I agree with David about quality seamed tubing. I designed a drive shaft on the ammunition container of the F-15E fighter aircraft as a 4130 straight gage tube with a silver brazed lugged joint at each end (where did that clever idea come from). The mil-spec tubing was available in either seamed or seamless and there was absolutely no difference in any property or tolerence. I specified either could be used. It is important to recognize that the seamed tube is heat treated after welding to yield more uniform properties at the joint.
Joe
At 11:40 AM 10/17/00 -0700, dave bohm wrote:
>
>Oh, this is good into different tubing types:
>
>
>> Nice essay, Dave, and very helpful. My concern on the thinwall tubing
>> starts at the factory -- and may end there. True seamless tubing is made
>> by forcing a ram through a billet, and then rolling things out. I've
>never
>> seen (or looked for) a study on tolerances in wall thickness. With the
>> successive rolling exercises, it would be easy for a 0.4 nominal wall to
>be
>> a 0.3 on one side and a 0.4 on the other. Unless the factory has x-rayed
>> (or ??? as equivalent), I'm uncomfortable with a really thin wall. The
>> reason I'm uncomfortable is that thinner tubing walls are more likely to
>> fail by buckling, not just dimpling. So, I'd love to try something else,
>> but for now I stick with good old 531, 4130 in all its permutations, and
>> 6061-T6 (aluminum).
>>
>> harvey sachs
>> mclean va
>
>You are absolutely right Harvey. Tubing wall thickness does vary quite a
>bit. In addition many tubes are not very round either. I use a micrometer
>on all my tubing and, at time rejected certain tubes I thought were too far
>out of tolerance.
>
>I am leading to the debate of Seamed tubing VS. Seamless. We have all be
>lead to believe that seamless tubing is the cats meow and that seamed tubing
>is only good for making mail box poles. In reality this is not true. Both
>types of tubing have advantages and disadvantages. Welded tubing is
>metallurgically superior in many respects to the seamless tube material.
>Primarily in the area of prior work (hot work, and cold work). Early on in
>the production of the strip the billets are
>cross-rolled to distribute nonmetallic discontinuities and essentially erase
>the effect of these discontinuities. Discontinuities of this nature can be
>preserved through the processing of seamless tubing since it is worked in
>only one direction.
>
>As the industry has moved to oversize tubing with thinner walls, seamed
>tubing can actually be technically superior. The reason is that as the
>seamless billet progresses from short billet to long thin tube, the mandrels
>inside the tube can get pushed off center a few thousandths in the course of
>manufacture. If a mandrel gets off center, there is no reason or mechanism
>to put it back to concentricity. When you get down to .4 or .5 mm walls, .05
>mm (.002") of eccentricity creates a difference in wall thickness of .1 mm.
>In a seamed tube, the wall is drawn down from only about 1 mm to the final
>.4 or .5 mm, which is done cold, so there is no opportunity for eccentricity
>to develop.
>
>Well, there is my rant on seamed (welded) tubing. I have been using quite a
>bit of True Temper recently and find it to be very accurate and a joy to
>build with. Over and out.
>
>David Bohm
>Bohemian Bicycles