空壓機葉片破損原因分析

The Failure Analysis of the Centrifugal Compressor Impeller

吳宗峯(Tsung-Feng Wu)

《防蝕工程》 36卷1期 (2022/03) Pp. 23-32

https://doi.org/10.6376/JCCE.202203_36(1).0003

摘要

某廠空壓機葉輪多個葉片發生破裂及裂紋現象，表面亦可觀察到明顯的蝕孔，進行破損分析藉以釐清破裂之主因。分析結果顯示：葉片材質之Cr含量偏低，不符合原設計之17-4PH析出硬化型不銹鋼規範要求，而為Cr含量僅有14.2%之15-5PH不銹鋼，故導致耐氯鹽腐蝕能力不足；但其機械性質與冶金組織無異常現象，並無明顯機性劣化之情況發生。葉片表面腐蝕生成物中並無高溫氧化相存在，顯示並無明顯過熱的現象發生，然可偵測到Cl、S等元素之訊號峰，顯示運作環境中存在造成孔蝕之腐蝕因子存在。葉片表面出現許多發生蝕孔，且破裂之起始恰為表面上因氯離子誘發形成之孔蝕位置。由此研判破裂初期由單一蝕孔起始，因葉片旋轉離心力及間歇性反覆應力造成疲勞傳播；傳播中後期，主裂縫與因其他蝕孔誘發之次要裂縫串連而造成破斷，屬於氯離子誘發孔蝕所造成之疲勞破斷。破損起因乃為使用Cr含量低之備品，導致葉片表面於運轉中發生氯離子誘發孔蝕現象，造成應力集中而發生破裂起始，最終導致斷裂發生。

關鍵字

空壓機葉輪葉片 ； 17-4 PH不銹鋼 ； 孔蝕 ； 疲勞破斷

並列摘要

The cracks and pits are observed on the impeller surface of an air compressor in a certain factory. Failure analysis was performed to clarify the main cause. There is no evidence on the metallurgical and mechanical degradation of the impeller, however, the chemical composition of the impeller is not meet the standard requirement of 17-4 PH stainless steel. The lower chromium content might rise the risk of pitting corrosion in the Cl-containing environment. EDS results show that both Cl and S elements are detected inside the pits. Furthermore, the locations of pits are highly corresponded with the maximum stress sites of the impeller during the operation from reference report. The rupture starts from a single pit, and then propagated with the fatigue mode. It is resulted from the centrifugal force of the impeller rotation and the intermittent repeated stress. In the end of the propagation stage, several cracks initiated from different pits meet together then impeller failed. The failure mode belongs to the fatigue rupture caused by chloride ion-induced pitting corrosion. The failure cause is resulted from using lower Cr-content impeller material. The unqualified impeller leads to chloride-induced pitting on the surface in the Cl-containing operation environment. Then the cracks are initiated on the pits with stress-concentrated effect, and eventually lead to fatigue failure.

並列關鍵字

Centrifugal compressor impeller ； 17-4PH stainless steel ； pitting corrosion ； fatigue fracture

參考文獻

“Effect of SO42- and Cl- anionic attack on the localized corrosion resistance and morphology of 409 stainless steel”, R. T. Loto, Results and Physics, 12 (2019), pp. 738-742.

“Fatigue life assessment of centrifugal compress impeller based on FEA”, S. Liu, C. Liu, Y. Hu, S. Gao, Y. Wang, and H. Zhang, Engineering Failure Analysis, 60 (2016), pp. 383-390