Do temperature changes cause rust?

[The One]

I understand that if in a humid environment occasionally heating a garage can cause more rust to bare metal than leaving the garage at a consistent temp.

Is the same true for humidity controlled garages?

I have a lot of bare metal in my garage workshop that I'd like to keep as rust free as possible until I get to using it. I do have a dehumidifier and a 97% furnace which both keep the garage under 40% RH at all times.

Will there be a difference in the rate rust forms if I keep the garage at 65F at all times vs allowing the garage to drop to 55F at night and heating back up to 65F during the day?

 

[chinboys]

Rust comes from iron in your metal reacting with water to make a compound called iron oxide.

So, you need to prevent the two from getting together.

Either paint or coat your metal to prevent water in liquid or moisture (dew point) to be able to react with or zero out the RH in the air regardless of its temperature (higher temperature holds more moisture).

I would just spray a light machine oil on the metal or move the metal into a conditioned and low RH level smaller room.

 

[Phantomd]

Dew point, temperature, and humidity all work together (Dew point is a result of the other two actually.)

If you have a dehumidifier in the garage you are on the right path. Keep the temperature of your garage above the dew point and moisture will not rapidly condense on any surfaces.

Here is an interesting item, it will measure the humidity in your garage and tell where the dew point is. It also has an alarm. all for $12
https://www.amazon.com/dp/B075F4Y2NZ/?tag=atomicindus08-20

 

[Showkey]

Indoor humidity in Wisconsin winters with heat is usually very low. (Usually) No need to run a dehumidifier in a shop with insulation and some what sealed building. My shop runs about 28-38% in winter with temps from 50-65* depending on the work being done. Summer I do run a dehumidifier keep the humidity under control.

In home living space many do the opposite......run a humidifier to increase the comfort levels to 50% humidity. Comfort is trying to avoid dry skin, cracked lips, cracked hands and static discharge.

If you’re pulling wet, melting snow covered vehicles in and out and open the doors often .......then controlling temperature and humidity can be more challenging. But cold air at 0* is very dry and can not hold very much humidity.

 

[JimNC]

Short answer is no. If you’ve got it below 40% at 55 you won’t have condensation at 65 so everything will basically be fine. Long term you will get some surface rust, so wipe stuff with an oiled rag from time to time...like every few months.

For a long time I kept a polished nail at my bench, figuring that it’d rust before anything else. After a year you could tell that it was less bright, but there wasn’t any real rust.

 

[finn]

The correct answer is a qualified maybe.

If your tools are cold and the room air is stabilizes at the same temperature as the tool mass is, there will be no condensation on the tool body.

As the room air increases, the tool mas increases much slower than the air temperature does. The warmer air can hold more water vapor, so, if the day warms up, and the warm air enters the room, water can condense on the tool. It only does this if conditions are right for condensation, though, ie the tool temperature has to be below the dew point of the warmer, potentially more humid, air.

If the relative humidity of the warmer air entering the room is low, such that the temperature of the cold tool is above the dew point, there will be no condensation.

I generally try to keep the doors closed in an unheated garage in the spring unless the weather conditions include low humidity days. It sometimes takes until late June until the 6” slab increases in temperature enough to avoid a wet, slippery surface from condensation.

 

[Showkey]

Typical temperature and humidity in the shop in winter......heat on, no dehumidifier: