I just read an ad for a bike made of "531 seamless tubing". That's redundant, right?
I've got this kind of nice Raleigh frame but you can see seams when you look down the tubes. That would make it definitely not 531, right?

supposedly...but there have been stories down through the years of "531" frames (that had the decals on them) which developed splits in the tubes along a...seam. Seems that some French bikes (of noted brand name) were the flagrant examples of this, but I'd bet there were others, from other countries, too. I'd also bet they were cropping up in the "bike boom" when a lot of corners were cut, especially by the big brands with tall orders to fill.

I believe they put the word "Seamless" on the decal to differentiate themselves from their competition, some of whom used seam-welded tubing (Peugeot, for example).

Ok, thanks. This bike came without any stickers so I don't even know the model. I'm pretty sure it was built between '66 and '68 at the Carlton shop and it doesn't look like they were in a real hurry. They made pretty good gaspipe bikes so it's not like my ego is getting crushed.
I just saw that extra adjective and got to thinking.

Definitely not 531, which was an extruded pipe and a different alloy than the rolled and welded 501. There were other differences too in regards to the length of the butts and tapers. But, IMHO the differences should not include quality of production. In other words, I cannot believe that you will see or find a seam in 501 tubing. Perhaps I can be contradicted. Apparently, Raleigh did use their own proprietary tubing about which their is more in the BF archives. BTW, I own a 501 bike and like it a lot. 501 gets a bum rap these days, but only because 531 was the preferable tube, not because there was anything intrinsically wrong with 501 — like gaping seams for instance.

I think that many make too much of a deal worrying about seamed tubing. As long as manufacturing quality control was maintained, there shouldn't be any problems with seamed
tubing. Peugeot made jillions of bikes using their seamed "Carbolite" tubing, and I never heard of any problems related to their construction ever.

Chombi

In the case of the Reynolds seamed tube, the specifics of it allowed for speeded mass production — for one thing — by virtue of how it reacted to applied heat from brazing. I suspect that the lugs used could make more of difference than the disparities between extruded and seamed tubing. However, I can't speak to tubing that shows the seam. I for one would interested in a picture if it were clear enough. Might be cool for the archive too. sailor ... is that possible?

Raleigh used Reynolds 531 tubing in their top frames... it was of course their own product and TI and Raleigh merged in 1960.

They controlled pretty much everything that went into their bikes and this included their tubing... the only comparison on this side of the pond would be Schwinn who who still bought much of their tubing from TI for their high end racing models like the Paramount.

Here's my best shots. Not much depth of field and the flash is out so I'm holding the frame with one hand and the camera with the other hand and the mag light with the other hand.

Might be one of these;

sure looks like a seam, at least in those 2 tubes...still possible you might have real 531 in the others. It's pretty common to see big volume builders sub a cheaper head tube, and those are often seamed...but when one of the main 3 is seamed I'd say you can't trust that any of the others will be 531 (butted or plain gauge) which should always be seamless. Not sure about the (rare) Reynolds "A" tubing, that was a light and good quality tube but not sure whether cold-drawn and seamless (though I had assumed it was).

Well, you can see seams in the chainstays and the downtube too, but there's no way I'm gonna get this idiot proof camera to pull focus on those.
I'm still happy with the frame, it has chrome lugs and I'll take that over 531 any day.

run a thoroughly seam welded tube thru a few dies to thin the tube walls and Butt it ,
and the seam gets pretty homogenized..

the build may be DB on the top and down tube , and a money saver for the seat tube..

Hmmm ... guess I'll be shining some mag lights down my 501 bike the next time it comes apart. Thanks for the pics Sailor. They worked out fine despite the challenges.

I've seen seams that aren't much more that a dark grey discoloration on light grey metal. Maybe I'll photograph that bike tomorrow.