Corrosion resistance of metalized layers on steel parts in ventilation mill

Bore V Jegdic,Slavica Ristić,Biljana M Bobić,Bojana M Radojković,Marija M Krmar

doi:10.30544/340

Abstract

Corrosion behavior of metalized layers, obtained by Plasma Transferred Arc (PTA) process and by High-Velocity Oxygen Fuel (HVOF) process with the purpose to improve the wear resistance of vital parts of ventilation mill in a thermal power plant, has been tested. The test is performed using three electrochemical techniques, in a solution containing chloride and sulfate ions. It is shown that the steel surface (base metal) dissolves uniformly, without pitting or other forms of local dissolution. Morphology of metalized layers surface indicates that dissolution is non-uniform, but it still can be considered as general corrosion. The corrosion rate of base metal and metalized layer obtained by PTA process is rather low, while the corrosion rate of the metalized layer obtained by HVOF process is much higher. Also, the difference in corrosion potentials between the base metal and the HVOF layer is pretty high but slightly less than maximum allowed difference (prescribed by the standard), to avoid excessive galvanic corrosion. The values of corrosion rate obtained by different electrochemical techniques are in excellent agreement.

Highlights

Wear of ventilation mill parts in power plants occurs when the mixture of coal powder and sand particles flows over the surface of these parts
The appearance of the steel surface after electrochemical testing by linear sweep voltammetry (LSV) technique indicates that dissolution of the base metal is uniform, without pitting or other forms of local dissolution, which means that corrosion on the tested steel is general corrosion in the applied test conditions
The corrosion behavior of metalized layers obtained by Plasma Transferred Arc (PTA) process and by High-Velocity Oxygen Fuel (HVOF) process as well as of base metal in solution which contains chlorides and sulfates, has been tested

Summary

Introduction

Results of corrosion resistance testing of metalized layers and base metal (steel) using different electrochemical techniques are presented. Material Metalized layers A and B were obtained by Plasma Transferred Arc (PTA) process and by High-Velocity Oxygen Fuel (HVOF) process. Value of Rp is inversely proportional to corrosion current density jcorr, and to corrosion rate vcorr .Metal (metallized layer or steel), which is in the corrosion environment, is polarized in a narrow range of potential (E = ± 20 mV) relative to corrosion potential Ecorr, starting from cathodic to the anodic region, and the corresponding current j is recorded. The corrosion current density jcorr is determined directly from the obtained diagram E – log j by extrapolation of linear parts of anodic and cathodic polarization curves to the corrosion potential Ecorr. LPR experiments are carried out at 0.167 mV s-1 sweep rate, while LSV experiments are performed with 1mV s-1 sweep rate

Results

A B Base metal

Conclusion