Results of field tests of ultrasonic checking systems for the stress-strained state of pipelines on a hydrostand are considered. Biaxial mechanical stresses induced by a combined load, i.e., internal pressure and bending, are determined. Results of testing a microcrack locator that uses nonlinear acoustic effects are presented. The error of strain-gage measurements of mechanical stresses did not exceed 10 %. The use of sensors with magnetic fastenings in the first ultrasonic system and the second complexes, as well as the use of a beam-type strain gage that does not require preparation of a pipelines surface for its installation in an second complex, shortens the readiness time of equipment under real-life operational conditions. The use of two different physical methods (ultrasonic and strain-gage) in the complex increases the objectivity and reliability of the inspection of pipelines operational states. Crack detection in pipelines can be performed by a nonlinear acoustic method. Cracks can be modulated by excitation from the pipelines surface by a vibrostand (particularly, an electromagnetic oscillator), which excites the pipe at different vibrational modes. Excitation of the pipe at several frequencies helps avoid omissions in crack detection in those cases when, for a certain mode, cracks are situated in a node of oscillation and cannot be modulated. Mechanisms (compressors) that operate near the pipe can also modulate the acoustic resistance of cracks. The result obtained indicates the fundamental possibility of detecting cracks in underground pipelines without having to dig a prospect-hole but by using a stationary arrangement of ultrasonic sensors with signal output to the ground surface and low-frequency modulation of acoustic resistance of cracks from the ground surface, for example, oscillators. (7) The technique applied allows discrimination of the type of the flaw revealed (a cavity or a crack). The reliability of detecting a cavity increases if the cavity is the first reflecting object along location path. (8) Excitation of a pipe is possible without damaging the insulating coating. Crack detection is possible during location directly from the insulating coating. Good acoustic contact of the insulating coating with the pipe surface is necessary. (9) The use of the equipment being developed for investigation of the stress-strained state and microcracks in beams with an intricate profile requires additional experiments.


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    Title :

    Testing systems for ultrasonic inspection of the stressed state of metal structures and a microcrack locator using nonlinear acoustic effects


    Additional title:

    Prüfsystem mit Ultraschall für Metallstrukturen im gespannten Zustand und ein Mikrorissortungssystem mit nichtlinearen akustischen Effekten


    Contributors:

    Published in:

    Publication date :

    2005


    Size :

    7 Seiten, 15 Bilder, 9 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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