304/L vs. 316/L stainless

Date 12-17-2003 21:37

I have been told that 304/L ss is better suited in an alkaline environment and 316/L ss is better suited in an acidic environment. Is there any basis to this? We work primarily in the pulp and paper industry and I see a lot of 304L and 316L ss material going through the doors and I'm wondering what the actual basis for deciding which ss alloy to use.
What about using 316L electrode on 304L material? Could this create corossion problems in the weld metal and possibly heat affected zone in the parent metal in an alkaline environment?

Do I have this right? Am I even close? :)

Perhaps someone out there can help clear some of this up for me???

By Niekie3 (***)

Date 12-18-2003 19:07

Hi Dagwood

The big difference between 304 and 316 is that 316 contains around 2 - 3% Molybdenum. Mo helps 316 to have a better pitting resistance than 304. In a service where there is a possibility of pitting corrosion, 316 would be a better alloy to use than 304.

Alloy 304 is however better in oxidizing acid service, such as Nitric Acid. It is also somewhat cheaper than alloy 316, so it is used where the pitting resistance of 316 is not required.

It is generally not recommended to use 316 filler to weld 304, because the ferrite content will probably not be what it should be. In addition, if you need resistance to oxidizing acids such as Nitric acid, the weld metal will perform poorer than the base metal.

In many alkaline environments, S/Steel is not required, because these environments tend to be non aggressive to C/Steel, so why pay more. This is however only a basic approximation and should not be taken as being a hard and fast rule.

Hope this helps.

Regards
Niekie Jooste
Fabristruct Solutions

By Dagwood (*)

Date 12-18-2003 19:42

Niekie, thank-you for your reply! Another variable in the question, how about a caustic environment? 316/L would be the choice in a caustic service?
Thank-you again, Dagwood.

By Niekie3 (***)

Date 12-18-2003 20:13

Hi Dagwood

Yes, in caustic (NaOH) 316 will give a much wider usefull range in terms of temperature and concentration than 304.

Regards
Niekie Jooste
Fabristruct Solutions

By Dagwood (*)

Date 12-18-2003 20:16

Neikie,
Thanks for the info. I just wanted to have another opinion on the matter.
This forum is just too damn cool! Oops, did I just say that! :)
Dagwood.