Session: MF-24-01 Matls & Fabrication for Refining-Toughness Issues in Alloys at Elevated Temperatures

Paper Number: 122452

122452 - Aging Embrittlement of 1¼cr–½mo–si and 1cr–½mo Steels 

In refineries, it is now very common to see pressure vessels and piping which have been operated longer than the initial design life, which is typically specified as twenty or thirty years. When 1¼Cr-½Mo-Si or 1Cr-½Mo steel is used above 825 °F (440 °C) for such an extended period of time, aging embrittlement is often observed in destructive mechanical tests of such used steels. This phenomenon is toughness degradation of materials and is different from creep related damage in welds which is known as “creep embrittlement” or “low creep ductility (LCD) cracking.” Although temper embrittlement (TE) is assumed to be one of the main causes of such embrittlement, other phenomena, such as carbide formation, may also be the cause. In this study, chemical compositions and mechanical properties of used 1¼Cr-½Mo-Si and 1Cr-½Mo steels (up to about fifty years) were evaluated. These materials were taken from pressure vessels or piping in catalytic reforming or fluid catalytic cracking units. The extent of the aging embrittlement was assessed based on the chemical composition of the materials, such as X-bar ((10P + 5Sb + 4Sn + As) /100 ≤ 15 (ppm)) and J-factor (Si + Mn) × (P + Sn) × 104 ≤ 100 (wt.%)). In addition, the microstructure of the used steels was characterized using transmission electron microscopy (TEM) to investigate the cause of the embrittlement.

Presenting Author: Mikihiro Sakata JGC

Presenting Author Biography: - Material & welding expert with 15 years + experience.
- Working for JGC Corporation, a Japan-based EPC company.
- Active member of API Corrosion & Materials commitee.
- Current chairperson of API 938 B task group.
- Certified welding engineer
- Got a PhD degree from Osaka University
- Published 20 + technical papers including ASME and NACE conference papers and Elsevier scientific journals.
- His previous work co-authored with Sylvain Pillot from Industeel received Best Paper Award in PVP 2018.

Authors:

Mikihiro Sakata JGC
Charles Le Nevé TotalEnergies