OS2507 Microstructural characteristics and SCC susceptibility near the fusion boundary of dissimilar weld joint with Ni-base weld metal and low alloy steel

2011 ◽  
Vol 2011 (0) ◽  
pp. _OS2507-1_-_OS2507-2_
Author(s):  
Hiroshi ABE ◽  
Yutaka WATANABE
Keyword(s):  
Weld Metal ◽  
Alloy Steel ◽  
Weld Joint ◽  
Low Alloy Steel ◽  
Fusion Boundary ◽  
Microstructural Characteristics ◽  
Dissimilar Weld

A Study of Thermal Aging Effects on Microstructures of Dissimilar Metal Weldment

2013 ◽  
Author(s):  
Kyoung Joon Choi ◽  
Jong Jin Kim ◽  
Ji Hyun Kim
Keyword(s):  
Weld Metal ◽  
Alloy Steel ◽  
Thermal Aging ◽  
Base Alloy ◽  
Boundary Region ◽  
Low Alloy Steel ◽  
Aging Effects ◽  
Fusion Boundary ◽  
Dissimilar Weld ◽  
Dissimilar Metal

Characterizations of microstructure and mechanical property were conducted to investigate the effect of long-term thermal aging on the microstructural evolution in the fusion boundary region between weld metal and low alloy steel in dissimilar metal welds. A representative dissimilar weld mock-up made of Alloy 690-Alloy 152-A533 Gr. B was fabricated and aged at 450°C for 5,500 hours. It was observed that the region near the fusion boundary was generally divided into several regions including dilution zone in the Ni-base alloy weld metal, fusion boundary, and heat-affected zone in the low alloy steel. A steep gradient was shown in the chemical composition profile across the interface between A533 Gr. B and Alloy 152. The precipitation of carbides was also observed along and near the fusion boundary of aged dissimilar metal joints. It was also found that the precipitation of Cr carbides was enhanced by the thermal aging near the fusion boundary.

PWSCC Experience of Pressurizer Dissimilar Metal Welds at Tsuruga Unit-2

2004 ◽  
Author(s):  
Hiroyuki Kobayashi ◽  
Kimihito Takeuchi ◽  
Shohei Nakama ◽  
Masayuki Mukai ◽  
Takahiro Ohta
Keyword(s):  
Alloy Steel ◽  
Weld Joint ◽  
Repair Process ◽  
Visual Observation ◽  
Low Alloy Steel ◽  
Relief Valve ◽  
Metallographic Examination ◽  
Dissimilar Weld ◽  
Root Cause ◽  
Non Destructive

During the 13th refuel outage in September 2003, the small boric acid deposit was observed at one dissimilar weld joint between Relief Valve Nozzle and Safe End of Pressurizer in Tsuruga unit 2. The other four indications were also observed at the weld joint by non-destructive examination. Similar indications were also observed at Safety Valve Nozzle. Both Nozzles were under the steam condition at 345°C. As the first root cause investigation, the visual observation after etching was conducted at these weld joint on site. The observation revealed the repair weld print. Both weld joints with cracks were taken to conduct some investigations such as metallographic examination of fracture surface at hot laboratory. Hot laboratory examination results revealed that all cracks were extended axially in the Ni base metal weld joint, and there was no evidence of any cracks extending into the low alloy steel Nozzle and stainless steel Safe end. All cracks were interdendritic and branched. Metallographic examination results revealed that the crack growth mainly was caused by interdendritic stress corrosion cracking (IDSCC). These Nozzles including the weld joint with indications were repaired by jointing the spool piece as new Safe ends. The repair process includes the weld buttering on the low alloy steel Nozzle and joint welding between Nozzle and the spool piece. These welding were conducted by GTAW using alloy 52. It took twenty days to complete the repair works.

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