Welding or brazing stainless steel

[Lord Stig]

I have a fine crack around a third of the circumference of the centre section of my BSM exhaust, close to the joint with the down pipe. It doesn't blow much, but I'll be needing to put my AT through an MOT very soon, and in any case it would be far better to deal with it before the crack results in the centre section falling apart.

It's stainless, so a line of weld should put it right, but so far I haven't been able to find any companies up here who are small enough to bother with this kind of repair while at the same time being kitted out to weld stainless. There must be some, I probably haven't looked hard enough.

As an alternative, does anyone know if stainless can be brazed and, if so, what the best filler metal is? I suspect the repair won't be as strong as a fillet of weld, however. Any thoughts?

[Boris]

Not sure where you are in Fife but Dave Charles of JC Welding in Livingston almost certainly welds stainless and would no doubt be your man

JC Welding
01506 461925
Mobile 07979863811
1 Arrol Square, Deans
Livingston, United Kingdom
EH548QZ

[thetimkirby]

I read somewhere that weld has a strength of 25 tonnes per sq. inch, brazing around 16. This applied to mild steel, but stainless has only a similar yield strength to mild steel. Brazing is often used as the limiting effect on strength of the weld is the heat affected zone next to the weld, not the weld itself. Brazing doesn't need such high temps, so no HAZ problem.

For an exhaust, strength may not be such an issue. I'm told that brazing does work on s/s, but I've never tried it. Be interested to hear how it goes. Brazing is often used where there is a good contact area (like a patch or overlap seam), so it may not work on a crack in thin walled pipe. Good luck.

[Lord Stig]

Thanks to both of you, very useful to know. From what you say thetimkirby it might not be a good bet even if the braze takes - after getting the base clean as possible by abrasion the metal will be even thinner, and if the overall strength (assuming I can fabricate an incredibly close fitting patch) isn't good with just a fillet of braze, I can see the repair fracturing in a relatively short time. At the moment I don't know why the metal has cracked, but there's sure to be a reason.

Boris, I think I might give your people a try. I'm up in the Lochgelly area, but work in Granton, so a trip over into West Lothian wouldn't be the end of the world if they don't mind such a small job.

Or I could splash out on a different exhaust...

[thetimkirby]

Not sure whether to call you Your Honour, Lord, Lord Stig, Stig or what. Anyway, re-read your post and its probable that it cracked near the weld because of this heat zone problem. The weld bead is effectively a line of cast steel, quite hard and inflexible. Further away from the weld, the parent steel is softer and more flexible. The band in between is the heat affected zone and is almost always where a weld cracks. It is brittle because it cools quickly after welding.

One of the ways to help prevent this is to 'normalise' the weld. After welding, you heat the weld to cherry red to allow the steel to creep and absorb the welding stresses. You then let the weld cool slowly by moving the heat source gradually away. Obviously, this is not possible with Mig, but you can use an oxy-acetylene torch after Mig-ing.

Brazing may not work, for the reasons you gave. It's often used to fill a crack in thicker material, but you normally grind a v-groove to increase the contact area. If you can't make a patch and the metal is thin (and under constant heat cycle stresses), forget brazing and get a good welder to do it for you. I understand that the correct welding wire is important to match your stainless grade: a good welder will know this.

Only time I would braze on this type of fix, is if the metal is too thin (rusted) to take a weld without popping through. Then I'd make a patch, use a good flux, braze it, and save up for a new part, as it probably won't last much longer.

Good luck

Tim

[Lee Halsall]

Granton is close to me,If you can get it to Glenffidich distillery,I can tig it up for you . Maybe after work monday ( 4.30pm )?
Let me know if I can help.
Lee

[BobA]

Granton is close to me,If you can get it to Glenffidich distillery,I can tig it up for you . Maybe after work monday ( 4.30pm )?
Let me know if I can help.
Lee

There's a fine offer. The power and helpfulness of forum members never ceases to amaze me.

Nice one

[Boris]

Granton is close to me,If you can get it to Glenffidich distillery,I can tig it up for you . Maybe after work monday ( 4.30pm )?
Let me know if I can help.
Lee

There's a fine offer. The power and helpfulness of forum members never ceases to amaze me.

Nice one

Yes it is... Only problem is I suspect we are talking about two different Grantons about 120 miles apart

As for JC Welding. Dave C (son of JC) when he was a young 'un used to work for us at the Karting Centre across the road. Nice lad. I'm sure he can help but phone first to make sure he can do stainless.

[StumpyFingers]

I used to use TIG for welding stainless, it gave a much better weld.
Then superheat the object and allow it to cool on its own.

[Lord Stig]

Crikey, I'm off line for a few hours and there's loads of replies - good ones too! Thanks to you all, and Lee Halsall, that's a great offer! Unfortunately, as Boris suspected, this is the Granton that's west of Leith in north Edinburgh. Tempting offer nonetheless!

Thetimkirby, you've answered a question I've had in mind for some time - I'd noticed cracks tend to form adjacent to the line of weld, and what you say makes perfect sense. I doubt BSM bother with any heating or anealing of any kind. To be honest, though I was initially very pleased with the exhaust, I have had plenty of problems, one of them serious enough in that the gasket between the centre section and end can tends to fall apart over time; in one case this caused hot exhaust gasses to be directed onto the rear brake line, melting it!

I think if the chaps in Livingston are willing I might just ask them to weld the two peices together permanently, as there's really no benefit to having a two piece set up other than allowing BSM to mass manufacture the can, while only having to produce model-specific linking centre sections.

By the way, if anyone has ever wondered where the "Lord Stig" user name comes from, it doesn't stem from delusions of grandeur (or real grandeur come to that) but from a letter a friend (oddly enough currently a 650 TA owner, and the person who introduced me to TAs when he bought one of the first in 1989) wrote to me back when we were at school. He adressed it to 'Lord Stig and the New Pagan Uprising'. It stuck. When I Google myself (Stig Walsh) I get loads of relevant hits, but when I Googled 'Lord Stig' 'he' turned out to be a cartoon character who rules the Underworld, and wears a shirt and tie......but no trousers. Not sure how to take that.