Session: MF-24-01 Materials and Fabrication for Refining - 1

Paper Number: 105856

105856 - Reheat Cracking in Welds of 1¼cr-½Mo Steel Pressure Vessels During Fabrication 

The material 1¼Cr-½Mo steel has been widely used in fluid catalytic cracking (FCC) reactors, continuous catalyst regeneration (CCR) reactors and desulfurization reactors, as these reactors operate at temperatures of between 400 °C (752 °F) and 520 °C (968 °F).  The first part of this paper presents a case history of a reheat cracking in the weld metal of a 1¼Cr-½Mo steel pressure vessel during fabrication.  The indication was first found in the weld metal by MT after PWHT at 691 °C (1,276 °F).  Metallurgical investigation revealed that the cracking was intergranular and probably caused by a high boron (B) content in the weld metal.  The cracked weld metal contained more than 60 ppm of boron, which was unusual for the authors.  To evaluate the effect of boron to susceptibility of reheat cracking in the weld metal, a reheat cracking test using C-ring type specimen was conducted at various temperatures between 600 °C (1,112 °F) to 690 °C (1,274 °F).  The result indicated that cracking occurred in boron-contained weld metal regardless of the test temperatures, while not found in boron-free weld metal.  The last half of this paper is to review literatures which focuses on the effect of boron on reheat cracking in 1¼Cr-½Mo steels.  It was found that even 5-10 ppm boron might increase susceptibility to reheat cracking.  The mechanism of how boron induced intergranular cracking was also discussed.  Finally, this paper provides some recommendations to reduce the risk of reheat cracking in 1¼Cr-½Mo steel weld metal.

Presenting Author: Kazuki Suda JGC Corporation

Presenting Author Biography: Kazuki Suda received his Master's degree in Materials engineering. Has more than 5 years' experience of materials. Worked as a materials engineer in JGC Corporation.

Authors:

Kazuki Suda JGC Corporation
Mikihiro Sakata JGC Corporation
Shigekazu Miyashita JGC Corporation
Hideaki Takauchi Kobe Steel, Ltd.