半導體廠製程廢水排放管線腐蝕肇因分析

Corrosion Leakage of the Wastewater Discharge Pipe in a Semiconductor Plant

304不銹鋼具有均衡的耐蝕性及加工性及經濟性，因此為工業界使用最廣泛的不銹鋼結構材料，但若使用環境條件未受適當控制，可能使得不銹鋼產品提早腐蝕損壞。本文即探討某半導體廠採用304不銹鋼為製程廢水排放管線之結構材料，使用約3年時間即發生腐蝕穿孔現象。分析項目包含背景資料收集、目視檢查、化學組成分析、腐蝕形態及顯微組織觀察等，綜合各項結果顯示：發生腐蝕穿孔的管線屬於備用管線，管線底部長期有廢水殘留，在空氣和廢水交界處因氧濃差效應而形成許多蝕孔，最終導致腐蝕穿孔。此外，廢水含有的固體物容易沉積於管線底部，而沉積物與管線表面形成間隙環境，同時也因氧濃差環境而增加腐蝕速率，而此現象為300系列不銹鋼常見的洩漏破壞模式。

Type 304 austenitic stainless steel is a commonly used as construction material for many sectors of industries which demonstrate a desirable compromise among corrosion resistance, mechanical properties, and cost advantage. However, premature failures may occur under adverse operating conditions. This case study is to investigate the leakage cause(s) of a wastewater discharge stainless steel pipeline in a semiconductor plant. The analysis works include background information collection, visual inspection, chemical composition analysis, morphological and microstructural examination. The failed pipe, sampled from a backup wastewater line, shows huge amount of corrosion products and sediments on the inside surface, and an obvious waterline corrosion is also found at the bottom half of pipe. The oxygen concentration cell is convinced to initiate corrosion pits at waterline and eventually perforate the pipe wall. Lots of sediments are formed and resulted in crevice corrosion between sediment and pipe wall to corrode pipe wall, but to a lesser extent. Therefore, this backup pipeline is believed to contain residual wastewater for a prolonged duration after leak or functional testing in the construction phase.