water pipe vs DOM

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.
--jsw

"The most common, and lowest grade of pipe is ASTM grade A120, welded or 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:
--jsw

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.

I just filed and Scotch-Brited an old work-holding fixture turned from black pipe. It's smooth and shiny but on the low end of the samples I'd show an interviewer to prove I can run a lathe. --jsw

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.

Oh. Like Chinese "M60 equivalent" high-speed steel. d8-)

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.





|1002|1016|1047|1049

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 practice.
Wasn't there a problem with chrome-moly frames so strong and stiff they overstressed and killed the driver instead of progressively absorbing energy?
--jsw

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 condition.
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 websites.
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.

Old piper cubs were mild steel, so was the original Lotus 7. Our Pegazair is 4130.

Thanks for all the discussion, everybody.
This sounds like the typical penny wise, pound foolish problem.
I'll by the DOM and not worry about material problems.
thanks Karl

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 joint.
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:
--jsw

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. Eric

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 debunked.
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 what doesn't.
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.