The influence of ppb levels of chloride impurities on the stress corrosion crack growth behaviour of low-alloy steels under simulated boiling water reactor conditions

Abstract

The effect of chloride on the stress corrosion crack (SCC) growth behaviour in low-alloy reactor pressure vessel steels was evaluated under simulated boiling water reactor conditions. In normal water chemistry environment, ppb-levels of chloride may result in fast SCC after rather short incubation periods of few hours. After moderate and short-term chloride transients, the SCC crack growth rates return to the same very low high-purity water values within few 100 hours. Potential long-term (memory) effects on SCC crack growth cannot be excluded after severe and prolonged chloride transients. The chloride tolerance for SCC in hydrogen water chemistry environment is much higher.

Effect of ammonium bisulphite and chloride on the pitting and stress corrosion cracking resistance of super duplex stainless steel pipes under combined internal pressure and axial tension

“…A number of researchers have found that the occurrence of pitting corrosion was an important contributing factor in crack initiation during the process of SCC . Furthermore, many other researchers have shown that the temperature of maximum SCC susceptibility is between 80–120 °C .…”

“…Most of the published research to‐date on pitting and stress corrosion cracking (SCC) are based on single mode or uniaxial loading of the material in CO 2 /H 2 S or chloride environment. Test results from four‐point bend specimens of austenitic stainless steel in chloride environment showed increased susceptibility to pitting corrosion with increased pre‐existing surface roughness or damage while compact tension test results in simulated boiling water reactor conditions showed that ppb level of chloride may result in fast SCC of low alloy steels . SCC of 22 and 25Cr SDSS under evaporative seawater conditions using uniaxial tensile specimen has been shown to depend on the level of applied stress and the test temperature; as the applied stress increased the threshold temperature for corrosion and cracking decreased .…”

The influence of ppb levels of chloride impurities on the strain-induced corrosion cracking and corrosion fatigue crack growth behavior of low-alloy steels under simulated boiling water reactor conditions

“…In the past, the focus was placed on the effect of water chemistry transients on SCC in stainless steels [33][34][35][36][37] and these investigations clearly revealed that low concentration levels of sulphate and chloride (> 5 to 10 ppb) can result in significant acceleration of SCC crack growth in BWR normal water chemistry (NWC) environment. In recent investigations by Paul Scherrer Institut (PSI) [23][24][25] and General Electric Global Research (GE GR) [26], a tremendous effect of small amounts of chloride in the ppb concentration range was observed on the SCC growth behaviour of low-alloy RPV steels in simulated, highly oxidizing BWR NWC environment. In this environment, even small amounts of chloride (≥ 3 ppb) may result in acceleration of the SCC crack growth by one to three orders of magnitude after rather short incubation periods of a few hours [25].…”

“…In recent investigations by Paul Scherrer Institut (PSI) [23][24][25] and General Electric Global Research (GE GR) [26], a tremendous effect of small amounts of chloride in the ppb concentration range was observed on the SCC growth behaviour of low-alloy RPV steels in simulated, highly oxidizing BWR NWC environment. In this environment, even small amounts of chloride (≥ 3 ppb) may result in acceleration of the SCC crack growth by one to three orders of magnitude after rather short incubation periods of a few hours [25]. The accelerated, fast SCC crack growth rates in the range of 10 -9 m/s to 10 -8 m/s hereby approached the high-sulphur SCC crack growth curve of the Ford & Andresen model [27,28].…”

“…Most cracking incidents in pressurized water reactors (PWR) involved aerated feedwater under specific start-up operating conditions (no application of nitrogen blankets in condensate storage tanks) or at special locations (e.g., locations with air present during shut-down), where the normally low contents of oxygen during operation cannot be assumed upon start-up. All these cases were attributed either to strain-induced corrosion cracking (SICC) or very low-frequency/very low-cycle corrosion fatigue (CF) during plant transients like start-up/shut-down or hot stand-by and can be rationalized by the mechanistic [1,2,4,8,27,28] and experimental background knowledge on SCC [9,13,17,18,[21][22][23][24][25][26][27] and SICC / CF [5-12, 14-16, 19, 20, 27-30]. Both service experience [1][2][3] and appropriate laboratory experiments confirm the high resistance of carbon and low-alloy steels to SCC under static loading conditions in highpurity water (representative of steady-state power operation) and clearly reveal that slow, positive (tensile) straining, with associated (localized) plastic yielding and sufficiently oxidizing conditions are usually necessary for EAC initiation in high-temperature water.…”