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New stainless steel developed for urea production

Sandvik Coromant UK : 30 August, 2001  (Company News)
A new stainless steel has been developed by Sandvik Steel, specifically for use in the production of urea.

Produced in cooperation with leading urea process system designer and operator, Stamicarbon of Holland, the new grade, called Sandvik Safurex, has improved corrosion resistance in carbamate solutions and greater resistance to stress corrosion cracking if chloride content in the process is high. Sandvik Safurex is designed to resist much higher chloride concentrations at higher temperatures than both of the commonly used urea grade stainless steel materials - 316L Urea Grade and Sandvik's own Sandvik 2RE69. As a result, the higher performance capability of Sandvik Safurex in carbamate solutions makes it an ideal choice for key parts of the urea process such as strippers, high pressure condensers, scrubbers, high pressure piping and reactors.

The properties of new Sandvik Safurex are already being proved in service. Tubes in the new grade were selected for installation in a high pressure carbamate condenser, fabricated by Schoeller Bleckmann Nooter in Austria and installed at the Police Zaklady Chemiczne urea plant in Poland. Over 22000 metres of 25mm outside diameter tubing were supplied by Sandvik from its manufacturing plant in Sandviken, Sweden.

Selected to overcome a problem of leaking stainless 316L urea grade tubes, caused by too high chloride content in the boiler water, the key Safurex property is its improved resistance to stress corrosion cracking. It also has higher mechanical strength which will also contribute to a longer service life. Before installation of the condenser with Safurex tube, several tubes in the previous condenser needed to be plugged due to leakage. Such stoppages can typically last between 3 and 5 days incurring substantial costs in lost production.

After one year in operation, the new condenser has been inspected by Stamicarbon and no corrosion has been found in the weld area or heat affected zones where the first evidence of corrosion would be expected. Special eddy current testing of the tube wall has also revealed no signs of corrosion. Similarly, there are no signs of any deterioration in the protective oxide layer on the tubes indicating that the oxide layer is resisting the harsh environment in the condenser.

Although only one year into an expected service life in excess of 15 years, because of the excellent condition of the tubes, Sandvik is confident of the ongoing performance of the new material.

Sandvik Safurex is available in all product forms - tube, pipe, fittings, plate, bar and welding consumables.
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