On 1/23/2011 9:27 AM, RicodJour wrote:
On Jan 23, 7:48 am, wrote:

To the above I would add that the comparison to the boat use of zinc
as a
sacrificial anode is invalid, unless the pipe in question is being
used in
an environment where it's EXPOSED TO AN ELECTROLYTE. The
electrolyte essentially completes a circuit that allows current to
flow. In
the case of boats, that electrolyte is water, or even worse, salt
water.
With the boat, you have sacraficial zinc plates electrically bonded to
the
underwater metal parts, ie shafts, props, struts, etc. The circuit
looks
like two different metals, ie bronze and zinc, sitting in a beaker of
salt
water. Very similar to the experiment kids can do, using a lemon, a
dime, and a penny to make a battery. As the current flow, the zinc
erodes and slowly disappears.

With galvanized pipe installed on a gas line indoors, you don't have
an
electrolyte. If it were buried, then you could have an issue. But
buried
you have an issue with black steel too. I think it's still being
allowed in
some areas. But it's supposed to be coated and or wrapped with tape
to prevent corrosion. A process that is far from perfect. I've
seen
black steel pipe fail underground in as little as five years. It
looked
like swiss cheese, hard to believe. But it was obvious what had
ocurred. You could see where the installers had used black pipe and
then poured the tar like coating over the top of it after it was
installed
in the trench. The bottom portion did not get coated and that is
where the failure ocurrred. I remember at the time, mid 90s, we had
the gas company involved in recommending what to do at a 120
unit condo. At that time even they were undecided which was better
for that application, either black pipe correctly installed or
galvanized.
Today, for corrosion issues, plastic is now widely used underground.

Over the years gas companies have looked at ALL the issues, including
not only what the pipe is carrying, but where it is being used. The
only
potential problem with galvanized that I've ever seen documented in
any way is that which DPB brought up, which is the
concern that certain impurities in the gas could lead to the zinc
flaking
off and ultimately clogging orifices, etc. I don't believe it was
ever
an issue of the pipe failing, leaking, etc. If galvanic corrosion
were a
real issue with gas pipe in an application inside a house, the gas
companies that allow it would be pretty stupid, no? As would the fire
rating, safety, insurance companies, etc.

I can not argue with any of that, even though it does poke large holes
in my argument.
On the plus side - I did get to get in a nice plug for the marine
industry.

We've agreed on the following:
- that the IRC and many other codes allow mixing galvanized and black
iron pipe in distribution lines
- that there is little likelihood of there being any problems by doing
so
- that some local codes and gas utilities prohibit using galvanized
pipe
- that it is mandatory that people contemplating using galvanized pipe
in gas installations check with their gas utility and/or local code to
see if it is permitted.

Now, how do we erase all of the extraneous back-and-forth on the topic
on the Internet so people will have a clear, simple grasp of the
issues?

R

How can something so simple become so complex? :-)

TDD