Determination of the corrosivity of Pb-containing salt mixtures

Abstract

The composition of deposits from waste firing boilers is dominated by calcium-, alkali-chlorides and sulfates. Additionally, significant quantities of heavy metals such as Zn and Pb are usually present during waste combustion. In this high temperature corrosion study, two boiler materials, a low alloy ferritic steel (10CrMo9-10) and an austenitic stainless steel (AISI 347), were exposed to PbCl2–ZnCl2–KCl, PbCl2–KCl and PbCl2–K2SO4 salt mixtures as well as to the single salts of PbCl2, K2SO4 and KCl. In the tests, the salt or the salt mixture was put on a pre-oxidized and cleaned steel sample and then heat treated at 400, 500 and 600°C for 168h (1week) in a horizontal tube furnace. After the test, the metallographic cross-sections of the specimens were characterized with a SEM/EDX analyzer and the thickness of the corrosion layer was determined for each sample. The corrosion layer thickness measurements showed severe corrosion on 10CrMo9-10 already at 400°C when 5wt.% PbCl2 was mixed with KCl or K2SO4 With all the PbCl2 containing salt mixtures at temperatures around and above 500°C a significant corrosion was observed on both materials. In order to estimate the relative corrosivity of PbCl2 containing salt mixtures, the results from the laboratory experiments in this work were compared to an earlier study done with a corresponding ZnCl2 containing salt mixture.