Overpressure for fixed-roof tanks dishes the roof, pulling the roof-shell junction radially inward and uplifts the bottom plate adjacent to the shell plate. It usually results in a failure of the roof-shell junction when the stress in the junction reaches the yield point of the material.
E. E. Morgenegg dealt with these problems and indicated the importance of frangible roof design. Then, he showed the failure mechanism of a frangible roof and recommended design rules based on the experience with actual failures. But the dynamic effects on the collapse of tanks under impulsive internal pressure are not yet clear.
So, the author has developed a finite element code CNCL-ND especially for nonlinear dynamic analysis of tanks. By CNCL-ND, calculations are carried out for the typical fixed-roof tank under various load conditions, and numerical results clearly show dynamic effects on nonlinear behavior of tanks.

View full abstract

In order to better understand soil-structure interaction effects and thus produce economical but safely designed structures, it is clearly desirable to obtain observations of field performance and to analyze the motions and structural responces with the object of verifying analysis and design procedures.
Earthquake observations of an LPG storage tank near Tokyo Bay in Japan are performed for these purposes.
In this paper, the three-dimensional behavior of LPG storage tank in several recorded earthquakes and analyses of this behavior are described. Then, they are compared with the computed responses.
Although the computed responses generally agree well with the recorded responses, the significant torsional vibrations of the concrete foundation slab, which are not usually taken into account, are observed for all the recorded earthquake motions.

View full abstract

For severer operating conditions of pressure vessels in oil refineries, the effect of V on hydrogen attack of 21/4Cr-1Mo steels is studied metallurgically. The addition of V and reduction of N improve resistance to hydrogen attack significantly and V-modified 21/4Cr-1Mo steel shows higher resistance to hydrogen attack than ordinary 3Cr-1Mo steel. Electron microscopic observation indicates that V addition changes the shape, distribution, and composition of precipitates in the steel significantly. Fine precipitates in V-modified steel strengthen grain boundaries and as a result inhibit growth of methane bubbles during exposure to high temperature and high pressure hydrogen.

View full abstract

A life assessment method based on micro-damage mechanisms for high temperature components is presented. This method is emphasized on distributed micro-cracks and micro-voids behavior which nucleated and grew up to macro-crack initiation in the components. A growth law of these micro-damage and a statistical treatment for the distributed micro-cracks are also considered in this life assessment procedure. microvoid density as creep damage is investigated for non-destructive damage detection methods. A replication technique using the grain boundary etching method as NDE of material embrittlement is researched and developed.
CrMoV steels including a long term used materials are investigated on micro-crack and micro-void nucleation and growth behavior. Based on the experimental results and the damage mechanisms, a residual life assessment method is discussed.
These results verified the damage of the components would be accurately assessed by the method based on the micro-damage mechanisms.

View full abstract

In the study of Leak Before Break analysis, configurations of through cracks before and after penetration and the deformation of the surface around the crack are considered as most important to clarify the requirements for LBB conditions. Here, we tried to measure the local deformation field at a back surface by using an laser equipment.
The data were processed by a desk top computer and deformation maps were plotted using a spline function method.
Finite element methods were also applied and the results were compared with the results from experiments. It was shown that the state of deformation can be used to predict whether the component is likely to show LBB condition or they will be broken rapidly.

View full abstract

The evaluation of corrosion rate of zinc in alkaline solutions with and without chloride ions by means of polarization resistance method was realized. The corrosion mode of zinc in alkaline solution depend on the stability of the oxide or hydroxide films deposited at the surface. The mechanism and its stability of the film was analysed by referring the potential-pH diagram. Polarization resistance method was useful for the evaluation of the corroison rate which was a function of pH of the solution, the concentration of chloride ion, and alkaline cations. Time trajectory of polarization conductance vs. corrosios potential clearly showed the depassivation process of zinc by chloride ions.

View full abstract