Vessel for sampling liquefied anhydrous ammonia for subsequent trace oxygen determination

Abstract

A vessel for the sampling of anhydrous liquid ammonia in pipelines and storage vessels is described. The apparatus allows a representative sample of the liquid ammonia to be taken and completely vaporised. Complete vaporisation of the liquid sample ensures that the gaseous sample subsequently presented to a laboratory gas chromatograph for analysis is truly representative of the original liquid. By using the gas-chromatographic technique described, oxygen can be determined in the range 0.2–50 p.p.m. V/V. Hydrogen, nitrogen, argon and carbon monoxide can also be determined on the same chromatogram. Measurements of the oxygen content of ammonia in various storage vessels has allowed an inspection policy for such vessels to be formulated for early detection of stress-corrosion cracking initiated by oxygen. By correct choice of the liquid and expansion volumes of the sample vessel, it could be used for sampling other liquefied gases.