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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2007

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Formation of corrosion products protecting surfaces of the boiler proper tubes from the combustion chamber

Król S., Pietrzyk M.

Journal of Achievements in Materials and Manufacturing Engineering

2007

Vol. 21, nr 2

45-48

Purpose: The aim of this paper is to determine how the oxidation product layer of the steel applied for the radiant tubes should increase if we are going to obtain the lowest possible corrosion losses. Design/methodology/approach: Boiler tubes, made of 13CrMo4-5 steel were subjected to tests. In the boiler BP-1150, the tubes phi 30 x 5 mm are joined by fins and form a membrane shield. According to the maps of tube wall thickness, in the zone of the highest heat load, sectors of the shield were sampled in the places where the tube wall thickness was equal or greater than 4.3 mm, i.e. the minimum calculation thickness, according to the specifications given by the boiler manufacturer. It means that the corrosive loss could be determined as small, in spite of a long operation time (more than 60.000 hours). Findings: The authors have determined structure and chemical and phase compositions of products and deposits forming in the radiant tubes in the regions of low corrosive losses after long-lasting operation (up to 60.000 hours). Then, they discussed a mechanism of formation of a compact layer protecting a steel surface against excessive oxidation under combustion gases. Practical implications: The layer on the tubes with small losses of wall thickness are characterized by the following properties: good compactness, very good adhesion to the metallic base, low amount of sulphur, especially in magnetite, no aggresive components at the phase boundary product - steel, small development of the phase boundary product-steel. Owing to those properties, even presence of sulphur in the products do not reduce their passivation qualities. Originality/value: Determination of the oxidation product layer of the steel applied for the radiant tubes.