Corrosion Protection - Mike Holt's Forum

I have an installation where I have to bury RMC in concrete. I am concerned that over time, the pipe will rust and I will have to dig it up and redo the installation. 344.10(B)(1) says this is acceptalbe "where protected by corrosion protection". I assume this refers solely to the original galvanizing of the pipe. Is there some sort of spray-on coating that I can use to get a longer life out of this?

Well before pvc coated conduit came out and still today in on most projects we brush coat all rigid elbows with black jack bitumen paint 2 coats applied you can brush it on or roll it on or spray it on your choice .
Your supply house has it ask for electrical conduit bitumen its not just tar !


If we run rigid 100 % underground meaning all rigid on the project.

We tape the conduits we apply it to the full length with 1/2 lap of each rap down & each 10 foot stick 1 #in to 6# in with temflex its a pipe tape for electrical conduit it comes in rolls 4 inches wide .

Put the conduit in a mule and one guy spends 8 hours a day for 8 months lots of fun rolling tape .

We dont tape conduits before bends we bend first then tape its just some advice .

Most projects spec we see today & in the past just call out painting the rigid elbows thur the concrete below grade and thur slab but not above slab .


But we never tape the rigid couplings they must be painted only if you tape theres a void for water then rust and its no good .

We run lots of rigid conduit theres a trick with taped conduit in the bender if you get in a jam meaning you forgot a bend and its already taped
spray the conduit with blue cutting & threading fluid you know the stuff we use on aluminum conduit when you thread it works great no slips no rips in the tape while bending and no residue on the shoe .


Or get another stick !

Thanks aerodog for being the voice of reason.

This discussion was beginning to sound less than professional. Once in awhile, a question may seem outright basic, or border on stupidity based on the knowledge and experience of the person reading it. But don't forget, no one engineer is all-knowing, and everyone is subject to different experiences. This forum should be a place that an engineer, or engineer-in-training, can ask a basic question, if need be. It should also be a place where a very involved technical question can be asked, as the more opinions gathered, the better the possible solution. I have found many helpful hints, or at least some information that has pointed me in the right direction in these fora. Many engineers are working as the only engineer in a construction firm, or a manufacturing facility, and may have no peer with which to consult. I don't believe a professional should ever put down a fellow professional for asking a question. It never hurts to get a second opinion. My only warning to all (and I believe most of you already are aware of this) is that because of the variety of experience levels of the many persons in these fora, the information provided should always be verified with further document research, etc. You alone, as the professional-of-record, are liable for your final work product.

Now, back to the subject at hand . .

I believe, as aerodog does, that the jury is still out. However, there are several items to consider . . .

Large pipes and tubes, such as single-pole sign posts can be "seal" welded using E60 electrodes after the structural welding is complete. Even with this, the large interior volume is susceptible to moisture and subsequent condensation. Usually, the deterioration of these poles begins at the weld between the pole and the base plate, where the condensation usually collects.

Smaller pipes and tubes are best protected by galvanizing inside and out, followed by capping, etc. Many assemblies have small penetrations (bolt holes, etc.) where water can enter, particularly when rain is followed by a drop in temperatures, and the reduced pressure inside will suck the moisture inside. Other assemblies, that may be fully sealed, still seem to allow moisture penetration, as the welding and sealing may not be perfect. It doesn't take very much moisture to begin corrosion. If moisture can penetrate, so can the air that is needed for oxidation. Low points in the assembly are collection points for the condensation, and this is usually where the corrosion begins. Ambient temperature changes may cause the water to evaporate and condense within the assembly, exposing the steel to further oxidation potential. I have seen many welded steel tube amusement rides, railings, etc. that have corroded from the inside with no apparent means of moisture penetration.

I believe it is virtually impossible to completely seal steel pipes and tubes against corrosion from within. There is no easy answer, and in some cases, it may be more suitable to provide small weep holes at low collection points, such that any condensate can weep out.

In short, you should study each pipe and tube assembly as an individual case, and ascertain which is the most effective means of protecting against corrosion from the inside.
Going back to the original post - The requirement is to repair an already defective hollow section (or sections).

First - verify that the existing section is strong enough in its current corroded state.
Second - attempt a fix.
Third - Check your work to ensure that it is doing the job on-site and that it will continue to do the job into the future.
Now, the second part is actually the least important! I don't have any definitive answers but suggest the following.
IF the moisture and air are getting into the section through known holes, these should be sealed either as the whole solution or following some internal treatment.
IF the moisture and air are not getting in through known holes then the welding is suspect and should be ground back and replaced...
Internal treatment of a sealed section is difficult and can involve drilling holes and pumping fluid or air through to remove debris. This can be followed by protective coatings but there is no good method of checking how effective this might be. The new coating is less likely to adhere to the corroded portions. Once this is done the section can be re-sealed - I like the candle idea!
I'd guess that the cost of the above is high. It's always worth considering replacement, either right now or at some future date when the corrosion will become more of an issue. Most metal work in coastal environments needs replacing at some stage.