Damage Failure of Two Alloy Seal Rings Paired with Impregnated Graphite
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摘要:
某石油化工泵分别采用Cr合金密封环和YG-6硬质合金密封环，在300～400 ℃与浸渍石墨密封环配副，发现Cr合金密封环长期服役仍能保持良好的密封性能，而硬质合金密封环运行一段时间后发生气体泄漏. 为探究2种合金密封环服役性能差异的缘由，对失效密封环进行表面形貌、化学成分与力学性能表征，分析失效机制. 研究结果表明：Cr合金密封环材质为含Cr的马氏体钢，未作表面强化处理，表面硬度和弹性模量分别为（629.8±14.2） HV30和（244.7±17.4） GPa，与浸渍石墨配副接触区出现以轻微犁削效应为主的环形磨斑，磨损表面粗糙度显著降低；硬质合金密封环表面硬度和弹性模量分别为（
1 475.3 ±60.1） HV30和（815.3±57.2） GPa，密封环表面残余应力高，存在氧化腐蚀诱导的材料脆化，配副接触区无明显磨损，但出现氧化开裂导致的块状缺损；Cr合金密封环表面的低刚度和高粗糙度导致其配副接触区发生磨粒磨损，但磨损表面存在打磨抛光行为，与浸渍石墨配副仍能保持良好的密封性能，而YG-6硬质合金密封环表面高残余应力和高温服役环境诱导的材料氧化脆化，导致配副接触区发生开裂破坏，密封失效.Abstract:Cr alloy seal ring and YG-6 cemented carbide seal ring were used to pair with impregnated graphite seal ring in a petrochemical pump at 300–400 ℃, respectively. It was found that the Cr alloy seal ring maintained good sealing performance for a long-term service, while gas leakage occurred to the cemented carbide seal ring after a short time of service. To explore the reasons for the difference in service performance of two kinds of alloy seal rings, the surface morphologies, chemical compositions, and mechanical properties of the failed seal rings were characterized, and their failure mechanisms were analyzed. The results show that the Cr alloy seal ring is made from martensitic Cr-containing steel without surface strengthening treatment, and the surface hardness and elastic modulus are (629.8±14.2) HV30 and (244.7±17.4) GPa, respectively. On its contact area with impregnated graphite, an annular wear scar characterized by a slight ploughing effect is observed, and the surface roughness of the wear significantly decreases. The surface hardness and elastic modulus of the cemented carbide seal ring are (1475.3±60.1) HV30 and (815.3±57.2) GPa, respectively. There exists high residual stress and material embrittlement induced by oxidative corrosion in the seal ring surface. No obvious wear occurs on the contact area with impregnated graphite, but blocky defects caused by oxidation cracking appear. Due to low stiffness and high surface roughness, the Cr alloy seal ring suffers from abrasive wear on its surface with impregnated graphite, but the wear surface has grinding and polishing behaviors, maintaining its good sealing performance when paired with impregnated graphite. For the YG-6 cemented carbide seal ring, defects by cracking occur in the contact area with impregnated graphite under the action of the high surface residual stress and the material oxidation and embrittlement induced by high temperatures, resulting in sealing failure.
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Key words:
- seal rings /
- Cr alloy /
- cemented carbide /
- failure analysis /
- abrasive wear /
- oxidation embrittlement
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图 3 Cr合金与浸渍石墨密封环端面环形磨斑形貌LCSM照片
Figure 3. LCSM images of annular wear scars on end faces of Cr alloy and impregnated graphite seal rings
图 4 硬质合金密封端面环缺损形貌
Figure 4. Morphologies of end-face defects of cemented carbide seal ring
图 6 Cr合金密封环表面EDS图谱与拉曼图谱
Figure 6. EDS spectrums and Raman spectrums of Cr alloy seal ring surface
图 7 硬质合金密封环表面EDS图谱与拉曼图谱
Figure 7. EDS spectrums and Raman spectrums of cemented carbide seal ring surface
图 8 2种密封环表面维氏压痕形貌LCSM照片
Figure 8. LCSM images of Vickers indentations on two seal rings
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