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Rust is the Enemy

Susquatch

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Seems there is a lot of factors in this % humidity temperature, air flow rust is always happening , my question is what % of humidity do you think you start to see a real increase in the rust forming is 30% or 50% too much? obviously less would be better and less would mean it would take longer to produce the same amount of rust.

Thankfully, I don't think that's true. The % relative humidity may have a miniscule effect but only in closed environments where you can have localized dew points reached because of localized temperature differences. Even in these conditions, the overall humidity is not nearly as important as the temperature (because the rate of corrosion goes up with temperature), whether or not you have localized condensation, whether the dew point has been reached, corrosive elements (eg salt) in the air, and especially when you have disimilar metals in contact with each other. Water and dissimilar metals create a battery effect that is much stronger than wet metal. It helps to remember that all corrosion is the result of a charge differential. No differential - no corrosion. But even the grain structure of a metal can create a battery effect because each grain is slightly different than its neighbour.

All other things being equal, the name of the game is to keep the humidity/temperature below the dew point as opposed to targeting a particular % relative humidity. Mind you, the easiest ways to do that are to keep the overall humidity low and/or to heat the localized air (which raises the temp above the dew point for a given mass of air).

Another way to look at it is to assume a room is full of 100% relative humidity. If you put a light bulb in a cabinet that is inside that air, it will warm the enclosed air in the cabinet above the dew point and prevent corrosion.

Yet another way to look at it is to understand that water in pure vapour form (a gas) does not cause corrosion. On the other hand water in liquid form can cause corrosion by creating a localized battery effect.
 

Susquatch

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Seems there is a lot of factors in this % humidity temperature, air flow rust is always happening , my question is what % of humidity do you think you start to see a real increase in the rust forming is 30% or 50% too much? obviously less would be better and less would mean it would take longer to produce the same amount of rust.

At the risk of complicating matters even more, I realized I might have misled you a little.

It actually is possible to determine the % relative humidity needed to prevent corrosion. To do this, you need to know the current temperature and the current relative humidity. You can then use Psychometric charts to determine the temperature at which the dew point will be reached. Some relatively inexpensive humidity meters do the calculation for you.

Conversely, if you know the minimum temperature you expect to reach during a given time period, you can use the charts to determine the % relative humidity that is required at the current temperature to reach the dew point at the minimum temperature. If you lower the % relative humidity at the current temperature below that relative humidity from the chart, then the dew point will not be reached at that minimum temperature.

But the charts and graphs are complicated to use so it's generally easier to just play it safe by heating the space in the winter - which automatically reduces the relative humidity, and by dehumidifying in the summer. 50 to 60% is a good target under most conditions.

I hope that's a better answer for you.
 
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francist

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50 to 60% is a good target under most conditions.

Indeed that is a good goal.

To further split the hair, in the collections management world (caring for museum artifacts) the gold standard for maintaining a mixed collection is 50 percent RH plus or minus 2%, and 20 degrees C plus or minus 2 degrees. If you can manage to attain that over a full year seasonal cycle you’ve hit the top tier rating for storage of artifacts. Few places actually can, and even fewer small to medium-sized museums. Even with all the gizmos and automation there is still a large level of human intervention to tweak the dials this way or that to try to keep ahead of it.
 

Susquatch

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T
Indeed that is a good goal.

To further split the hair, in the collections management world (caring for museum artifacts) the gold standard for maintaining a mixed collection is 50 percent RH plus or minus 2%, and 20 degrees C plus or minus 2 degrees. If you can manage to attain that over a full year seasonal cycle you’ve hit the top tier rating for storage of artifacts. Few places actually can, and even fewer small to medium-sized museums. Even with all the gizmos and automation there is still a large level of human intervention to tweak the dials this way or that to try to keep ahead of it.

That is great info. I didn't know that.

I am speculating a bit here, but I suspect that the museum goals are not really corrosion related. I'd guess that it's probably more about keeping things from drying out or becoming too moist and cracking or swelling in some way or expanding and contracting due to temperature. It may also be related to chemical stability for paints and other substances that can volatolize in low humidity or high temperatures. I suppose chemical stability is a nightmare for those poor folks.

Good stuff! Thanks for sharing!
 

combustable herbage

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That's a hell of an answer I wish I had read the second one before the first one:) I think I have to learn more about the dew point and humidity I never really payed much attention to it maybe its why I have a difficult time sprouting seeds. I think the dehumidifier setup you have is the way to go, for my garage the door is open 18 hours a day so what's outside is inside and coming from the west I definitely have learned to spray everything down especially the snow blower.
 

francist

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probably more about keeping things from drying out or becoming too moist and cracking or swelling in some way or expanding and contracting

Correct, although corrosion and or other material degradation can and does occur albeit slower, so the objective is always to slow the mechanisms down as much as possible. Most damaging though, as you surmise, is repeated fluctuation between the highs and lows. I’ll often tell a contractor it’s not about going back and forth trying to hit that magic number but picking a number within the zone that you can stay at and sit there. Way better for the artifacts in the long run.
 

Chicken lights

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Indeed that is a good goal.

