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Abstract
In this paper, a support stiffness monitoring scheme based on torsional guided waves for detecting loss of rigidity in a support of cylindrical structures is presented. Poor support performance in cylindrical specimens such as a pipeline setup located in a sloping terrain may produce a risky operation condition in terms of the installation integrity and the possibility of human casualties. The effects of changing the contact forces between support and the waveguide have been investigated by considering variations in the load between them. Fundamental torsional mode is produced and launched by a magnetostrictive collar in a pitch-catch configuration to study the support effect in the wavepacket propagation. Several scenarios are studied by emulating an abnormal condition in the support of a dedicated test bench. Numerical results revealed ultrasonic energy leakage in the form of bulk waves when a mechanical coupling between the cylindrical waveguide and support is yielded. Experimental results showed that the rate of ultrasonic energy leakage depends on the magnitude of the reaction forces between pipe and support; so different levels of attenuation of mode will be produced with different mechanical contact conditions. Thus, it is possible to relate a measured attenuation to variations in the supports condition. Results of each scenarios are presented and discussed demonstrating the feasibility and potential of tracking of the amplitude of the as an indicator of abnormal conditions in simple supports.
Highlights
Pipelines in service are continuously affected by corrosion, erosion, chemical attacks, stress, extreme climate conditions, among others
The inability to detect ∆ ( TOF ) may be attributed to the phase velocity in a specific pipe cross-section for a bending pipe is radius dependent due to the linear stress distribution in r, going from tension to compression or vice versa at the same cross section, i.e., the magnetostrictive sensor is capturing at the same time, torsional waves propagating at different phase velocities, in the case of tension stresses
Experimental results showed an unnoticeable influence of pipe normal stress levels, generated by bending, in the velocity of the T (0, 1) mode as a consequence of the acoustoelasticity effect
Summary
Pipelines in service are continuously affected by corrosion, erosion, chemical attacks, stress, extreme climate conditions, among others. Pipeline stresses have great influence in its performance during operation, affecting strength, expected operational life and dimensional stability. Stresses occurring in service, which are difficult to diagnose and identify, can unexpectedly appear and turn into invisible due to the apparent absence of an external load, such as loss of rigidity in the foundation of the pipeline supports. Pipe and fluid masses may develop important normal stresses via bending moment that can compromise the integrity of the pipelines. Supports integrity inspection presents several challenges, e.g., mechanical stress variations are produced along the pipeline when the support loads are changing.
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