Abstract
Tensile armor in flexible pipes consists of two or more layers of steel wires. Damage to the outer sheath may cause ingress of seawater in the annular space and thus corrosion of the armor wires. This work focused on the susceptibility of these wires to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) using a slow strain rate test (SSRT) under a bending load in an environment that contains chlorides. The behavior of two different microstructures was compared: martensite and pearlite plus ferrite. Furthermore, the materials were mechanically and metallurgically characterized. The results indicate that martensitic steel is more sensitive to both hydrogen embrittlement and stress corrosion cracking than pearlitic-ferritic steel.
Highlights
Flexible pipelines are offshore equipment extensively employed in oil and gas sector as oil production and gas injection pipes; the former conducting oil and hydrocarbons and the second mostly employed to enhance oil production capacity of old wells
The nobler character of pearlitic can be seen through the extrapolation of the Tafel lines: even with no consistent differences in the corrosion potential, a slightly shift of the corrosion current density was observed; the martensitic structure presented an icorr of 91.0 ± 5.4 μA.cm-2, while the pearlitic structure showed an icorr of 48.5 ± 16.5 μA.cm-2
These values represent the total charge of hydrogen reduced onto the steel surface 42 but do not necessarily denote the amount of hydrogen that diffuses through the material
Summary
Flexible pipelines are offshore equipment extensively employed in oil and gas sector as oil production and gas injection pipes; the former conducting oil and hydrocarbons and the second mostly employed to enhance oil production capacity of old wells. The riser is composed of polymeric layers that work as sealing, insulating and/or anti-wear components[3,4], while the metallic layers withstand imposed and structural loads[1,5,6,7]. One of these metallic layers, the tension armor, is a structural layer with a lay angle between 20 and 55 degrees[8]. This layer consists of helically wound flat metallic wires that are typically counter-wound in pairs and are generally made of carbon steel 9, can completely or partially sustain the tensile loads of a pipeline[1,10,11,12,13] and are the object of study in this paper
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