Corrosion Behavior of Nonferrous Alloy Feedwater-Heater Materials in Neutral Water With Low Oxygen Contents

Abstract

Copper bearing alloys are widely used in steam generation feedwater heaters, and although corrosion rates are minimal, copper corrosion product release has caused some undesirable deposition in BWR plants. Only limited prior data exist for prediction of corrosion product input to high pH, low oxygen fossil plant feedwater, and essentially no prior data are available for predicting input to BWR type operation of neutral pH and low oxygen feedwater. The copper problem was resolved in later BWR plants by changing to stainless steel feedwater heaters. Concurrently, a test program was instituted in 1965 to study copper alloy corrosion product release behavior in BWR feedwater conditions of flowing, neutral pH water, containing less than 10 ppb oxygen, in a temperature range from 150 to 400 F (66 to 204 C). The alloys examined were Admiralty brass, 90–10 copper nickel, 70–30 copper nickel, 70–30 copper nickel iron-modified and Monel alloy. Corrosion product release was determined gravimetrically on coupons, made from tubing furnished to ASTM feedwater heater specifications, as a function of time and temperature in a recirculating dynamic facility. Essentially 100% of the corrosion products generated on all alloys tested were released to the feedwater at all temperatures, with the release rates being invariant in time. The release rates of Monel alloy varied from 1 mg/dm2-mo at 150 F (66 C) to 80 mg/dm2-mo at 400 F. Those of the four other alloys were low, and nearly identical, ranging from 1 to 3 mg/dm2-mo at 150 F to 8 to 12 mg/dm2 -mo at 400 F.