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Chapman Engineering
August 2007 Newsletter 

Corrosion Protection – How To Rebuild A System

To Our Valued Customers:

Many of you own tank systems, pipelines, or other structures that need protection from corrosion.  And you probably know that Chapman Engineering designs, builds and maintains these systems – most commonly called “cathodic protection” (CP) systems.

Why do you see such wildly different estimates for CP systems, from one contractor to another?  We had a long-time customer who just found out he needed a new anode bed – the part of the CP system that gets sacrificed, really consumed, over time to give protection to the steel tanks or pipeline metal on site.  Well, he got a proposal from our firm, for several thousand dollars – we saw the need to put six new anodes in the ground.  And then he got a proposal from someone else, who said only two anodes would do the job.  And, yes, the price was a lot lower.

Here are some of the factors that each contractor should be evaluating:

• How much electric current is Mother Nature taking away from the underground steel structure?  That’s the nature of corrosion.  The CP system must provide at least as much current, to offset or cancel out what Mother Nature is taking away.  Here’s why:  for every one ampere (or “amp”) of current leaving the underground steel structure, 20 pounds of metal a year are turning into rust;
• How much resistance does the CP system have to overcome to apply that current which cancels out Mother Nature, thereby protecting tanks and pipelines?  The fewer the anodes in a system the higher the resistance; the smaller the wire is that carries current, the higher the resistance; and the sandier the soil is, the higher resistance goes;
• How good are the connections in the CP system?  Bigger-diameter wire, good splices to join wires to anodes, and especially good bonding connections to “touch off” the tank and pipeline metal to the CP circuit – all of these keep circuit resistance low, and put the protective current where we want it;
• Finally, it takes more anodes for the system to have a longer life.  The more current gets run through an anode, the faster that anode is consumed, and the shorter the system’s life.   And, the more anodes put in a CP system, the less  power it takes to operate the system. 

Remember, too, that whenever you get a CP system rebuilt, you need new design documents that show the design is appropriate.  The TCEQ rules require a design done to the NACE International standard, and sealed by either a NACE-registered cathodic protection specialist or a professional engineer.