Brackish Sewage and Stainless Selection

[sow]

Posted on the stainless forum, was advised to post it here...

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]

This has been posted before and answered in the stainless steel forum.

 

[sow]

metengr

As I said at the start of the query, I was advised by other users of the steel forum to post here.

Not sure of the purpose of your post above.

Regards

sow

 

[metengr]

sow;
The purpose of my post was to inform you that cross posting is discouraged. Why? Because it results in fragmented responses. There are many members that frequent multiple fora so posting in one forum will be seen by many members. There is no need to create duplicate posts.