[retrosandkush]

Hi guys! So i have been working on this job, it is made from 316l 16ga stainless. It has to be welded inside and out. I personally weld the outside first then the inside. When i am done welding the inside i am getting a green color in the heat discoloration. Is this any cause for concern??? Problem with contamination possibly???

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[Coldman]

Green is an indicator of the presence of chromium, which of course there is plenty of in 316. Not necessarily a problem but could indicate separation of sorts.
Are you shielding the inside when you weld the outside? And vice versa?

[retrosandkush]

Thank you for the response. Im very new to welding so i havent encountered anything like this before. I do not do any shielding. I just back with aluminum when welding the inside. The shape wont allow for an easy back purge. Ill post a pic of a finished one for better prospective. I also forgot to mention i was using .035 er255 wire.

[Coldman]

Aluminium backing should be ok. I am unfamiliar with er255 and can't seem to find any info on it. Can you post a pic of the pack label? I am intrigued.

[retrosandkush]

I can post a pic tomorrow at work. It it ferralium255. Hopfully i spelled it right. I also have a pdf about the wire. I will try and share. Suppossedly my company uses it because they were having a problem with them rotting out. Detergents go inside. So they used this wire and it melts easier i guess so you can weld the inside a little easier. They dont allow .pdf files but i did find it. And apperently its like $1000 for 5lbs.

[Coldman]

Interesting. Your 255 is a specialized duplex steel for protection against chlorine corrosion.
Since your fabrication is from 316L, and the tank panels are not corroding only problem with weld deterioration, I can only assume it was not welded properly. If properly welded with 316 filler, you should expect the same service at the weld as the rest of the part.
Your company's solution is to use 255, ok, it works for them at a price they are willing to absorb. No metallurgy harm.

Getting back to the original question, 255 is very high in chromium, 25.5%, therefore your green discoloration I think is normal and to be expected given the high percentage. You are using aluminium backing and the welds look very good, no undercut, good fusion, no excessive heat or haz evident. I would say keep doing what you are doing, all looks good to me.

[Coldman]

I hope you are using good ventilation and or filtered air supply to your hood. Who knows how much hexavalent chrome is present in the high percentage filler.

[Coldman]

Having another look at your welds, where they are green you can see a slightly larger heat affected zone than the purple areas and the smallest haz where you have the straw colour weld. I don't consider the green HAZ to be excessive but maybe you should aim for the straw beads (we all should) as this gives the smallest HAZ and disrupts the metallurgy the least.

[Rick_H]

Interesting. Your 255 is a specialized duplex steel for protection against chlorine corrosion.
Since your fabrication is from 316L, and the tank panels are not corroding only problem with weld deterioration, I can only assume it was not welded properly. If properly welded with 316 filler, you should expect the same service at the weld as the rest of the part.
Your company's solution is to use 255, ok, it works for them at a price they are willing to absorb. No metallurgy harm.

Getting back to the original question, 255 is very high in chromium, 25.5%, therefore your green discoloration I think is normal and to be expected given the high percentage. You are using aluminium backing and the welds look very good, no undercut, good fusion, no excessive heat or haz evident. I would say keep doing what you are doing, all looks good to me.

I agree with this, I weld a lot of 316L tanks, piping, but have not delt directly with Chlorine and use 316L filler. I also second the sentiment to be wearing a respirator while welding stainless in general

You could back purge that shape with gas with no issues, you should see of the things I purge...lol
Fit up would be important. Do you pickle of passivate after the fact?

[retrosandkush]

Having another look at your welds, where they are green you can see a slightly larger heat affected zone than the purple areas and the smallest haz where you have the straw colour weld. I don't consider the green HAZ to be excessive but maybe you should aim for the straw beads (we all should) as this gives the smallest HAZ and disrupts the metallurgy the least.

Thanks for the responce and advice. I have only been welding for a year and anything will help!. The color is not the color after i welded it. That is the color on the outside after making the inside pass. I aim for silver!!!!!!

Here is a pic of an inside pass before cleaning

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[retrosandkush]

I hope you are using good ventilation and or filtered air supply to your hood. Who knows how much hexavalent chrome is present in the high percentage filler.

We have overhead fume extractors. I hope that is good enough. Like i said i am new to welding so any advice is much appreciated.