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

Tim De Seranno,Arne R D Verliefde,Tom Depover,Ellen Lambrechts,Kim Verbeken,Evelyn De Meyer,Wolfgang Hater,Nathalie De Geyter

doi:10.3390/met10121628

Abstract

This work evaluates the effect of film-forming amines (FFA) on the acidic stress-corrosion cracking (SCC) resistance of NiCrMoV turbine steel. Contact angle measurements show an increased hydrophobicity of the surface when coating the steel with oleyl propylene diamine (OLDA). According to potentiodynamic measurements and post-mortem scanning electron microscopy (SEM) analysis, anodic dissolution and hydrogen embrittlement still occur when the steel is FFA coated. In situ constant extension rate testing (CERT) in acidic aqueous environment at elevated temperature of FFA-coated steel shows a ductility gain compared to non-coated steel, explained by a decrease in both corrosion rate and hydrogen uptake.

Highlights

Appropriate control of the water chemistry is of major importance in steam-driven power plant operation
As boiler feedwater chemical treatment, the pH was controlled by the addition of ammonia or alkalising amines, realising an alkaline environment, to counter acidic conditions where rapid corrosion is promoted by deteriorating the natural protective oxide layer of the metal [1]
When ammonia/alkalising amines are combined with the removal of oxygen—the corrosion rate depends on the oxygen content—

Summary

Introduction

Appropriate control of the water chemistry is of major importance in steam-driven power plant operation. Several chemical treatments have been developed to maintain a stable material–environment interaction, as such minimising corrosion and fouling of the materials used in these plants. Thereafter, the need to investigate the influence of FFA on the resistance to acidic stress-corrosion cracking (SCC) of steam turbines is demonstrated. As boiler feedwater chemical treatment, the pH was controlled by the addition of ammonia or alkalising amines, realising an alkaline environment, to counter acidic conditions where rapid corrosion is promoted by deteriorating the natural protective oxide layer of the metal [1]. When ammonia/alkalising amines are combined with the removal of oxygen—the corrosion rate depends on the oxygen content—

Methods

Results

Conclusion