Stamicarbon and Sandvik have developed a new duplex stainless steel material, which does not require the high concentration of oxygen in the process streams to maintain a passive layer. Laboratory corrosion tests never resulted in active corrosion even under conditions that oxygen concentrations were possibly zero. This material has been named Safurex^®.

The use of Safurex^® as construction material in the urea synthesis made Stamicarbon decide that the oxygen content in the CO₂ can be safely reduced to below 0.04% (vol.).

The passivation air is therefore minimized. Consequently the chance that during upset plant conditions the inert vent gas from the synthesis section becomes flammable is now almost non existing and makes the plant intrinsically safe.

The use of Safurex^® as construction material in urea plants is becoming more and more common and Stamicarbon has since 2001 made it its standard. Fabrication of urea synthesis equipment is experienced as easy. The corrosion resistance of the material is better than the corrosion resistance of the traditional urea quality stainless steels. The resistance of Safurex^® against stress corrosion cracking due to Chlorides in tubes of the traditional HP carbamate condensers is far better than experienced with austenitic materials, which are sensitive for stress corrosion cracking. The investment in Safurex^® equipment is below the investment in equipment using traditional materials. All equipment and parts needed for a complete grass roots urea plant in Safurex^® are commercially available.

Investment

Safurex^® has a significantly higher mechanical strength than the austenitic stainless steels traditionally used in urea plants. This property allows designers to reduce the thickness of liner plates, tube walls in heat exchangers and HP pipe wall thickness while maintaining even better life time expectations of the equipment.

The overall investment costs of Safurex^® equipment, as a consequence of this increased material strength, is lower than the costs of traditional equipment (about 5 to 10%).

Besides the above, the reduction in tube wall thickness results in a larger inner diameter of the heat exchanger tube, which in turn has an impact on the dimensions and finally the weight of the equipment.

Availability of Safurex^®

To be able to reduce the oxygen concentration in the CO₂ to zero, the synthesis section must be constructed completely in Safurex^®. Therefore, besides plates, bar, tubes, pipe, weld consumables and the like, also check valves, safety valves, block valves and control valves in contact with the process medium are available in Safurex^® too.

Stamicarbon and Sandvik have solved the availability topics with a number of suppliers of these parts, resulting in proper and competitive availability of these materials.

As Safurex^® has been developed by Sandvik together with Stamicarbon, the material is principally available for use in projects using the Stamicarbon urea technology.

For more information you can download the Safurex ^® paper [1810 kb].

Experience

Increasing numbers of customers choose Safurex^® for their newly built equipment and piping as evidenced by the growing list of references. Several high pressure carbamate condensers and strippers as well as complete synthesis equipment and piping have been delivered.