Step 7 – Corrosion Guide Vickars（步骤7 - Vickars腐蚀指南）.pdfVIP

Step 7 – Corrosion Guide Introduction Corrosion is defined as the degradation of a material or its properties due to a reaction with the environment. Corrosion exists in virtually all materials, but is most often associated with metals. Metallic corrosion is a naturally occurring process whereby the surface of a metallic structure is oxidized or reduced to a corrosion product such as “rust” by chemical or electrochemical reaction with the environment. The surface of metallic structures is attacked through the migration of ions away from the surface, resulting in material loss over time. Given enough time, the material loss can result in significant reduction of area, which in turn leads to a reduction in the structural capacity of a given metallic element. When corrosion eventually destroys a sufficient amount of the structure’s strength, a failure will occur. The corrosion mechanisms involved with buried metallic structures are generally understood, but accurate prediction of metal loss rates in soil is not always easily determined. This section of the design manual provides an introduction to the concepts of underground corrosion and the factors that influence this corrosion in disturbed and undisturbed soils. A few design examples are provided to give the reader a better understanding whether corrosion is a critical factor in a helical screw foundation application. This section is by no means intended as a rigorous design guide, but rather as a “first check” to see if corrosion is a practical concern given the specific project site conditions. A qualified corrosion engineer should be consulted for a site-specific recommendation if helical screw foundations are to be used in a known corrosive soil. Experience over the past 50 years has shown the vast majority of square shaft and pipe shaft helical screw foundations have a calculated service life well in excess of the design life of the structure (typic