Metal corrugated ducts are produced from hot-dipped galvanized steel sheet special tubeformer machines.
These thin-walled (0.25mm-0.60mm）, ribbed sheet metal ducts provide high rigidity that can withstand being embedded in concrete without deformation. The duct corrugation provides excellent bond behaviour between the tendon and concrete.
Metal ducts also provide a fair secondary corrosion protection to the strands. Primary protection provided by the alkalinity of grout and concrete.