On Jan 12, 2:35*am, Richard Clark wrote:
On Mon, 11 Jan 2010 21:17:13 -0800 (PST), Tom Horne

wrote:
If I use a dielectric union for the joint and bond around it for
lightning safety will that solve the corrosion problem by preventing
direct contact between the two dissimilar metals or would the bonding
cause the same destructive current flow as the direct contact?

Hi Tom,

I don't know what you mean by bond that is both insulative to cathodic
action, and conductive to lightning. *To me, bonded metals don't
introduce a complaint of anticipated galling. *If they are bonded
(soldered, brazed, or welded), you don't expect to disconnect them and
suffer galling problems. *If they are soldered, brazed, or welded,
then the seam can still support cathodic action - it is simply a cell
loaded with the short of the bond if I read it that way.

I don't often find myself in your situation, so I have little to go on
beyond the common discussion. *I have had to deal with these issues
with fine measurement where it is always lingering and it often took
heroic effort (careful, this is hyperbole unless you have to make a
living at it) to succeed.

Jimmie may have something more to offer.

73's
Richard Clark, KB7QHC

Jimmie & Richard
Sorry for not being more clear. I was asking if the use of a
dielectric union to join the two pipes would prevent the corrosion of
the threads of the union now used instead of a galvanized coupling
even if I still had lightning down conductors connected to the bottom
of both pieces of pipe. In other words the two pieces of pipe would
still be joined mechanically by a dielectric union and electrically by
the lightning down conductor. What would be different is that the
electrical connection would no longer be occurring at a point of
contact between dissimilar metals which would be separated from each
other by the non conductive washer of the dielectric union.
--
Tom Horne, W3TDH