Can you say “Electrolysis?”
How about “Danger?” (Look closely at the botom of the tag….)
Can you say “Electrolysis?”
How about “Danger?” (Look closely at the botom of the tag….)
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Replies
Almost forgot this ....
The photo of the valve is confusing. That looks more like leakage thru the packing than electrolysis. The adjacent flex conduit and the brass valve parts should get along fine. What am I missing?
Went to a fire call last weekend where the janitor had left a mop head hanging next to the water heater to dry. I guess he figured that the best place to hang it was from the piping for the PRV, which had a 90 in it about a foot from the floor. The burner cooked the mop head and scorched the side of the unit. I didn't get to stay long enough to inspect, but I bet they have inadequate combustion air and the flame rolled out in search of oxygen (the HWH is in a closet). There was no damage from the incident, luckily, but it could easily have spread to a couple of other mops and brooms nearby and then up a broom handle to a wooden shelf loaded with cleaning chemicals. Yum.
>>The photo of the valve is confusing. That looks more like leakage thru the packing than electrolysis. The adjacent flex conduit and the brass valve parts should get along fine. What am I missing?No doubt about the leak, but I'm pretty sure the amount of corrosion was aided by the bx - it was fairly new but had a lot of corrosion where they were touching.Re mop: yikes!>>I bet they have inadequate combustion air and the flame rolled out in search of oxygen I haven't seen that, but I've seen plenty of rollout on lightoff where the pilot light is too far from the burner and the gas has some time to buildup before ignition.
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Sojourners: Christians for Justice and Peace
A speaker at JLC Live touched on the subject of flame rollout from gas water heaters. Apparently there are plenty of them installed in small rooms or closets without adequate combustion air. Once the burner lights it stops cool air from migrating down the stack (which it can do if the burner is off), and the oxygen supply dwindles, so the flame has to look further for oxygen. And of course a lot of people put their brooms, mops, and other stuff next to the water heater.
The valve in your photo... it appears to have some sort of capped-off port in the side. Wassup with that?
>>Once the burner lights it stops cool air from migrating down the stack (which it can do if the burner is off), and the oxygen supply dwindles, so the flame has to look further for oxygen. Interesting, I hadn't heard of that. Any idea of what sort of time frame we're looking at?>>The valve in your photo... it appears to have some sort of capped-off port in the side. Wassup with that?Beats me - the valve was for a hose bib.
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Sojourners: Christians for Justice and Peace
I don't have any solid info on this, just hearsay. The main issue I've heard about is that when the clothes dryer and the water heater are in the same room, the water heater stack is a potential source of air for the dryer (which is pumping air out of the room as it runs). Then when the water heater turns on, the exhaust has to try to push the incoming cool air back up the stack. The results can apparently be either (a) oxygen shortage for combustion and/or (b) CO in the room.
That's what the draft hood is intended to do, keep any air coming doen the flue from going all of the way down though the water heater's internal flue to the combustion chamber."Supposed to" isn't always the sane as the same "does"I'll start looking for thatAnd, of course, when there is insufficient combustion air, the CO levels can shoot up, something I have seen numerous times
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Sojourners: Christians for Justice and Peace
Electrolysis seems the likely cause of the problem in the first picture but it might be worth checking to make sure that neither the water line not the armor have any leakage current on them. If the armor is being used as a ground path a fault downstream may impose a trickle current on the armor which, especially if the armor is inadequately grounded, loose connector or ground screw, may cause the leakage to the valve.
It can also operate the opposite way in that a trickle voltage in the water line could seek ground through the armor.
In either case a small leak at the bonnet and increased moisture in the vicinity would only make it worse.
The second case looks to my untrained eye like a fairly minor case of corrosion at the T&P but the corrosion on the flue may be an indication of inadequate air supply. Normally the pilot would keep the flue warm enough that the exhaust gasses, carrying water vapor, wouldn't condense in the exhaust stack and drip down.
Any back-flow or even the dripping condensate could extinguish the pilot. Not too big a problem if the gas valve safety operates correctly. IMHO the greater risk is carbon monoxide back-flow into the house or the catastrophic, but rare, consequences of the regulator not cutting the gas supply with a possible explosion.
On the other hand in really cold weather, certainly not here in Florida, it might be the case that the flue might rarely collect some small amount of condensate and drip a drop or two. In which case it might, just might, not be considered a problem.
The third case looks like some water has already caused some corrosion. It looks to be a poor siteing of the drain in relation to the panel. A drip pan might be fitted under the drain line and cleanout but, as far as it goes, I have seen worse.
On a minor point both the conduit going to the meter and the PVC run sticking up could be sealed with some duct seal. The exclusion of outside air from the panel can help control any fire and limit corrosion, both in the panel and meter can I assume is on the other side of the wall, by keeping warm moist air away from cold enclosures and buss bars.
Some inspectors would require the vertical run be terminated with PVC FA and a large NM connector. Again to prevent any chimney effect and limit the spread of any fire. I think the duct seal does a better job. Some use fiberglass batting or mineral wool.
