A Study Of Repair Technology Of LPG Spherical Tanks Crack

Any forms invalidation of pressure vessel will make enormous losses for the State, people’s life and property because it stores flammable and combustible, poisonous and harmful products. Especially, the invalidation of liquefied gas spherical tank caused by crack has become an important safety problem concerned by business circles, scientific and technological circles. Therefore, how to purposely, reliably and economically diagnose, forecast, guard against and repair the flaw of inservice pressure vessel has become an issue, which is worth being explored and researched.Carrying out the quality inspection work is the key process for confirming the defects of spherical tanks, which includes means such as surface inspection, wall-thick measurement, nondestructive test, hardness determination, etc. All these means can preliminary find out the practical safety situation of spherical tanks, which can furthermore analyze the causes of cracks and explore the entry point for its defects reparation. This paper has done a lot of research work such as inspection and detection, especially through the on-site spherical tank’s wall thickness and hardness measurement, giving a proof for the causes of cracks. By comparing the measured value of wall thickness with the designed size, it shows the spherical tank’s wall thickness is meeting the requirements. While, by comparing the tested figure of spherical tank’s hardness with the provided technological requirements, it illustrates that the hardness in the spherical tank’s welding zone is a little bit higher. Therefore, it can be inferred that the main reason for flaws existing is stress oriented. After safety evaluation for the crack, it is revealed that the spherical tank has safety problems and can not be used anymore. And compared with analytic solutions, it can know the reliability of the result, and also solve part of the problem that the complex crack can be solved by finite element software without exact solution. Moreover, based on the research of the spherical tank’s crack, proper welding repair procedure is found out. After welding repair, partial heat treatment will be conducted on spherical tank for improving quality. At last, by air-tight test and hydraulic test, it is proved that the repaired spherical tank has reliable quality and can be used in safety.In this paper, some exploratory research work is carried out aiming at the phenomenon that the inservice liquefied gas spherical tank existing cracks. And some basic principles, technical routes and repairing methods are proposed for repairing the crack of inservice liquefied gas spherical tank. According to the practical examples of the inservice liquefied gas spherical tank in some refinery factory need repairing because of judging as unacceptable, and the on-site welding situation and crack’s testing result, causes of crack existing will be examined out. Measures for repairing the spherical tank and quality assurance are also provided. It suggests the partial heat treatment eliminate hydrogen and reduce residual stress, on the condition that the structure safety is quarantined, so as to improve the internal status of spherical tank. What’s more, by pressure testing and hydraulic testing, spherical tank’s reparation quality can be guaranteed, which recovers the safety usage of the unacceptable liquefied gas spherical tank. Finally, a systematic method of repairing and preventing the cracks of the liquefied gas spherical tank is also explored.