Measurement of residual stress shakedown in pressure/tensile armour wires of flexible pipes by neutron diffraction
The manufacture of unbonded flexible pipes (flowlines andrisers) involves wrapping steel wires to create pressure andtensile armour layers. The forming of armour wires fromvendor supply conditions to a helix shape on the pipe involvessignificant plastic straining and the wires that are wrapped ontot...
| Published in: | Volume 5A: Pipeline and Riser Technology |
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| Main Authors: | , , , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
American Society of Mechanical Engineers
2015
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| Subjects: | |
| Online Access: | https://research.manchester.ac.uk/en/publications/03cba1e6-d62a-40ba-a5d3-053c10dd1501 https://doi.org/10.1115/OMAE2015-41328 |
| Summary: | The manufacture of unbonded flexible pipes (flowlines andrisers) involves wrapping steel wires to create pressure andtensile armour layers. The forming of armour wires fromvendor supply conditions to a helix shape on the pipe involvessignificant plastic straining and the wires that are wrapped ontothe pipe are not unloaded. Therefore the armour wires inflexible pipes are expected to contain significant residual stress(RS) as a result of the plastic straining and loading duringmanufacture and placement. This may lead to detrimentaleffects on the strength, durability and the service integrity ofthe pipe. It is postulated that the unfavorable RS introducedduring pipe manufacture reduces due to stress shakedownduring the factory acceptance test (FAT) where the pipe issubjected to a high internal pressure.This paper describes the first attempts to measure RS in thearmour wires in unbonded flexible pipes. The key developmentis the use of a neutron diffraction method which allows themeasurement of RS in-situ on the manufactured pipe throughthe whole wire sections. Pipe samples were prepared exposingthe relevant metal layer and the measurements were performedon pipe samples taken before and after performing thepressurized FAT. The effect of the FAT on the shakedown ofresidual stress in pressure armour wires is discussed. As shownby the measurements, the elastic strains and stresses in thepressure armour wires are much larger in the hoop direction ofthe pipe (i.e. along the length of the wire) than radial or axial tothe pipe. In pre-FAT pipe the hoop stresses are essentiallytensile on the extrados and compressive on the intrados. Theresults have shown that the FAT reduces the hoop strains andstresses to approximately 1/3 of their as manufactured level. |
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