Ultrasonic Testing And Analysis Of The High Temperature Hydrogen Attack For Pressure Vessels

At the condition of high temperature and high pressure, some equipments in the chemical industry, petroleum refining industry, petroleum chemical industry, coal industry are attacked by the hydrogen. High temperature hydrogen attack (HTHA) is one of the typical damage, it has great harmfulness, has great influence on safe operation of equipments and has great threatening on people’s lives and property.Combining with research achievements in the HTHA experiment before Specimens made of20steel and Q345R steel are exposed to hydrogen gas at450℃with a hydrogen partial pressure18MPa for18hours, the degree of corrosion is characterized and evaluate by velocity ratio、thickness measurement, TOFD, macroscopic and microscopic examination and hardness test. Comparing with data from the samples corroded36hours and80hours, we have summarized the relationship between corrosion degree and the time of filling hydrogen and examined the HTHA by the ultrasonic method.Research results show that:(1) After have corroded for18hours36hours80hours, the sample experienced the process from no changing on the surface to having a dense bubbling, then to appearing cracks.(2) Along with corrosion time increases, surface decarburization and completely decarburization near surface and grain boundary microcrack appears in order on the samples.(3) The longer corrosion time is, the greater material properties falls, the more hardness value drops.(4) The thickness of sample increases after corrosion, and the corrosion degree increase continuously by time.(5)The velocity ratio increases by the time after the corrosion of18hours, velocity ratio change a little,the HTHA stays at early stage.Velocity ratio exceed0.55after corrosion of36hours The material has been hydrogen corrosion. the velocity ratio is about0.57and the sample corroded more.(6) The direct wave of TOFD occurred the time delay after corrosion, velocity wave becomes slower. Through the changes of direct wave position, we can obtain the data of longitudinal velocity. from the data,we can see that the velocity reduce most after corrosion of80hours,and the velocity reduce least after corrosion of16hours.(7) The longer corrosion time is, the worse corrosion of sample is, the harder attenuation is.(8) Specimens made of20steel and Q345R steel are exposed to hydrogen gas at450℃with a hydrogen partial pressure18MPa, and the critical time of performance degradation is18hours nearby.