A combination of corrosion and weather instruments are used to measure the corrosion rates of various materials in relation to the atmospheric conditions and environment.

Atmospheric conditions can vary widely by location, therefore, while a material may be suitable for one application, it may experience a high corrosion rate elsewhere. Factors that may affect atmospheric conditions include salt spray and salty air from a nearby ocean or estuary, rain pattern, discharge from a cooling tower, and air pollution. Data obtained from a corrosimeter, corrosion coupons, weather instrumentation, and an air sampler can be combined to determine the corrosiveness of an environment and the suitability of a material for a specific application. A sensitive corrosimeter determines times and rate of corrosion that are then correlated to the environmental conditions.

Corrosimeter - The Jonas, Inc. Corrosimeter (Figure 1) is a sensitive field instrument based on the change in electrical resistance of the tested material, which is in the form of a special foil sensor. The change in electrical resistance is proportional to the decrease of cross-section of the sensor by corrosion or erosion. To achieve the highest accuracy, two identical sensors are used, one exposed to the corrosive environment and one not (a reference sensor). The advantage of this monitor is its high sensitivity (0.01 mils for steels), which results in almost instantaneous measurement of corrosion rate.

Corrosion Coupons - Corrosion coupons (Figure 2) are used to determine the long-term corrosion rates for various materials (metals, plastics, coatings, etc.) exposed to the atmosphere. Two types of tests can be used. The first conforms to the ISO9226 standard where four specific materials are tested: carbon steel, zinc, aluminum, and copper. All of the coupons are evaluated after 1 year of exposure. The second type conforms to the ASTM G50 standard and can use any customer specified materials. Coupons are typically evaluated after 6 months, 12 months, and 24 months of exposure.

Air Sampler - A high volume air sampler is used to obtain samples of particles and aerosols in the air at the test location. Samples can also be obtained during significant weather events, such as a strong wind from the ocean or from the direction of a cooling tower, etc. The samples are then analyzed to determine what corrosive impurities are present in the atmosphere.

Weather Instrumentation - Weather instrumentation, including wind speed and direction, temperature, pressure, and relative humidity, is used to monitor the environmental conditions during the test period. In addition, a surveillance camera can be installed to monitor a specific environmental factor (i.e., cooling tower plume) and the overall conditions during the testing.