EVALUATION OF CHARACTERISTICS OF RESISTANCE OF PROPAGATION OF CORROSION- FATIGUE CRACKS OF LONG-TERM OPERATED DRILL PIPES

The aim of the proposed article is to determine the patterns of the corrosion-fatigue cracks in long-term operational metal elements of drill strings (steel 45, 36G2S, 40HN) when drilling wells in corrosive environments (drilling fluid "Biocar", potassium polymer mud and on the air). Based on the obtained results of experimental studies, diagrams of cyclic corrosion crack resistance for the studied systems "metal - medium" were drawn. The cyclic crack resistance characteristics of long-used metals of drill string elements are determined - the values of constants (C and n) in power dependence of Paris, as well as the values of threshold and critical stress intensity factory. The influence of drilling mud of the corrosion crack resistance of the investigated metals of drill string elements was estimated quantitatively. In particular, in the environment of drilling mud "Biocar" the process of corrosion-fatigue crack development in the studied metals of the elements of drill strings is not significantly, in the range of 1-5%, differs from the development of fatigue crack on the air. Whereas in the potassium polymer drilling mud media, the rate of corrosion-fatigue cracks development in the investigated metals of the drill strings elements significantly, in the range of 15-35%, differs from the development of fatigue cracks on the air. It is established that under the influence of working loads the process of the corrosion-fatigue crack development in long-operated elements of drilling string is accelerated by more than 10% in the media of the potassium polymeric drilling mud than in the environment of drilling mud "Biocar".

Development of In-Situ Monitoring Technique on a Crack of Steam Generator Tubing: The Effect of Thermal Treatment on the SCC of Alloy 600

TT (Thermal Treatment) for mill annealed Alloy 600 highly improves the resistance against IGSCC (Intergranular Stress Corrosion Cracking) in caustic solution, but its treatment changes the microstructure. The change of microstructure can affect the SCC resistance in various corrosion environments. This kind of corrosion can be monitored using an electrochemical noise measurement. Therefore, in this study, the effects of heat treatment on SCC resistance in Alloy 600 have been evaluated 0.1M Na2S4O6 at 25 °C from electrochemical noise measurement, and quantification has been tried for resistance against crack formation. While there was no generation of the stress corrosion crack of Alloy 600MA by reverse U-bend method in 0.1M Na2S4O6, the stress corrosion crack was generated in sensitized Alloy 600SE, SE+, and TT materials. The cracking could be detected using an electrochemical noise monitoring. Also, if the aging heat treatment is performed, the stress corrosion crack resistance is reduced. In the case of this behavior, it is analyzed that the stress corrosion crack resistance is closely related with the grain boundary corrosion rate based on the results of the micro-structural analysis for the chromium carbide distribution, the DL-EPR method, and the measuring of the grain boundary corrosion rate through the modified Huey test.