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【Daily Question No. 253】September 11, 2017: Leaks in the tube bundle inside a heat exchanger are generally inspected using a gas-tightness test method. ( ) Judgment: The reference answers will be visible after responding; points can be earned by identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) The answer to the daily activity question has changed; today’s answer will be shown in subsequent questions. For management purposes, if you need to view content from a few days ago, please access it through the summary post below. Summary thread for Q&A questions in 2017 (updates have begun): http://bbs.hcbbs.com/thread-1657793-1-1.html Summary thread for daily questions in 2017 (updates have begun): http://bbs.hcbbs.com/thread-1657794-1-1.html Summary thread for Q&A questions in 2016 (updates completed): http://bbs.hcbbs.com/thread-1597792-1-1.html (Source: Haichuan Chemical Industry Forum) [Q&A Question No. 248] September 6, 2017: Multi-stage compression is used in piston compressors to reduce the exhaust temperature. Regarding [Q&A Question 249], dated September 7, 2017: Generally, ( ) is used to measure the performance of catalysts. A. Specific surface area, pore size, pore volume B. Activity, selectivity, stability C. Density, lifespan, specific surface area D. Activity, pore size, density B 【Question and Answer No. 250】 On September 8, 2017, a short circuit in the motor’s windings can cause the motor to trip, and may even lead to the motor burning down. Regarding [Q&A Question 251], September 9, 2017: Piston rings have the characteristic of self-sealing. （ ） Regarding 【Q&A Question 252】 September 10, 2017: When the lubricating oil pressure of the engine unit drops suddenly, the accumulator can temporarily help stabilize the system’s oil pressure. ( ) Correct