What I'm Seeing Now

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Galvanic Corrosion

This might seem technical, but this is a post about galvanic corrosion.

Let's simplify it.

When certain (dissimilar) metals touch one can cause the other to corrode.  This process is called, variously, galvanic corrosion, dissimilar metal corrosion, and electrolytic corrosion.

Essentially, electrical current can pass between two dissimilar metals.

Some metals are more "noble," meaning they are more electro positive and therefore protected, also called cathodic.  These metals include copper, bronze and brass.

Other metals are less "noble," meaning they are more "anodic" toward those further up the galvanic scale.  Anodic means they are more capable of corrosion because when joined to those more noble metals they are electro negative.  Electrical current passes more easily from them.  Their metal is corroded and carried toward the more noble.  These less-noble metals include zinc, galvanized steel, aluminum, steel and iron.

When more and less noble metals, or "dissimilar metals," touch, the generated electrical current passes from the less noble (anodic) to the more noble metal (cathodic).  The anodic metal corrodes and deposits itself onto the cathodic metal.   This corrosion process is more likely in the presence of salt water or acidic solutions, but even moisture in the form of condensation can cause corrosion, though it is less likely.

However, it is always a best practice to keep dissimilar metals from touching.

Yes, home inspectors look for this stuff!  The most frequent place we usually see dissimilar metal corrosion is at water heater connections.  Leaking is often the result.

Recently, in brand-new construction, and a final walk through inspection, seeing this over a basement AC unit, I thought I should mention it.

You might think it pedantic of me to do so (pedantic means overly fussy or finicky), but I did anyway.  Look at the photo on the right.  That is copper touching steel.  There is the potential for condensation from the AC line.  Could it be acidic?  I don't know!  But it is easy to separate the metals now.  No touch, no problem.

Many years ago I installed a whole-house water filter in my house.  Yes, we are on public water, and it's amazing how cruddy the filter gets in two months!  See the sand at the bottom now?  That filter is one month old.

But I digress.  The left photo shows what I used to better attach that plumbing, and additional weight, to the floor joist above. 

The plumbing is copper.  The hanger is copper.  Similar metals!

And yes, you can see my bonding cable connecting the pipes left to right.

My recommendation:  when in doubt, it is always best to keep metals separated.  Even the slightest possibility over time may cause a problem.  So, why not eliminate that possibility now?  Yep, the picky, picky, pedantic home inspector.  That's me...

 

 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


Comment balloon 14 commentsJay Markanich • July 30 2015 12:35AM

Comments

 Good Thursday morning Jay. I often see plumbers using copper fittings on galvanized nipples. That is a huge no-no.

Posted by TeamCHI - Complete Home Inspections, Inc., Home Inspectons - Nashville, TN area - 615.661.029 (Complete Home Inspections, Inc.) about 5 years ago

Jay Markanich seems like a simple inexpensive solution to me . It may save time and money in the future

Posted by Hannah Williams, Expertise NE Philadelphia & Bucks 215-953-8818 (Re/Max Eastern inc.) about 5 years ago

Because no thinko, Michael, or no understando.  That's perfect Spanish.

Hannah - it is at this point!  Those touching metals might never be a problem, but why let them touch?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

I bet you come across this often.  I bet most people snoozed during this chemistry lesson and/or forgot it.

Posted by Debbie Gartner, The Flooring Girl & Blog Stylist -Dynamo Marketers (The Flooring Girl) about 5 years ago

Trade schools, or REAL tradesmen, teach this stuff, or should, Debbie.  But all might not listen.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

Jay, you are the perfect spokesman for "getting a home inspection"! Keep the advice coming. Enjoy your day!

Posted by Wayne Martin, Real Estate Broker - Retired (Wayne M Martin) about 5 years ago

Good morning Jay.  Apparently the installer was taking a nap during class on this one.

Posted by James Dray, Exceptional Agents, Outstanding Results (Fathom Realty) about 5 years ago

Thank you Wayne.  And I will.

James - if there ever was a class.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

Good morning Jay,

Might also help it the local inspector's also knew what they were looking at!

Make yourself a great day.

Posted by Raymond E. Camp, Licensed Real Estate Salesperson Greater Rochester (Howard Hanna Real Estate Services) about 5 years ago

I wonder what percentage of sub contractors learn their trade at trade schools...

I learned alot about sacrificial annodes in my former life at a petroleum company. We used them to protect our piping and storage tanks from corrosion. Good stuff!!

Posted by Fred Hernden, CMI, Albuquerque area Master Inspector (Superior Home Inspections - Greater Albuquerque Area) about 5 years ago

Fascinating.  Absolutely fascinating.

I wonder if a new home warranty would cover this.

Posted by Lenn Harley, Real Estate Broker - Virginia & Maryland (Lenn Harley, Homefinders.com, MD & VA Homes and Real Estate) about 5 years ago

This was in the basement Raymond.  I have never seen those guys go anywhere but the kitchen.

Trade schools Fred?  They still out there?  There is a trade high school in this area and I bet they teach it there.

Lenn - I see serious corrosion all the time due to dissimilar metal contact.  It's pervasive.  This one may have been caught in advance, but condensation is not a likely cause, just a possible one.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

Thanks for the lesson.  This explains the corrosion of my galvanized watering wand attaching to my brass hose connector. 

Posted by Stephen Weakley (Nationwide Mortgage Services) about 5 years ago

Run for the hills before you're electrocuted Stephen!

Oh, wait, it's not that kind of current...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 5 years ago

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