Kret N. Peculiarities of corrosion-hydrogen degradation of ferrite-pearlite steels of the objects of hydrocarbons exploration and transportation

An actual scientific and technical task has been resolved in this work devoted to establishment of the main regularities of corrosion-hydrogen degradation of ferritic-pearlitic steels in formation water and development of the method for their protection against corrosion and corrosion-mechanical fracture with environmentally friendly inhibitor. The object of the study is corrosion-mechanical fracture of ferritic-pearlite steels in the as-received state and after long-term operation. The purpose of the research was to establish the basic regularities of corrosion-hydrogen degradation of ferritic-pearlitic steels taking into account composition of model formation waters and type of operational loading, as well as to study the possibilities of increasing their corrosion resistance and resistance to corrosion-mechanical fracture with environmentally friendly inhibitor. Research methods: electrochemical methods; gravimetric method; determination of characteristics of strength and plasticity, impact toughness, fracture toughness, resistance to stress corrosion cracking, fatigue and corrosion-fatigue crack growth; metallographic analysis; fractographic analysis; methods of mathematical statistics. It has been established that the initial stage of corrosion of the ferritic-pearlitic steels in an acid chloride solution modelling formation water consists in the predominant dissolution of structural-free ferrite, the fraction of which in the steel microstructure is the dominant factor of corrosion intensification. The influence of microstructure features of ferritic-pearlitic steels of casing pipes on resistance to hydrogen embrittlement under preliminary electrolytic hydrogenation has been revealed: the steel with higher strength and with more dispersed microstructure is less susceptible to it than the steel with lower strength and with coarse-grained microstructure. For the first time, degradation degree of the low-alloyed steels of pump rods after their long-term operation has been estimated by reducing their corrosion resistance, resistance to stress corrosion cracking, fatigue and corrosion-fatigue crack growth and durability in an acid chloride solution and their effective inhibitory protection against corrosion and corrosion-fatigue with environmentally friendly tannin has been proposed. An electrochemical method for predicting the effectiveness of inhibitory protection of rod steels against corrosion and fatigue failure in formation water has been developed. It has been established that hydrogenation and long-term operation increase the anisotropy of brittle fracture resistance characteristics of rolled pipeline steels. The results of the work in the form of developed methods and recommendations were implemented in Affiliate "Prykarpattransgaz", Firm "Dolynaftogaz" and LLC Firm "Dialab" LTD.