How to determine if this is a crack or a scratch?

[greenmeansgo]

My bike has been making a noise for several weeks. A noise like a cracked frame - metallic, sort of a tick noise, every once in a while. Sometimes coincides with going over bumps.
I've disassembled, cleaned, greased reassembled several parts, cleaned the bike then inspected welds for cracks, all to no avail. It happens more often in the cold.

This evening I spotted something! I can feel a discontinuity with my finger nail, but how to determine if this is a crack? I haven't managed to flex the frame enough to open it up.

[LittleWheelsandBig]

It probably is a crack. It is a little unusual for the crack to be perpendicular to the weld.

Remove some paint and do a dye penetrant test. That should confirm the crack.

[Wowbagger]

Why would it be a scratch?

It looks just like a crack to me.

[Torslanda]

No, it's not a scratch. Time to go shopping.

[Blodwyn Pig]

OH! I have been there!! .  It might be a scratch.....or it might be the crack of doom! A pencil  mark, or some such, will tell it t moves along. Start looking for plan B.

[Brucey]

A crack will hold dye, a scratch won't.

A scratch will often polish out, a crack won't.

A crack will grow, a scratch won't.

You would need a much better photograph than that to be sure.

My vote is 'scratch' BTW....

cheers

[greenmeansgo]

Ok thanks guys. Not time for shopping, though. Time for warranty!

Now that I know about it, I'm not so keen to keep riding it. Any thoughts? I don't suppose it's going to suddenly fail on me.

Sorry the photo is rubbish, but that's the best I can do. I'm fairly sure it's a crack, mainly from the noise the bike's been making. It's often hard to tell where a noise is coming from but I've only heard this noise when sitting or rising out the saddle.

[Cpt Sisko]

What's the material?

[LittleWheelsandBig]

Aluminium

[Asterix, the former Gaul.]

Doesn't look like a scratch.

Enlargement shows that it branches off just like a crack. Maybe when the frame is on the welding jig it was put under some stress to ensure a good fit before the weld was done and somehow it was overdone or the tube has a flaw.  In use, the paint has given way and revealed the problem. 

My steel frame cracked 18 months after an impact with a vehicle.  It was almost invisible but the bike made the noise you describe.  The tube had a tiny dent and had been minutely deformed by the impact.  My LBS had inspected it and failed to spot the damage, so I couldn't claim at the time.

[greenmeansgo]

Yep it's aluminium. Currently waiting to see what Planet X have to say.

[Jurek]

Not a scratch .
Good luck with Planet X.

[Brucey]

London Road?  Ah...  I have heard of one other frame of this sort that was intractably creaky and at the time the blame was assigned to the slack fit of the seat pin in the frame.  So (cracked or not, I was being optimistic on your behalf before....) the noise could be that.  Of it could be that the other frame was starting to crack as well.

If it is a crack, it is an unusual one.  Possibly it will have something to do with the fact that the tube end is shaped (squashed) near the seat cluster.

cheers

[Veloman]

If it is a crack, it is an unusual one.  Possibly it will have something to do with the fact that the tube end is shaped (squashed) near the seat cluster.

I think it is more likely to do with an 'inclusion' being in the weld pool and crack resulted due to the welding process not being 100%.  The inclusion would act as a localised stress raiser which is sufficient for micro-failure and enable a fatigue crack to propagate well ahead of what would otherwise have been expected in terms of fatigue life.  Seems to be the reason why so many titanium frames crack as the welding process used (inert gas shroud) is very different from that for critically stressed aerospace components (which tend be welded in a vacuum).

Hence the reason why welds in aerospace turbine assemblies tend to be 100% high definition x-ray tested to ensure welds are completely free of those nasty little inclusions.

http://www.weldpedia.com/2014/08/solid-inclusions-that-impair-weld.html

[LittleWheelsandBig]

Now that I know about it, I'm not so keen to keep riding it. Any thoughts? I don't suppose it's going to suddenly fail on me.

Not wanting to ride it is understandable. The crack looks like it is progressing along the neutral axis, so continuing to ride for a little while mightn't be too much of a drama. Personally, I have other bikes, so would simply put it aside.

If I had to keep riding it, I'd be marking the end of the crack and closely examining it every ride. For an experiment, a friend rode an Al-framed Concorde with a cracked head tube (badly inserted headset) for a few years before the crack grew catastrophically. On a steep Tasmanian climb, he ended up stepping over the front of the bike when the forks separated from frame. He was quite glad that it didn't happen on a downhill.

[Brucey]

If it is a crack, it is an unusual one.  Possibly it will have something to do with the fact that the tube end is shaped (squashed) near the seat cluster.

I think it is more likely to do with an 'inclusion' being in the weld pool and crack resulted due to the welding process not being 100%.  The inclusion would act as a localised stress raiser which is sufficient for micro-failure and enable a fatigue crack to propagate well ahead of what would otherwise have been expected in terms of fatigue life....

The most common type of failure by far in TIG welded joints of this kind is where there is a stress raiser at the weld toe (which can be an inclusion of some kind but is more likely to be a small lack of fusion) which initiates a fatigue crack. Often the crack will then run around the edge of the weld.  It isn't unusual for the crack to do something strange (direction and growth-rate-wise) once it runs into the parent material, because the material properties are a bit, uh, 'variable' there.

