Sewer Gas Corrosion

[racobb]

Have any of you experienced copper corrosion as a result of sewer gases? I have been made aware of a lift station installation that is about 1 to 2 months old that has had several (as in 5 or more) pump breakers "burn up" as I am told. One of the breakers was off and flashed over to ground. All of the exposed copper has a black coating on it.

I asked if the smell was like rotten eggs thinking that it was probably hydrogen sulfide gas, but can not get anyone that can tell me for sure. All they can tell me at this point is that the odor is unusually strong.

Seems to me that without some special treatment of the gas, explosion proof boxes/piping is the only answer.

Any thoughts?

Thanks

Alan

 

[dpc]

H2S is a common problem in wastewater treatment plants. Tin-plated copper should be specified for all buses. Improved ventilation is probably necessary as well.

I don't think explosion-proof fittings are going to help much.

David Castor

http://www.cvoes.com

 

[ScottyUK]

Tin-plated, insulated buswork. No silver or silver alloys, except main contacts where you're probably going to have no alternative. Insulate everything you can, tape bus joints, fit interphase barriers if appropriate. If you can get it, epoxy encapsulated bus is better than PVC or LSZH sleeving in terms of corrosion-resistance. Siemens and ABB list, or used to list, H2S-resistant breakers. Get the electronic overloads conformal coated (and any other PCBs, like those in a VFD or soft start.) Oh, and buy lots of spares.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[andybro]

Also
Do not rely on colour coding for cable identification. PVC insulation will all be a uniform shade of brown in a matter of months. The only thing which is likely to work under these conditions is ventilation. You need to get rid of the problem rather than try to live with it.

 

[racobb]

Sounds as though the ventilation fan was inop. Not Good!

Thanks for your feedback.

Alan

 

[rasevskii]

It must be a rather badly designed station. The wet well (inflow well) should be ventilated with an extraction fan or other means so that the H2S gets drawn off continually.The electrical panels or kiosks should be in a fresh air location or a separate building. There is also possibly an explosion risk due methane. If submersible pumps are used, only the pumps themselves should be in the sewage, other electrical equipment has to be located elsewhere.

rasevskii

 

[racobb]

Yep! I have told them the gas has got to go....many issues.

Thanks

Alan