Are Agency Soil Corrosivity Testing Guidelines Sufficient?

Many geotechnical engineers rely on corrosion control guidelines provided by transportation agencies when providing corrosion control recommendations for residential and commercial structures without realizing that highway guidelines focus on carbon/structural steel and concrete with little thought regarding aluminum, copper, brass, or stainless steel. As highways deal mainly with rebar and carbon steel piles, general (large area) corrosion is more of a concern than localized pitting corrosion which can produce leaks. Most agencies suggest that soil resistivity is the prime factor to categorize soil corrosivity only recommending additional testing of soil pH, minimum resistivity, water soluble sulfates and chlorides, if the resistivity is below 1,500 ohm-cm. These tests have come to be known as the “Corrosion Series” by geotechnical engineers with only sulfate testing being required by the International Building Code (IBC). By not also testing for ammonia, nitrates, sulfides, and REDOX the potential corrosion risks for other important general construction materials for residential and business projects are missed. These other factors affect pitting and intergranular corrosion of stainless steel and copper based alloys greatly as well as probability of corrosive bacteria presence also known as MIC. In order for the soil side corrosion to occur, there must be moisture present to allow ion exchange in the oxidation reduction reactions. Few remember that underground condensation can occur on metal surfaces and that significant dew can fall in the evenings. In the opinion of this author, it is hoped that the 1,500 ohm-cm limit is removed or raised to 5,000 ohm-cm and that four extra tests are added to the “Corrosion Series” typically ordered by geotechnical engineers to avoid pipeline leaks, failure of copper water lines, copper electrical grounding systems, aluminum hardware, stainless steel hardware, ductile iron pipe, and brass hardware and fittings.