Welding Tips and Tricks

A guy in town that builds custom cars wants me to come work for him on a stainless race car chassis and cage. In speaking with him I told him that all the welds would need to be back purged and he disagreed with me. He said that sugaring was only a problem in food prep, not in race car cages I want him to understand why it needs to be back purged as I want to do the job right. What would you stainless guys tell him? I told him my reasons but I want to know what you guys think.....Thanks in advance!

I would tell him not to build a race car from stainless. The goal is to reduce weight, not add it. Besides that, I don't believe that you could ever get it certified. Even if certification isn't a problem it's gonna be the heaviest and slowest car on the track.

Tell him that sugaring leads to rusting and that stainless isn't stainless anymore when you don't purge.

Anyone who wants to hire you to do a job they can't ( especially on a race car !!) , but then proceed to tell you what you need to do and not do is a dick head. Plus a stainless cage, even purged, would be a nightmare for stress and shrinkage.

Don't waste your time, save yourself a lot of aggro.

RamboBaby wrote:I would tell him not to build a race car from stainless. The goal is to reduce weight, not add it. Besides that, I don't believe that you could ever get it certified. Even if certification isn't a problem it's gonna be the heaviest and slowest car on the track.

Tell him that sugaring leads to rusting and that stainless isn't stainless anymore when you don't purge.

It's actually going to be more of a show car so weight isn't really a factor. I basically told him what you and kiwi2wheels just said and I got nothing. He is probably shopping me tonight so I will lose out to someone that will weld it his way If you guys could see some of the lizards he has working in his shop OMG but he's talking serious money because he can't find a Tigger and I was recommended.

If you can get a "boilerplate" waiver of liability (involve a lawyer, and put the hour of service in your bill), stating the show car purpose of the construction and itemizing the reasons why, make that money. If he lied, and tries to race it, it's his own ass, then, and we'll have another nominee for this year's Darwin awards.

Steve S

Hey brother, you can't fix stupid.
Watching that thing come unbuttoned in service should be interesting.........

If its a 100% show car its ok. Stainless will work harden at cyclic stress points and fracture anyway no matter how good the welds are.

Incidentally there are mechanical tests that show that sugaring does not necessarily weaken a welded joint, but if present, the front side may not polish up nice so what's the point? The big thing with sugaring is that it is a rough surface and can also have internal profiles that are stress raisers that will break under fatigue. Here is an article that is interesting reading.
http://www.epri.com/abstracts/Pages/Pro ... 0001009717

I just talked to the guy again and he was ok with purging. He wants to put me on his payroll to build this thing I asked him why they didn't go with Chromolly and he said because the whole thing is polished SS ...That had to hurt somebodies wallet I'll let you know how this whole thing unfolds 8-)Thanks guys!

That's good for you that you go on his payroll cause then you can't get blamed as an employee following instructions. It's all on him.

Coldman wrote:That's good for you that you go on his payroll cause then you can't get blamed as an employee following instructions. It's all on him.

I wondered why he never asked me for a quote and just offered to hire me for awhile and after I thought about it I thought that was awesome. Hell I only have general liability insurance anyway. Even a really stupid lawyer would have ran me off with a gun when he found out

Run for the hills!

Is it an actual chassis or just a typical cage?

Rick_H wrote:Is it an actual chassis or just a typical cage?

From what I gather, it's a cage and some frame ties. He hasn't made it real clear what he wants to build, only that he needs a Tigger to weld it. After sleeping on it, my new concerns aren't sugaring or back purging, it's liability. I can simply say no but I am going to wait and see what he actually wants to build before I make a decision. I'll update when I hear something.

Coldman wrote:If its a 100% show car its ok. Stainless will work harden at cyclic stress points and fracture anyway no matter how good the welds are.

Incidentally there are mechanical tests that show that sugaring does not necessarily weaken a welded joint, but if present, the front side may not polish up nice so what's the point? The big thing with sugaring is that it is a rough surface and can also have internal profiles that are stress raisers that will break under fatigue. Here is an article that is interesting reading.
http://www.epri.com/abstracts/Pages/Pro ... 0001009717

Very interesting link. I was just asking about this as I am working on some stainless headers. And found purging to be very expensive when it's on your own dime, vs working for someone and you don't care how much argon is being used.

Since the headers are for a drag car, I may opt out of purging since the headers don't build up moisture as a street car does.

Sent from my XT1254 using Tapatalk

I know West Coast Choppers builds stainless motorcycle frames. All the pictures I have seen, not one of them you see any kind of back purging.

On another note the Noble M600 super car has a chassis made out of stainless steel.

NHRA has some regulations on chassis and roll cages. I don't see stainless steel mentioned.

You might wonder who's going to be the engineer-on-record for this stainless steel design with his signature on the blueprints?

http://www.nhra.com/UserFiles/file/Gene ... ations.pdf

I heard that some off-roaders prefer mild steel cages/chassis because it's much softer in a crash than CroMo.

I have a question on the back purging.

Can the purge be done with CO2 while welding with argon?

http://www.google.com/search?q=nitrogen ... GGHP_en-GB

There was also some in depth discussion about the use of nitrogen somewhere in this forum.

Then there's always Solar Flux, if it's not for an oil or cooling system ( problem is internal flux residue )

http://www.solarflux.com/Pages/Productinfo.html

No CO2 can not be used for purge - it's a reactive gas - cheapest alternate gas would be nitrogen but that assumes you do enough to warrant renting another bottle just for purging so unless you do a lot it's easier & cheaper to use 2flow gauges off your argon regulator.

Wood Welder wrote:I have a question on the back purging.

Can the purge be done with CO2 while welding with argon?

Nitrogen can be used as a back purge instead of Argon...

Rick_H wrote:

Wood Welder wrote:I have a question on the back purging.

Can the purge be done with CO2 while welding with argon?

Nitrogen can be used as a back purge instead of Argon...

..so long as the Nitrogen does not see the heat of the actual electric arc, right?

I was thinking dry ice since it has been used to purge pipes that are too large to purge from welding cylinders.

Wood Welder wrote:I was thinking dry ice since it has been used to purge pipes that are too large to purge from welding cylinders.

That's still CO2, just in a solid form. If you're working with TIG, it is a reactive gas and can play havoc with your weld.

With MIG, CO2 is useful, but messy.

Wood Welder wrote:I was thinking dry ice since it has been used to purge pipes that are too large to purge from welding cylinders.

I think Ive seen Steve aka @Otto Nobedder mention he has used dry ice to purge vessels. Personally Ive always used Argon.

Rick_H wrote:

Wood Welder wrote:I was thinking dry ice since it has been used to purge pipes that are too large to purge from welding cylinders.

I think Ive seen Steve aka @Otto Nobedder mention he has used dry ice to purge vessels. Personally Ive always used Argon.

While I've never used dry ice to purge vessels, I have suggested it for purging fuel tanks, for removing all oxygen before grinding or welding to eliminate explosion hazard.

I will use nitrogen to purge large volumes when ASME code does not apply.

When code DOES apply, I'll run however much 1/4" brake line it takes to put a purge box behind the weld, and use argon.

Steve S