NH3冷凝器鋁熱交換管件的腐蝕行為研究

The Study of Corrosion Behavior of Aluminum Heat Exchange Tubes in a NH3 Condenser

本研究為一設備破損案例分析，主要是針對煤化學場NH3冷凝器之鋁熱交換管的腐蝕破管行是出探討。為了解其腐蝕發生的途徑、起因和機構，本研究利用SEM觀察蝕破管材之外側、內側及剖面等表面結構，以及利用EDS分析腐蝕生成物的化學成分。利用分光分析儀（Spark）及感應偶合電漿原子激發光譜分析儀（ICP-AES）分析熱交換管管材的化學成分和冷卻水的水質，以了解在材質選用上是否有誤和冷卻水之水質是否產生變異。利用動電位極化曲線試驗（(Potentiodynamic polarization test），以評估冷卻水中抑制劑是否仍具有抑制腐蝕之效應。此鋁熱交換管之破損經分析研究可歸因於，該殼管式冷凝器之器殼及端板（材質為碳鋼）腐蝕所產生的鐵銹，沉積在鋁熱交換管上，導致鋁熱交換管發生間隙腐蝕（Crevice Corrosion）或沉積腐蝕（Deposit corrosion）。此外，冷卻水中的高氯離子含量會助長腐蝕的惡化。

This case study was performed to shed light on the corrosion mechanism of aluminum heat exchange tubes of a condenser, used for condensing NH3 vapor. To understand the corrosion cause and mechanism, many supporting tests were carried out. The corrosion of aluminum heat exchange tubes was observed by using scanning electron microscopy (SEM). The chemical compositions of corrosion products were measured by energy dispersive spectrometer (EDS). Spark and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were used to clarify whether the proper material was applied. The corrosivity of cooling solution was also evaluated by ICP-AES. Potentiodynamic polarization test was conducted to verify whether the inhibitors added in the cooling solution work or not. The damage of the heat exchange tubes can be attributed to the deposition of rust originating from the corroded shell and bottom plate of the condenser (made of carbon steel) on the surface of aluminum heat exchange tubes, resulting in the occurrence of crevice corrosion or so-called deposit corrosion. In addition, the presence of chloride ion (Cl-) in the cooling solution has further accelerated the attack to the aluminum heat exchange tubes.