How much of this corroded pipe do I need to replace

[JamieRI]

I will replace as much as I should, but would rather not do needless work.

Is this a problem with a single bad solder joint at the right side of the elbow at the top? What needs to be replaced?

(I am DIY but have probably soldered 300 copper joints without any obvious issues)

 

[Diehard]

Yes it would appear that the problem is that leaky elbow.
I suggest cleaning the rest of the pipe.

"The green stuff is cupric chloride, a byproduct of corrosion of the fitting or possible copper leachate in the water. Either way, it's typical of water leakage where the water is of low pH. The white stuff (sometimes feels fibrous like cotton candy) is just efflorescence "

 

[JamieRI]

Thank you Diehard, Well-Known Member

The cupric chloride corrosion certainly looked like it was growing for some time.

I made a slurry of baking soda and vinegar as suggested by some web site, it came out OK. I am hoping to buy new cabinets this year, and if it is dry in the morning,

If it is dry in the morning, I am assuming the worst eventual issue is more of the same, not a substantial leak. The metal must be thin at some point, yet my 40 psi water pressure is pretty kind to older plumbing. Is that logical?

 

[CT18]

40 psi is on the lower side. The joint looks ok, it must of had a blob of flux left on it and thats what happen. Back in the day La Co flux was notorious for turning green like that if not cleaned after.

 

[frodo]

You have a seeper leak
to verify. wrap the pipe with toilet paper

if there's a leak you will see the wetness on the paper

that joint needs to be taken apart. cleaned, with a brush on the inside and outside
te pipe also needs to be cleaned both to a shine

reassembled

flux left on a pipe does not run down the pipe, that is water,not flux

 

[JamieRI]

Thank you all! The joint was dry to the touch this morning. I will put the toilet paper on and check tonight.

I realize I put in this elbow about 26 years ago when I changed out the sink, so I take back "without any obvious issues" in my first post!

 

[Riickk]

S-L-O-W leak. If you're sure you are doing the kitchen over this year, I'm guessing you could leave it like that, complete with tiny leak. Me, I'm too OCD, and it would bug me until I fixed it.
Looks fairly easy to remove the elbow and replace it, since you have a piece of flex at the far end.