It also depends on what ...

It also depends on what industry you are working with.  If you are involved in the food industry then the next question becomes is there any live steam injection?  If the answer is yes , then there can be no treatment to the boiler steam.  If the condensate is not for the food industry, then treatment can be used.  DEHA removes oxygen in the boiler feed and is volatile and removes oxygen in the condensate or more importantly converts rust to stable magnetite under alkaline conditions and so needs neutralising amines as well.

There are filming amines, which help protect the pipework. 

If you are a high pressure boiler, then demineralisation is the answer.  In many boiler plants the first stage of pre-treatment is Base exchange softening.  This only removes calcium and magnesium and converts them to sodium.  Sodium bicarbonate breaks down to form sodium hydroxide in the boiler and carbon dioxide which flashes off with the steam and forms carbonic acid, which is the cause of grooving in the condensate.  The higher the level of bicarbonate in the water the higher the level of CO2 and therefor the higher the level of corrosion.

The use of a de-alkalisition plant or more recently RO in conjunction with BX softening reduces the bicarbonate and reduces condensate corrosion.  

There is another form of corrosion, which is caused by the boiler carry over.  This occurs due to either priming, or foaming.  I have seen severe damage to superheaters caused by the boiler foaming then baking hard generating crystalline cracking.  This same process can occur on heat exchangers.  As a result good control of boiler conditions is essential. 

It may sound basic but the correct design of boiler plant is also essential.  A boiler rated at 6000 kg per hour will only provide 100kg per minute providing the feed water is @100 ºC.  Most boiler feeds are at a lower temperature and as such are no longer able to produce a full load.  Once the load is exceeded, then the boiler can prime causing water carryover, which in turn causes corrosion.  Dry steam does not cause corrosion, it is only when it is wet steam or when the steam condenses that corrosion can take place.  So the boiler plant needs to operate within its loading limit to maintain pure steam and control condensate corrosion.