Pipe-Wrap for Underground RGS Conduit ?

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barclayd

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Colorado
In the past, we always used non-metallic conduit for concrete-encased ductbanks, and wrapped the RGS elbow stub-ups with a double layer of 10-mil pvc pipe wrap tape.
A recent design shows some RGS conduits mixed in with non-metallic conduits in the same ductbank.
Does the entire run of RGS need to be taped?
I've never used RGS in a ductbank before, but I've seen a lot of corroded metal underground conduit.
Wrapping the stub-ups seemed to eliminate, or reduce, the major corrosion that always occurs where the metal conduit comes up out of the conctete.
Does anyone have experience with the corrosion aspects of concrete-encased RGS? Wrapping seems like cheap insurance if it reduces corrosion.
thanks
db
 
Smart $ said:
PVC-coated rigid steel conduit.
Click to expand...
$$$

Do you think it's necessary to be coated somehow? I've used the Rob Roy coated stuff before, and it be pricey.
The tape applied by an apprentice is much more "cost effective".
Still trying to determine if it helps.
thanks
db
 
From the UL White Book for Rigid Ferrous Conduit (DYIX).
Corrosion Protection and Coatings Galvanized rigid steel conduit installed in concrete does not require supplementary corrosion protection.
Galvanized rigid steel conduit installed in contact with soil does not generally require supplementary corrosion protection.
In the absence of specific local experience, soils producing severe corrosive effects are generally characterized by low resistivity (less than 2000 ohm-centimeters).
Wherever ferrous metal conduit runs directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.
Click to expand...

In general you only need to provide supplementary corrosion protection for the rigid conduit for a short distance on each side of the concrete/earth interface.
 
barclayd said:
In the past, we always used non-metallic conduit for concrete-encased ductbanks, and wrapped the RGS elbow stub-ups with a double layer of 10-mil pvc pipe wrap tape.
A recent design shows some RGS conduits mixed in with non-metallic conduits in the same ductbank.
Does the entire run of RGS need to be taped?
I've never used RGS in a ductbank before, but I've seen a lot of corroded metal underground conduit.
Wrapping the stub-ups seemed to eliminate, or reduce, the major corrosion that always occurs where the metal conduit comes up out of the conctete.
Does anyone have experience with the corrosion aspects of concrete-encased RGS? Wrapping seems like cheap insurance if it reduces corrosion.
thanks
db
Click to expand...

There is an extensive discussion in this thread from 2005.
 
don_resqcapt19 said:
From the UL White Book for Rigid Ferrous Conduit (DYIX).

[/B]In general you only need to provide supplementary corrosion protection for the rigid conduit for a short distance on each side of the concrete/earth interface.
Click to expand...

The way I read it, the supplementary protection would need to be either on the entire concrete encased portion or on the entire portion in contact with the soil. Galvanic corrosion can happen on any two electrodes joined by a conductor, not just in the area where the two zones meet.
In the case of a stub up through earth, the portion to be protected is already limited in length. But if you transition from a section in concrete to a section in earth you need to use a different material (e.g. PVC) or protect it.
 
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