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<p>This paper investigates duplex stainless steel failure in welded process piping systems, focusing on the microstructural and mechanical properties related to welding corrosion. The detailed examination involved the following tests: optical microscopy, field-emission scanning electron microscopy with electron dispersive spectroscopy, tensile test, bend test, V-notch impact test, and Vickers microhardness test. The KNN supervised machine learning algorithm was employed as an image processing technique for microscopic image segmentation and quantification of presented phases. The weld zone indicated an imbalance in microstructural metallurgical phases where the ferrite content was 24%. This resulted in localized corrosion in weld zones; precisely because its composition is predominately austenitic structure; which is the root cause of duplex steel's reduced resistance (localized corrosion initiation and progressive damage) against aggressive piping system's transferred fluid (oily sour water extracted from oilfields reservoirs and separated from crude oil via gravity-assisted 2-phase separation process in a high-pressure unfired vessel). Mechanical testing results showed that welding tensile properties complied with the minimum requirements; the weld metal had higher yield and tensile strengths than the base metal. The bend test, however, disclosed a root bend specimen failure, attributed to surface cracks along the weld root. Toughness results from impact testing were satisfactory and thus did not indicate any embrittlement. Microhardness tests revealed a slight hardness decrease within the weld zone compared to the HAZ and base metal zone, which was largely due to microstructural changes and a higher cooling rate in HAZ.</p>

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Metallurgical and Mechanical Failure Investigations of a Welded Duplex Stainless Steel Flange–Elbow Joint

  • 期刊论文

  • 发表日期：

    2025年5月29日

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  • Murtadha A. Jabbar,
  • Mohammed Y. Yousif,
  • Dhurgham A. Mohsin,
  • Zainab A. Ibrahim,
  • Ali D. Ahmed

摘要

This paper investigates duplex stainless steel failure in welded process piping systems, focusing on the microstructural and mechanical properties related to welding corrosion. The detailed examination involved the following tests: optical microscopy, field-emission scanning electron microscopy with electron dispersive spectroscopy, tensile test, bend test, V-notch impact test, and Vickers microhardness test. The KNN supervised machine learning algorithm was employed as an image processing technique for microscopic image segmentation and quantification of presented phases. The weld zone indicated an imbalance in microstructural metallurgical phases where the ferrite content was 24%. This resulted in localized corrosion in weld zones; precisely because its composition is predominately austenitic structure; which is the root cause of duplex steel's reduced resistance (localized corrosion initiation and progressive damage) against aggressive piping system's transferred fluid (oily sour water extracted from oilfields reservoirs and separated from crude oil via gravity-assisted 2-phase separation process in a high-pressure unfired vessel). Mechanical testing results showed that welding tensile properties complied with the minimum requirements; the weld metal had higher yield and tensile strengths than the base metal. The bend test, however, disclosed a root bend specimen failure, attributed to surface cracks along the weld root. Toughness results from impact testing were satisfactory and thus did not indicate any embrittlement. Microhardness tests revealed a slight hardness decrease within the weld zone compared to the HAZ and base metal zone, which was largely due to microstructural changes and a higher cooling rate in HAZ.