Specific features of hydrogen-induced corrosion degradation of steels of gas and oil pipelines and oil storage reservoir
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SPECIFIC FEATURES OF HYDROGEN-INDUCED CORROSION DEGRADATION OF STEELS OF GAS AND OIL PIPELINES AND OIL STORAGE RESERVOIRS E. І. Kryzhanivs’kyi1 and H. M. Nykyforchyn2
UDC 620.178:620.181:620.194
We analyze general regularities of degradation of the mechanical and corrosion-mechanical properties of steels of oil and gas main pipelines and oil storage reservoirs after 28–40 years of operation. The transported oil product not only causes corrosion damages of the internal surface of pipelines and reservoirs, but also becomes a source of hydrogenation of the metal. As a result, it degrades already under the long joint action of mechanical load and hydrogen. Changes in (degradation of) the mechanical properties of the sections of a pipe or a reservoir that contact with the transported medium during operation indicate this fact. First of all, this manifests itself as embrittlement of the metal, i.e., as decreases in the plasticity and resistance to fracture. Comparison assessment of operated and nonoperated steels showed the high sensitivity of the electrochemical properties to the state of the metal, which offers prospects for the development of electrochemical methods for assessing its in-service degradation. Keywords: pipeline, long operation, hydrogen, corrosion, fracture, crack, electrochemistry, nondestructive testing.
Most oil and gas main pipelines are functioning for a time exceeding the design life, and their further safe operation is of great strategic and economic importance. For this reason, in recent years, much attention has been given to this problem in Ukraine [1–7]. One of the fundamental factors that must be taken into account in diagnostics of the technical state of pipelines is the possible degradation of pipes. Here, the degradation of their surfaces and the degradation of the material “in volume” should be distinguished. In the former case, we mean damage of a surface under the action of mechanical, corrosion, and other factors, and in the latter case, we mean degradation of properties of the whole metal or its volume comparable with the characteristic sizes of the pipe (e.g., the thickness of the wall or the lower part of the pipe). Both structural-phase changes and the development of damage may be the cause of this. This casts some doubt on the operation of a pipeline even in the absence of macrodefects. In the last decade, the Karpenko Physicomechanical Institute of the Ukrainian National Academy of Sciences and the National Technical University of Oil and Gas performed a wide complex of joint investigations of properties of steels of oil and gas main pipelines focusing attention on the aggressive role of the transported medium in these processes. In what follows, we systemize results of these investigations, in particular, the regularities of degradation of pipe steels depending on the operation time. General Aspects of Hydrogen-Induced Corrosion Degradation of the Properties of Durable Structural Steels Main methods for the assessment of the residual life are based on taking into account the k
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