Rust Forming On 304 Stainless

[Wendelspanswick]

A pal of mine restores old cast iron solid fuel ranges, he asked me to TIG up some open topped water boilers that he'd fabbed from 1.6mm 304 stainless. These sit behind the cast iron facade alongside the firebox and provide hot water from a tap poking out through the front.
He's had one sat full of water before fitting and he's reported that the tank is streaking with rust on the inside seams, which is a pain as it's the only bit you see!
Trying to workout the source of the rust and the only culprit I can think of is that he used a 9" cutter to cut the sheet and the cutting disc had previously used for cutting mild steel.
Is this the likely culprit?
On my side of the job I used 2 strands of 1.2mm 316 stainless mig wire twisted together as filler (coz I have 15kg of it!) and no back purge as I am not geared up for it.
I wire brushed all the seams with a rotary stainless wire brush I use exclusively on my aluminium jobs.

 

[J.B. Welding]

I recon its the grinder disk for sure-also stainless welds will rust a wee bit if not properly treated. Can you get some pickling acid in there to clean it up?, it might be the easiest cure.

 

[AndyStobbs]

My 304 exhaust is red rusty in less than a year

 

[TechnicAl]

My 304 exhaust is red rusty in less than a year

304 or any Ni bearing stainless doesnt like Sulphur which is in exhaust fumes

 

[beefdog]

sounds like grinder, cross contamination

 

[Kent]

contaminated disc is my bet! Years ago I had to go away and sit a stainless course for a particular job, it opened my eyes to contamination no question about that. Proper Fab shops doing high grade stainless should in my opinion ideally stick to just that and many do or rather did when there was stacks of it

 

[hotrodder]

304 or any Ni bearing stainless doesnt like Sulphur which is in exhaust fumes

Dunno about levels in exhaust fumes but they've been reducing sulphur levels in fuels steadily over the years Al http://www.ukpia.com/industry_issues/fuels/sulphur-free-petrol-diesel-and-non-road-fuels.aspx

FWIW one of my cars has a stainless tailpipe welded to an aluminised silencer, gotta be over 10 years since i made it and while the silencer is now mostly rust both the weld and the 316L hygienic bend are still pretty much spotless with no signs of rust

He's had one sat full of water before fitting and he's reported that the tank is streaking with rust on the inside seams, which is a pain as it's the only bit you see!
Trying to workout the source of the rust and the only culprit I can think of is that he used a 9" cutter to cut the sheet and the cutting disc had previously used for cutting mild steel.
Is this the likely culprit?
On my side of the job I used 2 strands of 1.2mm 316 stainless mig wire twisted together as filler (coz I have 15kg of it!) and no back purge as I am not geared up for it.
I wire brushed all the seams with a rotary stainless wire brush I use exclusively on my aluminium jobs.

The inside seams that are rusting... are they fillet welds or did you set the joint up as a partial penetration closed outside corner?
While contamination from cutting/grinding discs is likely without a purge it's relatively easy to cook out a bunch of the chromium on 1.6mm. If it was a partial pen outside corner then you've got crevices to aggravate things too http://www.cdcorrosion.com/mode_corrosion/corrosion_crevice.htm

 

[langy]

If you want rust proof you need 316, 304 doesnt rust as such but often gets a sort of rust coating on it.

 

[AndyStobbs]

304 or any Ni bearing stainless doesnt like Sulphur which is in exhaust fumes

Not sure how permeable stainless tube is, but I'm referring to the outside of the pipe, which isn't in a sulphurous environment.

 

[Wedg1e]

If you want rust proof you need 316, 304 doesnt rust as such but often gets a sort of rust coating on it.

Yep, we supply calibration blocks in 304 and 316 and the 304s often need a polish-up before despatch... they're also slightly attracted to a magnet which is how I get our stores staff to double-check they don't ship the wrong type.