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<p>15-5 PH (Fe−15Cr-5Ni-3.5Cu-0.4Nb) martensitic precipitation-hardenable stainless steel was selected for the fabrication of flange closure for pressure testing of LOX-kerosene turbo pump of a rocket liquid engine. To meet high-pressure-test requirements, 15-5 PH flange was used in the peak-aged (i.e., H900) heat treatment condition to achieve the highest strength in this alloy. During hydro pressure test, leak was observed and further investigation revealed through-thickness cracks in the split flanges. Fractographic and microstructural analyses were performed on samples extracted from the failed flange. Fractographic analysis indicated a brittle mode of failure. Optical microscopy of the sample revealed the network of delta ferrite and inhomogeneous microstructure confirming improper thermomechanical processing of material used for flange. Chemical composition, hardness, tensile, and impact toughness properties were analyzed on samples extracted from failed flange.&#xa0;Due to the presence of network of delta ferrite and inhomogeneous microstructure, achieved tensile and impact toughness properties do not confirm the specification requirements. Repeat H900 heat treatment on failed sample dissolved the inhomogeneity in microstructure; however, delta ferrite is unaltered. Finite element (FE) analysis of hydro pressure test condition revealed inadequacy in achieved property. Root cause of failure is found to be inadequate working that resulted in remnant cast microstructure showing lower properties, which finally failed under the designed load as confirmed by FE analysis.</p>

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Metallurgical Analysis of Failure Observed on 15-5 PH Stainless-Steel Flange Failed During Hydro Test

  • 期刊论文

  • 发表日期：

    2026年5月31日

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  • R. Santhoshkumar,
  • Bodasingi Thavitiraju,
  • C. R. Anoop,
  • Jagtap Yuvraj Vasant,
  • S. Vivek,
  • Rohit Kumar Gupta,
  • M. Arumugam

摘要

15-5 PH (Fe−15Cr-5Ni-3.5Cu-0.4Nb) martensitic precipitation-hardenable stainless steel was selected for the fabrication of flange closure for pressure testing of LOX-kerosene turbo pump of a rocket liquid engine. To meet high-pressure-test requirements, 15-5 PH flange was used in the peak-aged (i.e., H900) heat treatment condition to achieve the highest strength in this alloy. During hydro pressure test, leak was observed and further investigation revealed through-thickness cracks in the split flanges. Fractographic and microstructural analyses were performed on samples extracted from the failed flange. Fractographic analysis indicated a brittle mode of failure. Optical microscopy of the sample revealed the network of delta ferrite and inhomogeneous microstructure confirming improper thermomechanical processing of material used for flange. Chemical composition, hardness, tensile, and impact toughness properties were analyzed on samples extracted from failed flange. Due to the presence of network of delta ferrite and inhomogeneous microstructure, achieved tensile and impact toughness properties do not confirm the specification requirements. Repeat H900 heat treatment on failed sample dissolved the inhomogeneity in microstructure; however, delta ferrite is unaltered. Finite element (FE) analysis of hydro pressure test condition revealed inadequacy in achieved property. Root cause of failure is found to be inadequate working that resulted in remnant cast microstructure showing lower properties, which finally failed under the designed load as confirmed by FE analysis.