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Collaborating Authors
di Biagio, Massimo
Low-Cycle Tearing in a Deep-Water Buckle-Arrestor Assembly Girth Weld During S-Lay Installation
Selker, Ruud (INTECSEA) | Liu, Ping (INTECSEA) | Jurdik, Erich (South Stream Transport BV) | Chaudhuri, Jay (South Stream Transport BV) | Fonzo, Andrea (RINA Consulting-Centro Sviluppo Materiali) | di Biagio, Massimo (RINA Consulting-Centro Sviluppo Materiali)
S-Lay installation of inline buckle arrestors in deep water can introduce plastic strain to girth welds. The welds are repeatedly loaded by large-strain cycles when traversing the stinger. A material-testing program was launched to assess the impact of this load sequence on the welds' integrity. It is essential to establish the correct mechanism of crack growth caused by a limited number of sequential large-strain cycles. Segment specimens with increased specimen “daylight” length were tested. Fracture morphologies of ductile tearing and fatigue growth were distinguished; ductile tearing was identified only for the first load cycle, whereas subsequent cycles were dominated by fatigue crack growth. Introduction The TurkStream Offshore Pipeline was developed by South Stream Transport BV (SSTTBV). It is a major gas-transmission system that currently comprises two pipeline strings installed in up to 2,200 m water depth, connecting large gas reservoirs in Russia to the Turkish gas-transportation network through the Black Sea. The system currently has a capacity to transport 31.5 bcm of natural gas annually over a distance of more than 900 km. The pipeline's outer diameter (D) is 32 inches, and its wall thickness (t) is 39 mm. Material grade is DNV SAWL (submerged arc-welded longitudinal) 450 with supplementary requirement F, D, U, and (light) S according to offshore standard DNV-OSF101 (Det Norske Veritas, 2010) plus project-specific modifications. Pipe joints are produced by UOE (U-ing, O-ing and expansion) and JCOE (J-ing, C-ing, O-ing and expansion) pipe-forming methods. Ultra-deep water in combination with the large pipeline diameter makes this project one of the most challenging pipeline projects ever, pushing the boundaries of the industry. The first portion of the pipeline was installed in 2017–2018.
- Europe (1.00)
- North America > United States > California > San Francisco County > San Francisco (0.28)
Low Cycle Tearing in a Deepwater Buckle Arrestor Assembly Girth Weld During S-Lay Installation
Selker, Ruud (INTECSEA) | Chaudhuri, Jay (South Stream Transport BV) | Liu, Ping (INTECSEA) | Fonzo, Andrea (Centro Sviluppo Materiali) | Jurdik, Erich (South Stream Transport BV) | di Biagio, Massimo (Centro Sviluppo Materiali)
ABSTRACT For a major deepwater pipeline project in the Black Sea, buckle arrestors will be deployed to prevent catastrophic buckle propagation in the unlikely event of collapse. If large diameter pipe is installed in deepwater using S-lay, plastic strain will develop when the pipe travels over the stinger. Presence of a relatively stiff feature will enhance straining locally. The thick buckle arrestor is girth-welded to thinner pipe sections. Consequently, strain concentration will occur in the girth weld. When traversing the stinger, tens of sequential loading-unloading cycles are introduced. The girth weld is loaded when the buckle arrestor is on top of a roller box and unloaded when located in between two roller boxes. To support assessing the impact of such load sequence on the integrity of the girth weld, a material testing program is launched. Fracture behaviour is investigated both qualitatively and quantitatively. It is essential to confirm the correct mechanism of crack growth under repetitive cycles of large strain. To establish the correct mechanism, segment tests with increased specimen "daylight" length are performed. After testing, the fracture surface is examined, measured and classified using a Scanning Electron Microscope (SEM). Fracture morphologies of ductile tearing, fatigue growth and brittle fracture can be distinguished. Ductile tearing is observed in the first loading cycle. Subsequent cycles are dominated by fatigue crack growth, which can be quantified using Paris Law. INTRODUCTION South Stream Transport BV (SSTTBV) is developing a major gas transmission system that comprises up to four (4) pipeline strings to be installed in water depths up to 2200 m. The system will have a massive capacity to transport 63 billion cubic metres of natural gas per year over a distance of more than 900 km through the Black Sea. The pipeline steel outside diameter (D) will be 812.8 mm (32-inch) and its wall thickness (t) 39 mm. Material grade of the linepipe is DNV SAWL 450 SFDU and, depending on the supplier, it is manufactured using either UOE or JCOE method. This project can be considered as one of the most challenging pipeline projects ever, stretching the limits of present-day industry.
- Europe (1.00)
- North America > United States (0.68)