Problem No. 30: What is the best stainless steel for urea?

Ammonium carbamate is an intermediate product in the production of urea from carbon dioxide and ammonia. Ammonium carbamate is very corrosive under the synthesis conditions in a urea plant. The various process licensors have developed different solutions to assure sufficient safety and reliability levels. In the early days titanium and 316L Urea Grade stainless steels were applied. The process conditions in the high pressure stripper are the most severe, i.e. the highest temperatures and lowest oxygen partial pressures are present. A new stainless steel 25-22-2 with a higher chromium content was developed specifically for the high pressure CO₂ stripper. Super duplex materials like Safurex® and DP28W™ and Omega-Bond™ (a combination of zirconium with titanium) are the latest developments and have proven to be better than earlier materials, but what is the best material?

Mr Janusz Mac´kowski of Zch Police in Poland starts the Round Table discussion: What is the best material for the stripper (tubes and liner) and the other synthesis equipment in a urea plant: Safurex®, Super duplex, DP28W™ (Sumitomo), bimetallic with Zr/25-22-2, any others? What is the actual level of oxygen they need? What is the best material for the urea reactor liner?