空壓機轉子葉片破損肇因分析

Failure Analysis of Air Compressor Rotor Blades

本文針對某石化廠之空壓機轉子葉片斷裂之肇因進行探討，分析方法包含外觀檢查、截面金相觀察及電子顯微鏡分析等。分析結果顯示，葉片根部表面無明顯紅銹腐蝕產物之存在，然而，皆有塑性變形及低合金鋼轉軸碎片鑲入根部表面之情況，其中以suction side入口側上肩部及pressure side入口側下肩部最為明顯，顯示此兩區為葉片根部及轉軸震動擦蝕時受力最大之區域。次外，於suction side入口側上肩部可觀察到一穿晶型疲勞裂縫，而葉片表面及裂縫內部僅能偵測到微量的腐蝕因子，故腐蝕效應對於裂縫成核及成長之影響極為輕微。故依據本研究之分析結果，葉片斷裂之主因可研判為空壓機入口端氣流分佈不均，致使葉片根部與轉軸產生嚴重震動擦蝕，造成高週期疲勞破壞所致。相對而言，外在環境的腐蝕效應影響輕微。

This study investigated the root cause of the broken compressor rotor blades from a petroleum plant by visual inspection, cross-sectional metallographic observation and electron microscopic analysis. The results displayed there was no obvious red-rust corrosion product formed on the blade root surface. However, a plastic deformation layer embedded with shaft scraps can be observed on the blade root surface, particularly at the upper shoulder of SS inlet side and the lower shoulder of PS inlet side. This finding demonstrated these two specific locations were suffering from the highest cyclic stress during vibration and fretting between blade root and shaft. A fatigue crack can be observed at the upper shoulder of SS inlet side of blade root, and only small amounts corrosion species were detected inside of the crack. Based on the investigation result on this failure case, the root cause of blade fracture was mainly due to high cycle fatigue, which was an inevitable consequence of non-uniform air flow induced vibration. The contribution and influence of corrosion effect was relatively minor in this failure case.