTM G85 Annex A5 and ASTM D5894. The limit values and acceptance criteria to be applied are defined in the product standard; The version valid for your product is confirmed in writing at the offer stage.

Which products does Prohesion apply to?

Mainly applied to Industrial paint systems, Structural steel coatings, Powder-coated surfaces and Outdoor metal components. Whether your product is included in the scope is determined by examining its technical specifications and intended use.

Under what conditions is Prohesion done?

The determining parameters are: Solution — Dilute solution of ammonium sulfate and sodium chloride (defined in ASTM G85 A5), Cycle — Duration of wetting and drying stages defined in the specification and Temperature — Defined in the standard according to the stage. The full terms are in the "Test Conditions" section on the page and vary depending on the product standard.

What kind of sample is needed for Prohesion?

Generally at least three specimens, Scribe pre-damage is applied per the specification and Coating system and dry film thickness should be recorded. The number of samples is determined according to the product standard and the scope to be reported.

How long does Prohesion take?

Depends on the total duration defined in the specification; typical programmes take weeks. This duration belongs to the experiment itself; sample preparation, queuing and reporting are also evaluated. A realistic schedule for your product is given in the offer.

What is the Prohesion result called "appropriate"?

The acceptance criterion is given in the specification as maximum corrosion spread around the scribe and blistering grade.