Pipes offshore

Cathodic protection has been traditionally used for a long time to protect structures in seawater. Zinc bracelet anodes are installed on pipelines immersed in seawater to provide sacrificial CP to the outer surfaces of the steel pipe. Offshore structures for gas and oil exploration, drilKng, and production are commonly protected by the use of aluminum anodes on the steel structures. Cathodic protection is employed by several power plants located near coastal sites for protecting steel structures submerged in seawater. 

UKOOA Specifications and Recommendations for the use of GRP piping offshore. Part 4, Fabrication and installation (1994)... 

As in the construction industry, piling of the conductor is done by dropping weights onto the pipe or using a hydraulic hammer until no further penetration occurs. In an offshore environment the conductor is either piled (e.g. on a platform) or a large diameter hole is actually drilled, into which the conductor is lowered and cemented. Once the drill bit has drilled below the conductor the well is said to have been spudded. 

Cathodic Protection This electrochemical method of corrosion control has found wide application in the protection of carbon steel underground structures such as pipe lines and tanks from external soil corrosion. It is also widely used in water systems to protect ship hulls, offshore structures, and water-storage tanks. 

Offshore anodes are similar in shape to tank anodes. They are, however, much larger and weigh about 0.5 t. They are predominantly manufactured from aluminum alloys. On the basis of strength, most of them are cast onto pipes or profile iron as supports on which lateral protruding shackles are welded. The cross-section is usually trapezoidal (see Fig. 6-15). 

As drilling technology moved the pursuit of hydrocarbon resources into higher-cost offshore and hostile environments, intentionally deviated boreholes required information such as azimuth and inclination that could not be derived by surface instruments. Survey instruments, either lowered on a sand line or dropped into the drill pipe for later retrieval, to some degree satisfied the requirements but consumed expensive rig time and sometimes produced questionable results. 

The most fundamental difference found between onshore and offshore drilling occurs when the wellhead is located at the seafloor. This configuration makes communication with the well more complex. A marine riser provides communication and circulation capability between the surface and the seafloor, and is used at some point during most offshore drilling. The riser consists of large-diameter (17-20) in.) steel pipe joints of approximately 50-ft lengths, with quick-connect couplings. The riser can be connected at the seafloor to a wellhead or to a subsea blowout preventer stack. A diverter system is usually attached at the... 

API Recommended Practice 14E, Fifth Edition Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems, October 1991. 

For firewater, steel pipes are used but corrosion products can block sprinklers. Cement asbestos pipes are utilized but pressure limitations restrict their use. For critical applications, including offshore oil installations, cupronickel alloys and even duplex stainless steels are used. Fire-retardant grades of fiber-reinforced plastics are now available. 

D. Osborne. The development in the use of FRE (fiber reinforced epoxy) pipe systems for industrial and offshore applications. In Proceedings Volume, number 7, pages 27 5. 10th BHR Group Ltd et al Pipe Protect Int Conf (Amsterdam, Netherlands, 11/10-11/12), 1993. 

Offshore Oil Storage Platform Fuel Tank Explosion due to welding on piping connected to tanks still containing oil 9 Fatalities... 

Isolation - It has been shown that the addition of isolation valves at periodic intervals is not as cost effective as prevention measures such as thickness inspections or tests. However all pipelines should be provided with a means for emergency isolation at it entry or exit from a facility. Offshore facilities may be particularly vulnerable to pipeline incidents as the Piper Alpha disaster has shown. In that accident a contributing factor to the destruction was the backfeed of the contents of the gas pipeline to platform once the topside isolation valve or piping lost its integrity. Further isolation means (i.e., a subsea isolation valve SSIV) were not available. 

The use of pads or other means of pipe attachment at support points should be considered for piping systems subject to wear and pipe wall metal loss from relative movement between the pipe and its supports (e.g., from wave action on offshore production applications). 

No general rules-of-thumb are available for plastic tanks/containers failure criteria should be based on available test data (SINTER, 1997). FRP is used offshore for fire water lines in order to reduce weight. Wet pipe FRP systems may be effective in afire scenario because water is flowing, allowingthe heatto be carried away. If the pipe is dry, failure may rapidly occur. 

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