Compatible Materials For Chloride and PH of 5

[vonbad]

I would like to confirm my ideas on material selection.

I will be running a water/glycol (basically a 50/50) mix through a vessel and filter. The solution will have approxiametly 100 ppm of chloride and a worst case scenario of ph 5. Maximum temperature of 235°F and psi 55.

I am planning to passivate 316 SS for the housing and all piping (after welding). Flanges will be used as well with a graphite (graphonic) gaskets.

A disposable polyester filter with a 316ss core. As the cartidge will not be in place for long periods (more than 2-4 weeks) I do not see a problem?

Does anyone see any problems with material compatibility. Advice on packaging for valves? Any advice would be appreciated.

 

[vonbad]

I just received a change on the parameters. The chloride can reach as high as 1000 ppm

 

[stanweld]

I wouldn't recommend 316 SS due to potential for pitting and stress corrosion cracking. Consider using 2205 duplex S.S.

 

[schrijen]

Choosing 316 SS is asking for problems with such a high level of chlorides.
The best economical choice is using the standard ferritic-austenitic steel type "Duplex" (2205) with a minimum level of nitrogen of 0.15 %.

 

[moltenmetal]

If you must go with an unlined metallic material for this service, 2205 is a good choice. But it is difficult to weld (with a very low maximum interpass temperature) and the fittings are far more expensive than 316, though cheaper than some higher alloy alternatives or exotics like titanium. It's relatively cheap as raw alloy or plate, but more expensive in finished forms like fittings, valves etc. than would be expected from its composition- unless you're using lots of it. Don't be seduced by the cost comparison charts offered by the alloy suppliers- get prices on the real stuff you'll be using and compare on that basis or expect to get stung in the pocketbook.

Your pressure and temperature are both relatively modest. What about FRP or lined carbon steel pipe, valves and housing? Depending on a variety of parameters, either of these options may give you a less expensive system than doing the same in 2205. And the result will not only be resistant to SCC- they'll be immune to it. PFA-lined ductile iron plug valves (Xomox, Durco etc.) are surprisingly inexpensive compared to what you may find in 2205 etc.

Doubt you'll have problems with your filter internals given the duration of service. But 316 for the housing is definitely out of the question for this chloride level and temperature. SCC is a serious concern.

 

[stanier]

check out

http://www.nidi.org

for a vast wealth of information on stainless steels. they even have consultant metallurgists who will recommend the material for this difficult application.

 

[vonbad]

Gentleman, thank you for you advice and education on this application. I really appreciate your assistance on this and I didn't know there were so many types of ss.

 

[SJones]

Hold on a moment. Where is this SCC risk with 1000 ppm chlorides? I certainly don't see it with Bruce Craig's paper:

http://www.nickelinstitute.org/mult...erature_pdfs/10000_technical_series/10073.pdf

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[stanweld]

Steve,
Craig's paper is based on the absense of Oxygen in the media and it is well documented that the potential for SCC in similar environments without oxygen is essentially nil if no chloride concentrating mechanisms are available. If Oxygen is present, there is a much greater potential for SCC in the water/glycol environment described. Also, if there is a potential method for chlorides to concentrate, SCC could easily result.

With the filter replacement and environment as described, I can not believe that Oxygen would not be introduced if not already present; therfore, I stand my recommendation not to use 316 SS.

 

[EdStainless]

Give me a 300 series stainless, a couple of S atoms and a little bit of Cl (ppm will do). Let me select the stress and temp. I can give you CSCC. I have seen real CSCC failures at near ambiant temp, as well as in systems with no detectable oxygen levels. Stagnant conditions can kill you.

Seriously, I wouldn't worry about CSCC at 1000ppm in 316. It will fail from pitting even if it dosen't crack.

Look at the duplex grades. If the chloride level will not any higher than 1000ppm you might consider a lean duplex.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[robsalv]

At our plant we avoid austenitic stainless steels in any service where chlorides are at levels >50ppm and service temperature >65C [149F]. Both these thresholds become meaningless is there's significant stress, sulfur, or concentration of the chloride e.g. in a crevice.

A petro plant not far from here installed a sea water fire water system in their tank farm. The ring mains were stainless steel. One week after they started up the pumps, leaks sprung up in multiple locations. CSCC!

A lined or duplex stainless vessel seem the way to go.

Cheers

Rob

 

[SJones]

There are a lot of assumptions flying around in this thread - not least the presence of a free aqueous phase in a glycol water mixture and stagnant conditions. Perhaps, now that the originator of the thread has seen some of the factors that can play a part in materials selection, they may care to elaborate upon actual process conditions in a bit more depth?

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[vonbad]

Gentleman,
As Sjones mentioned there are a lot assumptions being made. Unfortunately, I am dealing with a new client and they do not have all the ducks in a row as of yet. I was asked to submit a bid on the application.

Thank for all your assistance and pointing me in the right direction. I have researched it in depth and made my proposals based the original request. I did note all the issues that you brought to my attention. It's a starting point.

For example, I am still waiting on the particulars of the water/glycol solution as well as the exact form of chloride.