Corrosion in a ammonia threw compressor

[Tiquibola]

Dear Sirs,

I would like you can help me to analyse causes for corrosion found in rotors and shell of an ammonia compressor.

The step where corrosion is observed works at 15 Kg/cm2g and 90ºC.

Ammonia is pure and contains a 0,2% of water.

I include photos for observing the corrosion.

Ammonia compressor is new and it was startup last may, almost five months old.

Please could you help me to determine cause of corrosion.

Many thanks.