About Corrosion Coupon Tests

The concept of using corrosion coupons to characterise potentially damaging data centre environments, was first introduced in the Instrument Society of America Specification ISA-71.04-1985, Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants. This standard was updated in 2013 although the basic procedure, still followed, dates back well into the last century.

This standard divided environmental corrosion risk into four bands based on the extent of corrosion of a pure copper surface over a one month exposure period. The range and identification is from mild (Class G1) to severe (Class G4) and is determined by the thickness of the corrosion film created. This concept has been adapted and extended by ASHRAE (ASHRAE 2011. Gaseous and Particulate Contamination Guidelines For Data Centers) and adopted by most major IT manufacturers to gauge the effect of this type of damage on equipment reliability. When lead was removed from solder connection technologies, ASHRAE introduced silver coupons to better reflect the changes in circuit card metallurgies.

Each of the four Classes is associated with a limit of film thickness growth for each metal over a one month interval. ASHRAE strongly advise that Class G1 is the preferred requirement for IT locations, with appropriate filtration of incoming air if this level cannot be naturally achieved.