1.1 This guide presents two methods for estimating the atmospheric corrosion resistance of low-alloy weathering steels, such as those described in Specifications A 242/A 242M, A 588/A 588M, A 606 Type 4, A 709/A 709M grades 50W, HPS 70W, and 100W, A 852/A 852M, and A 871/A 871M. One method gives an estimate of the long-term thickness loss of a steel at a specific site based on results of short-term tests. The other gives an estimate of relative corrosion resistance based on chemical composition.