51315-5717-Fatigue Life of Armour Wires in Flexible Pipes in Sour Deaerated Artificial Seawater and Air Environments by Dynamic 4-Point-Bending

Available for download

Product Number: 51315-5717-SG

ISBN: 5717 2015 CP

Author: Eigil Ottesen-Hansen

Publication Date: 2015

Member Price: $0.00

Non Member Price: $20.00

Price: $20.00

Qty:

A flexible pipe consists of multiple unbonded layers. The middle part of the pipe the annulus consists primarily of pressure and tensile armour wires. These wires are made of carbon steel and are cold and/or hot rolled to pre-determined dimensions.The fatigue life of the whole pipe is to a large extent determined by the fatigue life of the tensile armour wires. Developing S-N curves that represent the fatigue life is time consuming and the oil and gas industry have high demands for the quality of these data so carbon hydrates may be produced safely.Dynamic deflection-controlled 4-point-bending is a good and stable method to generate a fatigue curve where a multitude of wire samples over several stress ranges are used.Armour wires corrode easily when in contact with a wet corrosive environment. A comparison between the fatigue life in different environments with regards to different grades and suppliers shows the level of test uniformity and supplier control.By examining the fatigue life in different test environments for each grade of armour wire as well as for different suppliers the fatigue properties are better understood and the data form a solid background within the material quality documentation programme.For two different grades of armour wires it is shown that fatigue lives vary when comparing air deaerated artificial seawater and sour (H2S) environments.The fatigue life in air is roughly a factor of 15 higher than for seawater. Compared to a sour environment the fatigue life in air is a factor of 100 higher within the target stress ranges. The difference in fatigue life between the environments increases at lower stress ranges.It is shown that for two different suppliers of the same grade of steel the fatigue life is the same within each environment air deaerated seawater and sour environment.Keywords: Corrosion fatigue; air fatigue; S-N curve generation; H2S; artificial deaerated seawater;unbonded flexible pipe; 4-point-bending.