Assessment of the residual service life working in hostile environment

Abstract

Degradation staly at long operation - difficult and dangerous process. It covers various processes and factors: change of structure of metal and corrosion and electrochemical characteristics, external damages of a surface, deterioration of mechanical properties and so forth. The processes happening during degradation staly are interconnected, but their interrelation difficult and is insufficiently investigated. Estimations of current state of metal of the equipment which fulfilled considerable term, and forecasting of its residual resource it is possible to consider as a complex task which covers also a choice of the sensitive characteristics of metal which are subject to an assessment and a technique choice. It causes an imperative need of development of scientific approaches to an assessment of current state of the equipment and the equipment and methods of forecasting of a residual resource. For a service life assessment one of the main indicators is the speed of corrosion processes. The resource at such approach is defined by division of a stock of thickness of a wall of the equipment into corrosion speed. Such methods will possible to predict a resource only on condition of course of uniform corrosion. Corrosion speed control methods by means of samples witnesses, korrozimetr estimate only the average speed of superficial general corrosion, but in actual practice always there are fluctuations of parameters of technological process. For an assessment of degree of danger of defects to a steel pipe use such parameters as pipe wall thickness, depth and length of corrosion damage, nature of stratification became. In case of hit of defect in a safe zone, it is clear that further operation is possible, but with periodic control. When defect gets to a destruction zone, operation should be stopped immediately. If gets to the zone demanding expert estimation, depending on additional conditions, for example, the locations of the point corresponding to defect on graphics of individual requirements make the decision on the possible subsequent period of operation. The offered approach gives the chance to estimate in general a residual service life. But practice showed that local damages of metal are inherent in the equipment of chemical and oil processing industry. It causes need to estimate also residual resource of "problem places" of the equipment. It is established that unplanned stops (sometimes to 10 times and more in a year) significantly influence dynamics of development of local damages and their area. For this reason the resource can sometimes decrease in tens times.