NDTnet 1998 Aug, Vol.3 No.8

Abstract

In a number of cases the technical condition of petrochemical equipment can be determined by changing some parameter. These parameters may be divided into technological (pressure, temperature and qualitative factors of the obtained product) and mechanical (wall thickness, presence of defects in welded seams and basic metal, degree of strength variation and so on). Observing dynamics of controlled parameter variation, one can forecast predict resourse (servise life) of equipment before limiting state is reached. A limiting state is characterized by probable values of a parameter. Prediction validity is defined mainly by accuracy of measurement and the number of parameter measurement. Validity of the forecast of a servise life also must depend on degrees of danger of destroying a vessel of pressure and consequences of this destruction. There has been nominated four degrees of danger of destroying: very strong, strong, average and weak. Calculations show that the following best values of validity of the forecast of servise life of equipment () - 99%, 95%, 90% and 80% correspond to it.

The best graphical approach to the evaluation of the remaining servise life of petrochemical equipment may be show in case, when the main damaging factor is corrosionerosion wear-out, and as a controlled parameter there is taken thickness of a wall. On the bases of the analysis of technical documentation under the most disadvantageous correlation of field-performance influences (temperature, pressure, working fluid) and local concentrations of tensions (nodes of union nippers, lower part of vertical devices, joining shells of different acerbity, area between full tilts of horizontal devices and so on) are defined potentially dangerous units (PDU). According to the results to measurement within PDU theres is defined minimum probable thickness of a wall. Such an approach is stipulated by the fact the general area of measurements forms only a small part from total area of PDU. It is calculated, with the assumption that in the process of measurement actual minimum thickness has not been discovered. Residual servise life is defined by the moment when predicted wall thicknesses reaches its limiting value. Wall thickness limiting value corresponds to the minimum permissible value ensuring structural strength under operating loads.

In such a manner residual service life is evaluated for all PDU on examined equipment. Residual service life of examined equipment is specified to be equal to minimum value of all the calculated PDU. PDU with the minimum residual service life is considered to be the weak place and the very place is to receive primary consideration.
On the base of given approach is designed program of evaluation of residual servise life on the criterion corrosion-erosion wear-out.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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