Wet Steam

Definition - What does Wet Steam mean?

Wet steam is a mixture of steam and liquid water. It exists at a saturation temperature containing more than 5% water. It is said to be a two-phase mix: steam contains droplets of water that have not changed phase.

Wet steam may cause corrosion in vulnerable equipment such as turbine blades, low-pressure steam piping and heat exchangers. Wet steam lowers the heat transfer efficiency of steam, which results in an inefficient sterilization procedure.

Wet steam is also known as supersaturated steam.

Corrosionpedia explains Wet Steam

Wet steam is generated by heating water, which then turns to steam at the first stage. If additional heat is added to wet steam at a set pressure, the temperature remains the same until all the liquid is evaporated. Only then does the temperature rise above saturation, allowing the formation of wet steam.

The quantity of water in wet steam is designated by the quality. The superiority of steam refers to the percent of steam flow that is steam and water by weight. Steam that is 90% steam and 10% water is known as 90% quality steam. Wet steam is the most difficult type of steam to measure.

Problems that are caused by wet steam in a steam system include:

  • Hydraulic water hammer - An accumulation of condensate or humidity in pipelines or appliances is carried by rapidly moving steam.
  • Erosion - Excessive presence of water in steam lines promotes erosion.
  • Deposits of water-treatment chemicals - Degrade heat transfers by forming deposits in heat exchangers.
  • Contamination - Traces of treated water in the steam can contaminate the product.
  • Destruction of turbines - Water droplets literally destroy the vanes of a turbine.

It is very important that the boiler, steam traps and piping be routinely maintained so that the problem of wet steam caused by the distribution system can be avoided. If they become filled with water and dirt, they may not work effectively, or at all.

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