Merc Exhaust - galvanised?

[elebub]

Got to replace the seals on the mid section of a 1993 Mercedes W124 E220TE exhaust which meant cutting slits in the pipes to get it off. Before I weld the cuts up again can somebody advise me if this is galvanised steel. Cannot recall coming across a galvanised exhaust before but this looks a bit rust free (apart from the welds) for a mild steel one.







Cheers

Andy

 

[NTwoO]

Has a zinc coating. I'm not sure how it is applied (could be galvanising or hot dipping or some other technique). It needs to be cleaned off before you start

 

[Paul.]

Its most likely aluminised, very common in exhaust systems, just clean it off local to the weld, although its nowhere near as bad to weld with as zinc, we used to oxy acetylene weld aluminised sheet with no preparation at all, Mig and Tig may benefit from cleaning, try it

 

[hotrodder]

If it's the OE exhaust (or OE quality replacement) there's a good chance it'll be 409 stainless. As said, cheaper ones are usually aluminised

 

[elebub]

Thanks for the replies. How do I tell whether it is stainless or aluminised, or do I just weld it with SS wire to cover either possibilities?

 

[malcolm]

Stainless tends to go a bit yellow on an exhaust. Aluminised stays silver. Yours isn't stainless so a mild steel wire would be best.

Other un-scientific way to tell (apart from the looks and checking for rust) is to cut it with a hacksaw. Stainless will ruin the blade once it's got a bit hot.

 

[Chipper]

Stainless is usually not magnetic, might give an indication. If it's like my W126 was, it's aluminised mild though.

 

[elebub]

Magnet sticks to it and as Malcolm says its not stainless I will use mild steel wire. When I put this back together, do I use exhaust sealer - no-brainer or heresy?

 

[Paul.]

Magnet testing will only help to identify austinetic stainless steels, many exhaust systems are made from 409 which is a ferritic grade and is magnetic.
Not trying to confuse you here, just a comment for interest really, almost certainly that exhaust is steel.
Spark testing with a grinder is another method, with a bit of experience you will see the different colours of the grinding sparks, stainless has a much brighter spark than steel which tends to be more orange.

 

[Chipper]

Didn't realise that about stainless exhausts, just out of interest, 400's magnetic but more weakly than mild, is that right/wrong? Got a bike exhaust which is part stainless/part mild (welded together), the stainless bit's got no real interest in talking to welding magnets. It's a tailpipe, after the headers/collector, and flaring out to the silencer.

 

[hotrodder]

You're going to need to give the weld area a quick clean prior to welding, if it's coated then sanding it will 'feather' the coating (similar to feathering paint but less obvious). If it did turn out to be 409 then i'd just weld it with mild unless you've got some 309 filler kicking about- it's only a car exhaust and slip joints anyway.

My 409 suggestion was based more on the longevity of OE systems than the photos- had a w123 Merc that'd been in the family since new, origional exhaust lasted well over 15 years before the back box went, it was the seams on the silencer that went, pipework was still sound when i got rid of it

Ferritic stainless has a strong magnetic response, the austenitics can develop a mild response (you can feel the attraction but a magnet won't stick) after cold working and/or welding

 

[elebub]

The story so far......

Taking all your advice on board, managed to weld the cut after cleaning the area with a flap disc. Unfortunately the gap at one end was slightly wider and I managed to blow a hole. Three steps forward two back. Filled it using the methods described in numerous posts on the forum but I still have an irritating pinhole. I am using a Kemppi MinarcMig Adaptive 150 with 0.8mm wire and whatever setting I use the wire feed seems too fast. Will change the wire to 0.6mm tomorrow and see if that makes a difference.

Are there any Kemppi MinarcMig 150 cognoscenti out there who could share the mysteries of the settings with a novice? In theory they are very straightforward, in practice however.......


Cheers

Andy

 

[wyn]

I think the automatic settings are based on a fillet weld so if you dial in the thickness of the steel it probably gives a bit more power than you wanted.

When in automatic the dial on the right will give you a bit of control on the wire speed. In the manual it says it adjusts the length of the arc. It goes from -9 to +9 (or is it 7) the "-" gives a bit more of a convex weld bead so must be higher wire speed, and the + numbers less wire.

I think the welder always starts up on the last setting you had it on.

Try it on manual and give it a go on some scrap to find good settings and keep them written down somewhere.

It could also be that it is set to the wrong material....if it's set on aluminium that might give you a higher wire speed.

Don't know if that makes any sense......but that's how i've got my 180 sort of figured out in my head

 

[elebub]

Thanks for the reply wyn. I have the 150 which is manual with two dials; metal thickness described in the manual as "welding power control" and arc length trimmer which affects welding temperature. The main problem is not welding on a regular basis and thinking you can just pick up where you left off 6 months ago having mislaid all the test notes you very carefully made and stored in a safe place. When an MOT is looming the practice time goes out of the window and panic mode sets in. Back to the test pieces tonight.

 

[wyn]

Ah ! Thought it also had the display.

As you say it's a case of trying it out again and noteing down the settings.

On a clarke mig i have, all the good settings i've written on the casing with marker pen.

With the kemppi i have noted down the settings on the front of a cupoard..........all that orange casing was a bit tempting though

 

[zardoz]

Magnet testing will only help to identify austinetic stainless steels, many exhaust systems are made from 409 which is a ferritic grade and is magnetic.
.

As an aside, i found some "stainless steel" in the college skip last week. The welding tutor came out to have a look and pronounced it as being "Ferritic stainless" which id never heard of, we took it inside and it really did stick to a magnet, even though it has come off a serving trolly which was for obvious reasons stainless steel. I went into the canteen and tried the magnet on a similar food serving trolley in there. It was the same except for the surface top which was non magnetic stainless for some unknown reason ? What a puzzler!?

 

[Paul.]

As an aside, i found some "stainless steel" in the college skip last week. The welding tutor came out to have a look and pronounced it as being "Ferritic stainless" which id never heard of, we took it inside and it really did stick to a magnet, even though it has come off a serving trolly which was for obvious reasons stainless steel. I went into the canteen and tried the magnet on a similar food serving trolley in there. It was the same except for the surface top which was non magnetic stainless for some unknown reason ? What a puzzler!?

Austinetic grades are more durable than ferritic grades, so are often used for work surfaces, sink bowls etc, with the other components of the item being made from cheaper ferritic grades, a lot of cheap stainless sinks are made from 2 types of stainless and joined where the bowl meets the drainer,
You should also be aware of martensitic stainless such as 410, 416, 420, and 431 grades, these are also magnetic and can be hardened by heat treatment, they are often used in cutlery, surgical instruments etc.
There are also duplex grades which are a mixture, and are slightly magnetic.