In the urea plant carbamate corrosive environments are commonly found in the HP synthesis, MP and LP sections. Carbamate, especially in the HP synthesis section, is very corrosive, even for stainless steels.
For delicate diaphragms used for pressure and differential pressure measurements this proves to be an even bigger challenge as there is (almost) no corrosion allowance, the diaphragm’s thickness is somewhere near to 100 µm (0.1 mm/0.004 inch). The conditions are even worse for diaphragms in the vapor phase of such sections due to a phenomena called condensation corrosion.
Therefor the choice of material, the processing (shaping, welding) of such diaphragms and the application is particularly important.
The repair/replacement of a failed diaphragm type pressure or differential pressure instrument usually requires the shutdown of the process or the process unit. This leads to expensive downtime, capacity turn down or even potentially unsafe operations.
In 1996 Sandvik and Stamicarbon introduced Safurex®, a super duplex stainless steel specially developed for urea service. Now, after more than 25 years of operational experience, it is confidently confirmed that most of the typical corrosion problems that are present in urea plants, can be solved by
using Safurex®.
This paper presents the development of Safurex® thin foil diaphragms for pressure and differential pressure measurements in carbamate corrosive environments in urea plants and other corrosive environments.