Offshore Pipeline
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Offshore Pipeline
Addtime：2016-05-19 17:58:58 Print
Submarine pipelines are pipelines installed under water that are resting on seabed. Submarine pipelines can be divided into three different groups.
·offshore pipelines
·coastal submarine pipelines
·deepwater pipelines.
In general, the low and uniform resistivity of seawater simplifies the operation of cathodic protection systems for submarine pipelines. The current demand in different seawater locations varies upon temperature, salinity, and depth. For the majority of situations, the critical factor is water temperature.
Sacrificial anodes in bracelet shapes are the most preferable type of cathodic protection application for offshore pipelines. These sacrificial anodes are typically applied as “bracelets” and are installed at certain intervals along a new line. The standard materials for bracelet anodes are Aluminum-zinc-indium; however, zinc anodes are also used occasionally.
The use of zinc bracelet anodes is not recommended at applications where the pipeline surface can reach temperatures higher than 50?C. For elevated pipeline temperatures, we recommend using sled anodes, or anode beds, which are placed alongside the pipeline and are connected with a cable. It is also recommended to apply thermo-insulation inside the anodes using adhesive glue.
To achieve an electrical connection a copper cable is earthed and is thermo welded between the insert steel and the pipeline.
In order to provide adequate cathodic protection of the pipelines, sufficient direct current must be supplied on the external pipe surface, so that the steel-to-electrolyte potential is reduced to values at which external corrosion occurs at a minimal rate.
Cathodic protection is used in combination with a suitable coating system to protect the external surfaces of steel pipelines against corrosion.
Short pipelines can be protected by anodes installed at each end. This type of installation is typical for inter-platform pipelines, at which the anodes for the pipeline can be attached to the platform, if the pipeline is electrically connected to it.?
Design parameters
The design of a pipeline CP system shall be based on
· detailed information on the pipeline
· environmental conditions
· burial status
· the design life of the system
· information on existing pipelines
· information on existing CP systems
· availability of electrical power, electrical isolating devices, electrical bonds
· applicable local legislation
· construction dates, start-up date
· pipe, fittings, J-tubes, risers, clamps and other appurtenances
· performance data on CP systems in the same environment
?To achieve the maximum protection the field should be examined to identify features such as:
· protective current requirements to meet applicable criteria;
· electrical resistivity of the electrolyte, including seasonal changes if relevant
· pipe burial depth (if buried) and identification of exposed span lengths and locations
· water temperature at the seabed
· oxygen concentration at the seabed
· water flowrate at the seabed, including seasonal changes if relevant
· seabed topography.
In the previous：Docks Piers & Jetties·offshore pipelines
·coastal submarine pipelines
·deepwater pipelines.
In general, the low and uniform resistivity of seawater simplifies the operation of cathodic protection systems for submarine pipelines. The current demand in different seawater locations varies upon temperature, salinity, and depth. For the majority of situations, the critical factor is water temperature.
Sacrificial anodes in bracelet shapes are the most preferable type of cathodic protection application for offshore pipelines. These sacrificial anodes are typically applied as “bracelets” and are installed at certain intervals along a new line. The standard materials for bracelet anodes are Aluminum-zinc-indium; however, zinc anodes are also used occasionally.
The use of zinc bracelet anodes is not recommended at applications where the pipeline surface can reach temperatures higher than 50?C. For elevated pipeline temperatures, we recommend using sled anodes, or anode beds, which are placed alongside the pipeline and are connected with a cable. It is also recommended to apply thermo-insulation inside the anodes using adhesive glue.
To achieve an electrical connection a copper cable is earthed and is thermo welded between the insert steel and the pipeline.
In order to provide adequate cathodic protection of the pipelines, sufficient direct current must be supplied on the external pipe surface, so that the steel-to-electrolyte potential is reduced to values at which external corrosion occurs at a minimal rate.
Cathodic protection is used in combination with a suitable coating system to protect the external surfaces of steel pipelines against corrosion.
Short pipelines can be protected by anodes installed at each end. This type of installation is typical for inter-platform pipelines, at which the anodes for the pipeline can be attached to the platform, if the pipeline is electrically connected to it.?
Design parameters
The design of a pipeline CP system shall be based on
· detailed information on the pipeline
· environmental conditions
· burial status
· the design life of the system
· information on existing pipelines
· information on existing CP systems
· availability of electrical power, electrical isolating devices, electrical bonds
· applicable local legislation
· construction dates, start-up date
· pipe, fittings, J-tubes, risers, clamps and other appurtenances
· performance data on CP systems in the same environment
?To achieve the maximum protection the field should be examined to identify features such as:
· protective current requirements to meet applicable criteria;
· electrical resistivity of the electrolyte, including seasonal changes if relevant
· pipe burial depth (if buried) and identification of exposed span lengths and locations
· water temperature at the seabed
· oxygen concentration at the seabed
· water flowrate at the seabed, including seasonal changes if relevant
· seabed topography.
The next article：Offshore Platform & FPSO
