316 SS corrosion - Brackish water 1

[ucabjm]

Hi, I am designing a piping system for a small plant. We are going to move brackish water at 60 bar and Tmax: 40C. I am wondering if I can use 316SS for piping. My concern is the corrosion.

I am looking for any link or research someone might know of that can guarantee 316SS for use in brackish water application.

I don't have information of the chemical composition of the water. I am looking online for a chemical composition table for brackish water but I cannot find it.

Thank in advance for any reply.

 

[mcguire]

Alloy Cr Mo N Ni PREN Y.S. T.S.
2101 21.5 0.3 0.22 1.5 26 515 650
2003 20.5 1.5 0.18 3 29 515 725
2205 22 3 0.17 5 35 515 760
2507 25 4 0.27 7 42 550 8
304L 18 0 0.05 8 18 220 520
316L 16 2 0.05 10 24 220 520
317L 18 3 0.05 14 29 230 540
AL6-XN© 21 6 0.22 24 45 380 760
254SMO 20 6 0.20 18 43 380 750
You need a PREN of 35 for seawater at 40C. The max chloride level you will experience is required for a precise answer, but it is unlikely that 316 will be sufficient.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

Most brackish water systems are designed like seawater systems. The higher oxygen levels and biological activity often make them just as corrosive even at the lower salinity.
This would point to alloys such as 6%Mo superaustenitics and super duplexes (and for tubing superferritics).
The most available grades will be AL-6XN and 254SMO. These alloys are strong and very expensive. Use the lightest walls possible.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[mcguire]

2205 works well if you can avoid crevices. Otherwise go with 2507. Each are stronger than austenitic grades and contain less nickel, so should be cheaper with no compromise in corrosion resistance for 2507. A lot of it is used for subsea umbilicals in oil production.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[ucabjm]

thank you guys for your answers.

See the following information

We do not believe that there will be any corrosion issues with the 316L on brackish water. The chloride has to get well above 5000 ppm to be able to start to corrode stainless steel.

This is why I am wondering about the chloride concentration in brackish water.

 

[EdStainless]

I have seen 316L fail in a matter of weeks from crevice corrosion (no dissimilar metals, neutral pH, no MIC) at ambient temp in 500ppm Cl.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[kenvlach]

ucabjm,
1) The concentration of chlorides, etc. in your brackish water depends upon its source. If groundwater, the U.S. Geological Survey or state may have some info. Do a search. E.g.,

http://ca.water.usgs.gov/archive/reports/ofr01242/

2) Nobody will guarantee that 316 can resist 5000 ppm chloride at 40 °C because, as mcquire and EdStainless have already informed you, it won't. From the following figure, for 5000 ppm chloride water, 316 is expected to pit above 31 °C (print at 150% to show your boss).

Also, 316 is well-known for crevice corrosion and stress corrosion cracking. “As a general rule, crevice corrosion will occur at around 15-20 °C below the temperature at which pitting occurs.” See

http://www.assda.asn.au/asp/index.asp?pgid=17991&cid=34299&id=56951

 

[strider6]

in a rererence of NIDI, 1000ppm is taken as a "safe" limit of chlorides for 316SS. this limits is somehow relative to the environmental condition as has been said before. high velocity no crevice and low oxygen can rise this value, while high temp stagnnant conditions and possibility of crevice will lower it.considering the high temp and the possibility of 5000 ppm of cl-, as a minimum a duplex 2205 sholud be considered in my opinion as a starting point in materials selection.the final selection shall be based on a general assessment of all the piping, equipment and critidality of the service.

strider

http://www.corrosionist.com

 

[mcguire]

What will it take to get people to wake up and see that 316, with its 10% nickel and therefore high cost, low strength, propensity to SCC, is inferior to duplex? 2205 is a huge upgrade in corrosion resistance, so with thinner walls allows cost reduction. Better yet 2003. But most of all, they work well, which 316 does not.


Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[ucabjm]

Again, thank you for all your answers.

On regards the crecive corrosion, I got the following information:
our vendor components are machined from wrought pipe vs. cast, they virtually eliminate crevice corrosion. Is this true??

I am going to request information about using 2205 instead of 316.

 

[EdStainless]

Thanks for covering my back McG,
A duplex would be a good option, and it would pay IF you could reduce the wall thickness.
I would go to at least 2205. I like AL2003, but I don't feel that it is up to this application.

As for crevices, they can have a number of sources. A poorly machined surface that has some microscopic smearing will be crevice rich. How they clean/pickle/passivate is critical. Any mechanical joint will have crevices, and the tighter that they are the worse the corrosion risk.
Castings are often criticized, but a well annealed and cleaned casting is fine. Just like a poorly annealed piece of welded pipe may be crap.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[StoneCold]

Duplex is a good choice but for the temperature wouldn't it be cheaper to go with a lined piping system, like polypropylene lined carbon steel. At least for the major strait runs. I would also suggest fiberglass if you can bring the pressure down to less than 450 psig.

Regards
StoneCold