Brackish Sewage Stainless Selection 1

[sow]

We have the following application:

1) Various large diameter valves.
2) Various large diameter pipes / manifolds.

The fluid in question is sewage with around 30% seawater.

The temperature is 20 - 30 degree C (25 average).

The chloride content is 6500 -9500 (average is 8300).

We are considering a valve lined with 2205. Nominal design life 50 years.

We are considering the pipes as either lined with 2205 or full construction with 2205. Nominal life 100 years.

We have several pumps made from a material with a lower PREn than this (CD4MCu - PREn =32) that have shown no pitting or SCC after 12 years service (standing and operating).

My questions are:

1) From what I can see there is quite a bit of information suggesting that 2205 at thes concentrations/ temperatures would be suitable, as the pitting / SCC would be under the "threshold" for these failure mechanisms. Does anybody have any sources information / opinions on this?

2) If the 2205 is a lining, and isnt considered in the pressure calculations, therefore it seems that even with some craking the systems would not fail outright, whilst still affording protection.

3) Is the lack of pitting and SCC shown in the field indicative that these failure mechinsms are unlikley to ever occur. It seems to me that SCC/ piting should be present by now if it were to occur.

4) Any views on adding sacrifical anode / cathodic protection or painting to extend the life - this is all above ground / cast in concrete in a concentrated area, and is not a long pipeline.

Thanks

sow

 

[metengr]

Here is some information to review versus opinions;

http://www.nickelinstitute.org/en/N...ialsSelectionAndUse/Water/AlloySelection.aspx

 

[EdStainless]

A couple of good references.

http://www.imoa.info/_files/stainless_steel/Duplex_Stainless_Steel_2d_Edition.pdf

http://www.imoa.info/_files/stainless_steel/2205_Duplex_Pharmaceutical.pdf

I am not that concerned about good 2205 holding up in this service as I am about various cast and welded parts. These may have significantly lower corrosion resistance and could cause problems.
Proceed with caution.
I would advise using solid alloy and not clad. Make sure that you use as thin of pipe as practical. Using thicker will only make welding harder and add cost. this material is strong to you should take advantage of it. Thicker material will not have a longer service life. If you get pitting the thickness is irrelevant.
All weld procedures need to be qualified for corrosion resistance (both A923 and G48).


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Plymouth Tube

 

[clay87]

maybe try corrosion engineering forum

 

[stanweld]

2205 may not be appropriate if flow is halted for extensive periods due to potential for MIC.