J wrote:

I have a corroded soft copper tube (Type M?) hot water line that is
laying on the ground in a short crawl space under the kitchen floor.
I think the line corroded because it contacted the soil rather than
being hung from the joists. I want to repair the line. I cut a hole
in the kitchen floor to expose the work area. The defect is corrosion
pinholing.

The first fix I tried was to cut out a generous amount around the
defect and then splice in new Type L with 2 compression fittings on
either end. That did not work - probably because the soft copper
tubing had reduced OD and wasn't "snuggable" in the compression
fitting.

Next, I tried sweating in some couplers to a new splice. That did not
work; I had small partial failures at the joints. I had cleaned
(sandpaper) especially well (but obviously not well enough). I also
fluxed/pre-wetted the old ends by heating and flowing and then wiping
away the solder so as to keep it fairly thin. The old ends, when
sweating, just didn't flow like new. The joints to the new piece was
just fine.

Is there a particular technique to super clean old work? Is there a
different repair technique altogether?

Replacing the whole line is cost prohibitive - mostly because of
collateral damage to open up walls. I would likely go "above" (attic)
to run the new lines.

Can anyone help with a repair technique?

Thanks.
John

It will just leak again in another spot even if you get a good
connection to the replacement piece. Consider full replacement with PEX
tubing since the flexibility of the PEX should let you fish it through
walls with a minimum of openings.

Pete C.