Humidity vs. Temperature

[SN1007]

Hello all,

I am looking for some infor on the combined effect of temperature and humidity on the corrosion of steel.

My specific area is in the use of an engine heater on an aircraft engine and is there a negative effect of operating the heater on a timer when the aircraft is to be used vs. leaving it plugged in all the time.

Would a higher air temp and enthalpy promote more rapid corrosion for a given specific humidity, or would the higher relative humidity of a lower temperature be more detrimental, assuming the cooling did not create condensation?

 

[metengr]

Basically,most corrosion mechanisms are based on reaction kinetics. Typically, temperature plays a significant role in reaction kinetics, so I would say for a fixed humidity level, the higher the temperature the more rapid the corrosion. At some point, other rate-limiting factors, like oxide thickness, change of anodic or cathodic behavior, besides temperature, will affect corrosion.

 

[rcstrong]

Direct oxidation of steel is quite slow at low (ambient) temperatures. It isn't until you have an aqueous phase present that you will accelerate corrosion. Keeping the skin temperature 10-20F above dew point in most cases shouldn't cause any problems and should mitigate the effect of ambient thermal cycling and associated condensation. However, if you live in a coastal area where the air itself may occasionaly be "salty" you have the added risk of salt being present on the skin, and salt is hygroscopic. If you elevate the temperature on a hygroscopic salt enough to get it hot but not dry it out, corrosion will increase dramatically.