Experimental corrosion-mechnical studies of downhole equipment in the oil industry under dynamic loading in an aggressive environment

Abstract

For the first time, comprehensive experimental studies of full-scale welded assemblies and steel structures under dynamic loading in the presence of a corrosive medium, in particular, 5% salt solution and NACE, an environment in accordance with the requirements of the International Association of Corrosion Engineers, were conducted. The authors of this article have developed a test bench scheme and worked out the expected test modes for welded joints when programming the pressure and temperature of the medium and dynamic vibration modes.  All the main components of the installation are a hydraulic pulsator, a thermal chamber, which included pipeline blocks with test welded joints, heating devices, a pneumatic control panel, and a temperature and pressure control unit. The experimental results obtained made it possible to summarize the results, in particular: it was found that in the initial period (number of cycles N = 500), the crack growth rates in air and in 5% NaCl solutions are similar, and in the final period of testing they differ by more than an order of magnitude. Due to the more intense influence of the plane-strained state compared to the plane-stressed state, the crack propagates in depth and only after germination to the full thickness of the sample does its elongation begin. Significant reduction of the test period due to inducing a crack in the specimen with a high stress concentration at the crack tip, which allows for a significant reduction or modification of the initial period.  The ability to detect the sensitivity of materials to cracking, which is not detected when testing samples without a concentrator (for example, for pipe steels in seawater). At the same time, the fracture mechanics method, like any other method, has a number of specific limitations on materials, thickness, and environments related to the correct use of fracture mechanics.