316SS tubing

[ivanhoe374]

Can anyone think of any problems that may be associated with using 316SS tubing as an air line for a sewage treatment plant.

The air line will be fully submerged in aerated sewage. Pressure is 30Kpa. Size 1 1/2"

Also thinking of running the return activated sludge from the STP in 316SS tubing, pressure 30Kpa, 1"

 

[rnd2]

According to Philip A Schweitzer's Corrosion Resistance Tables, 316ss is attacked by ferric chloride >50 mils/year. I understand it is sometimes used in the treatment of sewerage. You may wish to investigate that.
Consider GRP or rigid plastic tube.

 

[ivanhoe374]

You are right rnd2 ferric chloride does attack 316SS, i have seen that first hand!

In this case however there will be no ferric chloride used in this STP. The reason we are using SS as apposed to plastic is that the aeration line can get quite hot.

 

[rnd2]

I have used Italian made 304ss submersible pumps for private domestic sewerage water pumping for more than ten years. Before this I used so-called dedicated sewerage water pumps and twice found them expensive and short-lived. The pumps are fully immersed and sit on a brick at the bottom of the septic tanks. There is no ferric chloride additive. Life of pumps seem to vary between 4 & 7 years. Cheap and easy to replace. Never noticed corrosion of the 304 metal jacket as cause of failure so have always assumed failure as electric or mechanical within the unit. On this tenuous rationale you should expect reasonable life with 316ss.
Good luck.

 

[EdStainless]

Will there be any joints? Threaded or welded? Both have issues, but in general high quality welds will hold up better. Threaded joints create a lot of crevices for corrosion to start in. If you need some welding done contact a local fabricator of sanitary (food plant) equipment.

Often sub-pumps fail becuase of pinhole leaks in the welded joints. A little water (dirty) gets in and it is all over.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[ivanhoe374]

They will be welded joints.

The fabricator does a lot of work in the food industry using the 316SS tubing.

 

[Capntom]

If corrosion is apparent use the 316L (UNS 31603) seamless tube. You will avoid chrome-carbide precipitation problems. L for < .30 Carbon as opposed to <.80 Carbon

 

[Capntom]

I meant galvanic corrosion in the welded joints

 

[unclesyd]

Based on my experience you will have to be careful with the design and layout in respect to the support. We had a system a similar system in a 60 ft dia. x 40' high tank where we experienced several fatigue failures on the sparger. It took a lot of work to get around this problem. We had to do things like use bends not fittings and no threaded joints. They even tuned the pipe by changing the tank level. They also worked with the air flow.

 

[quark]

Do you have any problems using HDPE? We generally use the same with our aerobic lagoons.