Somebody asked me what the advantage of 316 filler material might be when joining 304 sections up to 1/4 thickness (grooves and fillets) with GMAW and GTAW. They are working to ASME codes on food grade vessels.
I had no answer why 316 would be chosen over 308 for a filler. There seem to be no operating temperatures above 300F, no special impacts to satisfy.
Anybody have any ideas what may have been the justificatin for the 316? The practice has gone on for many years so the original decision maker is unavailable so I can't ask there.
Thanks in advance
As far as the effects alloying elements go, 308 and 316 fillers are pretty much alike except for the chromium content (18.0-21.0 for 308, 17.0-20.0 for 316) and nickel content (9.0-11.0 for 308, 11.0-14.0 for 316) of the two filler metals. Chromium promotes the formation of ferrite and increases resistance to oxidation and corrosion. Nickel promotes the formation of austenite and increases high temperature strength, corrosion resistance, and ductility.
The 316 also contains molybdenum for pitting resistance. I'm not familiar enough with the food industry to know if pitting in welds is a problem. Perhaps Chuck can shed some light on this.
You're right, Marty. The molybdenum content in 308 weld metal is 0.75, as opposed to 2.0-3.0 in 316. Quite a difference. Molybdenum improves strength at high temperatures, improves corrosion resistance to reducing media, and promotes the formation of ferrite.
By -
Date 03-13-2006 23:30
Hey Larry,
It seems that Marty and Scott covered all bases about the 316 filler metal. They are probably using the 316 on food grade (very common) because it is under constant washing with water, usually tap water. The calcium and chlorine in normal tap water will expose it to increased possibility of pitting corrosion, which molybdenum resists.
Chuck
Hello Lawrence, I hadn't heard it mentioned, but whenever you hear food grade the bottom line is to not have any sort of cracks, crevices, pits, etc. to promote the capture and growth of bacteria. Maybe this is already understood but I thought it worth mentioning. Regards, aevald
Some companies will use what rod or wire is on hand to get the job done. 316L wire is acceptable to weld 304 base metal, so why buy 308 wire when you have plenty of 316 on hand. My employer uses 316L exclusively, partly because we weld alot of 316 material (pipe & tube) and mostly 304 material is used for supports & hangers. If you only use 316L wire, than you are covered for both materials, whereas if you have 308 on hand.......you wouldn't want to mix it in while welding 316L base metal.