Alternately some BIs would require a PVC MA and a bushing although I think stopping the chimney effect would be more a concern than the odd chance the square cut end of a PVC conduit, assuming rudimentary deburring and chamfering, might damage cables run across it.
You lost me in ackronym land. What is a PVC FA and a PVC MA?I never thought about the flow of air through conduit from outside to inside and vise versa. I will use duct seal from now on. A BI has never questioned me about this. Frank DuValYou can never make something foolproof because fools are so ingenious.
Frank:
Up here in eastern Canada, electricians are required to use duct seal at the outer part of the horizontal run from the exterior elbow into the panel. A couple of things have been happening due to the air leakage:
(1) the cold air cools the panel box, causing condensation inside and on the outer panel box. I have a picture of a panel in a damp basement with the service on the north side of the home. The upper outside of the panel had about 1/2"+ frost on it!!!
(2) with the high winds we get here from "Nor'easters", the wind drives rain up the wires into the weatherhead where it drains down the conduit through the meter box to the elbow. As this continues, water from the elbow eventually flows into the panel!! The corrective action required now at installation is to drill a small drainage hole in the bottom of the elbow and also use ductseal for a dam/airseal as the horizontal conduit leaves the elbow.
Edited 12/24/2005 12:28 am ET by experienced
Edited 12/24/2005 9:38 am ET by experienced
Re: "What is a PVC FA and a PVC MA?"Sorry. Trade talk. 'PVC MA' is short for a Male Adapter made out of PVC. A plasic fitting with a socket which glues onto the end of a plastic conduit and has a male thread on the other end.Similarly an 'FA' is Short for Female Adapter. Socket for gluing to conduit on one end and a female thread on the other. Male adapters allow a plastic conduit to connect to a standard knockout, KO, on an electrical panel or box and take a locknut and, if called for, a bushing.A FA, Female Adapter will accept a male thread as on a NM connector.The sealing is listed under a couple of articles in the NEC, 300.7(A) being the best known, but it is an article that is seldom cited by inspectors. Partly because it refers to sealing being required where "condensation is a known problem". The part about conduits transitioning from/to cold storage is well known and usually enforced. But generally, at least in this area where temperatures are pretty well moderated, the transitions between inside and outside are seldom required by the BIs to be sealed. Most, at least the ones I have talked to, think it is a good idea but they want to 'keep their powder dry' for bigger issues. It is one of those finer points that are nice to do, doesn't take much time if you have the material handy, but most contractors don't unless the inspector says something. If you do wish to seal the conduit don't use anything that will be difficult to remove or that might damage the insulation. This alone may explain why sealing is not pushed harder. Don't use spray foam or caulk. Duct seal or batt insulation is usually OK.
Good info.At the time of the inspection, the water heater wasn't backdrafting, but the melted bottom of the plastic coated "Danger" tag showed pretty clearly that it had backdrafted big time in the past.The WH shared the chimney flue with the furnace, so there is a nice steady state draft established in the chimney during the heating season.I'm pretty confident that if it had been checked in the summer it would have been backdrafting.I'm not sure why the rust on the WH flue, but the whole thing needs attention.
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Sojourners: Christians for Justice and Peace
"Electrolytic corrosion" is the proper term for what you see in these pictures. The corrosion process of the joining of dissimilar metals.
Electrolysis is commonly used to describe the process of fusion.
The most common type of electrolytic corrosion is steel and aluminium. Even to this day, and millions of dollars of damages from this corrosion, builders continue to mismatch these two products.
Steel screws in aluminium frames, steel nails in aluminium flashings, etc.
Even installing aluminium flashing over a steel nail used to nail the top plate of a parapet will result in holes corroding through the flashing everywhere.
Gabe
My local HD is now (finally, after all my joist hangers are nailed in) carrying 10d and 16d HDG nails. I have to wonder if it is legal CYA because people have been using ungalvanized GripRite garbage on ZMAX hangers.
Just the simple impacting of the nails head and the hammer is sufficient to remove the gavanized coating on galvanized nails to create a potential corrosion situation.
The industry is slow to change old habits.
Gabe
Thanks, those are terms that some how remain muddled in my brain.
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Sojourners: Christians for Justice and Peace
Bob,
I notice a fine layer of rust on top of the exhaust behind the danger tag. That and the water drop on the valve handle in "electrolysis" would make me believe that 95% of the corrosion problem was a leak as a fine mist. Poor combustion byproducts in the atmosphere will accelerate corrosion.
The melted danger tag is another issue best determined by consideration of the environment and configuration of the stack itself.
Finally, at the safety valve we see galvy to black iron to brass containing a hot humid or wet space.
Samt
Sam (et al)Good points, although the valve with electrolytic corrosion was well away from the water heater.It's sometimes tough to say what has caused rust on flues, or more properly, what caused the water to be there to cause the rust.
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Sojourners: Christians for Justice and Peace
FWIW, I'm working on a "home safety program" through my church whereno of the objectives is to help people understand what they are seeing and when it is a problem. These comments will help termendouslyMany/most people don't seem to have a clue when a component is visibly in bad shape or OK.
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Sojourners: Christians for Justice and Peace