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지역난방 배열 회수 보일러의 유동 가속 부식 원인 고찰
홍민기,채호병,김영수,송민지,조정민,김우철,하태백,이수열,Hong, Minki,Chae, Hobyung,Kim, Youngsu,Song, Min Ji,Cho, Jeongmin,Kim, Woo Cheol,Ha, Tae Baek,Lee, Soo Yeol 한국재료학회 2019 한국재료학회지 Vol.29 No.1
Severe wall thinning is found on the tube of a low-pressure evaporator(LPEVA) module that is used for a heat recovery steam generator(HRSG) of a district heating system. Since wall thinning can lead to sudden failure or accidents that lead to shutdown of the operation, it is very important to investigate the main mechanism of the wall thinning. In this study, corrosion analysis associated with a typical flow-accelerated corrosion(FAC) is performed using the corroded tube connected to an upper header of the LPEVA. To investigate factors triggering the FAC, the morphology, composition, and phase of the corroded product of the tube are examined using optical microscopy, scanning electron microscopy combined with energy dispersive spectroscopy, and x-ray diffraction. The results show that the thinnest part of the tube is in the region where gas directly contacts, revealing the typical orange peel type of morphology frequently found in the FAC. The discovery of oxide scales containing phosphate indicates that phosphate corrosion is the main mechanism that weakens the stability of the protective magnetite film and the FAC accelerates the corrosion by generating the orange peel type of morphology.
지역난방 시스템의 순환수에 따른 보일러 튜브의 부식 특성
홍민기 ( Minki Hong ),조정민 ( Jeongmin Cho ),송민지 ( Min Ji Song ),김우철 ( Woo Cheol Kim ),하태백 ( Tae Baek Ha ),이수열 ( Soo Yeol Lee ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.6
In this study, corrosion behavior of a SA178-A alloy used in the boiler tube of a district heating system was investigated in different environments where it was exposed to pure water, district heating (DH) water, and filtered district heating (FDH) water. After the corrosion test, the surface morphology was examined for observation of the number of pitting sites and pitting area fraction, using a scanning electron microscope. The DH water and FDH water conditions resulted in a lower corrosion potential and pitting potential, and revealed a significantly higher corrosion rate than the pure water condition. The pitting sites in the DH water (pH 9.6) were approximately eighteen times larger than those in the pure water (pH 9.6). Compared to the DH water, the corrosion potential became more noble in the FDH water condition, where iron ions were reduced through filtration. However, the corrosion rate increased in the FDH water due to an increased concentration of chloride ions, which deteriorated the stability of passive film.
김영수 ( Youngsu Kim ),채호병 ( Hobyung Chae ),홍민기 ( Minki Hong ),송민지 ( Min Ji Song ),조정민 ( Jeongmin Cho ),김우철 ( Woo Cheol Kim ),하태백 ( Tae Baek Ha ),이수열 ( Soo Yeol Lee ) 한국부식방식학회 2019 Corrosion Science and Technology Vol.18 No.2
Corrosion failure in the convection part of peak load boiler (PLB) of the district heating system led to water leakage. Herein, Internal Rotary Inspection System (IRIS) inspection was employed to examine wall thinning and the cause of leakage in the flue tube. The corrosive products of the turbulator and tube were investigated using scanning electron microscope combined with energy dispersive spectroscopy, X-ray diffraction, and inductively coupled plasma (ICP). Majority of the serious corrosion damage was observed near the turbulator located in the upper flue tube. ICP analysis of the boiler water revealed oxide formation of sodium chloride in the lower end part of the flue tube. A cross-sectional view of the turbulator revealed the presence of double-layers of the oxide film, indicating environmental change during operation associated with water leakage. The outer surface of the turbulator consisted of the acid oxides such as NO<sub>x</sub> and SO<sub>x</sub> along with sodium and chloride ions. Dew-point corrosion is hypothesized as the main cause for the formation of acid oxides in the region of contact of the flue tube and the turbulator.