Low-Pressure Steam Turbine Disc Cracking—An Update

Abstract

This paper summarizes results of studies conducted in the U S A over the past jive years to identify factors responsible ,for .stres,s corrosion crucking (SCC) of forged, shrunk-on, low-alloy steel discs in low-pressure ( L P ) steam turbines used in nucleur power plants. Experience in the U K and subsequent research jndings .are reviewed, and results of a survey of U S experience and qf comp~*ehen.sit~ experimental programs are reported. Recommendations are presented to minimize SCC of LP turbine discs in exisfing andJuture power plants. I n general, the work performed revealed: ( i ) no specijic chemical contaminant is required for cracking; crack initiation and growth occur in pure condensed steam; (ii) the yield strength of a disc steel is the dominant factor governing cruck growth rutes; (iii) other factors being equal, a higher incidence of cracking may be expected in rotor designs huuing higher applied stress lez?els. Cruck initiation and growth in L P turbines may be minimized by control of the environment, by use of' low-strength alloys, and by-desi{jns which eliminate keyways and minimize applied stress levels.

Stress Corrosion Cracking of Steam Turbine Steel: The Influence of Organic Acid Characteristics

“…Therefore, when increasing the hydrogen proton concentration, the current densities of both the oxygen reduction reaction and the hydrogen proton reduction reaction, according to Equations ( 29) and (32), respectively, roughly increase linearly. When taking into account Faraday's law, cf.…”

“…For this situation, the current density can be written according to the Butler-Volmer equation, cf. Equation (32),…”

“…The acidified first condensate in steam turbines can cause significant corrosion damage [24][25][26][27], such as acidic stress-corrosion cracking [28][29][30][31][32][33] and corrosion fatigue [34]. In addition, electrochemical impedance spectroscopy (EIS) indicated that acetic acid facilitates pitting of steam turbine steel in first condensates containing chlorides [35].…”

Effect of Film-Forming Amines on the Acidic Stress-Corrosion Cracking Resistance of Steam Turbine Steel

“…However, water treatment technologies are increasingly faced with lower quality feed waters, because of among others the ongoing shift towards alternative water sources and climate change [21][22][23][24][25]. Especially the increasing amount of organic acids in the first condensate of low-pressure steam turbine sections can cause serious corrosion damage, such as SCC [26][27][28][29][30][31][32][33][34][35]. These organic acids originate from the breakdown of organic impurities by hydrothermolysis in boilers and superheaters [19,[36][37][38][39][40][41].…”