316ss vrs 2205ss

[iken]

Hi All,

Can anyone advise why 316ss shouldn't be used for pressure vessels dor a domestic water system. We have a contractor stating it must be 2205 but will not/can not substantiate this (other than 2205 will cost more - more for them).

Thanks,

 

[gr2vessels]

There is no reason for not using 316 SS for domestic water system, as long as the operating temperature is ambient and is potable water quality. Concern could raise if the water has contaminants and the pH is no longer neutral. However, please note the 316 SS is used in marine environment with success.
As far as 2205 Duplex Stainless Steel concerns, it has a superior corrosion resistance than 316 SS in specific corrosive environment, which does not seem to be your case. Accordingly, the 2205 seems an expensive alternative with no benefit.
Cheers,
gr2vessels

 

[iken]

Thanks gr2vessels,

I did forget to mention this for for domestic hot water, so the wtaer will be around 80 degC (tempered down at basins) and is an "open" system so is subject to town mains and the quality is not controlliable.

 

[Ripz]

What is your chloride content? The contractor is possibly looking at the susceptibility of the vessel to Chloride Induced Stress Corrosion Cracking.

 

[Ripz]

Your water supply with likely have Chlorides which can cause Chloride Stress Corrosion Cracking. Your 80 C temperature fulfils one of the conditions for this as well. What's your operating pressure?

2205 Duplex SS is resistant to this type of SCC.

 

[davefitz]

As I recall, 316 may be susceptible to SCC chloride stress corrosion cracking if it has a weld line + operates above 60C + exposed to chlorides + has a peak stress in excess of ( 9000 psi). Perhaps if you could obtain the material certs to prove the carbon content is below the H level then it might be accepted. Another issue is asme code permissives- the code may also prohibit SS316 in some cases.

"Whom the gods would destroy, they first make mad "

 

[Ripz]

davefitz. The grade of 316 does not affect it's susceptibility to SCC.

 

[JStephen]

I have run into quite a few cases through the years where a requirement gets written into a specification when it really doesn't make sense. You can ask and explain why you think it should be different, and either they change it or they don't, and you bid accordingly. In some cases, the person handling the project may not know the difference or maybe just doesn't want to fool with it. I've seen cases where the big consulting firm's expert on the other side of the country wrote the spec, and the local guy doesn't dare alter it in anyway. In some cases, you may have an owner with certain requirements, and the consultant doesn't want to go back and argue the case with them. Or maybe you're just wrong and they're right; more commonly, you get into Ford Vs. Chevy disagreements. In cases like this one, suggesting an alternate material is great, but be careful you don't make yourself the one responsible for choosing the material or guaranteeing it'll work. There's no real gain to selling them a less expensive vessel (actually, you should make less) and major egg on your face if it doesn't work out.

 

[innovation2]

Is 2205 susceptible to MIC????

Maybe this there is something they are concerned with from a microbial stand point since this is an open loop system.

 

[iken]

Thanks for all the replies.

We have no control over the quality of town supply conditions, so whatever it is today could change tomorrow. The consultants specified 2205 after tender (scope change) but no0one knows why (even the consultant looking after this cant explain why.

The manufacture of these tanks has claimed he will not supply 316. Turns out because he has 2205 as standard imported vessels.

We will run with 2205 (better safe than sorry).

Thanks again