Automotive corrosion and humidity
How We Can Help The Automotive Industry?
Corrosion issues with vehicle manufacture
For many years automotive companies have had corrosion issues with vehicle manufacture that started while the steel was in storage. For many years the normal procedure for the storage of such products was to increase the temperature in the storage area. This has the effect of expanding the air volume and lowering the relative humidity.
Steel will corrode if the relative humidity is greater than 55%. This was initially discovered in the 1930’s by Vernon and the acceleration rises vertically on a graph at this stage.
Four key factors are necessary for atmospheric corrosion to occur. These same factors are the same for regular aqueous corrosion to occur. The four factors are; there must be an anode, a cathode, an ionic conducting electrolyte and an electrical conducting path between the anode and the cathode. If any one of these four factors is missing corrosion does not occur. The steel becomes the Anode and Cathode and the humidity becomes the electrolyte. The amount of corrosion depends on the level of relative humidity as found by Vernon.
The Ford Motor Company were building a new facility to serve the Halewood motor plant in Liverpool, North West England and needed to look at storage for a large amount of very high quality automotive steel to ensure they would have no supply and demand issues with their production.
Automotive controlling humidity
The indirect method of controlling the relative humidity is by installing the normal dry heat method to heat the warehouse continually over the ambient conditions. However we proposed the concept of controlling the relative humidity by installing a desiccant dehumidifier, this being the method of removing the moisture directly from the air in contact with the steel.
In 1993 Desiccant Dryair Systems installed 3 x Dryair 10 000 VRF Gas Powered Desiccant Dehumidifiers delivering 10 000 m/hr of very dry air respectively. Each machine will remove 60 kg of water every hour.
Desiccant Dryair installed the entire system. The introduction of an accelerated opening door entry system ensures the Controlled Humidity Environment would not be totally forfeited every time the door is opened. Desiccant Dryair also installed all the natural gas, electrical and controls infrastructure as well as the Dryair delivery ductwork. The entire warehouse is kept at less than 45% relative Humidity, which is acceptable as a compromise between cost of running and achieving the desired result.
Less than 50% relative humidity will slow atmospheric corrosion and if a level of less than 40% relative humidity is held, corrosion will cease.
The Dryair Desiccant Dehumidifiers hold this condition throughout the year regardless of activity through the door.
The warehouse houses steel from TATA, Wellbeck and other steel manufacturers. The steel arrives with minimal protection to give a quick unpack rate onto the production line.
Even with no coil protection there has never been a recorded case of corrosion at the Widnes steel facility in 25 years.
We are now in the process of installing a new facility for the storage of aluminium coil which will require Dryair VRF(HP) units opposed to the standard Dryair Desiccant Dehumidifiers. They are still desiccant dehumidifiers but use heat pump technology to control the relative humidity and the temperature in one packaged unit which assists with the pressing process of the aluminium.
Dryair standard range of desiccant dehumidifiers.
Dryair VRF(HP) Desiccant dehumidifier with heat pump technologies.
Painting / Spraying
Painting and finishing booths require a relatively high humidity in the air to keep overspray to a minimum level using laminar flow technologies.
Keeping overspray to a minimum ensures that the final finish is exceptional.
Rolls Royce Chichester, Aston Martin at Gaydon, Coventry have had such issues with the paint lines due to overspray.
Adiabatic humidifier – solution
We installed Adiabatic humidifiers at Rolls Royce, Chichester in 2002 and Aston Martin, Gaydon, Warwickshire in 2004. These systems require a combination of both heating and cooling to achieve the desired temperature and using the adiabatic line, (wet bulb temperature) we humidify to achieve the desired level of humidity.
The required off conditions were 24.0°C and 65% relative humidity. The tolerance of the Rolls Royce system was relative humidity +/-1% and temperature +/- 1.0°C and had to reach the desired level within 20 minutes from start up.
Both systems are still operational today in 2015.
Humidity control products
- Humidair evaporative (adiabatic) Humidifiers
- DDS AHU to control the temperature onto the humidair system.