In-service property prediction of X80 self-shielded flux-cored (FCAW) girth weld metal based on strain ageing kinetics

ABSTRACT

In order to achieve in-service safety evaluation of girth weld, property prediction of X80 self-shielded flux-cored girth weld metal based on strain ageing kinetics was conducted. Strength increment (ΔY) and toughness reduction (ΔCVN) relationship was obtained through tensile and Charpy impact test using specimens before and after strain ageing. 1% prestrain was conducted and then aged at different conditions (150°C/100°C for 1–6 h, 80°C/50°C for 1–120 days). Strain ageing kinetics was investigated based on experiment results, and diffusion activation energy (Q) was calculated as 88.1 kJ/mol. The correlation equation of ageing temperature and period was obtained: $\mathrm{l}\mathrm{n}\frac{t_1}{t_2}=10597.4\left[\frac{1}{T_1}-\frac{1}{T_2}\right]$, T₁<T₂ <423 K. It is predicted that, since occurrence of 1% prestrain, toughness of girth weld metal would drop down to <80 J after 3.9 years service in the present case, and its service safety should be reconsidered. Other prediction should be based on experimental results of specific consumable and welding parameters.

KEYWORDS:

• High strength pipeline
• self-shielded flux-cored welding (FCAW)
• girth weld metal
• strain ageing kinetics
• property prediction

Acknowledgments

The authors wish to acknowledge the financial support from the project of “National Defense Science and Technology Innovation Special Zone Project” (No. 22-05-CXZX-04-04-29) and “Research on failure mechanism for girth weld of high steel pipeline” (NO.WZXGL202105).

Disclosure statement

No potential conflict of interest was reported by the authors.