344.10 Uses Permitted. GRMC

[Goroon]

I need a come back, friendly conversation.

The statment was made that Galvanized steel Conduit can not be used in concrete or in direct contact with the earth.
I indicated that 344.10 [Uses Permited] has 2 parts.
(A) (1) Galvanized Steel and Stainless Steel RMC. Galvanized steel and stainless steel RMC shall be permitted under all atmospheric conditions and occupancies.

and that there is an 'or' in..

(B) Corrosive Environments. (1) Galvanized Steel, Stainless Steel, and Red Brass RMC, Elbows, Couplings, and Fittings. Galvanized steel, stainless steel, and red brass RMC elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.

My coworker comes back with "344.6 Listing Requirements" and the UL White book does not evaluate Galvanized Steel for "concrete or in direct contact with the earth" there for is not listed for that application.

 

[don_resqcapt19]

I need a come back, friendly conversation.

The statment was made that Galvanized steel Conduit can not be used in concrete or in direct contact with the earth.
I indicated that 344.10 [Uses Permited] has 2 parts.
(A) (1) Galvanized Steel and Stainless Steel RMC. Galvanized steel and stainless steel RMC shall be permitted under all atmospheric conditions and occupancies.

and that there is an 'or' in..

(B) Corrosive Environments. (1) Galvanized Steel, Stainless Steel, and Red Brass RMC, Elbows, Couplings, and Fittings. Galvanized steel, stainless steel, and red brass RMC elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.

My coworker comes back with "344.6 Listing Requirements" and the UL White book does not evaluate Galvanized Steel for "concrete or in direct contact with the earth" there for is not listed for that application.

The white book guide information for Rigid Ferrous Metal Conduit (DYIX) says:

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.
Conduit that is provided with a metallic or nonmetallic coating, or a combination of both, has been investigated for resistance to atmospheric corrosion. Nonmetallic outer coatings that are part of the required resistance to corrosion have been additionally investigated for resistance to the effects of sunlight.
Nonmetallic outer coatings of greater than 0.010-in. thickness are investigated with respect to flame propagation detrimental effects to any underlying corrosion protection, the fit of fittings and electrical continuity of the connection of conduit to fittings.
Conduit with nonmetallic coatings has not been investigated for use in ducts, plenums, or other environmental air spaces in accordance with the NEC.
Rigid metal conduit with or without a nonmetallic coating has not been investigated for severely corrosive conditions.

 

[renosteinke]

Just to repeat the obvious: there's no substitute for local, specific experience.

I've seen aluminum perform quite well in 'acidic' environments that the handbooks will say 'stay away from.' I've seen stainless steel (even the 'good stuff') turn to black sand in conditions that simple cast iron survived well. Another common experience is simple brass outperforming stainless alloys.

Even among ordinary 'steels,' there's quite a variation. For example, the slight difference in alloy between a simple nut and the bolt next to it will often express itself as very different corrosive performance.

While it's tempting to try to play 'engineer,' actual field experience will often differ considerably from what the textbooks would have you expect.

Getting to the OP's scenario: we have two distinct situations.

Pipe in concrete: concrete is somewhat alkaline, and quite a good chemical buffer. This means that it tends to maintain conditions that are pretty friendly to steel (though the zinc coating may look awful). Concrete is a porous sponge, though .... and if the area is constantly wetted with something bad for steel, eventually the concrete will start helping degrade the pipe.

Buried pipe: The key element here is: oxygen, rather than water. After a certain depth, soil tends to pack tightly enough that it keeps air away from the pipe. No air, no rust. That's why a pipe entering the ground will often show rapidly increasing corrosion down to about 6-8", after which there is very little rust. Simply wrapping the pipe with plastic tape can provide an enormous amount of protection.