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<p>A problem of premature ball breakage in “ball-and-seat valve” used in sucker-rod oil pump was studied to find failure causes. A failure analysis procedure was applied in the present study including; chemical analysis, visual inspection, stereomicroscopy, light microscopy, microhardness testing, scanning electron microscopy, energy-dispersive spectroscopy microanalysis EDS and X-ray diffraction XRD techniques. The chemical analysis and microscopic examination indicated that the balls are made of cast cobalt-base alloy “Stellite 20”. The SEM, EDS and XRD analyses identified the presence of Cr-rich, W-rich carbides and Co-W intermetallic in cobalt-rich matrix. This structure has relatively high hardness and abrasion resistance; however, it is brittle and has low impact resistance due to its coarse carbide structure and the presence of casting defects. The ball outer surface was found to undergo impact and erosion wear damage. The casting defects, brittle coarse carbides in addition to the repeated impact of balls during operation caused the initiation and propagation of fatigue cracks and ultimately resulted in fatigue fracture.</p>

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Failure Analysis of Balls in “Ball-and-Seat Valve” in Sucker-Rod Oil Pump

  • 期刊论文

  • 发表日期：

    2026年3月7日

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  • M. H. Ahmed,
  • M. A. EL-Zomor,
  • F. S. Ahmed,
  • M. A. Elhelaly

摘要

A problem of premature ball breakage in “ball-and-seat valve” used in sucker-rod oil pump was studied to find failure causes. A failure analysis procedure was applied in the present study including; chemical analysis, visual inspection, stereomicroscopy, light microscopy, microhardness testing, scanning electron microscopy, energy-dispersive spectroscopy microanalysis EDS and X-ray diffraction XRD techniques. The chemical analysis and microscopic examination indicated that the balls are made of cast cobalt-base alloy “Stellite 20”. The SEM, EDS and XRD analyses identified the presence of Cr-rich, W-rich carbides and Co-W intermetallic in cobalt-rich matrix. This structure has relatively high hardness and abrasion resistance; however, it is brittle and has low impact resistance due to its coarse carbide structure and the presence of casting defects. The ball outer surface was found to undergo impact and erosion wear damage. The casting defects, brittle coarse carbides in addition to the repeated impact of balls during operation caused the initiation and propagation of fatigue cracks and ultimately resulted in fatigue fracture.