Dissimilar metals at antenna Mount
 

I have a collinear J pole that I made out of copper pipe. It is
mounted on a galvanized iron coupling at the top of a piece of
galvanized iron pipe. I want keep all parts of the mount at ground
for lightning protection while avoiding corrosion between the two
types of piping. If I use a dielectric union to connect to the
galvanized iron mounting but I still bond both the support pipe and
the antenna base to ground can I avoid the galvanic action that
already caused the two pipe threads to gall.
--
Tom Horne

Dissimilar metals at antenna Mount
 

On Sun, 10 Jan 2010 19:37:33 -0800 (PST), Tom Horne
wrote:

If I use a dielectric union to connect to the
galvanized iron mounting but I still bond both the support pipe and
the antenna base to ground can I avoid the galvanic action that
already caused the two pipe threads to gall.

Hi Tom,

Galvanic action occurs at the interface of two dissimilar metals with
an electrolyte between them. Each metal/electrolyte combination
constitutes a "half cell" with a potential characteristic to that
metal. When combined, they form a total potential which supports
current flow and metal migration. You can build a chain of such
reactions through intermediate steps (a chain of connections); but the
current flow still is a product of the electrolyte between them (the
half cell chemistry) and if you can break the chain, you break the
current and the metal migration.

The chemistry is not complex, and it occurs in nature without too much
difficulty - hence the problem with weather and poor sealing. A
sal****er environment is classically the most brutal. Toss in acid
rain too. The solution is fairly simple, but the success of
implementation, as the devil, is in details. One simple problem is
you may seal the joint or connection from the outside elements, but
you may also be sealing the contaminant in with the joint or
connection. Now you may observe that two solutions are required.
There are a variety of products that can be used to flood the joints
to reduce/prevent both these problems. Others will chime in with
commercial names and their experience.

As there is potential developed, and a current flow, you could in
theory detect a bad coupling. Oddly enough, the two metal combination
could by absolutely dry, free of contaminants, and still give a
voltage indication. This would occur on the basis of a temperature
driven migration of current (the Seebeck effect) and you have what is
called a thermocouple. This, however, is a very small potential in
comparison but could still surprise the investigator. Here, the
effect is not chemical but is a heat characteristic of each metal
(which means the two metals combine to create the perceived voltage
through their individual contributions just as in the galvanic cell).
Given that most metal joints in a circuit occupy the same temperature
environment there is no potential difference developed.

Most technicians consider these potentials as inconsequential (barring
the corrosion), but when it comes time to make accurate measurements
of small potentials, they can become galling to the patience.

One consequence of these interfaces becoming contaminated is that you
can also develop a non-linear conductor or a primitive rectifier. If
this is a path for RF currents (a common mode from your transmitter)
you can generate or receive spurious frequencies. Oh happy day.

73's
Richard Clark, KB7QHC

Dissimilar metals at antenna Mount
 

Richard Clark wrote in
:

On Sun, 10 Jan 2010 19:37:33 -0800 (PST), Tom Horne
wrote:

If I use a dielectric union to connect to the
galvanized iron mounting but I still bond both the support pipe and
the antenna base to ground can I avoid the galvanic action that
already caused the two pipe threads to gall.

Hi Tom,

Galvanic action occurs at the interface of two dissimilar metals with
an electrolyte between them. Each metal/electrolyte combination
constitutes a "half cell" with a potential characteristic to that
metal. When combined, they form a total potential which supports
current flow and metal migration. You can build a chain of such
reactions through intermediate steps (a chain of connections); but the
current flow still is a product of the electrolyte between them (the
half cell chemistry) and if you can break the chain, you break the
current and the metal migration.

The chemistry is not complex, and it occurs in nature without too much
difficulty - hence the problem with weather and poor sealing. A
sal****er environment is classically the most brutal. Toss in acid
rain too. The solution is fairly simple, but the success of
implementation, as the devil, is in details. One simple problem is
you may seal the joint or connection from the outside elements, but
you may also be sealing the contaminant in with the joint or
connection. Now you may observe that two solutions are required.
There are a variety of products that can be used to flood the joints
to reduce/prevent both these problems. Others will chime in with
commercial names and their experience.

As there is potential developed, and a current flow, you could in
theory detect a bad coupling. Oddly enough, the two metal combination
could by absolutely dry, free of contaminants, and still give a
voltage indication. This would occur on the basis of a temperature
driven migration of current (the Seebeck effect) and you have what is
called a thermocouple. This, however, is a very small potential in
comparison but could still surprise the investigator. Here, the
effect is not chemical but is a heat characteristic of each metal
(which means the two metals combine to create the perceived voltage
through their individual contributions just as in the galvanic cell).
Given that most metal joints in a circuit occupy the same temperature
environment there is no potential difference developed.

Most technicians consider these potentials as inconsequential (barring
the corrosion), but when it comes time to make accurate measurements
of small potentials, they can become galling to the patience.

One consequence of these interfaces becoming contaminated is that you
can also develop a non-linear conductor or a primitive rectifier. If
this is a path for RF currents (a common mode from your transmitter)
you can generate or receive spurious frequencies. Oh happy day.

