High Temperature scaling

Describe your system & process first.

What are you heating pipe or flat surface? where are you heating inside pipe or in furnace? what are you heating for? and? and ? How do you expect to get an answer to a senerio of which you and only you can visualize?

The furnace is rotary kiln and product is cement. Usually at inlet and out let end cooling cowl is provided. Cowl is an annular ring made up of M.S plate mounted over kiln shell at both end. Atmospheric air through blower is used between kiln and cowl, to cool tip of kiln shell.

The scaling is observed on kiln shell surface. Its an unusual phenomena and rarely observed.

350ºC Is not scaling Temp.

Maybe some corrosion inducing gas coming out.

In any case--Aluminium Enamelling after sand blasting should stop the scaling.

Ask Enamel supplier how to prepare surface prior to enamelling.

I'm unclear about your specific application (piping system or ???).

You may coat the steel surface with inorganic zinc paint material. I expect that your system is also insulated for heat conservation.

662 degree Fahrenheit (350 degrees C) should not produce mill scale on mild steel. Temperatures of 1600 degrees F will produce scale - normalizing temperature. If you are getting scale at 350 degrees C, I have to ask what is the product, how are you measuring the temperature?

Under normal condictions you should not be getting scale!

The furnace is rotary kiln and product is cement.

Usually at inlet and out let end cooling cowl is provided. Cowl is an annular ring made up of M.S plate. Cowl is mounted at both the ends. Atmospheric air through blower is used between kiln and cowl, to cool tip of kiln shell.

The scaling is observed on kiln shell surface. Its an unusual phenomena and rarely observed.

Please inform whether any analysis of the cooling air that is being blown in is available.

The humid atmospheric air through blower which is used between kiln and cowl, to cool tip of kiln shell is the cause of scaling. The moisture at the atmospheric air causes a rust, therefore try to use a dry atmospheric air with a relatively higher temperature.

Here is a simple solution:

use 302 and green the stainless at 900'C in N2 with H20 vapor injection. Nothing will form or stick to a greened SS surface unless you beat on it with a big stick.

We use greened SS to prevent scaling of fixtures used in a high temperature hydrogen/nitrogen annealing system.

Simple. Eliminate divalent ions such as calcium, magnesium, sulphate and carbonate, and also eliminate silica in the water before it wets the <...mild steel...>. The water is best kept mildly alkaline (typically a pH of around 8.5), and then scale and corrosion will not occur.