Cathodic Deep Well Venting absolutely needed?

[GasMask]

How detrimental is it when installing a Cathodic Deep well (500ft deep Cathodic Ground Bed) to either cap off the Vent Tube or to not install a Vent tube all together?

I know that the anodes will out-gas hydrogen and this could potentially create gas pockets next to the anodes, thus driving up the resistance of the ground bed. How quantitative of an effect have you people seen this effect your ground beds? Will it increase it 1-2 Ohms or less?

I searched the NACE website and I cannot find any articles written specifically on this topic so I do not know the extent of the effect?

Do you have any experience you could share or an Article you could point me to?

 

[SJones]

It's not the hydrogen but the chlorine that will be the problem. NACE SP0572 Design, Installation, Operation, Maintenance Of Deep Wells and its associated references should guide you.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[GasMask]

My apologies. You are correct the Chlorine is produced at the Anode and the Hydrogen is produced at the Cathode. Going from memory I got them mixed up.

The issue I am facing is that we drilled and installed one of our typical Cathodic Deep wells with a vent tube and after everything was installed and running, we observed the vent tube was issuing a substantial amount of methane gas. I have capped off the vent tube for now due to the ignition hazard. The question I have is whether or not the gas blockage due to the Chlorine gas will cause the deep well to become unusable? The deep well was not designed to be capped off and unvented.

We have come across this issue before but we were able to vent off the excess methane after a few days. This time the situation is different with substantially more methane needing to be vented. Until we are able to remediate the excess methane I will need to keep the deep well capped.

From your experience, if I run the rectifier for the next year with the well capped, will the detrimental effects to the well’s effectiveness be much of a concern?

 

[fdac]

Good design practice requires gas venting of deep well anodes. The bed will work, for a while, depending on how hard you're driving it. Then you will probably suffer 'gas blocking' where the combination of heat and chlorine dries out the backfill and creates voids around the anodes. No backfill contact = no current from the anode. This can happen relatively suddenly; I think a year is too long to wait with the vent capped.

Depending on how the well is capped you may be able to re-wet the backfill and get it working again, but best to avoid the failure in the first place. How much current are you driving, what are the dimensions of the well and the soil resistivity?