ASTM G50: Standard Practice for Conducting Atmospheric Corrosion Tests on Metals

Key Test Parameters

Site & Exposure Configuration

• Standard Orientation: Test racks should generally be positioned at an angle of 30° from horizontal, facing the Equator, with the lowest specimens at least 30 in (760 mm) above the ground.
• Location: Test sites should be chosen that are representative of where the metals/alloys might be used, such as industrial, rural, or marine environments.

Specimen & Mounting Specifications

• Standard Dimensions: The preferred specimen size for sheet material is 4 × 6 in. (100 mm by 150 mm), with a suggested minimum thickness of 0.030 in. (0.75 mm) for adequate rigidity.
• Electrical Insulation: Specimens must be mounted using glazed insulator knobs and non-corrosive fasteners (such as stainless steel or nylon) to prevent unintentional galvanic corrosion with the rack. 
• Exposure: Rack design must allow maximum airflow to the underside of the panels, as the groundward surface often corrodes at a different rate than the skyward surface.

Removal & Evaluation Schedules

For proper data collection and analysis, ASTM G50 outlines a structured approach for intermediate evaluations and specimen removals.

• Standardized Removal Intervals: Reliable results are typically achieved using a schedule of 1, 2, 4, 8, and 16 years to monitor how corrosion rates evolve over time. Shorter exposures for less-durable materials may warrant more frequent evaluations
• Statistical Validity: Using at least three specimens for each examination period is recommended to ensure data consistency and reliability.
• Annual Surface Inspections: Regardless of the removal schedule, all specimens should be evaluated annually to record the color, texture, and uniformity of oxide coatings on both skyward and groundward surfaces.
• Pre-Exposure Documentation: Every specimen must be weighed precisely and its dimensions recorded prior to exposure to establish a baseline for future mass-loss calculations.