ABSTRACT

Atmospheric corrosivity poses a severe threat to steel structures and assets. Hence, knowledge about the corrosivity is crucial in order to specify the suitable corrosion protection solution, estimate lifetime of assets and plan maintenance.

The ISO 9223(1) provides guidance on how to calculate the corrosivity rate at a certain location based on input data such as temperature, humidity, pollution and chloride deposition1. And although weather and climatic data has been readily available in various open-source meteorological databases for several years, other required data is site specific and requires direct measurement at the location of interest over one full year, e.g. sulfur dioxide and chloride deposition.

This paper presents a method for estimating first year corrosion rate for any given location based on data collected from various open-source data bases containing climatic and environmental data, including sea salt distribution and sulfur dioxide concentrations. The method utilizes various techniques such as linear interpolation for estimation of sea salt distribution, humidity and temperature, and correction of the coastal areas. ISO 9223 has then been used to estimate first year corrosion rate and corrosivity category for any location. Estimated corrosivity rates and categories have been verified and validated using literature data and collected data.

INTRODUCTION

Low alloyed carbon steels are the most used materials for infrastructure, energy, transportation and other industries and assets. Depending on the environment, carbon steel will corrode when exposed to atmospheric conditions. In order to prevent atmospheric corrosion of the mentioned materials, corrosion protective coatings are used. A protective coating system, often comprising several layers of inorganic and/or organic coating products will also have a finite lifetime whereupon it will no longer effectively protect the underlying steel substrate against the environments. Obviously, a corrosion protective coating system will respond to the atmospheric conditions in a different manner than bare carbon steel. However, studies have shown that atmospheric corrosivity is one of the most important parameters to assess proper corrosion protection and maintenance intervals for steel constructions2. Further, when specifying, testing and qualifying corrosion protective coating systems according to internationally accepted standards and specifications, e.g. ISO 12944-series, the expected corrosivity category of the project or as given in the customer specification is governing the selection of a suitable corrosion protective coating system3. The estimated or expected corrosion category given in such specifications are often based on subjective experience or tradition rather than an objective measurement of corrosivity for the specific location of the project or asset.

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