Butt Welding Mast Extrusions
 

Ahoy All , I had a forespar aluminium mast, that developed corrosion bubbling under the paint.
This occurred about 5 1/2' up from the bottom end of the mast , seen inside the cabin, as the mast is keel stepped .

The corrosion / bubbling paint went right around the mast about 2" wide .

In the sail track I noticed a horizontal indented line , at the middle of the corrosion , but not elsewhere .

Could it be that the mast was extended by butt welding a (+ -) 5 1/2' piece onto it , and sanded smooth then painted over ?

It depends
 

Hi,
It is entirely possible that a piece was added on, and the location is perfect if there is a reinforcing sleeve inside, with generous overlap. There almost certainly is, but it were good to make sure. One way to tell is to take the mast out and have a look. Another is to drill a discreet hole or two, and look there. If you do the latter, you can always plug the hole with a fastener.
Fair leads,
Brion Toss