To further split the hair, in the collections management world (caring for museum artifacts) the gold standard for maintaining a mixed collection is 50 percent RH plus or minus 2%, and 20 degrees C plus or minus 2 degrees. If you can manage to attain that over a full year seasonal cycle you’ve hit the top tier rating for storage of artifacts. Few places actually can, and even fewer small to medium-sized museums. Even with all the gizmos and automation there is still a large level of human intervention to tweak the dials this way or that to try to keep ahead of it.
To further muddy the waters the one place I was at in Texas wanted their building UV controlled to protect the exhibits. So temperature, humidity, UV and I’m assuming sunlight controlled building yet still have doors that open and close for tourists

Tall order indeed
 

Susquatch

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...... my garage the door is open 18 hours a day so what's outside is inside and coming from the west I definitely have learned to spray everything down especially the snow blower.

I don't live there so I don't know what your conditions are really like. But I gotta tell you that I think an open door is a recipe for problems.

For example. Let's just say it's a really hot humid day outside. The door is open so that hot wet air from outside ends up inside where it's shady and therefore cooler. The temperature drops, the dew point is reached, and moisture forms on everything. Rust is inevitable.

You are way better off closing that door and dehumidifying the inside of your garage.

FWIW, the opposite happens in winter. That cold air outside can't hold much water to begin with. But when it comes in from outside, it gets warmed up and the humidity dives. Stuff starts drying out and cracking. Corrosion is not a problem as long as it's warmer inside than outside.

It never hurts to oil the crap out of stuff the way you do though. Just wish I could find the perfect oil!
 

Susquatch

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To further muddy the waters the one place I was at in Texas wanted their building UV controlled to protect the exhibits. So temperature, humidity, UV and I’m assuming sunlight controlled building yet still have doors that open and close for tourists

Tall order indeed

Should we call you superman?

How did it turn out?
 

Chicken lights

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Should we call you superman?

How did it turn out?
It was very well designed, not by me. Small man door controlled by a park ranger admitting entrance. Windows strategically placed. There was a walkway over the whole exhibit to keep human interaction away from the open excavation.

You can tell by the quietness of such buildings how tight they are, it’s truly amazing. If I had to guess it was roughly 100’x300’ inside, very impressive
 

Susquatch

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Wish I found that thread before I started this one. It's always easier to build on what others have done that to start fresh.

But ya, that's galvanic corrosion of dissimilar metals for sure. All it took was a little moisture in an enclosed container from a fishing trip, or a sub-zero winter night below the dew point of the trapped air, or even one of those hydrous rubber wormy things, to get those galvanic batteries going and the result was inevitable. Even in Alberta!
 

historicalarms

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Yup, and the most damaging of all of those is…wait for it… humans.

you should see the ancient history museums in Greece, dozens of them with thousands of unreplaceable artifacts thousand of years old with huge sunlight domes overtop most every room...and every room will have a sign posted everywhere..."no flash Photo's allowed, punishable by federal law # 535"
 

Susquatch

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you should see the ancient history museums in Greece, dozens of them with thousands of unreplaceable artifacts thousand of years old with huge sunlight domes overtop most every room...and every room will have a sign posted everywhere..."no flash Photo's allowed, punishable by federal law # 535"

Saw the same thing visiting a Kincaid Art Gallery in the USA. Big huge windows and individual spot lights on all the paintings. But no flash allowed. Only thing worse than a fool is a whole crowd of em. Skylights in Greece prolly don't even have UV screening.
 

Susquatch

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you should see the ancient history museums in Greece, dozens of them with thousands of unreplaceable artifacts thousand of years old with huge sunlight domes overtop most every room...and every room will have a sign posted everywhere..."no flash Photo's allowed, punishable by federal law # 535"

I'm surprised they don't have a law that forbids the sun from shining. That's what the Canadian govt would do.
 

Susquatch

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Mine you can set it to pump all the time or it fills the internal bucket, with some way of shutting it down once the bucket is full. You’d basically be replicating that system on a larger scale. Not a bad idea at all

7 days later and the dehumidifiers seem to have stabilized at 55%. The 5 gallon buckets were both about 3/4 full. That jives nicely with the calculation.

I still plan to add float based safety shutoffs, but it looks like two big 5 gallon pails and a willingness to dump once a week should do the trick. I'll also dump everytime I open a barn door.

The small permanent electronic unit for my travel trailer should be here next week.
 

Tom O

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You could hook up a pump to the overflow switch that could run for a minute or so to empty the bucket rather than having to remember to empty it.
 

Susquatch

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You could hook up a pump to the overflow switch that could run for a minute or so to empty the bucket rather than having to remember to empty it.

So therein lies the problem I've tried to resolve.

My barn has no floor drains. Under the cement is hard packed clay. Originally, I was going to put a drain through the wall. In that scenario, I don't need a pail at all. Just hook the Dehumidifier to the wall drain and go.

However, I really didn't like putting a drain through the wall. So the solution I came up with was a 5gal pail (or a series of cascading pails) to replace the much smaller built-in reservoir.

I am pleased to have learned that one pail for each of my two dehumidifiers is adequate for my needs and only needs to be dumped once in a week or so.

Maybe in time I will grow tired of dumping pails and put in a wall drain. For now, I am thrilled to have a nice dry barn to work in.
 
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