Numerical Research On Strength Of Tube Trailer Cylinders Mouth

As a kind of transportable pressure vessel, tube trailers are comprehensively used to transport industrial gas in China. Tube trailer is usually made up of semitrailer, semitrailer frame, large capacity steel seamless cylinders and safety attachments. Tuber trailer cylinders are fixed in the frame by screw joint. It is found that the wear of mounting threads is very common during the process of in service tube trailer’s periodical inspection, and the potential safety hazard could not be neglected. For the seriously worn cylinder, the remachined method often used, but it will weak the strength of cylinder mouth. So it is significant to research the wear characteristics, abrasion reasons of tube trailer external threads.Supported by Administration of Quality Supervision, Inspection and Quarantine Science and Technology project "Research on the strength weaken and assessment methods of tube trailer cylinder mouth"(Grant No.2013QK021), the present status of Chinese tube trailers is counted, the abrasion reasons of cylinders mounting threads and the strength weaken are preliminarily researched by numerical simulation. The main research work and conclusions are summarized as follows.(1) Statistical analysis on Chinese tube trailers present status. The basic information and characteristics of Chinese in service tube trailers are obtained, they are epitomized as follows: The annual amount of tube trailers put into service is increased markedly, and tube trailers are comprehensively used in thirty provincial administrative regions in China. A trend of enlargement for tuber trailer cylinders is appeared, there is few traditional small capacity cylinders put into service. The wear of cylinder mounting threads is a typical flaw for tube trailer cylinders. For the serious wear of cylinder external threads, preliminary analysis is done based on statistical data, and it is confirmed that the wear of threads are affected by tube trailers usage region, cylinders external thread structure and the mounting location of cylinders on semitrailer frame.(2) Research on the mechanical stress of tube trailer cylinder external threads. A two-dimensional axisymmetric model is built, including cylinder, flange and supporting steel plate. Elastic plastic analysis is done, it shows that the first engagement thread root of the cylinder bears large stress which is greater than material yield stress under internal pressure and inertial load, and may result in strain strengthening and material embrottlement. Affected by cyclic internal pressure and reciprocating inertial load, the contact surface of threads will bear alternating contact stress. The long term effects of alternating stress may result in crack on the friction surface or in inner surface, and then the material of surface layer flakes off, as well as thread abrasion. So, surface contact fatigue wear may be an important reason for threads abrasion. The wear behavior of threads is nearly one by one, but not at the same time, which is determined by the concentration stress at the thread region.(3) Research on the strength weaken of tube trailer cylinder mouth. Based on the neglecting of thread structure, the models of cylinder and support structure are built, as well as cylinders which are remachined for thread. Analyses are done for the model at corresponding loads, such as internal pressure, self weight and inertial load. The research shows that cylinder mouth strength will be weaken because of the pin holes and thickness reduction of cylinder mouth. This kind of tube trailer cylinder mounting threads should not be remachined more than three times based on the rule that the maximum stress is not allowed to exceed the maximum stress of the cylinder.