Possible failing or staining on copper pipe

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Matt Garrettt

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Hello All, was fixing a pinhole leak in my 2" copper drain pipe (from kitchen) and noticed discoloration along the underside of the pipe; most of pipe is dark/blackish, but there is a shinny (like new copper) 'vein' running along the length. Pictures are attached.
Don't know if this is failure/deterioration of pipe from use over time; water that hasn't fully drained sitting in there, drying, eating away. Is this a common thing? I live in South Florida, so I don't know how caustic the water is.
My other thought is that water has been leaking from pinhole, running down the length of pipe (the discoloration is down the grade of the drain, does not occur in the other direction), and causing the discoloration on the outside/exterior of the pipe.
New home owner, so I don't know the age of the pipe, but with the house built in 1950's, could be as old as that. However, the pipe itself looks to be in fine shape; no green oxidation anywhere, no other serious discoloration.
Is it common to have this shinny, 'like-new' discoloration on the bottom of copper pipes? The location of the pipe in question is running inside concrete block in the interior of the house. The only access I have is through the small hole where the drain bends out of the wall to the sink basin connection (no crawlspace). Would certainly like to avoid tearing out a whole wall/cabinets to replace only to find it was cosmetic staining on the outside.
Any advice is very much appreciated! Thank you all!
-Concerned 1st time plumber
 

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It's fine, my thinking is, that's where the pipe has the most contact with the water. That's why it isn't stained like the rest of the pipe.
 
a pin hole?
that's not good.
I would take a screwdriver and scrape the bottom of the pipe
if it breaks through ...you have your answer. replace the pipe
if it does not penetrate. pop a top on a ice cold beverage

my opinion
if one pin hole, their are more
 
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Yup, what Frodo said. Copper kitchen drain arms are going to corrode through eventually, what with all of the detergent and such that gets drained through kitchens. I probably replace one or two a year.
 
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a pin hole?
that's not good.
I would take a screwdriver and scrape the bottom of the pipe
if it breaks through ...you have your answer. replace the pipe
if it does not penetrate. pop a top on a ice cold beverage

my opinion
if one pin hole, their are more

I conferred with some contractor friends and they seemed to think the discoloration surrounding the rest of the pipe (black, darkish) is external corrosion, likely from all the humidity in the area (there was standing water in the concrete block below), and that the shinny vein seen on the underneath is where the water was collecting as condensation. Since this area remained wet, it corroded less.
I scrapped a screw driver along the bottom, and it seemed very sturdy/solid, and (from advise of the contractors) used a piece of sand paper on the top and it shinned right up, lending me to believe that all the coloration, either black or shinny, is external.
Does this sound logical/plausible?
 
Whats all that black stuff all over the block around that drain line

Unfortunately, that is mold which is another issue all together. With the dripping pipe, water collecting in the concrete block below, and the FL humidity, the enclosed area was/has been extremely humid/moist.
 

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