Heating 316 Stainless Steel

In my experience, 316 can get brittle around a weld site. Is this for food grade or pharmaceutical work?

Neither... this unit is used to evaporate production water from a gas well pit !

Heat affected zone is vulnerable :

316HAZ

If you don't know metallurgy, just stop with the third sentence of the executive summary here:

http://www.igcar.gov.in/benchmark/science/7-sci.pdf

Even in France:

http://cat.inist.fr/?aModele=afficheN&cpsidt=4825098

Sand blasting CAN destroy the "stainless nature" of the material if the abrasive media is contaminated with steel or iron, Setting up corrosion cells.. I would passivate after sandblasting, but, then, I;m a pretty conservative guy, professionally speaking.

milo

I agree completely with you about passavating the stainless afterwards. We used to have to do it both manually and automatically via a CIP system from time to time.

Please see my reply to "Milo" !... Thanks.

This unit is used to evaporate production water from a gas well water pit (Apex), see our web site at www.resourcewest.net, it has been sandblasted and welded twice where it has broken up on the upper pyramid of the sheet metal. Now it has only been in operation for about 10 days and has already cracked severely on the sheet metal again approximately at least 10 inches from any of the previous weld sites !... Comments ?

mmm, does that mean 316 would be unsuitable for a 14m catamaran? would a few knocks on a reef spell doom?

I took a look at your website and saw the info on the "Apex" unit and watched the video. The first thing that came to my mind is, how much vibration do these units produce?

The 316 grade is prone to cracking from vibration stress. Saw it many times on 316 based cones in use in food grade powder handling equipment. What we did was weld in place strips of 304 & 316 grade angle iron to the non food contact surface to "stiffen" the construction. kind of similar to a "rip stop" chord in aircraft construction. That helped quite allot. Perhaps doing similar on the inside of your pyramid may help.

That sounds like a great idea ! I will take it to "the board" for consideration... Thanks tons for all of your input !!!

in my opinion you should consider chloride stress corrosion cracking, if you evaporate produced water from a well then it could be possible that water contains chlorides. SS 316 suffer from SCC at temperature above approx 50-60°C. Also if in the well there is H2S you can also have problem of SSC, sulphide stress cracking...

the weld can increase the problem if the hardness is too high...

S

corrosion prevention

For what its worth, why use SS at all?

Use a MS or an abracian steel such as Hardox with sufficient corrosion allowance, that means thicker. After 5 years you replace it. No cracking, likely of lower cost too. That would be my approach. Good luck.