If the OP's 'thing' is a crack, it is not behaving at all 'normally'. One possibility is that the tube forming has caused a longitudinal crack inside the frame tube at that point.  I have seen this happen inside handlebars (where the diameter changes); when the bars have broken it is quite clear that there were pre-existing cracks inside them.

FWIW plenty of aerospace components are welded using gas-shielded processes these days. 

cheers

[Veloman]

FWIW plenty of aerospace components are welded using gas-shielded processes these days. 

Totally agree, but I was referring to critically stressed components and those materials subject to inclusions such titanium, hence my reference to titanium.

Regards the frame, back to the supplier/shop soonest!

[Brucey]

FWIW plenty of aerospace components are welded using gas-shielded processes these days. 

Totally agree, but I was referring to critically stressed components and those materials subject to inclusions such titanium, hence my reference to titanium.

there are all kinds of joining processes used on all kinds of 'critical' parts these days.  'Inclusions' are not usually the main issue with Ti weldments, and they certainly are not the main reason that you might choose to use a vacuum-based process over a gas-shielded one.   The shield quality is critical in gas-shielded Ti weldments simply because oxygen and nitrogen dissolve and then react strongly with Ti.   In some processes this is obvious because the appearance of the weldment is altered. In others it isn't.

In bike frames you (the customer) don't get a chance to see because the back beads are not visible and the top beads are always cleaned using abrasive or similar.

In the early days of Ti welding it was thought that a hardness increase in the weld might be a good indicator of contamination; however careful tests (which IIRC are summarised in Lancaster's book on welding metallurgy) showed that a hardness increase of about 10-15HV (which is only just detectable amongst the scatter in the data) in Ti 6,4 could correspond to a reduction in ductility of about 30%, i.e. the weldment could be seriously compromised without there being much sign, hardness-wise.

There are many different ways of making unsound Ti weldments and after the job is done telling the difference is very difficult. When buying a Ti frame it is a leap of faith, hopefully backed up by a good track record and a good warranty.

cheers

[Torslanda]

Scrape the paint off with a chisel. If the line's still there it's definitely NOT a scratch . . .

[Asterix, the former Gaul.]

The bellend has caused excess stress on the tubewall.

[Veloman]

In the early days of Ti welding ........ Ti 6,4 ...

Just as well I spent so many years working at IMI Titanium in the R&D department as a metallurgist working on the development of welded tube, welding in general, melting and manufacturing of titanium products including specific work with IMI 318 which was the IMI trade name for the 6Al 4V titanium alloy!  And that's the thing with heat treatable alloys such as IMI 318, when used for the intended aerospace purposes it needs to be heat treated after welding to ensure the microstructure, and therefore mechanical properties, are homogenous, whereas for the manufacture of cycle frames it is just welded and left with no post weld heat treatment which results in an inhomogeneous structure.  We had great fun making a race wheelchair for a friend of my work colleague during lunch hours and after work and the challenges were significant when using the best facilities available at the time.  Similar challenges were identified with the old Speedwell titanium cycle frame which we worked on, although that used CP grade titanium as it was all 'too difficult' to use alloy such as IMI 318, and as a result the frame lacked rigidity.

http://www.classicrendezvous.com/British_isles/speedwell/Speedwell_brochure.htm

The further years spent doing research with National Physical Laboratory and the University of Birmingham specifically looking at the formation and effect of inclusions in aerospace alloys was also informative when considering what happens when metal is melted and subsequently cools, particularly the effect of nitrogen and oxygen, and the role of the environment in terms of gas or vacuum.

I agree that buying a frame is a leap of faith and that is true for any material.  Folk tend to buy frames based on reputation which itself tends to be built on customer experience.

[Brucey]

chapeau sir, I would love to talk shop (maybe in another thread?), I am sure you have some tales to tell. I am a materials scientist by training and spent 25 years working (mostly in R&D) mainly with EB welding machines.    Interestingly in thin gauges of Ti 6,4 it isn't clear that heat treatment of low heat input (eg EB) weldments (past a stress relief treatment) is of much benefit. There are quite a few applications where they don't bother.

I also own a few (modern) Ti frames.  I remember the speedwell frame; a (very rich) lad in my first cycle club had one back in the mid 1970s.

Of the modern Ti frames I have examined/owned, my favourite (from a welding standpoint) is one made by Moots; it is welded using a two-pass technique, with an autogenous root run and then a filler pass on top.  You can see the root beads in some places and they look nicer than the top beads in some other frames.   

cheers

[greenmeansgo]

Update:
Planet X didn't think it was cracked. Before sending it back to me, I had a discussion about their reasoning, so as to avoid repeatedly sending it back and forth. In essence, because the mark doesn't follow the weld, and they couldn't open it up by flexing the frame, they said it wasn't cracked. Ok then, but what about the noise?

Could be anything, but I mentioned the seat post being a loose fit. They measured it, deemed it to be out of tolerance, and have replaced the frame. You can already guess the next bit:

The seat post is is a loose fit in the new frame too. Apparently they measured it, and it is within tolerance. I guess there's not much I can say to that. See what you think:

https://goo.gl/photos/u52cHkrCJFPPFHEWA