ASTM G31 Standard Guide for Laboratory Immersion Corrosion Testing of Metals

    ASTM G31 Introduction

    Under severe chemical or aquatic environments, metals are susceptible to corrosion, causing a decline in mechanical integrity and loss of service life. ASTM G31 is a systematic protocol to determine how a special metal or alloy will react when submerged in a particular environment. The standard does not specify a specific corrosive medium, but rather enables customization according to service conditions. By standardizing sample preparation, testing time, cleaning, and measurement protocol, this test-to-test variability is reduced. The ASTM G31 test results compare corrosion performance to help engineers and material scientists assess the efficacy and screen alloys of protective coatings for novel applications. This creates an important resource for industries that rely on rust control, including oil and gas, chemical processing, and marine engineering.

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    ASTM G31 Test Method

    Exposure DurationImmersion periods typically range from 24 hours to several weeks, depending on the intended simulation.
    Solution ControlCorrosive medium prepared to specified composition, pH, and temperature; monitored periodically for stability.
    Corrosion Rate MeasurementWeight loss is determined after cleaning specimens, calculated in mils per year (mpy) or mm/year using the formula defined in the guide.

    ASTM G31 Equipment and Sample Preparation

    Specimen PreparationSamples cut to precise dimensions (commonly 25 mm × 50 mm × 3 mm), edges deburred to prevent localized attack.
    Test VesselNon-reactive containers (glass, plastic, or coated metal) sized to maintain at least a 20:1 solution volume to specimen surface area ratio.
    Cleaning ApparatusIncludes ultrasonic bath or soft-bristle brushes and solvent rinses to remove corrosion products without damaging the base metal.

    ASTM G31 Test Results and Interpretation

    After immersion, the specimens are cleaned in accordance with procedures outlined in ASTM G31 to eliminate corrosion products without impairing the unaffected surface. Weight loss is translated into corrosion rates, which may be compared among materials or environments. Uniform corrosion yields repeatable mass loss, while localized pitting or crevice corrosion is determined through visual examination and dimensional measurement. These results establish suitability for service and direct protective action.

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    The ASTM G1 provides procedures to prepare and clean corrosion test samples. The ASTM G44 cycling salt addresses the risk of metals in fog and immersion for a more severe environment. The ASTM G48 specifies methods for the evaluation of pits and corrosion resistance of stainless steels in chloride-containing solutions.

    Materials Commonly Tested with ASTM G31 

    ASTM G31 is often used to evaluate materials such as carbon steels for structural use, stainless steels for chemical process equipment, aluminum alloys for marine use, and copper alloys for tubing in heat exchangers. Coated metals are also examined to confirm protective performance when immersed.

    Applications of ASTM G31 in Industry

    Industries such as offshore oil production, desalination plants, chemical manufacturing, and shipbuilding rely on ASTM G31 data to predict physical lifespan. Testing is equally important for metal assurance programmes for suppliers and in research laboratories that develop new alloys or corrosion barriers.

    Safety and Best Practices in ASTM G31 

    The ASTM G31 emphasizes safe handling of corrosive chemicals, requiring proper individual safety tools, a fume hood for volatile solutions, and appropriate waste disposal processes. Testing vessels should be carefully handled to avoid contamination or accidental risk. To maintain accuracy and security, temperature-controlled bath and solution mixture should be constantly monitored.

    Importance of ASTM G31 

    The importance of ASTM G31 lies in its ability to repeat the real-world immersion situation in a controlled environment, which produces reliable, quantitative corrosion data. It supports informed material selection, design improvement, and maintenance planning, reduces failure risks, and expands service life in corrosion-prone applications. By following the guide, the industry receives a consistent, scientifically grounded approach to combat one of the most expensive forms of physical degradation.

    Updated on September 17, 2026

    Davis Scott
    About Author
    Davis Scott
    Davis Scott is an Electrical and Electronics Engineer specializing in multidisciplinary validation, quality assurance, and comprehensive electro-mechanical testing.
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