What corrosion category does SS316 fall under? Is it C3? 2

[Arshad Ahamed]

Greetings,

Can you help me with the corrosion category under which SS316 would fall?

Regards.

Be curious, and furious in your pursuit for answers

 

[GGedge]

Are you referring to the corrosivity categories (C1 to C5) in ISO 9223, or other standard that relies on ISO 9223 data? If so the corrosivity category is specific to a particular metal, the standard includes carbon steel, zinc, aluminium and copper. The standard does not include stainless steels so the categories do not apply to those alloys.

Cheers

 

[kingnero]

If by C3 you mean the corrosion category according to EN ISO 12944-2, these are environment-related, not linked to materials.

 

[GGedge]

ISO 12944-2 refers to ISO 9223 and in the normative part of the table refers to corrosivity in the same way as ISO 9223 in terms of corrosion loss after the first year. The Informative (guidance) part of the table provides qualitative examples of environments that may result in that corrosivity category for either zinc or low carbon steel, the standard also notes those descriptions can be misleading.

Cheers

 

[kingnero]

I'm not sure I understand what you mean, however (and I indeed used a secondary standard because that's what I'm used to working with, I should have used the ISO 9223 as that's the base information) it doesn't matter which of those standards you refer to, the C1-CX refer to the rating of corrosivity of the atmosphere (in relation to a period of one year in a certain corrosion system), and not to the metal. A metal cannot be rated C3, a system can be though.

 

[GGedge]

Consider an example from two metals zinc and low carbon steel tested by weight loss at the same coastal location. At the end of 12 months the first year rates for the two metals are:

Zinc 1.5 microns per year which is in mid range C3

Low carbon steel is 90 microns per year which is C5

So what is the corrosivity category independent of the metal?

For avoidance of doubt the above is a real example.

A system includes the metal.
Cheers

 

[kingnero]

We're trying to make the same point I believe.

The OP asked if SS316 is C3. This cannot be (apart from the fact that 316 is not mentioned in these standards). Carbon steel is not C1 nor is aluminum C4.
You need a system (atmosphere/environment + material) to be able to identify the system as C1-CX. Would you agree on this phrasing?

 

[GGedge]

I do agree with that, good, succinct wording.

Cheers

 

[Arshad Ahamed]

Greetings All,

Appreciate the response.

I'll lay the context here. End-user has mentioned that the "SS316 Casting Pump to move Salty Water shall comply with C5 corrosion resistance". My client, who is sandwiched between the end-user and my company (pump supplier) has just this information available.

Be curious, and furious in your pursuit for answers

 

[GGedge]

If that statement is all you have, go back to your client/end user and seek clarification. The statement as written has no meaning assuming the C5 is a reference to ISO 9223 or derivatives. If it is some other C5 they should provide information to explain what it means. Note the following, again assuming C5 refers to the corrosivity category in ISO 9223.

1) Corrosivity categories (C1 to CX)refer to atmospheric exposure only, it might be relevant to the external surface (but see 2 below) if that is not immersed. C5 is not relevant to the internal parts that are immersed in salty water.
2) The corrosivity categories in ISO 9223 do not apply to stainless steels because those alloy are not included in the standard.
3) The client is specifying a material (SS316) but then asking for it to have some or other corrosion resistance. That is a poor specification, they should either specify the material and take responsibility for that or provide appropriate definition of the service environment to allow others to select an appropriate alloy.

CHeers

 

[EdStainless]

It may be what they mean is that the wetted parts must be 316, and the rest of it (exterior of motor, base, coupling, controls) should be suitable for C5 exposure.
But make them say that, do not assume.
And that said I would sidestep and use non-metallics wherever I could.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[chrysa1975]

Corrosivity categorization through ISO 9223 cannot be assessed for metals prone to pitting corrosion. General/uniform corrosion is the type of corrosion addressed in above ISO.
I would paint the external surface with a coating system consisting of a primer suitable for ss, an intermediate and a top coat, total DFT 200-300μm for protection from SCC.

 

[mfgenggear]

great post by EdStainless

I don't know jack about corrosion categories.
how ever the requirement is not clear and precise.
making it a guessing game which is bad news.
get them, not you to specify the correct and precise requirements.
if they don't know then better make the contract to indemnify your self's.