THE ELECTROCHEMICAL POTENTIAL CHARACTERISTICS OF A DEAERATOR FEEDWATER SYSTEM - MEASUREMENT, DATA TRENDS AND PLANT-OPERATION IMPLICATIONS

The serious problem of deaerator feedwater storage vessel cracking is addressed in the present paper together with an assessment of the elec trochemical potential (ECP) characteristics, which significantly dicta te crack extension rates prevalent within a working deaerator. Indeed recent modern day advances in the understanding of this particular cra cking problem have demonstrated that (i) the ECP of a component can dr amatically influence the crack growth behaviour of some low alloy stee ls and stainless steels and (ii) a critical ECP exists, above which cr ack growth rates are environmentally driven and can be well over an or der of magnitude faster than pure mechanical crack growth rates. The p resent study aimed to measure and record the ECP behaviour in a workin g deaerator feedwater storage vessel of a 20 MW boiler under varying o perational conditions. Relevant physical/chemical parameters such as f eedwater pH, conductivity, dissolved oxygen content, flow rate and uni t load were also closely monitored. The main features of the present s tudy identified that dissolved oxygen content at the feedwater inlet t o the deaerator and the load level (and more particularly load changes ) had major effects on the ECP values. Finally, the implications of th ese findings in relation to plant operation are discussed at length.