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Evaluating the Use of Phosphate to Mitigate Caustic-PbSCC of Alloy 690TT

Picture for Investigating The Effect Of Phosphates On Lead Induced Stress Corrosion Cracking Of Alloy 690TT
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PbSCC of Ni-base alloys is active over a wide range of environmental conditions but for the higher Cr content Alloys 800 and 690 only under abnormal crevice environment of high or low pH that can occur in the secondary side of Pressurized Water Nuclear Reactors (PWRs). Several experimental campaigns have aimed at understanding this phenomenon, concluding that PbSCC can develop in both acidic and caustic solutions, for low and high concentration of Pb, across a wide electrochemical potential range and in presence of chlorides contaminants.

Product Number: ED22-17293-SG
Author: Giulia B. Mazzei, Jonathan Duff,D.A. Horner, M.Grace Burke, Fabio Scenini
Publication Date: 2022
$20.00
$20.00
$20.00

Phosphate additions to Pb-caustic water chemistry were investigated as possible avenue to mitigate against caustic Lead-Assisted Stress Corrosion Cracking (PbSCC) of Alloy 690TT at around 310°C. Dosing with 1,700 ppm of phosphate promoted a small beneficial effect in PbSCC resistance. However, with 3,000 ppm of phosphate, mitigation was only achieved for as received surfaces, whilst polished surfaces displayed localized attack. Advanced materials characterization revealed that a similar crack tip composition was generated in different solutions. It is suggested that phosphate decreased the PbSCC kinetics by partly sequestering Pb from the bulk environment, although not below the threshold value required to prevent cracking.

Phosphate additions to Pb-caustic water chemistry were investigated as possible avenue to mitigate against caustic Lead-Assisted Stress Corrosion Cracking (PbSCC) of Alloy 690TT at around 310°C. Dosing with 1,700 ppm of phosphate promoted a small beneficial effect in PbSCC resistance. However, with 3,000 ppm of phosphate, mitigation was only achieved for as received surfaces, whilst polished surfaces displayed localized attack. Advanced materials characterization revealed that a similar crack tip composition was generated in different solutions. It is suggested that phosphate decreased the PbSCC kinetics by partly sequestering Pb from the bulk environment, although not below the threshold value required to prevent cracking.

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