What Is Stress Corrosion Cracking?
The stress corrosion cracking (SCC) test assesses crack initiation and propagation when the sample is exposed to a corrosive environment under constant tensile stress. Stress or corrosion alone may cause no damage, yet together they can lead to fracture.
Purpose of Stress Corrosion Cracking
The purpose is to determine whether a material-environment pair is susceptible to cracking under stress, and to prevent the risk of sudden fracture in service.
Which Products Is Stress Corrosion Cracking Applied To?
- Stainless steel pipes and vessels
- High-strength fasteners
- Aluminium and brass components
- Oil and gas equipment
- Welded structural joints
In Which Sectors Is Stress Corrosion Cracking Used?
Standards Related to Stress Corrosion Cracking
- ISO 7539 series
- ASTM G36
- ASTM G39
- ASTM G30
- ASTM G38
- NACE TM0177
- 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
Stress Corrosion Cracking Conditions
- Installation method
- U-bend (ASTM G30), bent beam (ASTM G39), C-ring (ASTM G38) or dead load
- Environment
- Medium containing boiling MgCl₂ (ASTM G36), chloride solution, or H₂S
- Temperature
- Defined in the standard; Boiling temperature in ASTM G36
- Time
- Exposure time defined in the specification
Equipment for Stress Corrosion Cracking
- Reflux boiling setup or autoclave
- Stress-application fixtures (U-bend, C-ring, bent beam)
- Fume hood and gas safety setup (for H₂S)
- Optical microscope and metallography line
Sample Requirements for Stress Corrosion Cracking
- Sample geometry must suit the chosen loading method
- Stress level must be set according to the specification
- The cracking zone must be specified in welded samples
- Generally at least three specimens
Duration of Stress Corrosion Cracking
Ranges from hours to weeks depending on the specification. Methods such as NACE TM0177 define durations on the order of 720 hours.
Stress Corrosion Cracking Procedure
- 1Samples are prepared and stressed using the defined method.
- 2The corrosive environment is prepared and conditions verified.
- 3Samples are immersed in or exposed to the environment.
- 4Presence of cracking is checked at defined intervals.
- 5At the end of the exposure, samples are examined metallographically.
Stress Corrosion Cracking Acceptance Criteria
The acceptance criterion is defined in the specification; usually no cracking after the defined duration, or crack depth not exceeding the limit.
Evaluation of Results
Visual inspection and metallographic cross-section examination are performed together. Internal cracks not visible on the surface may appear in cross-section.
Stress Corrosion Cracking Report
- Applied standard and loading method
- Stress level and sample geometry
- Environment composition, temperature and duration
- Crack observations and metallographic images
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 authorisationsRelated Regulations
- Oil and gas equipment specifications (NACE/ISO 15156)
- Pressure vessel standards
Corrosion Tests — What Does This Testing Field Cover?
The section below describes the field that the Stress Corrosion Cracking 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 Stress Corrosion Cracking
According to which standard is Stress Corrosion Cracking made?
Stress Corrosion Cracking is executed in scope ISO 7539 series, ASTM G36, ASTM G39, ASTM G30, ASTM G38 and NACE TM0177. 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 Stress Corrosion Cracking apply to?
Mainly applied to Stainless steel pipes and vessels, High-strength fasteners, Aluminium and brass components, Oil and gas equipment and Welded structural joints. Whether your product is included in the scope is determined by examining its technical specifications and intended use.
Under what conditions is Stress Corrosion Cracking done?
The determining parameters are: Installation method — U-bend (ASTM G30), bent beam (ASTM G39), C-ring (ASTM G38) or dead load, Environment — Medium containing boiling MgCl₂ (ASTM G36), chloride solution, or H₂S and Temperature — Defined in the standard; Boiling temperature in ASTM G36. 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 Stress Corrosion Cracking?
Sample geometry must suit the chosen loading method, Stress level must be set according to the specification and The cracking zone must be specified in welded samples. The number of samples is determined according to the product standard and the scope to be reported.
How long does Stress Corrosion Cracking take?
Ranges from hours to weeks depending on the specification. Methods such as NACE TM0177 define durations on the order of 720 hours. 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 Stress Corrosion Cracking result called "appropriate"?
The acceptance criterion is defined in the specification; usually no cracking after the defined duration, or crack depth not exceeding the limit.