Composite inspection of the condition and evaluation of the effectiveness of vessels and apparatus for cryogenic technology

Abstract

The necessity of determination of the condition and life of equipment operating under pressure is related to providing safe operation with prolongation of the service life beyond the standard. The system of planned preventive repairs in existence earlier made it possible to maintain equipment in satisfactory condition but did not provide sufficiently accurate information on the possibility of further service upon completion of the established service life.The high level of effective stresses and the accumulation of fatigue damage in zones of concentration and the change in microstructure of the material under low-cycle and multicycle thermal and force aetious may with the passage of time cause a reduction in allowable stresses with a simultaneous increase in the probability of brittle fracture of weld joints of metals. Taking into consideration these features in the behavior of metals, it must be pointed out that further service of equipment beyond the standard life must be only after a composite inspection using a special method, which include the following operations:-external and internal inspection of the surfaces and weld joints of the equipment; -technical impection and checking of the condition of vessels, apparatus, and piping with loading by the operating and test pressures with use of acoustic emission (AE) iuspection; -measurement of the wall thickness of metal subjected to the cryogenic action of the medium and other methods of nondestructive inspection; -a calculated evaluation of the effectiveness of the vessel with determination of the remaining life. Very pressing in diagnosing the condition is use of the acoustic emission method in combination with traditional methods of nondestructive inspection (ultrasonic iuspeetion, x-ray, penetrant inspection). The advantage of the acoustic emission method is, above all, the fact that it makes it possible to promptly record an embryonic crack and to take the necessary measures for elimination of an emergency situation.Diagnosing of the condition of a structure with use of AE inspection is done in two stages. In the f'trst stage the structure is analyzed, the most dangerous zones for placement of AE signal transducers are selected, measurements are made with loading of the object, and the measurement results are processed and documented. In the second stage the inspection results of the condition are analyzed, the strength and accumulated fatigue damages during the period of operation considered and evaluated, and a decision is made on the possibility of further, service.In the presence of dangerous defects, if necessary an inspection is made by one of the traditional methods of nondestructive inspection and repair work is done or further service of the part is prohibited.In production of vessels and parts operating under pressure for cryogenic technology, elements having a complex structure are used. In conducting acceptance tests and under operating conditions the elements of vessel structures are in the three-dimensional stressed and strained condition. Th...