Slavko Sebastijanović

A Study of Integrity Changes in Structures During Exploitation

Spherical and cylindrical pressure vessels are manufactured as welded structures, where cracks could be initiated/propagated during fabrication, pre-service hydro-test, service itself, service welding repair, or during the service hydro-test. In this case, fracture mechanics approach is necessary. This paper analyzes the stress state around cracks in the bottom head which is one of the main components in a cylindrical pressure vessel (radius of 1056 mm, wall thickness of 92 mm, pressure of 15.5 MPa and temperature of 454°C). Sizes of several detected cracks at the inner surface are determined by the NDE methods. Finite element analysis is performed to determine the stress zones in the vicinity of the most critical crack. Such analysis is done before and after the hydro-test. It will show the influence of the hydro-test on propagation of the existing cracks and fracture behavior of repaired cracks through the stress state analysis. Changes in material properties were analyzed. Results will be used to assess the pressure vessel integrity and estimate its useful life.© 2002 ASME

A Model for Shortening the Length of Activities in Construction and Overhaul Planning: UPROB

This paper presents a mathematical model of the UPROB (planning system for construction and overhaul) system that was developed for tank assembly lines, construction of thermal energy structures, and for performing an overhaul in complex plants. Planning technology includes utilizing linear diagrams with a direct usage of input data from a plant’s database. A model has been developed to determine the critical path and also, to define steps for the most economical shortening of the entire plan. Several plan variations are developed (according to specified goals) and the management determines the optimal variation. After selecting a plan, it is possible to control and create work orders for individual tasks in certain activities. Task completion percentage, activity cost, and the total cost of the plan are also provided.Copyright

Contribution to Production of Basic Oils by Hydrocracking

Abstract The largest part of contemporary lubricants has been obtained by different procedures of fabrication and processing of crude oil, mainly on the paraffin basis. Many contemporary plants for oil production have been designed and built a few years ago. The successful implementation of the existing technology in this field gives opportunities for optimisation of the existing technology and/or change of the existing production process with introduction of the new regime of work. In accordance with the results of laboratory and exploitation investigations in crude oil refineries and production of basic oils the possibility for reduction of the process of production of the basic oils, excluding vacuum distilling plant under alternation of regime of work of hydro-cracking has been examined. Hydro-cracking has been designed for production of fuels with total conversion of charge. Under changed conditions it is necessary to work with the residue, which has the same distilling interval as the distilling interval of the charge, and serves for production of basic oils.