Estimation of Damage to the Collector of a Water Economizer by Thermal Fatigue Cracks

Abstract

We study defects formed on the outer and inner surfaces of the input collector of water economizer of a TPP-312 boiler at the Ladyshyn thermal power plant. The collector was operating at a working temperature of 280°C under a pressure of 29.4 MPa. The period of operation of the collector prior to the analyzed maintenance shutdown was equal to 182,817 h (with 522 startups and shutdowns). A net of radial thermal fatigue cracks emerging from the holes made to attach coiled pipes (by welding) was found on the inner and outer surfaces of the collector. We propose a method for the evaluation of the degree of damage to the collector based on the computer processing of the images of cracks. To distinguish cracks in the images, we applied the method of segmentation of digital images based on the visual perception of local contrast. To determine the orientation of cracks, we used a model of crack in the form of a connected set of linear segments. As a result, the required orientation of cracks was determined by comparing the cracks with special radially oriented patterns. As a measure of damage, we used the distribution of the normed area occupied by the cracks inside the concentric circles drawn around the hole in the collector.