Immersion corrosion testing is used to determine resistance of a material to an aggressive, aqueous environment. Standard laboratory corrosion coupons are utilized to determine weight loss due to corrosion. The ASTM G31 test method normalizes corrosion rates to units of time, typically in mm/yr or mils per year (mpy). Test terms vary, but results can usually be obtained within a 24-hour, 10 or 20 day exposure cycle.
The solution and coupon material pair is often prescribed by the client, based on application. Test temperature and oxygen availability variables are also specific to the experiment. NACE test method TM0169-95 (281-228-6200) offers recommendations for determining optimum test times for immersion service testing.
Following testing, gravimetric analysis provides the corrosion weight. Surface analysis can also be performed by stereo microscopy or scanning electron microscope to further investigate the post test morphology.
Determine corrosion rates for metal in an aqueous environment
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Test durations range from 24 to 2,000+ hours
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ASTM A262, Practice A, B, C, and F - Intergranular corrosion testing
ASTM G28, Method A - Detecting susceptibility to intergranular corrosion
ASTM G48, Methods A, B, and C - Resistance to pitting and crevice corrosion
Samples are typically a circular specimen of about 38-mm (1.5-in.) diameter with a thickness of approximately 3mm (0.125-in.) and an 8-mm (5⁄16-in.) or 11-mm (7⁄16-in.) diameter hole for mounting
The cut edges of samples are often sanded