Carry over is a process to ...

Carry over is a process to carry the Impurities and water treatment chemicals from boiler water into steam through mechanical and vaporous carryover. I.e  salts of  oxides, hydroxides, and silica. It can deposit in area of process for production.

• Deposit on the turbine blade resulting in corrosion and efficiency losses.  
• Deposits in turbine valves prevent valve closure resulting destructive overspeed.  
• Deposits in the superheater and reheater can cause reduced heat transfer resulting tube overheating, and exfoliation.  

Mechanical Carry-over reasons are following,

• poor design, damage, or incorrect installation of steam drum moisture separators
• poor control of boiler drum level
• high rate of pressure changes
• foaming of the boiler water due to high concentrations ofTDS, alkalinity & organics.

Vaporous Carry-Over (Volatility) -  A distribution ratio concentration of a specific molecular compound in the steam to its concentration in the liquid water.  

I have cover practical problem of boiler water treatment in my book Fundamental Boiler Chemistry & Preventive