STUDY OF CRACK FORMATION DYNAMICS AND RESISTANCE OF PIPE JOINTS

Abstract

Pipe, deformation, crack, plastic zone, crack resistance.

Portlandcement, 3D construction printer, extrusion, nozzle travel speed, extrusion quality, design of experiments.

This study presents an in-depth investigation of the kinetics of crack formation in the weld metal and heat-affected zone (HAZ) under static and cyclic loading. The relevance of the topic stems from the need to improve the operational reliability of main pipelines under long-term service conditions. A correlation has been established between microstructural parameters, specifically the morphology of the ferrite-pearlite phase, and the metal’s resistance to the propagation of main cracks.Critical crack opening values and stress intensity factors for welds made under various process conditions were experimentally determined. Fractographic analysis methods were applied to identify fracture mechanisms—ranging from ductile pitting to brittle spalling. The scientific novelty of the work lies in the development of a refined model of crack initiation dynamics that accounts for residual welding stresses and the gradient of mechanical properties in the HAZ.The practical significance of the results lies in the ability to predict the remaining service life of pipe structures, taking into account the identified defects. Recommendations have been formulated for optimizing thermal welding cycles to ensure maximum resistance to failure. The obtained data can be used in the design of technical condition monitoring systems for high-risk facilities. A method has been developed for determining the energy criterion, which allows assessing the resistance to dynamic crack propagation in pipe steels of different strength groups (X50 – X70) and their welded joints made using different welding technologies. The energy parameter – AP was determined on DWTT type samples using a pendulum impact tester. A methodology has been developed for studying the corrosion cracking of pipes, taking into account the biaxial stress state and the correct use of the laws of linear fracture mechanics.

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