Corrosion of steels in carbamide

[technovel]

Hello all,
I will coat twice-layers coating on the inside surface of the reactor for synthesis of ammonium carbamide (urea).
First layer (bond layer) will be NiAl, flame spraying, 100 micron thickness.
Second layer will be SS 04Cr19Ni11Mo2, flame spraying, 350 micron thickness.

SS 04Cr19Ni11Mo2 : Carbon 0.014, Chromium 18.2, Nickel 11.8, Molybdenum 1.95, Manganese 1.88, Phosphorus 0.022, Sulfur 0.012, Silicon 0.53, Copper 0.093, Cobalt 0.24, Titanium 0.10

Material of the reactor is 724L stainless steel.
Working conditions:temperature of 200 degrees Celsius, pressure of 250 atmospheres.
Synthesis of ammonium carbamide (urea).

I suppose that this twice-layers coating will be protecting for steel and welding seams of reactor during 5 years.
But I have some doubts about low percent of nickel in SS 04Cr19Ni11Mo2.
If this twice-layers coating will not be protecting during 5 years, please correct me.

If first layer will be 150 micron, will twice-layers coating be protecting for steel and welding seams of reactor more than 5 years?

If second layer will be 500 micron, will twice-layers coating be protecting for steel and welding seams of reactor more than 5 years?

[technovel]

Could you please help me to answer following question:
Will SS 04Cr19Ni11Mo2 provide the protection of inside surface of the reactor for synthesis of ammonium carbamide (urea)?

I haven't enough information. Could you please advise me patents or standarts or articles about corrosion protection of inside surface of the reactor for synthesis of ammonium carbamide (urea)?

[Gordon]

Hi technovel

Sorry, no real knowledge or experience with this one.

When you say ammonium carbamide, I assume you mean carbamide or diaminomethanal (Urea). I gather that the reactants are carbon dioxide and ammonia, under high temperature and pressure (don't know values). The reaction gives an intermediate product ammonium carbamate which then decomposes to urea and water.

I would suspect that your stainless steel coating in itself would be resistant to urea, but not so sure about ammonia and ammonium carbamate or any other reactant/catalyst that may be in there. I would feel happier using a NiCr alloy or alloys like Inconel 625 or Hastelloy C. Then there is a question of how to make the coating non-permeable to the environment.