AbstractCoupon and loop tubing material of AISI 316L type austenitic stainless steel has been exposed to the candidate liquid breeder material Pb-17Li at 500°C in the 100 liters forced convection loop MALICE. Detailed metallographic and microanalytical examination of the surface modifications were made. It has been found that the ferrite layer porosity, which is considered to be responsible for the generally observed linear or quasi-linear ferrite growth and the corresponding high corrosion rates, is a direct consequence of the formation of a continuous network of σ-phase in the ferrite ans the subsequent rapid dissolution of this σ-phase in the liquid metal.