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The tempering response in the heat-affected zone (HAZ) of low alloy steels during temper bead welding is heavily dependent on the experienced thermal history. Past work has developed quantification approaches for isothermal tempering conditions and single non-isothermal tempering cycles, whereas the temper bead welding processes impart multiple non-isothermal cycles throughout the HAZ. This work outlines a novel methodology for tempering response quantification that allows for prediction of the HAZ hardness in multipass welding. The quantification approach utilizes a modification of the Grange-Baughman tempering parameter that converts non-isothermal cycles into an equivalent isothermal cycle and correlate this with the resulting hardness. This relationship can be utilized to evaluate hardness distributions throughout the HAZ of low alloy steel temper bead weldments based on the experienced thermal histories. It was shown that, in contrast with conventional heat treatment, the temper bead welding in Grade 22 steel results in nucleation of high density, finely dispersed Fe-Cr rich carbides. The proposed methodology was applied for evaluation of the HAZ hardness in a particular heat of Grade 22 steel, resulting from multiple tempering reheats, and was experimentally validated using a three-layer weld overlay. It was found that the peak temperature of weld tempering cycles was the most significant factor in controlling HAZ hardness.
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Investigation of Relationship Between Microhardness and Charpy Impact Energy for Temper Bead Welding Qualification: Part 1
Abstract Temper bead (TB) welding is often used as an alternative to post weld heat treatment (PWHT) for repair of pressure vessels and piping in the nuclear power industry. Historically, qualification of TB welding procedures has employed the Charpy V-notch test to ensure acceptable heat-affected-zone (HAZ) impact properties. The 2004 Edition of ASME Section IX provided a new provision in QW-290 that allows temper bead qualification using a peak hardness criterion. The peak hardness provision is appropriate for industries such as oil and gas, where peak allowable hardness is specified to ensure adequate resistance to sulfide stress cracking in sour service environments. However, a peak hardness criterion is not appropriate where impact properties are specified for resistance to brittle fracture during low temperature conditions that can occur during certain postulated accident scenarios at a nuclear power plant. Work at the Electric Power Research Institute (EPRI) and The Ohio State University (OSU) show that a hardness drop protocol can be used to demonstrate acceptable impact properties in the HAZ of a temper bead weld. This paper presents a quantitative correlation between hardness measurements and HAZ microstructures with presumed optimum impact properties using a hardness drop approach. The overarching goal is to develop a hardness test protocol for temper bead weld procedure qualification for applications where impact properties are specified.
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- Award ID(s):
- 1822144
- PAR ID:
- 10175964
- Date Published:
- Journal Name:
- ASME 2019 Pressure Vessels & Piping Conference
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Dissimilar metal welds (DMWs) are routinely used in the oil and gas industries for structural joining of high-strength steels to eliminate the need for post-weld heat treatment (PWHT) in field welding. Hydrogen-assisted cracking (HAC) can occur in DMWs during subsea service under cathodic protection. DMWs of two material combinations, 8630 steel/FM 625 and F22 steel/FM 625, produced with two welding procedures, non-temper bead (BS1) and temper bead (BS3), in the as-welded and PWHT conditions were investigated in this study. These DMWs were subjected to metallurgical characterization and testing with the delayed hydrogen cracking test (DHCT) to identify the effects of base metal composition, welding and PWHT procedures on their HAC susceptibility. The HAC susceptibility was ranked using the time to failure in the DHCT at loads equivalent to 90% of the base metal yield strength (YS) and the apparent stress threshold for HAC. A criterion for resistance to HAC in the testing conditions of DHCT was also established. The results of this study showed that 8630/FM 625 DMWs were more susceptible to HAC than the F22/FM 625 DMWs. PWHT did not sufficiently reduce the HAC susceptibility of the 8630/FM 625 and F22/FM 625 BS1 welds. DMWs produced using BS3 performed better than BS1 DMWs. The post-weld heat-treated F22/FM 625 BS3 DMW passed the HAC resistance criterion.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1115/PVP2019-93950
