I've got a project where i need over a hundred feet of 1.38 ID by
1.625 OD DOM tubing.
Turns out this is almost exactly the same size as 1 1/4 water pipe,
MUCH less expenisve.
Need to do a lot of machining and some bending of a small tab. Will
water pipe work as well?
If it matters, recently purchased water pipe may not be particularly
round, especially at the weld. I have to adjust its position in a
3-jaw chuck to get it close to centered.
I made some half round stone splitting shims from it, involving a lot
of cold bending before and after welding, and it didn't crack. It
seems quite soft as steel goes, but doesn't tear when turning it. My
untested SWAG of its yield strength would be at the 25 KSI low end for
steel. It's easy to weld.
"The most common, and lowest grade of pipe is ASTM grade A120, welded
seamless pipe, back or galvanized. It's material composition *is not
controlled at all* !!!!"
I don't trust my amateur engineering calculations or welds and
proof-test the final assembly, currently with this:
My experience with it is that it's pretty gummy to turn, but that's
because it's usually made of something like AISI 1010. DOM typically
is 1020 or 1030.
When I say "like" 1010, I'm talking only about carbon content. As far
as I know, it's not graded material, or it's a special spec just for
water pipe. It is very low in carbon, however.
It's "nonspecific remelt" sourced from common "shred" - which
contains old washers and driers and refrigerators as well as 45 gallon
drums and other low-grade scrap.
If DOM is specified it likely has some strength requirements., or
possibly some dimensional requirements that water/gas pipe would never
come close to meeting.
I'd seen the term "DOM" mentioned a few times recently, and finally
decided to find out what it was. Here are some of the sites I visited
in my research which might be of interest to you, Karl.
Pipe seems to be made from a mutt steel; whatever they find. If I
were making a simple bench or something for intermittent use or of a
light-duty nature, I'd use pipe, the cheapest.
If I wanted a chassis for a vehicle of some sort, I'd definitely want
to go with DOM. It has a much higher safety factor. 1020 seems to be
the standard the 4-wheelers use.
I'd also avoid 4130. Chromoly is nice, but is way too expensive and
too finicky for proper welds.
Not really. It's easy to weld with O/A or TIG. You just have to know
how it behaves, and if you won't learn that, I wouldn't want to ride
in anything you welded, anyway.
1020 is (or was) used on NASCAR racers, for two reasons: The weight
restrictions allow(ed) you to use tubing so heavy that you're at the
limit of practical strength anyway, even with 1020; and if (scratch
that -- "when") you crash it, you can cut out old tubes and replace
them without worrying about it.
I didn't have any trouble welding 4130 aircraft tubing tees for
Wasn't there a problem with chrome-moly frames so strong and stiff
they overstressed and killed the driver instead of progressively
No, it's just somebody's old tale. I've heard it before, too.
First, the stiffness of 4130 and 1020 are almost exactly the same (as
is true of all steels, except for the slightly less-stiff stainless).
Second, there isn't *that* much difference in strength. (yield is
around 65 ksi for normalized 4130; 54 ksi for DOM 1020). The
ductility, elongation and ultimate tensile strength are better for
4130 than for 1020 in the hard-drawn condition. 4130 tubing is almost
always used in the normalized condition; 1020 in the hard-drawn
So you get some more strength and a lot more ductility with 4130. Your
welds can be somewhat stronger because hard-drawn 1020 loses a lot of
its strength from heating at the weld. 4130 is very slow-quenching --
on the verge of air-hardening, and, in thin sections (like the
light-gauge tubing used on aircraft and smaller race cars), it *is*
air-hardening. Strength *at the weld* is pretty good.
It can get tricky with thicker sections. There is a lot of voodoo
surrounding 4130, but the major welding equipment suppliers can clear
that up for you if you ask. They also have info about it on their
BTW, the Brits, including Lotus, Cooper, Vanwall, etc., used 1020 or
its equivalent for race cars through the '60s, and they performed as
well as 4130 cars. They bronze-brazed their chassis joints, for the
most part. Chassis stiffness is the issue, unless you care about the
safety of your drivers, which some didn't. 1020 is just as stiff.
Strange. I remember certifying on 4130 tubing "way back when". They
used to use it to build aircraft and for many other things.
It was also used to build frames for racing cars and motorcycles where
light weights were important.
If I remember correctly Norton built some of their racing frames using
"bronze-welding" and claimed that the brazed joints were an advantage
as they were less stiff then welded joints and didn't break as often
Oh, yeah, that was another source of voodoo. Many or most of the
one-off and low-volume Brit race cars were, supposedly, bronze
"welded" during the '50s and into the '60s. Bronze "welding" in that
parlance was brazing with a weld-like buildup of filler metal at the
The old authorities said there was no meaningful difference in
strength between that method and fusion welding. I think it was
treated in the classic chassis book:
A flexible end connection is called "pinned", and if done right it
allows the connected members to behave as centrally loaded columns
with no imposed bending to weaken them in compression.
The Tay Bridge collapse is a notorious example of a pinned-joint
structure whose failure was analyzed in detail. You don't hear about
the bridges that survived.
Figure 29 shows an intact and a failed pinned joint between the
columns and the diagonal braces. Subsequently the recently introduced
affordable steel quickly replaced wrought and cast iron for bridges.
The design should have been strong enough, but the casting of the
columns was seriously deficient and the supervising engineer was a
mason more interested in the troublesome footings.
The I-35 bridge in Minneapolis failed at a rigid truss joint:
That's a great book and every time I read it I get all enthusiastic
about building my own single seater car. I was surprised to learn from
some local race car builders that the book is still used a lot by
builders. The issue of 4130 as opposed to mild steel is covered in the
book and from the the book's point of view the chrome-moly steels
should only be used where the extra strength is needed, for example in
some suspension components, and not in the frames because there is not
enough advantage in rigidity and crashworthiness and a big
disadvantage when it comes to joining with heat.
A good friend of mine has built and rebuilt a LOT of Lotus 7 chassis,
and a LOT of motorcycle frames. "fillet brazing:" is the "british" way
of joining steel tubing. The flux is applied with the gas by bubbling
(im not sure if it's the O2 or the Acetelene) through a bottle of flux
so no flux paste or flux coating on the rod is required. It's a
different brazing alloy than used for normal "flow" frazing.
Me too. And I got my copy in 1965.
Costin and Phipps wrote a great book, but take anything they say about
welding or 4130 with a fat grain of salt. In fact, take anything said
about it by anyone in 1962 with a grain of salt.
For some reason, the Brits were slow to accept fusion welding -- O/A
or TIG -- for tube frames. They were slow to accept TIG, in fact. And
they were slow to adopt 4130.
They may have had some good reasons, but my feeling, having studied a
great deal about it over the past 50 years, is that they were a bit
caught up in popular misconceptions. There are some such
misconceptions floating around in the US, too, such as a need to
pre-heat even thin tubing before TIG-welding it, and the supposed
"grain opening" of 4130 if you braze it. These stories have been
Note that Brit homebuilt-aircraft builders aren't allowed to weld
their own tube frames unless they're CAA certified welders. In the US,
our EAA runs classes in welding 4130 with O/A and with TIG, and
hundreds of aircraft have been built that way. I think we have a more
extensive experience base with both the materials and the processes.
But I don't really know. I hope to get out to Jay Leno's garage again
next year, and I'd like to ask Bernard, the garage manager, about it.
He ought to know the whole story on the Brits. Also, the motorsports
instructors at Lincoln and Miller should know very well what works and
BTW, we have an article coming up on when and where you can use
lift-start TIG, later this year in Fab Shop. I think it will contain
some discussion about 4130.