About to weld my exhaust

[ampdog]

What's the best way to ID the type of metal? I think a portion is stainless, but I want to be sure. Also, I have a fitting I was thinking about using that is zinc coated, what are the "need to knows" when welding something like that?

Thanks!

[Jerry]

A simple test for stainless would be to check if a magnet will stick or not. It will not stick to stainless steel.

As far as the zinc coating goes just sand off edges where your going to weld and it should weld ok.

J P Streets Welding

[bitternut]

4oo series stainless is magnetic. It is usually shiny but not always. A lot of stainless knives are 400 series. Also most gas barbecue grill burners that are so-called "stainless" are 400 series. Thats why they don't last. They rust out before they burn out. Try a spark test on a grinder. 300 series is non magnetic and usually has a satin finish.

[Jerry]

Hey Bittenut, thanks for the info on 400 series being magnetic ,I'll have to check that out .

[Rocky D]

Originally posted by Jerry
Hey Bittenut, thanks for the info on 400 series being magnetic ,I'll have to check that out .

Jerry, it's magnetic, all right, but it doesn't pull quite like steel. Check it with a known piece of steel.



ampdog, stay away from the fumes of galvanized stuff, even if you grind most of it off. Also in welding a exhaust pipe that has been in service can pop on ya real loud, as the soot gets to the flash point. If you're not aware of it and it happens...you may have to take your pants to the cleaners!

[Mike Sherman]

I think there is alot of misinformation about stainless steel on this forum. Some stainless steels are magnetic, some aren't. It has nothing to do with it's quality. You must use the proper grade of stainless for the particular application. For example, some 400 grades of martensitic stainless have a higher carbon content for a reason, it makes them amenable to quench and temper heat treatment to produce high levels of strength and hardness. Just because it's magnetic does not make it inferior stainless. As I said, it is more important to use the proper grade for your application. As for identifying a particular grade of stainless without chemical analysis, you may be reduced to a spark test with a grinder. The simplest way to do this is to compare the sparks from a known piece of steel to the sparks from your part. This something of a forgotten art, but if you are good at it, it is effective.

[ampdog]

Thanks to everyone for the replies! Especially Rocky D cause I'm positive the Soot would have caught me off gaurd, I probably would have just put the welder down and walked away with no idea what just happened

I'm going to play with some different metal on the grinder and see if I can get the picture with the spark test.

If the pipe does turn out to be stainless 400 series and I want to weld the fitting to it (after I grind off the zinc), what kind of wire and process should I use?

[Mike Sherman]

Use E309. It is superb for joining carbon steel to stainless, and is good for high heat applications. If it really bothers you on the type of stainless, you can take a few shavings to your local testing facility and they can give you an analysis of the shavings. Then look up which stainless has that chemical composition. There is also a hand held tool called a Positive Metal Identification or PMI, I don't have one (yet) but I am told you just point and click and you get a very accurate chemical analysis.

[Rocky D]

Originally posted by Mike Sherman
Use E309. It is superb for joining carbon steel to stainless, and is good for high heat applications. If it really bothers you on the type of stainless, you can take a few shavings to your local testing facility and they can give you an analysis of the shavings. Then look up which stainless has that chemical composition. There is also a hand held tool called a Positive Metal Identification or PMI, I don't have one (yet) but I am told you just point and click and you get a very accurate chemical analysis.

Mike, where would I look to find info about this PMI?

[Mike Sherman]

Rocky, I am currently investigating where to get them myself. My guess is that you may need a second mortgage to buy it though.

[Roger]

Here is link that has instument that will work. Probably others available with search for hand-held XRF spectrometer.

http://www.oxinst.com/ANLPDP389.htm

[CyberianHusky]

Also in welding a exhaust pipe that has been in service can pop on ya real loud, as the soot gets to the flash point. If you're not aware of it and it happens...you may have to take your pants to the cleaners!

Thanks Rocky!!!!!!!

I've got to weld some old exhaust pipe in the near future, and now, MAYBE, ONLY my helper will need new shorts!

Don