On 13/09/2019 13:15, AJH wrote:
I need to solder a patch onto a rusty diesel tank, previously I used
60/40 tin lead solder but this is not readily available locally will a
lead free plumber's solder still wet fluxed steel?

AJH

It should, at least in theory.

At the risk of teaching you to suck eggs, you've got a couple of things
stacked against you. Soldering a corroded (rusty) surface, one that is
oily, and a vessel/tank.

Give the area a good clean with some degreaser, then some emery cloth or
similar, degrease again. Make sure the tank is open- you don't want the
heat used to solder to cause the air inside to expand an try and escape
via your joint/patch.

Tin the area, and the patch, flux both, place the patch in position and
heat. You may need a bit more solder but, hopefully, the patch will
'pull' into position (or nudge it) as the solder melts. Don't disturb
until it is cool, lead free is a s*d for 'dry joints' if moved while
cooling.

I'd be tempted, if the hole is small, to try and pull a bolt through
with a cotton thread. Place a nut on the outside, tighten, hold the bolt
thread with pliers, then solder over it. Clean the area first, as
before. I saw this done once, the chap used a wire through the hole to
tie the cotton to via the filler hole.