Investigation of Surface Cracking of Cr-Mo Steel Drill Pipe | ||
| International Journal of Materials Technology and Innovation | ||
| Articles in Press, Accepted Manuscript, Available Online from 13 October 2025 | ||
| Document Type: Original Article | ||
| DOI: 10.21608/ijmti.2025.425117.1131 | ||
| Authors | ||
| M.G. Mahmoud* 1; Waleed Khalifa2 | ||
| 1Mechanical Design and Production Department, Faculty of Engineering, Cairo University, Giza,12613, Egypt. | ||
| 2Department of Mining, Petroleum and Metallurgical Engineering, Faculty of Engineering, Cairo University, Cairo, Egypt. | ||
| Abstract | ||
| This study investigates the surface cracking of an intermediate-strength Cr-Mo steel drill pipe through integrated magnetic particle inspection, chemical and mechanical characterization, and metallographic examination. Routine inspection of materials stored for approximately six months revealed faint, intermittent longitudinal cracks up to 43 cm in length and widespread pitting corrosion on pipes reported as newly purchased. Although the material’s properties largely met the specifications for Cr-Mo steel, microscopic and EDS analyses identified substantial concentrations of sulfur (0.26 - 0.65 wt.%) and chlorine (0.21-0.65 wt.%) within the corrosion products. These findings contradict the claim of unused material and indicate prior exposure to aggressive downhole drilling environments rich in chlorides and sulfides, where surface pitting and cracking had initiated before the pipes were refurbished and resold. The failure was primarily attributed to hydrogen sulfide (H₂S) stress corrosion cracking (SSC), a form of environment-assisted cracking (EAC). Alternative mechanisms including fatigue cracking, hydrogen embrittlement, and conventional stress corrosion cracking were systematically excluded based on microstructural and fractographic evidence. The predominance of longitudinal cracking was linked to propagation under circumferential principal stress (CPS), the maximum tensile stress in a pressurized pipe. Additionally, a shallow decarburized layer (~70 μm deep) near the outer surface was observed, creating a mechanically weakened region that facilitated crack initiation. The failure was ultimately driven by the combined effects of the corrosive environment (Cl⁻ and H₂S), manufacturing defects, and operational stresses. | ||
| Keywords | ||
| Drill pipe; Failure analysis; Corrosion; Cr-Mo steel | ||
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