Steel piling

Steel piled jackets are the most common type of platform and are employed in a wide range of sea conditions, from the comparative calm of the South China Sea to the hostile Northern North Sea. Steel jackets are used in water depths of up to 150 metres and may support production facilities a further 50 metres above mean sea level. In deep water all the process and support facilities are normally supported on a single jacket, but in shallow seas it may be cheaper and safer to support drilling, production... 

Considerable stray currents can, of course, be caused by dc-driven cranes that load and unload ships where the rails act as the return conductor for the current. The rails run parallel to the harbor basin, quay walls of steel-reinforced concrete or steel piling walls. These can take up a large part of the stray current and conduct it further because of their small longitudinal resistance. Noticeable stray current inter-... 

Fig. 16-9 Cathodic protection of a steel piling with impressed current.

Steel piling, Elbe Tar pitch-epoxy 25,000 16 FeSi-Cr 380 4 20 X 100 >20... 

Harbor structures are very accessible and can be investigated without the effects of wave motion. Grounding of steel pilings presents no problems and the work can be carried out from the quay (see the left-hand side of Fig. 16-13). With steel-reinforced concrete structures, measurements have to be made from a boat if no reliable contact has been provided in their eonstruction (see the right-hand side of Fig. 16-13). 

Distribution of steel pile corrosion as a function of marine exposure zone and marine fouling... 

For protection of sheet-steel piling, the anodes are normally mounted within the re-entrants of the piles to prevent mechanical damage by berthing ships, dredging, etc. (Fig. 10.30). 

Figure 97. Steel piles with a blade on the tip and a rotation burying machine...

The corrosion rates of carbon steel pilings and test samples in different exposure zones with the placement of samples in vertical position show different degrees of severity of the zones. 

Uniform corrosion usually occurs in fairly aggressive environments that attack the whole surface. Examples include carbon steel in seawater or acids, or aluminum alloys in strong alkali. The rate of metal loss is usually rather high, but, because it is distributed over the whole surface, the performance can usually be predicted, and managed with corrosion allowances, in most situations. Thus, sheet steel piling is often used in seawater without any corrosion protection, the corrosion rate of around 0.1 mm/yr, coupled with the relatively thick steel sections, giving an acceptable life. 

Figure 3.13 Corrosion profile of steel piling after 5-year exposure to seawater (7).

Figure 8.9 Corrosion rate on steel piles as a function of sediment resistivity. (From Fisher and Bue [8.19]. Reprinted with permission of ASTM International, 100 Bar Harbor Drive, West Conshohochen, PA 19428.)...

FIGURE 4.30 Schematic presentation of orange bloom on a steel pile (not to scale). (With kind permission from Springer Science+Business Media Microbiologically Influenced Corrosion—An Engineering Insight, 2008, Javaherdashti R.)... 

This is another vital part of an impressed current system. The T/R must be rugged and reliable with minimal maintenance requirements. It should be easy to maintain with good instruction manuals, circuit diagrams for maintenance and easy access to fuses and other consumable and replaceable components. Compared with pipeline or marine CP applications (steel piles, etc.) the power demand is modest. Most steel in concrete needs less than 10 mA-m to provide protection, usually at less than 10 V. The power for a 100 watt light bulb will protect 10,000 m. This means that a single phase, air cooled T/R will usually protect even the largest structure and power consumption is rarely an economic concern. 

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