That's interesting. How could I tell? Maybe try to smash one with a
sledgehammer? I vaguely recall that I could try to grind one on a
grinder and look at sparks.
I did weld a black pipe nipple into a hole in a steel plate (think
bulkhead fitting) yesterday.
Nipples are usually steel, weld fine. 'T' and 'L's, are cast. Since most
of the big box store pipe fittings are imported, you have NO idea what
material they might be, nor what country they might come from.
One other option that you might discover is that they are leaded steels.
You'll often find that in threaded rod.
The manufacturer of these materials takes advantage of the machinability of
the free machining steels to the detriment of people who want to weld them.
So, I'd be wary of any threaded commercial product.
As others here (and your lawyer) say, 'it depends'.
You do need to identify what materials you are working with. You do not say
what air pressure you are designing for and also do not identify the type or
quality of T fitting.
If you are talking about common hardware store threaded T fittings then they
are probably a poor or dubious quality cast. With experience you can
identify different types of cast using a grinder and a spark test but the
easiest way is to test cut a fitting with a torch, if the fitting is cast it
will not CUT (burn) nicely but will just melt.
If you are talking about threaded fittings then the real question is - Why
do you want to weld them? Of course while hardware store threaded fittings
will (probably/maybe?) work you should be aware that they are designed for
water pressure and NOT for air pressure containment. Fittings designed for
air (and energy) containment will be stronger and better quality material
than water fittings. These pressure fittings are available from industrial
plumbing suppliers and are probably no more expensive than the consumer
hardware junk. These better quality fittings are available as threaded or
socket or beveled, for welding (with a socket or butt weld). Socket
fittings are easier to fit up and (fillet) weld. In this small size you
will need to be very skilled to do a pressure quality butt weld with SMAW,
TIG or OA is easier but still requires proper technique and skill level (and
rod). A proper butt weld root pass cannot be learned on Usenet.
Another option, (depending on the type of manifold you need) is to use a
larger (and thicker) steel pipe to make a header and to fit and weld the
smaller pipes onto it. You could also weld on 'threadelettes' which are
weld on fittings designed for this and also available from any good
industrial plumbing supplier.
An industrial plumbing supplier can show you the different types of fittings
and provide much guidance and advice.
The bottom line is that pressure (energy) containment is potentially very
dangerous and you need guidance that is more dependable than Usenet.
Make sure they are STEEL fittings and not cast iron.
Use 309L Stainless Steel filler to offset the poor quality steel.
Around 120 amps should be fine for the 1/8" wall thickness.
Clean the weld areas with sand paper or a flap wheel.
Welding Instructor - South Seattle Comm. Coll.
- Divers Institute of Technology
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