Offshore Pipelines

Pipeline Construction date Diameter rating Product Length (km) Anode weight (t) 

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In the case of older pipelines and offshore pipelines, protection current densities can amount to several mA m" For older onshore pipelines, the protection current densities are determined by a drainage test according to Section 3.4.3. 

Protection with impressed current, with galvanic anodes, and a combination of both processes is used for marine structures and offshore pipelines. Their properties, as well as their advantages and disadvantages, are given in Table 16-1. The protective measures must be optimized for every structure. In the impressed current protection of offshore platforms, for example, the difficulties of maintenance and repair will be of major importance, whereas in harbor installations these problems can be... 

Marine Structures and Offshore Pipelines 387 16.7.2 Harbor Structures... 

Where a.c. supplies exist, transformer-rectifiers are the most economical source of d.c. for cathodic protection systems. In the case of pipelines, standard transformer-rectifiers, either oil or air cooled, can be employed. They range in size from 5A, 5V for small systems to 100 A, 48 V for major pipeline schemes. A typical output for a well-coated cross-country pipeline in the UK would be 5 A, 48 V. In the case of sea-water jetties where the voltage required is usually low because of the lower sea-water resistivity, a typical rectifier size for a major installation would be 500 A, 18 V. For offshore pipelines and loading platforms where a fire hazard exists, it is usual to employ certified flameproof or intrinsically safe rectifiers to overcome any possibility of fire hazard should faults develop in the unit. 

Sydberger,T., Evaluation of Inspection Methods for Offshore Pipeline Cathodic Protection Systems , Materials Performance, 22 No. 5, 56 (1983)... 

Siting - The preferred arrangement of bulk transport pipeline systems is for burial underground. This provides for enhanced protection from overhead events. This is even the case for offshore pipelines where there have been numerous incidents of dragged anchors from fishing vessels to pipelines exposed on the seabed. A radius of exposure from a pipeline can also be easily calculated for fires and vapor explosions based on the commodity, pressure, release opening, etc. From these calculations a restricted zone or similar can be designated. 

Other failures of pipelines generally occur as a result of third party activity and natural hazards. Offshore, pipelines are generally more susceptible to fishing boats dragging their anchors on the seabed. Onshore pipelines are vulnerable to impacts from earth moving operations for construction or road grading. On occasion impacts from mobile equipment may also directly strike and damage the pipeline. 

Transportation in offshore pipelines located upstream from the outlet flange of each facility on the Outer Continental Shelf where hydrocarbons are produced or where produced hydrocarbons are first separated, dehydrated, or processed (whichever facility is farther downstream) ... 

The local annual production of Azerbaijan amounted to 4.5-6 bcm over the recent years. Because of limitations of the existing offshore pipelines capacity, more than half of the current gas production is reportedly flared or vented. The country s total demand is secured by imports of Russian natural gas (4-6 bcmp.a.). 

Offshore pipeline risk It is more difficult to repair an offshore pipeline than an onshore pipeline. It is therefore associated with an increased risk, or lower security of supply, to receive your gas from an offshore pipeline compared to an onshore pipeline. 

The Gas Directive defines upstream pipelines as those which are part of a production project or which are used to convey natural gas from one or more such projects to a processing plant or terminal or final coastal landing terminal (Art. 2 No. 2). A primary question is if all Norwegian offshore pipelines are covered by this definition. 

It could be claimed, strictly according to the wording, that pipelines from processing plants on land to a coastal terminal are not covered by the definition to a processing plant... or a final coastal terminal (our italics). It would, however, have been somewhat odd if these pipelines were not treated in the same way as other offshore pipelines. Alternative solutions have obvious weaknesses. 

Accordingly, all Norwegian offshore pipelines probably fall within the definition of upstream pipelines in the Directive. This is also the position of... 

It is possible that the Norwegian authorities have had something else in mind, cf. the statement in the report to the Storting No. 46 (1997-98) Olje og gassvirksomheten p. 11 Offshore pipelines to final terminal should, in accordance with established practice, still be regulated as part of the production sector (our translation). 

The gas-pipeline construction costs in 1983 showed a 1.05% increase for the composite gas pipeline cost index. Even though some of the materials (pipes, valves, and fittings, etc.) were discounted, some other costs such as labor, construction machinery and equipment increased and hence the total pipeline construction cost index showed an increase. Bigger pipelines (10—36 in.) contributed to most of the gas transportation in the United States. A comparison of costs of construction for land and offshore pipelines indicated that the offshore construction is three times as expensive as onshore projects. An annual cost index (Al) of 200 was published for the year 1983 for pipeline installation and an AI of 203 for compressor equipment and drive units in the compressor stations. The high pressure gas pipeline cost index in 1983 was the same as the previous year. 

Pipeline Cathodic Protection—Part 2 Cathodic Protection of Offshore Pipelines, ISO/TC 67/SC2 NP 14489, International Standards Organization, May 1, 1999. 

Edwards J. Internal corrosion offshore pipelines. Final report NTNF-project B.0601.T121. Part project 3, Trondheim SINTEF. 

Kolk, H.J., and Power, P.T. 1983. Advances in geotechnical investigations and design for offshore pipelines. European Seminar Offshore Oil and Gas Pipeline Technology, Oyez Scientific and Technical Services, London, 47pp. 

Milz, E. A., and Broussard, D. E. (1972), Technical capabilities in offshore pipeline operations to maximize safety. Proceedings, Offshore Technology Conference. Houston, TX, Paper OTC 1711, pp. 122-133. 

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