KCl Induced Corrosion of a 304-type Austenitic Stainless Steel at 600°C; The Role of Potassium

Abstract

The influence of KCl on the oxidation of the 304-type (Fe18Cr10Ni) austenitic stainless steel at 600 • C in 5% O 2 and in 5% O 2 + 40%H 2 O is investigated in the laboratory. The samples are coated with 0.1 mg/cm 2 KCl prior to exposure. Exposure time is 1-168 h. Uncoated samples are exposed for reference. The oxidized samples are analyzed by ESEM/EDX, XRD and AES. The results show that small additions of potassium chloride strongly accelerate high temperature corrosion, the oxide thickness being up to two orders of magnitude greater after exposure in the presence of KCl. The rapid corrosion is initiated by the formation of potassium chromate through the reaction of KCl with the protective oxide. Chromate formation is a sink for chromium in the oxide and leads to a loss of its protective properties. The resulting rapidly growing scale consists of an outer hematite layer with embedded K 2 CrO 4 particles and an inner layer consisting of spinel oxide, (Fe,Cr,Ni) 3 O 4 . Little or no chlorine is found in the scale or at the scale/metal interface.

High Temperature Corrosion under Laboratory Conditions Simulating Biomass-Firing: A Comprehensive Characterization of Corrosion Products

“…Initiation and sustaining mechanisms for the corrosion process are still being discussed in literature [22,27,30,38,39]. For Cr-containing alloys under oxidizing conditions, the K-induced breakaway corrosion of the initial protective Cr2O3 layer has been reported as the initiation process (equation 1) [5,21,40].…”

“…Simplified laboratory-scale corrosion studies using synthetic deposits (KCl, NaCl, CaCl2, etc. ), and in some cases, under HCl-or H2O-containing gaseous atmospheres, have revealed the respective roles of K and Cl in initiating and catalyzing the corrosion of alloys under oxidizing conditions [4,5,[21][22][23][24][25][26][27][28][29][30]. The results from characterization of corrosion products from most of these laboratory studies point towards an active oxidation type of mechanism.…”

KCl-Induced Corrosion of the FeCrAl Alloy Kanthal ® AF at 600 °C and the Effect of H2O

“…The evidence from SEM/EDX, XRD and IC clearly shows that KCl reacts to form K 2 CrO 4 on the alloy surface. As noted in the introduction, FeCrNi and FeCrAl alloys have been reported to react with KCl and water vapour to form K 2 CrO 4 [7,8,13,14] according to Reaction (1). For standard state conditions it is found that DG 873K = 90.5 kJmol -1 K [22] for Reaction (1).…”

“…It is well known that the high-temperature corrosion of chromia-forming steels in an oxidising environment is accelerated by alkali chlorides and by high concentrations of water vapour [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The accelerated effect of water vapour has been shown to be connected to chromia evaporation in the form of CrO 2 (OH) 2 [1,2].…”

Effect of Water Vapor on High-Temperature Corrosion under Conditions Mimicking Biomass Firing

“…KCl induced corrosion of high temperature materials has been the subject of a number of investigations [6][7][8][9][10][11][12][13] to clarify the mechanism of attack in order to pave the way for the development of advanced high temperature resistant materials. Laboratory investigations have shown that the alkali earth metal plays a role in the initial corrosion process [8,10,[14][15][16][17].…”