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Docks Piers & Jetties

 

Most of the current marine facilities (ports, docks, breakwaters, etc.) are composed of steel pipe piles or steel sheet piles. Due to the seawater immersion the steel structure are subject to corrosion. It is extremely important to protect these steel structures and increase the life of this infrastructures.

Factors such as water composition, oxygen concentration, sea life, and seawater velocity also accelerate the corrosion and thinning of steel materials.

A combination of coating and cathodic protection can deteriorate the corrosion affect. But also coating affected during installation and from the environment conditions. Coating degradation in embedded areas can be up to 50% during installation, and 1-2%/ year in underwater zone according the coating specification.. 

Cathodic protection is a technique that uses electrochemical methods for corrosion protection. It uses electrical technology to achieve uniformity of potential at various points on the metal surface, thereby reducing corrosion. Cathodic protection can extend the operating life of the facility, reduce maintenance costs.We can achieve Cathodic protection with Sacrificial anodes or with Impressed current systems.

 

Galvanic Anode Cathodic Protection (GACP)

  • In this type of CP, protection is achieved by connecting the protected structure to a sacrificial anode, which is placed close to the protected structure.
  • Sacrificial anodes are made from active metals such as zinc, aluminum, or magnesium for fresh water.
  • CP current is created by the potential difference between sacrificial anodes and the protected structure.
  • The type of anode used depends on electrolyte resistivity and the chemical compositions of the electrolyte to which the substrate is exposed.

Impressed Current Cathodic Protection (ICCP)

  • Wirth ICCP we can protect our structure by connecting to an anode bed through a transformer rectifier (TR). The anode bed is a series of buried anodes that are electrically connected and surrounded by backfill material trying to reduce their resistance to the earth. The anode bed should be placed remotely from the protected structure.
  • The now days two types of anodes commonly used the semi-soluble anodes made of graphite or high silicon cast iron (HSCI), and non-soluble anodes  made of platinum, mixed metal oxide, or polymer material
  • The main component of ICCP is the TR, which forces the current to flow from the anodes to the protected structure.
  • The type of anodes used depends on the chemical composition of the electrolyte, to which the substrate is exposed and the area to be protected.


The table below shows the corrosion rates for different areas.

 

Environment

Corrosion rate in Seawater

Corrosion Rate in Fresh water

Atmospheric zone

100 μm/year

50 μm/year

Splash Zone

300 μm/year

200 μm/year

Immersed zone

100 μm/year

100 μm/year

Embedded zone

50 μm/year

20 μm/year

 

Cathodic protection can reduce the corrosion rate of underwater and embeded zone by 95%. Special precautions are required in the splash zone and the atmospheric zone.

 

In order to achieve better corrosion protection, a combination of cathodic protection and a suitable coating can be used on the surface of the pipe.

 

Design potential parameters .

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Protection current density

The value of the protective current density is related to the type of seabed sediments, oxygen content, salinity and anions.

Recommended initial, mean and final design current densities (A/m2) for seawater exposed bare metal surfaces, as a function of depth and climatic region based on surface water temperature as per DNV RpB401

 

 

Depth (m)

Tropical (> 20 °C)

Sub-tropical (12- 20 °C)

Temperate (7-11 °C)

Arctic (< 7 °C)

 

initial

mean

final

initial

 

mean

final

initial

 

mean

final

initial

 

mean

final

0-30

0.150

0.70

0.100

0.170

0.80

0.110

0.200

0.100

0.130

0.250

0.120

0.170

>30-100

0.120

0.60

0.080

0.140

0.70

0.090

0.170

0.80

0.110

0.200

0.100

0.130

>100-300

0.140

0.70

0.090

0.160

0.80

0.110

0.190

0.90

0.140

0.220

0.110

0.170

>300

0.180

0.90

0.130

0.200

0.100

0.150

0.220

0.110

0.170

0.220

0.110

0.170

 

It is recommended to use a cathodic protection system in combination with the coating and PE jackets for splash zone to protect totally the pipe piles.

 

Here are the data you need for your design:

Tel. +86 21 56099265  Fax: +86 21 56099269  E-mail: sales@syncor-co.com  
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