"Wet" corrosion occurs under liquid electrolyte (a water solution with an electrical conductivity higher than zero). When H2O is in the form of vapor or ice it is not an electrolyte, therefore no "wet" corrosion. A very hot vapor (> 700°C) can also react with iron, but this is not "wet" corrosion, but hot gas corrosion, which has a completely different mechanism.

Dear Dr. Muralishwara Kakunje ,

wet steam is the water vapour including water droplets, dry steam is at the boiling point of water but has no water droplets, while superheated steam is the water vapour at a very high temperature than the boiling temperature at that pressure. The key difference between wet and superheated steam is that wet steam is at the boiling point of water and contains water droplets, whereas superheated steam is at a higher temperature than the boiling point of water and it does not contain water droplets.

In addition to what is correctly mentioned by Dr. Vadim Verlotski , in the case of steam flows containing water droplets within propulsion/drive/power systems (e.g. in the low pressure stages of a turbine) there may also be evident corrosion/erosion phenomena due to the impact microdroplets with the impeller blades, creating efficiency and maintenance problems, due to uncorrect operating mode in such conditions.

My best regards, Pierluigi Traverso.

Super heated steam does not have intrinsic moisture, whereas other types of steam do have intrinsic moisture. Worst is wet steam which has apart from water vapour, droplets of water in its structure which causes corrosion.

A.V.Sethuraman

Wet steam can deposit water in the pipework and if drainage is not good can cause water hammer or corrosion when the pipe is not in operation. The other issue with wet steam is erosive damage, as the droplets can be erosive if the steam velocity exceeds about 20 m/s. These effects do not occur when the steam is superheated.