How a vacuum LDS system is able to distinguish a false indication from an ammonia cloud in the atmosphere from a real liner leak ?
High pressure urea equipment consists of a carbon steel pressure bearing wall, which is protected against corrosion by a protective stainless, titanium or duplex steel layer. This protective layer can be an overlay welding, an explosive cladded layer or a loose liner. Any leak in a loose liner will lead to a dangerous situation in that a large surface of the carbon steel pressure bearing wall underneath the leaking loose liner compartment will be exposed to the extremely corrosive ammonium carbamate. Experience has shown that ammonium carbamate can corrode carbon steels with very high corrosion rates up to 1,000 mm (40 inch) per year.
When talking about active leak detection systems, one can distinguish a pressurized system, in which an inert carrier gas stream flows through the leak detection circuits and a vacuum based system, where one pulls vacuum pressure behind the liner. We recommend a vacuum based leak detection system for several reasons.
But how can a vacuum system distinguish a false indication from for instance an ammonia cloud in the atmosphere from a liner leak ?