METHOD OF CRYOGENIC VESSEL FLAW DETECTION Russian patent published in 1998 - IPC

FIELD: flaw detection of large thick-walled cryogenic reservoirs. SUBSTANCE: after cryogenic liquid is drained from cryogenic vessel and the latter is heated, cryogenic vessel is heated every time up to some constant temperature. Then it is controlled thermostatically and at the same time heat-insulating space is evacuated to some pressure $$$. In this case, pressure is checked by means of nitrogen trap positioned in front of manometric sensor. After pressure is stabilized pumping-out is stopped, and heat-insulating space is coupled with space which contains temperature-controlled nondispersed chemical absorber of nitrogen. Pressure reduction process in heat-insulating space to valve $$$ and process of pressure stabilization to value $$$ are observed and recorded. Then rate of pressure increase is determined, space containing the chemical absorber is separated from heat-insulating space, further process of pressure rise to value $$$ is observed, and pressure increment rate is determined. This done, dependence of summary hydrogen gas evolution from time of operation and number of cycles of thermocycling vessel is obtained. This dependence is used to determine porosity of surface turned to heat-insulating space. When porosity value becomes equal to maximum permissible one at number of cycles of $$$, the remaining permissible number of cycles is determined by formula $$$, where $$$ is safety margin factor according to number of cycles. EFFECT: higher accuracy of flaw detection process. 5 dwg