Abstract
The corrosion mechanism of stainless steel caused by high temperature decomposition of aqueous urea solution has been investigated. The relationship between aqueous urea solution, its thermal decomposition products and the corrosion mechanism of stainless steel is studied by FTIR spectroscopy, SEM and stereo microscopy. The corroded steel samples, together with deposits, were obtained from the injection of aqueous urea solution on the steel plate at high temperatures. Uniform corrosion underneath the deposits was proposed as the main driver for corrosion of the steel samples. At the crevices, corrosion due to the used geometry and due to high temperature cycling could play an acceleration role as well.
Highlights
IntroductionUrea is used as a source of nitrogen in the products, causing some corrosion problems [2,6]
The corrosion of stainless steel by hot urea solution has not been largely studied; on the one hand, this may be due to the limited industrial demand, on the other hand, urea itself is considered as non-corrosive for stainless steel, while some of its decomposition products at high temperature may lead to corrosion [1,2,3]
The corrosion mechanism in urea-related technology was explained in several ways; one such way was cyclic oxidation caused by thermal cycling [7], and another—external corrosion by road salts [8,9]
Summary
Urea is used as a source of nitrogen in the products, causing some corrosion problems [2,6]. The corrosion mechanism in urea-related technology was explained in several ways; one such way was cyclic oxidation caused by thermal cycling [7], and another—external corrosion by road salts [8,9]. There are studies on melamine, ammonia, nitrogen and g-C3 N4 (all of them exist during urea decomposition process) reactions with metal oxides, which attract attention as nitrifying and carburization reagents [12,13,14]. An intergranular corrosion mechanism, sometimes attributed to chromium depletion, and nitride precipitation at grain boundaries, and sometimes without any indication of decrease or increase in the amount of chromium at grain boundaries, was described [4,19,20]
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