Stainless Steel in Potable Water System

[a7992]

Hi!

We are looking at putting in some new piping and filters in our new potable water system and have a few questions on material selection (our galvanized carbon steel is very corroded and we need this section replaced). The water will have a pH between 7.5 and 9.1. The project manager was originally going to use PVC but has since decided to use 316L SS because the amount for the PVC with the extra support it would require was the same price as the 316L SS. In a few years this system will not be used all the time anymore and would only be a backup. My question is, is it ok to use 316LSS in this application? There are some chlorides in the water (probably 2-4 ppm) and when a shock treatment is done more chlorides would be injected into the system as required by the AWWA.

I'm thinking the 316SS should be fine with this amount of chlorides but I am concerned that leaving it out of service may cause problems if any stagnant water/moisture gets into the pipe.

Please help!!

 

[EdStainless]

I assume that this would all be butt welded tubing, no threaded joints.
Make sure that the welds are inspected for heat tint on the inside. Light yellow is fine but anything darker either needs to pickled or cut out.
Your concern is well placed. If the line is stagnant then microbial corrosion is very probable. Continuous circulation is the safest. Either that or drained and dried.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[a7992]

Hi Ed,

Thanks for the info.

Do you think the amount of Chlorides are fairly negligible in this case?

 

[EdStainless]

Don't worry about this chloride level.
316 is fairly safe up to 100 ppm in warm water (125F) and as high as 500 ppm in cold water (45F).
Fouling and microbial growth are what will kill you.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[a7992]

Hi Ed,

I'm not too familiar with microbial growth/corrosion and had a question. I'm assuming microbiological corrosion is harmful for either stainless or PVC right? Or would PVC be more resistant to this type of corrosion?

 

[strider6]

as Ed said SS316 can handle water with 500-1000 ppm depending on the operating temperature so in your case i'll see no problem regarding the chloride content.

SS in stagnant water can loose its passive layer and corrode.. and microbiological corrosion is a possibility..

Stainless Steel for Potable Water Treatment Plants

http://www.nickelinstitute.org/inde...04/search_keyword/Potable water/method/1.html

Application of Stainless Steel in the Water Industry

http://stainlessconstruction.com/Fabrication/General/Application_of_SS_in_Water_Industry.htm

http://www.ssina.com/publications/sswhd.html

hope this help

S

Corrosion Prevention & Corrosion Control

 

[EdStainless]

http://www.s-p-l-a-s-h.org/index.cfm/ci_id/13650/la_id/1.htm

here is a site dealing with SS in potable water systems.

Your PVC would be resistant to MIC, but it will need a lot of support and don't let the sun shine on it.

Build the SS system so that it drains well, use lots of slope.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube