Comparison of Types304SS and 316/316LSS 2

[Vonmagnuson]

Can anybody point to a decent practical comparison of 304 to 316/316l? I can find the metallurgical comparison charts I need. I work in an industry where these materials are used quite often in the products we make. Our standard product is made from 304. Some customers request 316/316l. These are usually Chem/Pharma folks. My question comes from the practical point of view. Why would I prefer 316 over 304? What are some of the applications for 316 where 304 will NOT survive? How would I describe the differences to a salesman who is technically disfunctional?

 

[mcguire]

To a layman one could say that 316 is 304 with added molydenum to stand up to environments that have more salt.
There is an FAQ above which gives the relationship that determines the resistance of a stainless steel to pitting and another one which gives the things in the environment which promote corrosive attack on stainless, which most often takes the form of pitting corrosion.
316 is seldom used in food service applications, but it is common is corrosive environments(seaside or chemical plants) or applications where no corrosion can be tolerated,e.g.pharmaceuticals.

 

[mcguire]

There's a lot of information at stainlesscenter.com, also, if you want to get your own data.

 

[testy]

The "L" designation means there is less Carbon added, this in turn prevents heat senstization in areas to be welded. If these parts are to be welded the "L" designation will impart greater corrosion resistance. However, unless you are worried about chemical(or salt as stated by Mcquire) corrosion, you can use 304L at about 1/3 the cost of 316/316L.

 

[pipewelder1999]

Aren't there also some applications in which 304 will perform better than 316? I thought I had read this once before and can't seem to recall the service conditions?


Gerald Austin

 

[mcguire]

There are no corrosion environments in which 304 is better than 316. It would have better high temperature oxidation resistance because 304 has more chrome which is good and less moly, which is not beneficial for oxidation resistance.
The lower carbon does not impart better corrosion resistance in austenitics per se. What it does is to keep welds from precipitating chrome carbides which would deplete the matrix of vital chromium. This precipitation can also be prevented by quenching or post-weld annealing.
The 316 thus treated is equal to 316L in corrosion resistance.
The book price of 316L is $1.98/lb vs $1.40 for 304 and $1.50 for 304L. The bargain grade is 201 at $1.28/lb, and it doesn't require low carbon to prevent sensitization.

 

[AdnanHussain]

Adding Moly in SS would increase pitting corrosion, I agree, but how ?
as Chromium is less in 316 would this decrease its oxidation resisitance ?
and why we increse Ni percentage in 316, also please can you tell me why Ni is good austenite former i mean what its influence on austenite ?

 

[Metalguy]

Both Cr and Mo are "ferrite formers", and if you add them together in 316 (approx.), you need more Ni to ensure you have aust. Ni is FCC, as is aust.

 

[CadAndy]

Two things
1) ASM had a study that Chlorine deteriorates
316 stainless Steel. I cannot remember the cause but
they had alot of failures when companies that used
Chlorine as a chemical and 316 Stainless Steel as a
metal.

2) 304 Stainless Steel becomes magnetic in a
cryogenic environmnet where as 316 does not.
FSU did a study on different materials in a cryogenic
environment.

Other than that, cost?
Cobalt can also be used to ensure an FCC structure
adding Nickel will increase workability also.

 

[Metalguy]

1. 316 is more resistant to Cl that 304, but it is not a good choice of material when Cl is involved,

The extra Ni in 316 stabilizes the austenite--it's much more stable than 304.

 

[dig1]

mcguire,

You have made the comment that "There are no corrosion environments in which 304 is better than 316."

I have read some papers that conclude 304L is superior to 316L in kraft liquor pulping because of the higher chrome and no moly. Similar discussions regarding 2205 and 2304 (most don't spec 2304 due to lack of availability and fabrication/welding experience compared to 2205).

Have you, or anyone else, ever seen these results and care to comment?

 

[mcguire]

dig1
I will double check my facts and respond. There is no doubt that higher chrome is a plus, regardless of what other changes occur in composition, but moly, to my knowledge, is never a negative except for high temperature oxidation.
I'll be back.

 

[25362]

I've been told that plants that -in their process- may encounter naphthenic acids at temperatures above 230^oC would benefit from SS 316 or even better from SS 317. As for carbon content, SS 304 L is also in the market.

 

[dig1]

mcguire
For clarification discussions are not related to SCC. A couple of references:

"In-Situ Coupon Immersion Study of Stainless Steels in Kraft Cooking", Nadezhdin & McDonald, 9th International Symposium on Corrosion in the Pulp and Paper Industry

"Corrosion Phenonmena in Black Liquor Evaporators", Klarin, 10th International Symposium on Corrosion in the Pulp and Paper Industry.

There are some other articles in the 10th ISCPP which show similar results in kraft liquor.

 

[bngreene]

Maybe the simplest way to describe the differences between these two grades is to say that 316SS is equal or superior to 304SS in ALMOST all environments. For this reason, most pump and valve manufacturers use 316SS (or its cast equivalent) as their standard construction material when austenitic stainless steel is specified.

Because of the lower chromium content in 316SS, there are, as others have pointed out, exceptions to this rule. These exceptions are highly oxidizing environments such as high temperature (>1500F) air, hot concentrated nitric acid, and some ranges of oleum. I believe, but am not certain, that 304SS may also outperform 316SS in concentrated chromic acid and sulfuric acid (>98%).

The "L" designation for stainless steel has been explained by others. But it may interest you to know that 'dual certified' materials are in wide use in North America. Dual certified materials are those that meet the requirements of both the standard grade and the "L" grade.

 

[davefitz]

Regarding high temperature properties, 316 H has superior high temperature allowable stresses than 304H, but both H series have chloride stress corrosion issues.