PSI - Issue 20

Sleptsov O.I. et al. / Procedia Structural Integrity 20 (2019) 130–135

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Sleptsov O.I. et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction

Accidents and failures associated with the impact of corrosive environments on the metal have one of the highest rates among the main causes of accidents in complex production systems. Traces of exposure to several types of corrosion can be detected on one product, among which the most dangerous are stress-corrosion cracks and defects arising by the mechanisms of pitting and intergranular corrosion. Most often, such defects can be detected in the zones of welded joints - along the fusion boundaries of welded joints and hot spots of the heat affected zones of the welded joint, that is, where the increased structure imperfection of the material at the macro and micro levels is originally established, what is shown in the work of Solntsev Y.P. and Ermakov B. S. (2006). The transfer of manufacturing, mining and processing industries to the northern regions of the country has led to another problem - the problem of the loss of reliability and durability of operation of the equipment, damaged by corrosion defects under conditions of low climatic temperatures. This problem has become quite acute for the equipment made of corrosion-resistant chromium-nickel steels. Such steels are widely used in the manufacture of large-sized equipment installed in the open air and operated under conditions of processing highly aggressive corrosive raw materials and products marked by Solntsev Y.P., Ermakov B.S. and Sleptsov O.I. (2008). The ejection devices for water recooling can serve as a classic example of the equipment destroyed mainly by corrosion damage. These systems are installed outdoors, and the vaporous water entering the cooling system may contain a significant amount of highly corrosive com-pounds of chlorine, sulfur, active oxygen, etc. Thus, during operation, the metal of the equipment heated to temperatures above 1000°C is exposed to intense attack of aggressive vaporous and liquid media, and during inter-operational shutdowns is cooled to ambient air temperatures – under the conditions of Siberia and the Far North – to 40-60°C below zero. The largest amount of corrosion defects of the equipment falls upon the zones of the welded joints, see Fig. 1.

Fig.1. Ulcerative and intergranular corrosion in the metal of the welded joint of chromium-nickel steel.

2. Materials and method of solution

Improvement of corrosion resistance of chromium-nickel steels used in the conditions of the Far North can be achieved by specifying their chemical composition, by alloying them with a number of elements that increase the resilience to aggressive corrosive environment. As shown in the works Gulyaev A.P. (1977) and Ulyanin E.A. (1980), among chromium-nickel steels, metastable steels containing 17–19% chromium and 9–12% nickel are the most common, sometimes they are additionally alloyed with molybdenum and aluminum, which increases the level of passivation or titanium, tantalum and niobium, which bind carbon into special carbides and prevent the formation of chromium carbides, keeping chrome in solid solution. One of the problems in choosing corrosion-resistant steel of the chromium-nickel class is rather considerable intervals within alloying of a particular grade of steel. For example, within the grade composition, the nickel content