SUMMARY
Humidity plays an important part in the atmospheric corrosion of metals. It also has a significant influence on the curing of coatings. An understanding of humidity and related factors such as dew point are essential for the corrosion engineer and coating specifier and applicator. This paper looks at humidity, its definition and the methods of measurement. It also covers its relationship to temperature and dew point, and how these affect the probability of condensation and corrosion. The paper concludes with a look at variations in relative humidity at various sites around Australia, and how they vary throughout the year.
INTRODUCTION
Effect of Humidity on Corrosion
Humidity has long been known to play a major part in the atmospheric corrosion of metals. Under humid conditions, a metal will corrode at a much greater rate than under dry conditions. This is because moisture in the air reacts with oxygen at cathodic sites to take up the electrons produced by a corroding metal at anodic sites. If there is no moisture, then this reaction cannot occur, and corrosion ceases. In the 1930s, Vernon (i) was the first to investigate quantitatively the effects of humidity on corrosion of metals, and his results, such as those shown in Figure 1, are widely quoted to this day.
http://www.pfa.org.pk/wp-content/uploads/2017/04/Humidity_and_Dew_Point_Their_Effect_on_C.pdf
