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Corrosion Fatigue Of X80 Weld In Mild Sour Environment

Pipelines and rigid risers made in conventional X65 grade require large wall thickness to withstand the high loads imposed during installation and under operating conditions in deep and ultra-deepwater field developments. The use of high-strength steels like X80 is an attractive alternative since it improves catenary weight by reducing wall thickness.

Product Number: 51322-17778-SG
Author: Laurent Ladeuille, Richard Jones, Yifei Zeng, Xin Yue, Chih-Hsiang Kuo, Florian Thébault, Grégory Toguyeni
Publication Date: 2022
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The developments in deep and ultra-deep waters require the application of heavy wall pipes for steel risers in conventional grades. The utilization of higher-strength grade such as X80 reduces the constraints related to the manufacturing and the installation by saving line pipe weight.
Seamless X80 pipes were manufactured in 323.9 x 25.4 mm and characterized. Girth welding was made using the Gas Metal Arc Welding (GMAW) process on these seamless line pipes. Four-point-bend tests were conducted as per NACE TM0316(2) to evaluate the Sulfide Stress Cracking resistance on X80 pipe and welds.

There are only limited results about the fatigue behavior of high-strength steel welded joints and, especially, in sour environments. Therefore, the performance of X80 mechanized girth weld was assessed in air and in mild sour environment. Fatigue endurance tests were performed in air at room temperature at loading frequencies of 4-8 Hz and completed by tests at 24°C, pH 5.9, 0.1 psi H2S partial pressure using a frequency of 0.2 Hz. The in-air fatigue performance of the X80 girth weld was found to be comparable to X65 tested in similar conditions; the results exceeded the BS 7608 class E target curve. The environmental knock down factor (EKDF), which was obtained by comparing the mean of the in-air data with the mean of sour data, is equal to 10.

The developments in deep and ultra-deep waters require the application of heavy wall pipes for steel risers in conventional grades. The utilization of higher-strength grade such as X80 reduces the constraints related to the manufacturing and the installation by saving line pipe weight.
Seamless X80 pipes were manufactured in 323.9 x 25.4 mm and characterized. Girth welding was made using the Gas Metal Arc Welding (GMAW) process on these seamless line pipes. Four-point-bend tests were conducted as per NACE TM0316(2) to evaluate the Sulfide Stress Cracking resistance on X80 pipe and welds.

There are only limited results about the fatigue behavior of high-strength steel welded joints and, especially, in sour environments. Therefore, the performance of X80 mechanized girth weld was assessed in air and in mild sour environment. Fatigue endurance tests were performed in air at room temperature at loading frequencies of 4-8 Hz and completed by tests at 24°C, pH 5.9, 0.1 psi H2S partial pressure using a frequency of 0.2 Hz. The in-air fatigue performance of the X80 girth weld was found to be comparable to X65 tested in similar conditions; the results exceeded the BS 7608 class E target curve. The environmental knock down factor (EKDF), which was obtained by comparing the mean of the in-air data with the mean of sour data, is equal to 10.

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