Session: OAC-06-01 Continued Safe Operation of Existing Assets-1

Paper Number: 123064

123064 - Embrittlement of 347h Stainless Steel Welds in 538 °C (1000 °F) Service 

A metallurgical evaluation was conducted involving 347H stainless steel welds removed from a resid hydrocracking unit hot hydrogen pipe system, after 5 and 15 years of service. The welds were found to have embrittled. The absorbed energy of Charpy tests was as low as 18 J (13 ft-lb). Tensile test ductility was as low as 7-9% elongation. The greatest embrittlement effect was on the creep ductility. The elongation to stress rupture varied from 0.5 to 0.9%. The Ω factor varied from 382 to 548. However, creep strength was as good as new 347H stainless steel base metal. Average magnetic ferrite number FN measurements indicated values of 1.4 to 2.1, on cross sections, and of 1.6 to 2.9 on the OD. All these welds were stabilize-heat treated at 900 °C (1650 ± 25°F) for a minimum of 4 hours when installed and again, to stress relief after welding. This reduced the FN. Solution annealing at 1066 °C (1950 °F) followed by water quenching fully restored Charpy absorbed energy values, tensile test ductility, significantly reduced the yield strength but caused no changes in the tensile strength. This solution annealing treatment increased creep strength but did not restore creep ductility at all. Creep brittle welds are more prone to form crack than creep ductile material, at high stressed locations, which are typically notch-like geometric configurations or defects. Thus, the high creep brittleness found at these 347H welds is a concern, which is why it was investigated.
Keywords: Stainless steel, stabilized stainless steel 347H, weld embrittlement, creep, Omega test method, initial strain rate, the Omega factor, resid hydrocracking.

Presenting Author: Jorge Hau Shell Global Solutions (US) Inc.

Presenting Author Biography: Senior Materials and Corrosion Engineer

Authors:

Jorge Penso Shell Projects and Technology
Jorge Hau Shell Global Solutions (US) Inc.
Mitul Dalal Mitul.Dalal@shell.com