Remanufacturing Technology Of Liquefied Petroleum Gas (LPG) Spherical Tank

With the rapid development of oil, chemical, metallurgical and urban gas industry, spherical tanks have been widely used to store medium and become one of the important facilities. Among the tanks, about forty percent are used to store liquid petroleum gas (LPG). LPG is a toxic and inflammable substance. Potential hazard exists in the process of its storage. The accident probability increases with the increase of amount in the tank. Failure, especially induced by cracks, occurred frequently in LPG spherical tanks in service, which could cause the leakage, fire hazard and explosion and lead to severe personnel casualty and economic losses. To assure the long-period and safe operation, it is necessary to study the remanufacturing technology(RT) of LPG spherical tanks containing cracks.The content of this thesis forms the major part of a project entitled "Remanufacturing Technology of Liquefied Petroleum Gas (LPG) Spherical Tank" sponsored by foundation of science and technology of China petrochemical Co.(NO. 02JSNJYZ101001) and natural science foundation of Jiangsu (NO.BK2001098). At first, the recent research advances on the remanufacturing, the service characters and failure models, remaining life of chemical equipments are reviewed in length. Furthermore,the recent concept of remanufacturing and redesign in 3R (Remanufacturing, Redesign and Recycle) modes are applied in chemical equipment. The engineering mode of remanufacturing of chemical equipment is obtained.The literature in recent 30 years about the service characters, failure modes and their influencing factors of steels for pressure vessels in corrosive environments containing wet H2S are summarized which provides full information concerning the condition assessment in the first stage of remanufacturing. The chemical behavior on the interface of steel and medium and the definition of wet H2S environment are expounded in detail. The effects of medium concentration, material performance and melallurgic factors on the failure of steels are also discussed.The residual stresses of SPV50Q, 16MnR welding panels are measured bynon-destructive magnetoelastic technique. Finite element analysis is also performed on the specimen model. At the same time, effects of the preheating temperature of base metal and the post-weld heat treatment (PWHT) on the welding residual stresses are semiquantitatively studied. The numerical results show that the welding residual stresses increase with the enhancement of preheating temperature of base metal and the temperature of PWHT. The testing and simulation provides the basis for the improvement of manufacturing technology of LPG spherical tanks.In order to further evaluate the stress corrosion cracking (SCC) behavior of SPV50Q, 16MnR weldments in H2S environment, slow strain rate testing (SSRT) on the weldments is carried out. The effect of H2S concentration, PWHT, Zn coating and material properties on the SCC behavior of SPV50Q, 16MnR steels in H2S environment is discussed in detail.As a fundamental research of Remanufacturing technology of LPG spherical tank, the effect of different PWHT techniques on the microstructure, tensile strength, impact ductility and microhardness of weldments of SPV50Q, 16MnR steels was also studied. The experimental results show that maintaining a temperature of 620C and 570C in PWHT is suitable for SPV50Q and 16MnR respectively.