The finite element method is applied to buckling analysis of cylindrical shells subjected to asymmetric external liquid pressures. The axisymmetric shell element is used and the load distribution, prebuckling and buckling displacements are represented by Fourier series expansion in the circumferential angle. The shells are assumed to stand vertically with the lower and upper ends simply supported. The analyses are performed for a wide range of the geometric parameter Z and the buckling pressures are obtained. The asymmetric and axisymmetric buckling pressures are compared and the effects of asymmetric pressure are obtained. The approximate treatment of tsunami pressure acting on tanks is proposed and buckling pressures are obtained.

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This paper shows the analytical and experimental results of pretension reduction for a bolted joint tightened by hydraulic tensioner. Pressure vessels, such as a compressor and pump operating in various plants, are required to be strongly tightened by bolted joints, and a hydraulic tensioner is frequently used for tightening bolted joints. A hydraulic tensioner is able to apply high axial tension to the bolt by oil pressure, and the tension force variation of hydraulic tightening is comparatively smaller than that of torque tightening. However, the axial tension remaining in the bolt is less than the initial tension loaded by oil pressure because of changing stiffness and moving of tightening parts after tightening procedures of seating the nut and unloading the pressure. The ratio of residual tension to initial tension is the most important factor to securely tighten the pressure vessel by hydraulic tensioner. Some estimation methods of the ratio were proposed, and these considered the stiffness of the tightening parts and contact surfaces. These methods are mainly applied to analysis within elastic deformation. And, there are a few examples of comparing finite element analysis and experiment of hydraulic tightening in the previous study. In this paper, estimation equations for the ratio of residual tension to initial tension were formulated by considering plastic deformation of the tightening parts. Then analysis method for estimating residual tension was developed by using finite element model simulated joint process with hydraulic tensioner. Furthermore, bolt tightening with hydraulic tensioner was experimented. As a result, it was confirmed that presented estimation equations and analysis method can estimate the ratio of residual tension to initial tension accurately.

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Bolted flanged connections have been widely used in a lot of plants such as chemical, petrochemical, nuclear and so on. Sometimes, leakage accidents occur from the bolted flanged connections in the plants. Thus, it is important to tighten a lot of bolts and nuts precisely in bolted flanged connections. However, it is difficult to tighten the bolts and nuts at target bolt preloads because a big scatter of bolt preloads occur due to the difference in the friction coefficients at the bearing surfaces and the contact surfaces in the engaged screw threads. Thus, better tightening workers are needed for better tightening bolts and nuts in a lot of connections with gaskets. In Japan, better workers for tightening bolts and nuts decrease because population in Japan decreases. Some better tightening workers are in bigger companies and it is difficult to keep them in smaller companies. In Japan, some companies of big plants want to keep the better tightening workers, thus they want to establish a certification system for keeping the better tightening workers. However, no certification system has been established. In our sealing technology committee, a working group started to investigate the certification system 3 years ago. Firstly, knowledge on the sealing technology which tightening workers should learn has been developed, that is, mechanical characteristics of bolted flanged connections and leakage phenomena. In addition, a method how to calculate a target bolt preload, bolt tightening torque is described in the text. Furthermore, two tightening procedures, that is, one way tightening specified in Japanese standard (JIS B 2251) and star sequence method specified in ASME PCC-1 will be studied. Actually, workers excise to tighten bolts and nuts in connections according to the above two ways. The workers also learn how to attach strain gauges at the bolts and the flange hub. Of course, they learn measuring methods of the stresses and the strains. They also learn a measuring method of an amount of leakage using 4 inch pipe flange. Now, the certification system is discussed in WG committee, in particular, problems are who can certificate the tightening workers, how to determine training facilities and the detail of training items. A new trial for establishing the certification system and the training items will be achieved as fast as we can for better tightening workers and the manager for bolted flange connections.

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