Rupture Disc Corrosion

[Yench]

I have experienced pitting corrosion of nickel rupture disc protecting anhydrous ammonia pressure vessel. EDS lab test indicates high amounts of chlorine at the pits. The source of the chlorine is unknown at this time. No other elements of any amount are present. Would chlorine cause the corrosion in an anhydrous ammonia gas atmosphere? During installation, water could possibly contaminate the area of the pipe where the rupture disc is installed.

Alternately,would ammonia cause corrosion of the nickel, possibly in combination with water as above. Also, present is stainless steel, carbon steel, rust in the pipe.

Just trying to pin down the source of corrosion. The chlorine shows up on some of the new nickel discs also.

By in large, the nickel discs are trouble free except for a few unexplained installations. Bad batch of nickel discs?

Any help appreciated.

 

[TVP]

I would recommend visiting the website for Special Metals, the largest producer of nickel-based alloys, or Allegheny Ludlum, another leading producer. Both of these companies have excellent technical data available on-line, which hopefully will be useful to you.

http://www.specialmetals.com/

http://www.alleghenyludlum.com/

 

[BarryMartin]

Any water in combination with chlorine would form hypochlorous and hydrochloric acid by hydolysis reaction. Hypochlorous acid is very aggressive towards nickel.

I don't understand where the chlorine would come from. Are you sure that this is not chloride ion. If it is chloride, then the formation of hypochlorous acid could not occur so the distinction is important.

Chlorine is a diatomic molecule, i.e., two atoms join to form the chlorine molecule. Chloride is a single negatively chaged ion.

 

[TVP]

BarryMartin,

Do you have an understanding of the EDS (Energy Dispersive X-ray Spectrometry) technique? If not, what you should understand is that it detects the presence of a chemical element, whether it exists as an ion or as the diatomic molecule in the case of chlorine. Most likely the chlorine is present as an ion, introduced from chlorinated water or some type of salt contamination during coating, transportation, etc.

 

[BarryMartin]

Perry's Handbook for Chemical Engineers shows ammonium hydroxide (i.e., ammonia dissolved in water) and nickel as not being a good match. Especially for a rupture disk. Rated as poor to fair in this service (1 on a scale from 0 to 6)