[TowerTalk] Screw Anchor Question

[ersmar@comcast.net]

Bill:

      In general, yes, a passive, sacrificial anode material can be used to protect against electrolytic corrosion.  But you have to know a lot more about the material to be protected and its environment than we have so far discussed here on TT.

     You can also use an active system in which a sacrificial anode is connected to the material to be protected but through a DC supply, usually in the vicinity of 100 Volts and adjustable.  This minute DC current (typically a couple hundred mAs) offsets the natural Galvanic current generated by the reaction of the metal in the wet electrolyte of the ground.  The anodic material and the set point for the DC rectifier feeding the whole shebang is determined a priori through measurements of the potential difference between the protected elements (ground rod, anchor screw, etc) and remote earth ground.  

     I designed a few of these cathodic protection systems for the electric utility I worked for some years ago.  Most of our Korean-War era substations had been built with buried ground systems made of scrap boiler steel pipes - copper was in short supply, needed for jacketing for ammunition at the time.  It was only at these 1950's substations where we had to install active cathodic protection systems.  Never had occasion to design another one since, though.

     If you have an underground pipeline (gas or oil) running through your region, you might want to check with their local engineer.  He/she might be able to give you some pointers about cathodic protection in your area, and maybe, for some coffee and doughnuts, give you a brief tutorial.

73 de
Gene Smar  AD3F


 -------------- Original message ----------------------
From: Bill Coleman <aa4lr at arrl.net>
> 
> On Jan 16, 2006, at 2:16 PM, k0dan wrote:
> 
> > The tower NEVER moved or
> > wobbled; retensioning of guywires never was necessary due to anchors
> > "floating", occasional retensioning only due to stretch of the wires
> > themselves It was a great installation. But, once that slow, hidden  
> > galvanic
> > action went past a critical point, BOOM!
> 
> Can't one use a sacrificial anode to avoid exactly this sort of  
> galvanic action?
> 
> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
> Quote: "Not within a thousand years will man ever fly!"
>              -- Wilbur Wright, 1901
> 
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