重油媒裂工廠之一氧化碳鍋爐水幕爐管破損分析

Failure analysis for CO-boiler tube in a residue catalytic cracking unit

一氧化碳鍋爐水幕爐管是煉油廠中重油媒裂（RCC）工廠的重要熱交換設備之一，操作時最高溫度可達980℃，且操作環境複雜。本研究乃針對長期處於高溫腐蝕氣氛之爐管破損件進行分析，以掃描式電子顯微鏡（SEM）觀察發生破損部位及其周圍材料之表面、橫截面形貌及微觀組織，利用能量散射光譜儀（EDS）和X光繞射分析儀（XRD）分析腐蝕產物之化學成分和物種鑑定，以解釋其破損原因及機制。實驗結果顯示，水幕爐管殼側銹皮中硫化物及氧化物同時存在，顯示操作環境中硫元素的活性高。以SEM觀察爐管破裂處橫截面，發現上游製程之催化物堆積，且管壁厚度發生縮減，顯示殼側破管為爐管與支撐架的震動和相互摩擦所引起。

CO-boiler is one of an important heat exchangers in residue catalytic cracking (RCC) unit in oil refinery plant, which normally operates in a high temperature (about 980℃) corrosive environment. In this investigation, the failure of a CO-boiler tube was examined and its root cause was analyzed. The surface morphology and cross-section microstructure of the failed part was studied using a scanning electron microscope (SEM). Chemical composition and phase identification of the corrosion product were analyzed by energy dispersive spectrometer (EDS) and X-ray diffractometer, respectively. Results indicate that shell-side is composed of sulfide and oxide, which shows high sulfur activity in operating condition. The SEM and EDS results for cross-section of crack part shows accumulation of catalyst particles and wall reduction. With all these analyzing results, vibration and wear contact between the tube and the supporting plate was deduced to be the main reason for pipe fracture. perforation of the boiler tube in the high temperature corrosion atmosphere.