Both laboratory and field testing have been conducted in order to reproduce selective weld corrosion experienced in real piping systems. All testing has been done with welded coupons which have been exposed for 6 to 16 weeks, The same type of attacks could be seen on the coupons and the ranking of the welds with respect to corrosion resistance was the same as experienced in the real pipe. Formation of protective layers seemed to be very important for initiation and growth of these localised attacks. The single water phase glass loop used in the laboratory with welded coupons has shown to be a practical tool for studying parameters and rankhrg of real welds for new developments.