Failure analysis of the left waterwall tube of boiler furnace in the steam power plant based on thickness changes and pressure

摘要

Purpose - The purpose of this paper is to analyze the failure of the left waterwall tube of a boiler furnace in the steam power plant which led to cracks and rupture. Macro visual observation showed the rupture like a fish mouth with slag adhering at the outer surface of the tube. Magnetite as a protective layer was peeled off. Changes in the thickness were analyzed through dimensional measurement. In this research, an analysis to find the cause and determine the fracture mechanism is presented. Design/methodology/approach - A physical analysis was performed through visual observation of changes in the thickness. Micro visual testing with a metallography test provided the data required to measure the change of grain size. The mechanical analysis used Von Mises criteria and API 530 standard and provided the pressure limits data. Findings - The thickness of the tube decreased at the peak curvature of the tube. The smallest thickness at the peak curvature of the tube was 0.108 inches. The working pressure was 40.74 percent from permit limits with Von Mises calculations. The percentage of pressure calculated by the API standard was 48.42 percent from permit limits. Larger crystal grains occurred only in the nearby area of the oxide layer and at the end of the crack tip. It indicated that part of the inner surface had a relatively high temperature and plastic deformation occurred because of the pressure from inside the tube. Combining all these factors ruptured the tube at this location because the cross-section could not hold up the pressure. Originality/value - The analysis of this discussion focuses on the combined effect of those factors causing the ability to decrease stress being received. It restricts the tube from holding up the stress and furthermore it will generate fractures.