What is an atmospheric exposure test?

       The atmospheric exposure test is to carry out the actual corrosion test on the sample rack (outdoor or indoor) of the various surface-treated samples under the condition of natural gas, and determine its protection life by regularly observing and measuring the characteristics and corrosion rate of a certain corrosion process. . The atmospheric exposure test is an important method to correctly judge the corrosion resistance of coatings or other protective layers, and the evaluation results are usually used as the basis for formulating coating thickness standards.



    Generally, atmospheric conditions are divided into the following four categories (including indoor and outdoor) according to the environmental conditions of the area where the exposure site is located;

    1) Industrial atmosphere. The exposure site is located in an industrial area where factories are concentrated, and has atmospheric conditions that are heavily polluted by industrial media (such as SO2; H2S, NH3, coal ash, etc.).

    2) Oceanic atmosphere. The exposure field is within 200m near the sea, and it is vulnerable to the atmospheric conditions of marine salt spray pollution.

    3) Rural atmosphere. The exposure field is located in the countryside far away from the city, the air is clean, and the substrate is not polluted by industrial media or marine salt spray.

    4) Suburban atmosphere. The exposure site is in the urban fringe area, with atmospheric conditions slightly polluted by industrial media.

    Atmospheric exposure fields are divided into outdoor atmospheric exposure fields and indoor atmospheric exposure fields according to various atmospheric conditions. There are strict requirements for site selection, otherwise the assessment results will be affected.

    According to the test purpose and requirements of the product, the atmospheric exposure of the sample can be exposed in the following ways;

    1) Open to expose. The open exposed sample is placed directly on the outdoor frame. The frame is made of material that can withstand corrosion. The sample is placed on the frame and faces south. The height of the plants near the frame should not be greater than 0.2m.

    2) Block exposure. The exposed samples are placed in a shelter with a height of not less than 3m. The shelter is in the shape of an umbrella roof, which strictly prevents the leakage of rainwater, and can completely or partially shield the sunlight from directly irradiating the sample.

    3) Closed exposure. The closed exposed specimen is placed in a louvered box. The louver box is required to prevent atmospheric deposition, solar radiation and direct strong wind, but it should be kept in circulation with the air from outside the box. Leakage is not allowed on the top of the box, and it is properly inclined, with eaves and rainwater grooves. The louver box is made movable around to ensure the exchange of atmosphere inside and outside the box, but rain and snow will not enter the box. The size of the louver box is determined according to the size and quantity of the sample. It is placed on the open space of the test site, and the distance between the two louver boxes should be greater than twice the height of the louver box.