Ultrasonic Testing Method For Vanadium Modified Steel Reheat Crack

Hydrogenation reactor is the major key equipment in modern oil refining industry, since 1960 s, the hydrogenation reactors were widely using 2.25Cr-1Mo steel to manufacture. In 1970 s, with the development of new technology of coal liquefaction, people have developed some Vanadium modified Chrome Molybdenum steel which has more advantages than the conventional Cr-Mo steel. In 2007, reheat cracks were found in Vanadium modified Chrome Molybdenum steel hydrogenation reactors. Studies have shown that they were produced after dehydrogenation heat treatment(DHT) or post-weld heat treatment(PWHT), and had some hidden, thus the accident was caused by reheat crack is unpredictable and was great dangerous. It has caused high attention that the prevention and detection technique of Vanadium modified steel reheat crack by domestic and foreign scientific and technical personnel. At present, the weld of thick wall hydrogenation reactor is commonly inspected by using TOFD technique. Implementation of reheat crack detection, will provide some technical supportion for the design/manufacture and safe operation of Vanadium modified Chrome Molybdenum steel hydrogenation reactors, has some engineering significance.Based on the summary of the reheat cracking which generating mechanism and morphology characteristics in vanadium modified steel, combining with TOFD detection conditions required, referring to the API RP934A-2010 standard, this paper has designed and fabricated one TOFD sensitivity demonstration block which can simulate reheat crack. By the TOFD detection and ultrasonic detection testing, they realized the detection and quantitative for the simulate reheat crack. The main research works and achievements are as follows:(1) According to generating mechanism and morphology characteristics of vanadium modified steel reheat crack, this paper has designed and fabricated one TOFD sensitivity demonstration block which can simulate the reheat crack. Research method is suitable to fabricate block of simulating the buried small flaws.(2) TOFD inspecting results show that using domestic current NB/T 47013.10(JB/T4730.10) standard recommended number of detection channels can be detected to a certain size to reheat cracking(3) With the differentence of conventional non-parallel scanning, special B-scan defect detection, surface dead zone is small, which TOFD image in near-surface can be clearly displayed and can accurate measurement the flaw depth and the flaw height.(4) TOFD+UT detection process, as combined with TOFD inspection used the special parallel scan and Manual pulse-echo shear wave ultrasonic testing, can achieve the detection and quantification of simulated reheat crack in vanadium modified steel; TOFD defect detection can be given the flaw depth and flaw height with highly precision, UT defect can also given flaw depth and flaw height, both the test results can authenticate each other.