15% and 70% ammonia corrosion

Under these operating conditions, carbon steel and low-alloy steel suffer from uniform corrosion. Corrosion resistance of the material: excellent, with an annual corrosion rate of <0.05 mm/year. Note: Carbon steel and low-alloy steel are prone to stress corrosion in ammonia systems; relieving stress can prevent stress corrosion cracking.

As I understand it, carbon steel and low-alloy steel tend to suffer from stress corrosion only in the presence of anhydrous liquid ammonia; in the presence of water, they only experience uniform corrosion. That’s incorrect; please correct it.

This post was last edited by nj1952 on 2017-8-5 09:10. (1) Carbon steel and low-alloy steel exhibit excellent corrosion resistance in dry ammonia and liquid ammonia, with a corrosion rate of less than 0.1 mm/year； The corrosion rate caused by wet ammonia gas and ammonia aqueous solutions is also low, at less than about 1 mm/year, and the form of corrosion in all cases is uniform corrosion. (Note: The author once observed shallow dish-shaped pitting in a localized area on the inner surface along the bottom of the shell of a horizontal liquid ammonia storage tank; the area affected by this pitting was approximately 1–2 m2, and it was determined at that time that it was caused by under-scale corrosion.) (2) Studies have shown that for carbon steel and low-alloy steel, stress relief in anhydrous liquid ammonia, along with the addition of 0.2% water and O2, can prevent stress corrosion cracking.