Possible Stainless Tube?

[Andrew R Stewart]

So I admit to having little experience with stainless steel tubes but... I think I have one I didn't know about.

A few years ago I bought a NOS Columbus genius tube set from a fellow infrequent builder. This week I finally got around to starting a frame with this set and the seat tube/shell is the first joint I do, as this will be a fillet frame I only tacked then flowed the miter/shell for this step. The final fillet would be laid down when the rest of the main frame was being done.

I had all kinds of problems starting with the tacks not wanting to wet out onto the tube, the shell took the C04 filler as usual. Being that this frame is for me I decided to press on and after confirming the alignment went on to trying to flow filler all the way around the miter. The same problems of the tube not taking the filler again happened. I "finished" this brazing step and again confirmed alignment after soaking off the flux. It was now that I noted the tube's different then usual color where the flux was dissolved off, kind of a motley/dull grey with no evidence of browns (which I expect with a cromo tube after an hour in the soak tank). I tested the tube and shell with a magnet and the tube is far less attracted then the shell (or known cromo tube) is. I would try a spark test but I've never been very good at that before.

I believe I have a stainless tube that was "miss marked" as a cromo one (as in a Genius one). Is my new belief off base? I've attached a couple of photos. Note the filler's boarder with the tube's surface. Some is wetted (where I tacked) and most have the filler not flowing out and onto the tube. Also note some filler boil off on the shell, This is because I was having trouble getting the brazing to work and I was pushing the time and temp.

I have no problem with this situation. I'll set the tube/shell aside and later cut them apart and mark the tube for the future. This frame will just get another seat tube and shell. It is interesting what you learn when things go other then intended:) Andy.
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[Andrew R Stewart]

IMG_1711.JPGSo I sort of answered my own question by deciding to scrap the ss tube and shell. The tube has been cut off the shell and both will become practice stock for the future. Here's a shot of the inside of the tube/shell joint. It's hard to see but the filler hasn't gone very far up the tube walls. The build up on the shell floor suggests how much filler i had fed in trying to insure a good internal fillet.

Before I cut off the tube i clamped the shell in a vice and worked the tube back and forth to see how well the brazing actually was. I really went to town in my efforts but no signs of failure, still i just didn't trust it. Andy

[Mark Kelly]

A good way to check for stainless is to apply a sulphuric / oxalic etchant* to the surface for the recommended period. The chromium content of stainless will cause it to form a black "smut" on the surface, ordinary steel will be a soft grey.


* This is the etchant recommended by Hunstman for surface prep prior to epoxy bonding; 30% sulphuric, 10% oxalic, 60 oC for 5-10minutes. The smut can be removed with chromic acid.

[Michael Gordon]

Have you checked it with a magnet?

While some stainless alloys are not magnetic, some are. Those which are, still often have less pull against magnet vs. regular steel.

[Andrew R Stewart]

Have you checked it with a magnet?

While some stainless alloys are not magnetic, some are. Those which are, still often have less pull against magnet vs. regular steel.

Yes, as posted. What I didn't mention is that the strength of the magnetism seems to be, maybe, half of a cromo tube. Where the magnet will easily lift a cromo tube off the bench top the tube in question will barely lift a tad before falling off the magnet. I have other known SS bits and none of them are as magnetic as this tube is.

I know that some SS alloys are somewhat magnetic and others are much less so/not at all. I wonder if this tube (28.6, single butted, about .7x.4, smooth and bright silver) being somewhat magnetic suggests which brand or version it might be. Andy.

[Scheisserad61]

Hi Andy,

For a short spell Columbus had a full set of stainless tubes around the time of the Genius set. Columbus called it Metax. I built two lugged OS tube frames with it around 1997-98.
They had it specced as .7-.4 for the main tubes, but all of the tubes except the fork blades were quite a bit heavier than claimed. Neither of the frames rode very well - they were overbuilt and somewhat "dead" feeling.
(Looking back, I believe those frames were the first of my many "this will be the last bike I will ever need" projects. Ha !)

Maybe thats what you've got there ? Perhaps it was a Friday afternoon packing job for that box at the Columbus factory ?

[Andrew R Stewart]

While I have moved on to a CroMo tube for this frame (although not quite as thin walled as I was hoping for, it is a roller/trainer stand bike so who really cares) I found that the head tube was also of the same material as the seat tube was. Same magnetic behavior, same finish/look in and outside. I found out the guy who I bought this set from had gotten it in a batch of tubes from another guy closing out his shop. So the miss packing could have happened at one of three points before I got my hands on the set. Andy.

[Mark Kelly]

What I didn't mention is that the strength of the magnetism seems to be, maybe, half of a cromo tube. Where the magnet will easily lift a cromo tube off the bench top the tube in question will barely lift a tad before falling off the magnet. I have other known SS bits and none of them are as magnetic as this tube is.
I know that some SS alloys are somewhat magnetic and others are much less so/not at all. I wonder if this tube (28.6, single butted, about .7x.4, smooth and bright silver) being somewhat magnetic suggests which brand or version it might be. Andy.

Sounds like a martensitic stainless eg 410: typical relative magnetic permeability around 1000 - 1500, compared to CrMo eg 4130 at 5000 - 6000. I don't know what kind of stainless Metax was but Columbus described it as "NiCroMox" so presumably it was a nickel bearing alloy, most of the 400 series are <1% nickel.