1. All metallic buried pipelines including duplex material pipelines, shall be coated externally.
2. Pipelines shall be coated externally by a suitable anti-corrosion coating, supplemented by cathodic protection.
3. Ensure that adequate cathodic protection can be demonstrated at all times, pipelines shall be electrically isolated individually from the plants to which they are connected.
4. The design of cathodic protection for onshore pipelines shall be carried out in accordance with company standard.
5. Pipelines installed above ground should be coated or the design of the pipeline supports should be such as to prevent pipeline corrosion at the support points.
6. NOTE: Short life pipelines (e.g. flowlines) may be installed above ground, without anti- corrosion coating, when experience can show that such arrangement does not lead to external corrosion (e.g. in dry climates).
1. All metallic buried pipelines including duplex material pipelines, shall be coated externally material pipelines, shall be coated externally by a suitable anti-corrosion coating, supplemented by cathodic protection for the part of the system below the water level.
2. Impressed current for cathodic protection of offshore pipelines is not recommended.
3. To ensure that adequate cathodic protection can be demonstrated, pipelines should be electrically isolated individually from platforms.
4. Alternatively mathematical modelling may be used to achieve confidence that adequate cathodic protection can be achieved in which case electrical isolation is omitted.
5. The sections of the pipeline located at the air/water interface (e.g. splash and spray zones) are critical with regard to external corrosion and special coating or claddings should be used (e.g. vulcanised polychloroprene, external cupro-nickel cladding).
1. The sections of the pipeline that are externally insulated (either for thermal requirements or fire protection) should be designed to prevent ingress of water in the annulus between the pipeline and the insulation, and should be inspectable for external corrosion.
2. Apart from the field joint areas, factory applied linepipe coatings, as opposed to field applied coatings, should be used.
3. Cathodic overprotection in terms of differential potential shall be avoided. Duplex stainless steels and high grade carbon steels (above X60) are particularly sensitive to hydrogen embrittlement caused by excessive cathodic protection voltage.
4. Electrical isolation of pipelines from plants or platforms should be by means of monoblock isolating joints located above ground or above water. The joints, preferably to be installed in an inclined or vertical position, shall be capable of withstanding any mechanical loads resulting from the adjacent pipework configuration.
5. When the transported fluid is conductive (e.g. high water cut), the
length of the isolating joint required to achieve sufficient electrical
isolation may be too large, and an internally coated isolating spool is
preferred (refer to DEP 30.10.73.31-Gen.).