Mechanism of intergranular reheating crack in butt-welded joint of 12Cr1MoV tube served for 40,000 hours

ABSTRACT

Cracking failure of butt-welded joint of 12Cr1MoV tube was comprehensively studied. Results show that both of initiation and propagation of the primary crack were circumferentially intergranular in the coarse-grained heat affect zone (CGHAZ). Many isolated and intergranular micro-cracks and cavities were observed near the primary crack．Neither oxide or corrosion products were observed in the isolated cavities or micro-cracks. According to the microstructure, location, propagation mode and morphology of the crack，the primary crack in butt-welded joint is concluded to be the intergranular reheating cracking (IRC). The crack failure is mainly due to poor welding quality, characterised by high residual stress and coarsened grain size. Mechanisms on the IRC based on previous laboratory research were studied on the failed tube sample, and results showed that the IRC is accumulation of high-stress induced creep damage, such as cavities along prior austenite grain boundaries (PAGBs). Neither segregation of alloys elements nor trace impurities were detected.

KEYWORDS:

• 12Cr1MoV
• intergranular reheat cracking
• failure analysis
• residual stress
• welding
• plant boiler
• creep damage
• coarse grain heat affect zone

Acknowledgments

This work was financially supported by the Science and Technology Project of China Huaneng Group [grant number HNKJ18-H45]. The authors are grateful for this support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Science and Technology Project of China Huaneng Group [HNKJ18-H45].