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S. Papaefthymiou
capacity to absorb energy. Steels with high number of penetrators show reduced
ability to resist failure at points of local stress concentration [7].
Another factor to be considered in pipelines is the fatigue limit of the used
steel, especially at low temperatures and in systems subjected to dynamic loads
and/or cyclic stresses. For instance, pressure changes or extreme stresses imposed
by external pressures and other challenges imposed by packed snow or high winds
need to be considered. Pipelines can easily be exposed to either frost heave or thaw
settlement and could experience large bending forces that typically create large
longitudinal strains [7].
For all these reasons, the steels used in such applications should have the necessary high strength and high ductility/toughness potential to suit such conditions.
Yield strength increase results in loss of fracture toughness leading to low formability and potentially to cracking. However, modern high strength low alloyed
(HSLA) steels (X80–X100 according to the API standards) tend to overcome this
issue. Micro-alloyed thermo-mechanical rolled and/or controlled processed steels
show microstructure-properties combinations suitable for such applications. High
strength–toughness combination increases formability in favor of the pipeline [7].
12.2.4 Deep-Sea Projects
The design of the submarine pipeline includes restrictions on the strength of the pipe
both externally and internally. During installation, the pipe is empty internally to
reduce as much as possible the tensile stress received by the pipeline at the bottom
due to the weight of the hanging part of the pipeline to be installed. As the pipe moves
deeper, the external hydrostatic pressure becomes higher and higher, and it is possible
that the pipe will collapse. In addition, in pipeline maintenance processes, the pipeline
is gradually decompressed internally. In any case, the durability of the pipeline in
external pressure and more specifically in hydrostatic pressure is a parameter of
design of outstanding importance [8].
12.2.5 Reeling Demands
Deep-sea projects demand laying out the pipeline in the seabed. During installation,
in addition to the external pressure (hydrostatic pressure), the pipeline is subjected
to axial tension caused by the clamp of the vessel that carries the pipeline, while, as
it approaches the bottom, it is subject to bending [9, 10]. The stresses that the pipe
receives differ depending on the installation method followed [9].
The process of installing submarine pipelines is carried out in a variety of laying
ways, namely S-, J-, reeled R-, and towed-lay.
S. Papaefthymiou
capacity to absorb energy. Steels with high number of penetrators show reduced
ability to resist failure at points of local stress concentration [7].
Another factor to be considered in pipelines is the fatigue limit of the used
steel, especially at low temperatures and in systems subjected to dynamic loads
and/or cyclic stresses. For instance, pressure changes or extreme stresses imposed
by external pressures and other challenges imposed by packed snow or high winds
need to be considered. Pipelines can easily be exposed to either frost heave or thaw
settlement and could experience large bending forces that typically create large
longitudinal strains [7].
For all these reasons, the steels used in such applications should have the necessary high strength and high ductility/toughness potential to suit such conditions.
Yield strength increase results in loss of fracture toughness leading to low formability and potentially to cracking. However, modern high strength low alloyed
(HSLA) steels (X80–X100 according to the API standards) tend to overcome this
issue. Micro-alloyed thermo-mechanical rolled and/or controlled processed steels
show microstructure-properties combinations suitable for such applications. High
strength–toughness combination increases formability in favor of the pipeline [7].
12.2.4 Deep-Sea Projects
The design of the submarine pipeline includes restrictions on the strength of the pipe
both externally and internally. During installation, the pipe is empty internally to
reduce as much as possible the tensile stress received by the pipeline at the bottom
due to the weight of the hanging part of the pipeline to be installed. As the pipe moves
deeper, the external hydrostatic pressure becomes higher and higher, and it is possible
that the pipe will collapse. In addition, in pipeline maintenance processes, the pipeline
is gradually decompressed internally. In any case, the durability of the pipeline in
external pressure and more specifically in hydrostatic pressure is a parameter of
design of outstanding importance [8].
12.2.5 Reeling Demands
Deep-sea projects demand laying out the pipeline in the seabed. During installation,
in addition to the external pressure (hydrostatic pressure), the pipeline is subjected
to axial tension caused by the clamp of the vessel that carries the pipeline, while, as
it approaches the bottom, it is subject to bending [9, 10]. The stresses that the pipe
receives differ depending on the installation method followed [9].
The process of installing submarine pipelines is carried out in a variety of laying
ways, namely S-, J-, reeled R-, and towed-lay.