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  • Stress Relaxation Cracking (SRC) Susceptibility Comparison in UNS S34709 and UNS S34751 Stainless Steel Welds for Petrochemical Piping Applications
Title: Stress Relaxation Cracking (SRC) Susceptibility Comparison in UNS S34709 and UNS S34751 Stainless Steel Welds for Petrochemical Piping Applications
Abstract UNS S34751 and UNS S34709 austenitic stainless-steel alloys contain thermomechanical properties required for use in chemical processing pipe applications with 900–1200°F (482–665°C) operating temperatures. UNS S34751 alloy has demonstrated improved sensitization resistance compared to UNS S34709, a precursor for polythionic acid stress corrosion cracking (PA-SCC), due to lower carbon (C) content (0.01 wt.%) and higher niobium-to-carbon (Nb/C) ratio with lower overall niobium content. The addition of nitrogen (N) in UNS S34751 alloy provides similar thermomechanical properties compared to UNS 34709. Additionally, stress relaxation cracking (SRC) susceptibility in UNS 34709 welds has been documented thoroughly in literature and industry, which poses a problem for long term service life, while UNS S34751 welds have potential for improved SRC resistance without the need for post weld heat treatment (PWHT). In this paper, a literature review of S34751 is explored, and testing matrix of experimental SRC tests using a Gleeble 3500® thermomechanical simulator is developed for S34751 gas tungsten arc welded (GTAW) pipe samples in comparison to S34709 welds. Additionally, initial thermodynamic and kinetic CALPHAD calculations have been completed to analyze potential detrimental phases in S34751 in comparison to S34709, e.g., z-phase. SRC testing has been mostly completed in S34709 welds made with W34710 (E347-16) and S16880 (E16.8.2-15) weld filler, respectively, and SRC comparisons to S34751 are in progress. Current results show higher resistance to SRC in S34751 HAZ and FZ than S34709 FZ and W34710 FZ at 800°C. In the following year, a full comparative analysis between S34709 and S34751 HAZ and FZ, in addition to welds with alternative filler S16880, is planned, including SRC testing at 600–750°C temperatures, metallurgical characterization of intergranular and intragranular precipitates, and additional thermodynamic analyses to complement microstructural observations. Final conclusions on SRC susceptibility comparisons between S34751 and S34709 welds, including alternative fillers, will be made.  more » « less
Award ID(s):
2052819
PAR ID:
10609309
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
American Society of Mechanical Engineers
Date Published:
ISBN:
978-0-7918-8850-6
Format(s):
Medium: X
Location:
Bellevue, Washington, USA
Sponsoring Org:
National Science Foundation
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