73's
Richard Clark, KB7QHC


Would sacrificial action be appliable? Magnesium blocks are sometimes used to
prevent chemical action taking place on less reactive metals electrically
connected to them. I'm not sure if it can be applied though, that trick is
usually done with grounded (usually buried) blocks to protect pipelines, etc.

Dissimilar metals at antenna Mount
 

On Jan 10, 10:37*pm, Tom Horne wrote:
I have a collinear J pole that I made out of copper pipe. *It is
mounted on a galvanized iron coupling at the top of a piece of
galvanized iron pipe. *I want keep all parts of the mount at ground
for lightning protection while avoiding corrosion between the two
types of piping. *If I use a dielectric union to connect to the
galvanized iron mounting but I still bond both the support pipe and
the antenna base to ground can I avoid the galvanic action that
already caused the two pipe threads to gall.
--
Tom Horne


I transitioned from galvanized to brass to copper by putting a brass
union between the antenna and mast.

Havent had any problems. I also use anti-sieze.

Jimmie

Dissimilar metals at antenna Mount
 

On Mon, 11 Jan 2010 04:16:37 -0600, Lostgallifreyan
wrote:

Would sacrificial action be appliable? Magnesium blocks are sometimes used to
prevent chemical action taking place on less reactive metals electrically
connected to them. I'm not sure if it can be applied though, that trick is
usually done with grounded (usually buried) blocks to protect pipelines, etc.

Well, I doubt if this could be put to use for Tom. Some of the
sacraficial methods actually use a reverse bias to combat not only the
anodic reaction, but currents that occur naturally or flow between
service grounds.

73's
Richard Clark, KB7QHC

Dissimilar metals at antenna Mount
 

Richard Clark wrote in
:

On Mon, 11 Jan 2010 04:16:37 -0600, Lostgallifreyan
wrote:

Would sacrificial action be appliable? Magnesium blocks are sometimes
used to prevent chemical action taking place on less reactive metals
electrically connected to them. I'm not sure if it can be applied
though, that trick is usually done with grounded (usually buried) blocks
to protect pipelines, etc.

Well, I doubt if this could be put to use for Tom. Some of the
sacraficial methods actually use a reverse bias to combat not only the
anodic reaction, but currents that occur naturally or flow between
service grounds.

73's
Richard Clark, KB7QHC


Yeah, I can't see a way to work it either. It would be a great method if it
did.

Dissimilar metals at antenna Mount
 

On Jan 11, 1:04*am, Richard Clark wrote:
On Sun, 10 Jan 2010 19:37:33 -0800 (PST), Tom Horne

wrote:
If I use a dielectric union to connect to the
galvanized iron mounting but I still bond both the support pipe and
the antenna base to ground can I avoid the galvanic action that
already caused the two pipe threads to gall.

Hi Tom,

Galvanic action occurs at the interface of two dissimilar metals with
an electrolyte between them. *Each metal/electrolyte combination
constitutes a "half cell" with a potential characteristic to that
metal. *When combined, they form a total potential which supports
current flow and metal migration. *You can build a chain of such
reactions through intermediate steps (a chain of connections); but the
current flow still is a product of the electrolyte between them (the
half cell chemistry) and if you can break the chain, you break the
current and the metal migration.

The chemistry is not complex, and it occurs in nature without too much
difficulty - hence the problem with weather and poor sealing. *A
sal****er environment is classically the most brutal. *Toss in acid
rain too. *The solution is fairly simple, but the success of
implementation, as the devil, is in details. *One simple problem is
you may seal the joint or connection from the outside elements, but
you may also be sealing the contaminant in with the joint or
connection. *Now you may observe that two solutions are required.
There are a variety of products that can be used to flood the joints
to reduce/prevent both these problems. *Others will chime in with
commercial names and their experience.

As there is potential developed, and a current flow, you could in
theory detect a bad coupling. *Oddly enough, the two metal combination
could by absolutely dry, free of contaminants, and still give a
voltage indication. *This would occur on the basis of a temperature
driven migration of current (the Seebeck effect) and you have what is
called a thermocouple. *This, however, is a very small potential in
comparison but could still surprise the investigator. *Here, the
effect is not chemical but is a heat characteristic of each metal
(which means the two metals combine to create the perceived voltage
through their individual contributions just as in the galvanic cell).
Given that most metal joints in a circuit occupy the same temperature
environment there is no potential difference developed.

Most technicians consider these potentials as inconsequential (barring
the corrosion), but when it comes time to make accurate measurements
of small potentials, they can become galling to the patience.

One consequence of these interfaces becoming contaminated is that you
can also develop a non-linear conductor or a primitive rectifier. *If
this is a path for RF currents (a common mode from your transmitter)
you can generate or receive spurious frequencies. *Oh happy day.

73's
Richard Clark, KB7QHC

Richard

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?
--
Tom Horne, W3TDH

Dissimilar metals at antenna Mount
 

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

Dissimilar metals at antenna Mount
 

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

All I know is I haven't had a problem with corrosion. Apparently the
brass is is similar enough to both copper and the galvanized steel or
maybe the rain here is not so corrosive, maybe its the anti-seize. I
actually cant say with certainty that if I connected the copper
directly to the galvanized pipe I would have had problems. Somewhere I
learned, possibly wrongly, you should join copper to galvanized
plumbing with brass.


Jimmie

Dissimilar metals at antenna Mount
 

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