Installation of offshore pipelines by reeling introduces plastic pre-straining. The pre-strain history is not homogenous and it will vary around the circumference of the pipe. The pre-strain history will modify the yield and flow properties. Also, the fracture toughness may be influenced by the pre-straining. The result is that the bending strain capacity of pipelines during operation will differ depending on how the bending moment coincides with pipe orientation during installation. Three full scale tests of 12″ x-60 pipes with wall thickness 19.3mm and a 3×100 mm outer surface defect were performed to investigate the effect of pre-strain history. Two pipes were pre-strained in bending to 2% strain in the outer fibre and then straightened to simulate the reeling. The final tests to establish the strain capacity during operation as a function of strain history were performed in four point bending with an internal pressure of 325 bar. The strain capacity for the side of the pipe that ends in tension and the side that ends in compression from pre-straining was 1.7% and 2.6% respectively. The strain capacity of the third test without pre-straining was 5.7%. The results show that pre-straining will modify the strain capacity and the effect must be taken into account in engineering critical assessment of pipes during operation. The effect of prestraining should be evaluated for all installation methods that involve plastic deformation during installation, and not only reeling. It is important to note that the notch size in the full scale tests was larger than what would normally be accepted for reeling. In addition the notch was positioned in base material and not in weld metal, which is a more realistic position for a notch. The welds are normally overmatched and this might reduce the effect of prestraining.
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ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering
May 31–June 5, 2009
Honolulu, Hawaii, USA
Conference Sponsors:
- Ocean, Offshore and Arctic Engineering Division
ISBN:
978-0-7918-4346-8
PROCEEDINGS PAPER
Large Scale Tests of Strain Capacity of Pipe Sections With Circumferential Defects Subjected to Installation-Induced Plastic Strain History
Ba˚rd Nyhus,
Ba˚rd Nyhus
SINTEF Materials and Chemistry, Trondheim, Norway
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Erling O̸stby,
Erling O̸stby
SINTEF Materials and Chemistry, Trondheim, Norway
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Zhiliang Zhang,
Zhiliang Zhang
University of Science and Technology (NTNU), Trondheim, Norway
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Erlend Olso̸,
Erlend Olso̸
SINTEF Materials and Chemistry, Trondheim, Norway
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Per Arne Ro̸stadsand,
Per Arne Ro̸stadsand
StatoilHydro, Oslo, Norway
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Pa˚l Are Eikrem
Pa˚l Are Eikrem
StatoilHydro, Trondheim, Norway
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Ba˚rd Nyhus
SINTEF Materials and Chemistry, Trondheim, Norway
Erling O̸stby
SINTEF Materials and Chemistry, Trondheim, Norway
Zhiliang Zhang
University of Science and Technology (NTNU), Trondheim, Norway
Erlend Olso̸
SINTEF Materials and Chemistry, Trondheim, Norway
Per Arne Ro̸stadsand
StatoilHydro, Oslo, Norway
Pa˚l Are Eikrem
StatoilHydro, Trondheim, Norway
Paper No:
OMAE2009-80146, pp. 259-266; 8 pages
Published Online:
February 16, 2010
Citation
Nyhus, B, O̸stby, E, Zhang, Z, Olso̸, E, Ro̸stadsand, PA, & Eikrem, PA. "Large Scale Tests of Strain Capacity of Pipe Sections With Circumferential Defects Subjected to Installation-Induced Plastic Strain History." Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation. Honolulu, Hawaii, USA. May 31–June 5, 2009. pp. 259-266. ASME. https://doi.org/10.1115/OMAE2009-80146
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