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Intergranular corrosion occurs as a result of precipitation of nitrides, carbides, and other intermetallic phases, such as sigma phase, that occurs along the grain boundaries. If materials with incorrect heat treatment enter service, they are liable to crack or fail by intergranular corrosion (IGC) much more rapidly than properly treated materials; ASTM A262 is a screening test to help find batches that are incorrectly processed.
Why should you select G2MT Labs for ASTM A 262 intergranular corrosion (aka intergranular attack) testing?
- We provide accurate, repeatable results along with world-class customer service.
- We offer ASTM A 262 testing from Houston for customers around the world; with overnight shipping, we can start immediately.
- We work with you to select the right method for your steel grade, and then deliver clear results in a reasonable time and budget.
How do you select the right ASTM corrosion testing method for your material?
The first and fastest step is the ASTM A262 Practice A, a rapid (same-day) screening method in Oxalic acid to determine the susceptibility to intergranular corrosion. Classification of the structure after A262 Practice A analysis will determine if the material is acceptable or if additional testing is required. If you are not sure, please contact us for assistance. Based on your materials, application, and requirements, the other 4 methods provide specific focuses.
In everyday applications, corrosion varies by materials and solutions. For example, in highly oxidizing solutions, intergranular attack can occur due to intermetallic phases, while attack of carbides may occur somewhat less oxidizing solutions. Due to the variance of attack in different materials, numerous methods (Practices B-F) are used to assess intergranular corrosion. The chart below comes from the ASTM A262 standard for selection of the appropriate test by alloy type:
The ASTM A 262 tests can determine if the proper heat treatment was performed or if the alloys are in danger of intergranular corrosion occurring in use. These tests are often run as a qualification test to ensure each batch of stainless steel is properly prepared. Each ASTM A262 Practice specification includes a list of the grades of stainless steels and the acceptable etch structures for the specific alloys. For example, many low-carbon and stabilized stainless steels (e.g. 304L, 316L, 317L, and 347) must be subjected to a sensitizing heat treatment prior to testing by the oxalic acid etch test (Practice A).
Practice A, the oxalic acid etch test is used as a rapid technique to screen samples of certain stainless steel grades to ensure they are not susceptible to intergranular attack (sensitization). The test is generally performed for acceptance of materials, but not sufficient for rejection of materials. Because it can be run quickly for screening, we often run this test first.
ASTM A262 Practice B – “The Streicher Test” – Ferric Sulfate – Sulfuric Acid
Practice B, also known as the Streicher test, uses weight loss analysis to provide a quantitative measure of the materials performance. This practice includes boiling the sample for 24 to 120 hours in the solution above, and measures the materials performance quantitatively. It is typically used for stainless alloys such as 321 and 347, Cr-Ni-Mo stainless alloys, and nickel alloys to evaluate the intergranular attack associated with the precipitation of chromium carbides at grain boundaries.
In Practice C, the Huey Test, samples are boiled for five 48-hour periods in a 65% Nitric Acid solution. The weight loss is calculated after each step, and reveals if the sample has been properly heat-treated. Please specify the maximum allowable corrosion rate and any available data on the sensitizing heat treatment performed. The Huey test works well to analyze chromium depleted regions and intermetallic precipitates, such as sigma phase, and is also used for materials in strongly oxidizing environments such as nitric acid
Practice E, the Strauss test, is performed to assess attack associated with chromium-rich carbide formation; it does not detect susceptibility to sigma phase formation. The Strauss test is commonly used to evaluate the heat-treatment of as-received material, the effectiveness of alloying additions of elements such as Nb and Ti, or the effectiveness of reducing carbon content to resist intergranular attack. The oxalic acid test is commonly used before the Strauss test to determine if a sample is susceptible; samples that pass method A will generally show low corrosion rates in the Strauss test.
The samples are boiled in a Cu-Copper Sulfate mixture for 15 hours and then bent 180° over an equal diameter bend. The test uses a visual inspection of the surface of the bent specimen to determine pass or fail. Duplicate samples from both sides of a sheet sample are evaluated to determine if carburization results in intergranular attack. The bent samples are examined at low magnification, where the appearance of cracks or fissures indicate intergranular attack.
Practice F, is a 120 hour weight-loss based analysis that provides a quantitative measure of the materials performance, and is commonly used to analyze as-received stainless steels. The test evaluates the resistance of extra-low-carbon steels to sensitization and intergranular attack from welding or heat treatment processes.
Additional ASTM A 262 Corrosion Testing Resources:
ASTM A 262 corrosion testing FAQ
What is your typical turnaround time? It depends on which Practice is selected, but typically ranges from 4-6 to 10-15 days for different tests. In many cases we can reduce that to as little as 24 hours more than the required testing time if you need fast results.
Where can I get ASTM A 262 corrosion testing performed?
G2MT Labs is one of the few labs to offer all five ASTM A 262 corrosion testing practices, as well as the expertise to help you determine which tests to use, what to do if a test fails, and other corrosion consulting as needed. Contact us now for pricing or a quote!