Study of TVA tubing samples representing both wastage-susceptible and wastage-resistant tube banks has indicated a wastage mechanism similar to that identified in previously-studied tube samples from Grimethorpe (UK). Metallurgical differences between the two TVA tube banks were also observed that are believed relevant to their wastage response. Wastage appears to occur through exfoliation of protective oxide scale caused by impingement and abrasion of fluidized bed materials. There is no evidence that chemical effects of elements such as sulfur or chlorine are responsible for or contribute to the wastage process. The tube from the wastage-resistant tube bank, in contrast to the tubes that experienced wastage, formed an alloy-enriched layer at the scale/substrate interface that is apparently oxidation resistant and seems to protect the steel surface from mechanical impacts and abrasion of bed materials. 47 refs., 22 figs., 2 tabs.