Intelligent Steam Power Plant Boiler Waterwall Tube Leakage Detection via Machine Learning-Based Optimal Sensor Selection

Boiler waterwall tube leakage is the most probable cause of failure in steam power plants (SPPs). The development of an intelligent tube leak detection system can increase the efficiency and reliability of modern power plants. The idea of e-maintenance based on multivariate algorithms was recently introduced for intelligent fault detection and diagnosis in SPPs. However, these multivariate algorithms are highly dependent on the number of input process variables (sensors). Therefore, this work proposes a machine learning-based model integrated with an optimal sensor selection scheme to analyze boiler waterwall tube leakage. Finally, a real SPP test case is employed to validate the proposed model’s effectiveness. The results indicate that the proposed model can successfully detect waterwall tube leakage with improved accuracy vs. other comparable models.

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

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.

Electrochemical Corrosion Behavior of Ultra-Supercritical Unit Waterwall Tube Material in Simulated Solution of Oxygenated Treatment at Room Temperature

The electrochemical corrosion behavior of ultra-supercritical unit waterwall tube material in simulated solution of oxygenated treatment (OT) with different concentration of Cl- and SO42- at room temperature was investigated by electrochemical impedance spectroscopy and Tafel slopes. The results showed that the polarization resistance Rp values decreased and corrosion current density (icorr) increased with increasing Cl-/ SO42- concentration in solution. Corrosion potentials (Ecorr) decreased with increasing Cl-/ SO42- concentration in solution.

Fatigue and Corrosion Fatigue Failures

A metallurgical failure analysis was performed for a hanger rod and a waterwall tube sample. The hanger is a rigid type and supports a long vertical run of piping. The fracture is in one of the threaded ends and the fracture surface consists of three regions. The outermost portion adjacent to the thread root has ratchet marks that are an indication of fatigue crack initiation. The center portion has concentric, oval shaped beachmarks. The oval shape is consistent with an applied loading due to two bending moments. The inner portion is the final fracture and is approximately 1/4 of the thread root area indicating relatively low remote stresses. The failure mechanism is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The lower slope waterwall tube failure had a window opening fracture appearance. The axial fractures forming the window are located at the edge of the membrane welds on the cold or backside. There are shallow toe cracks at the membrane weld on the tube outside surface. The fracture surface had multiple, thumbnail-shaped fatigue cracks connected to the inside surface. These fatigue cracks are due to the corrosion fatigue mechanism based on two factors: (1) the stress responsible for their growth is related to the unit thermal cycling and the welded panel geometry near the corner of the boiler, and (2) they are oxidized indicating a corrosion contribution.

Creep Failure of a Chromized Waterwall Tube in a Supercritical Boiler

In Spring, 2000, as part of a continuous mitigation program for circumferential cracking and waterwall wastage, 88 tubes, in panel sections of 22 tubes, were installed into the centerwall of a supercritical boiler. The replacement tubes were low alloy (1-1/4Cr-1/2Mo) steel chromized to a nominal depth of 12–20 mils (0.3–0.5 mm). After only three years of operation, one tube failed due to creep. Four months later, a second creep failure occurred in the same centerwall panel and four other tubes were removed due to visual variations in dimension. Two months later, two more tubes were removed with bulges. Two months following that, during the scheduled overhaul, seven other tubes were removed due to the formation of bulges and extensive creep damage was found in three of the four panels comprising the chromized tube section. Metallurgical evidence indicates tube metal temperatures in excess of 1000°F. Creep testing was performed on samples taken from this unit and its identical sister unit. The first data shows the creep properties to fall near the minimum band for this Cr-Mo alloy, but the testing remains ongoing.