ELECTROCHEMICAL POTENTIAL VARIATIONS IN A SMALL 40 MW FEEDWATER STORAGE VESSEL - THE INFLUENCE OF WELDMENT SURFACE CONDITION

This paper describes a study performed to establish the real in situ e lectrochemical potential (ECP) prevalent in 40 MW deaerator feedwater storage vessel weldments. It was demonstrated that (a) the Ag/AgCl ref erence electrode sensibly recorded the ECP over a period of 1000 h bef ore failure, (b) transients (in the positive, more active direction) w ere the result of abrupt working unit initial load changes, (c) an ini tial ECP hysteresis lasting 400-500 h was recorded where the values re mained much more positive than those normally associated with low diss olved oxygen levels and (d) a strong effect of weldment surface condit ion was evident inasmuch as the ECP values of the fresh bright weldmen t were consistently approximately 150 mV more positive than for the no rmal oxidised weldment. (C) 1997 Elsevier Science Ltd.