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Cathodic protection for plant ping with deep well anode system

Cathodic protection for plant ping with deep well anode system

Cathodic protection for plant ping with deep well anode system

(OP)
Dear All i have a question about the protection about an underground plant piping system.

I have to protect 18 Km of plant piping in a congested area where there is the presence of great aboveground structures like cooling towers and process equipments with concrete foundations.

The minimum pipe diameter is about 4 inch and the maximum diameter is 76 inches running in the center of the plant.

Along plant boudaries i have the presence of an underground 10 Inch pipe used for fire water system while in the center i have 76" UG pipes for water supply and return running in parallel.

My idea is to use a Deep well system to protect the entire plant.
Plant is located near the sea so i expect a low resistivity soil and deepwells are located inside the plant and on plant boundaries in order to create a uniform current distribution on the entire plant. I'm considering a spare on current of about 50% due to dreinage due to UG structures not protected, a spare for UG electrical grounding (made in galvanised steel) of about 20 mA per square meter and a coating breakdown factor of about 1.5% per year with an initial damage of 5% (coating is made by epoxy sysstem of about 1.5 mm in thk).
deepwells should be placed at 40m of depth with an active section of about 19 m the total number is about 44 with a soil resistivity supposed to be 20 ohm *m with an anode voltage not greater than 18V.
My question are:

1- this system is ok or have I expect some problems to be considered in the design phase? This system permits me to avoid a large ammount of shallow anodes sited along the pipes and a large ammount of cables to be positioned in a congested area with a great difficulty in finding spaces. My total calculated ammount of current is about 390 Amps at the end of life.

2- I want to use a von baekman equation to verify the mutual interference between anodes could anyone suggest me equations to use and a way to place anodes in the plant in order to guarantee a correct distribution?

3- i have used the Von baeckma formulas indicated by nace but the problem is if i increase current or resistivity increase also the radius of protection by one anode with difficulty to place 44 anodes in a space of about 800 * 500 meters? Is there a solution in spacing the anodes

4- Is there the possibility of a shielding effect caused by concrete foundations that could create problems to pipes protection?

Many thanks
vincenzo


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