Degradation processes in ammonia synthesis conditions

• Autorzy: Číhal V. , Stránský K.
• Konferencja: Metody oceny struktury oraz własności materiałów i wyrobów/sympozjum (XVI ; 11-13.12.2001 ; Opole - Komorni Lhotka)
• Języki publikacji: EN

Abstrakty

EN

Nitriding by ammonia synthesis gas causes a modification of the carbides, a decarburization and sensitization to hydrogen corrosion within a relatively thin metal layer near to the inner surface of the converters. Subsequently a sensitization to hydrogen attack occurs due to the reaction of diffusing hydrogen with carbon released by the carbides and a decar-burization by carbon diffusion to the surface. High local internal stresses perpendicular to the surface caused by surface nitriding lead to small inter-granular separations parallel to the surface without any significant effect on the integrity of the pressure vessel. As the nitrided layer hinders further nitriding of the steel, this phenomen is without any long-term consequence. On the other hand, if sufficiently high load and/or residual stresses apply in the axial or tangential direction to the vessel wall, cracks have to be expected propagating slowly across the wall, as crack growth is controlled by diffusion of nitrogen and carbide transformation. Consequently, the Nelson diagram for NH3-containing synthesis gas should be applied with only great care. Efforts are necessary to quantify as well the critical stress level for crack initiation, as the propagation rate of such cracks is controlled by nitrogen diffusion and the complex carbide reactions finish by chemically induced hydrogen cracking - hydrogen corrosion.

Słowa kluczowe

EN

ammonia synthesis conditions; degradation processes; hydrogen; synthesis gas

• Wydawca: Oficyna Wydawnicza Politechniki Opolskiej
• Czasopismo: Zeszyty Naukowe. Mechanika / Politechnika Opolska
• Rocznik: 2001
• Tom: z. 72
• Strony: 67--72
• Opis fizyczny: Bibliogr. 7 poz., tab.

Twórcy

autor

Číhal V.

autor

Stránský K.

• VŠB-Technical University of Ostrava, Faculty of Metallurgy and Materials Engineering, VUT - Technical University of Brno, Faculty of Mechanical Engineering

Bibliografia

• [1] CIHAL, V., Corrosion Mechanisms in Ammonia Synthess Equipment, 1st Int. Congress on Metallic Corrosion, London 1959. Published by BUTERWORTHS, London, April 1961, 591-595.
• [2] „Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants". American Petroleum Institute, Publ. 941, Washington DC, April 1990.
• [3] HEUSER A., Repair of Thick-Walled Ammonia Synthesis Converter Con-taining a Leak. AIChE, Ammonia Safety, Techn. Man. 32, 1992, 243-251.
• [4] HEUSER A., WAGNER G.H., HEINKE G., Hydrogen Attack in 2.25 Cr-1 Mo Steel below Nelson's Curve AIChA, Ammonia Safety, Techn. Man. 32, 1992, 252-267.
• [5] PRESCOTT G.R., Weld Failure in a 2.25 Cr-1 Mo Ammonia Converter. AIChE, Ammonia Safety, Techn. Man. 32, 1992, 217-231.
• [6] WATANABE J. et ah, Temper Embrittlement of 2,25 Cr-1 Mo Pressure Vessel Steel ASME 29th Petroleum Mechanical Eng. Conf, Dellas, Sept. 1984.
• [7] CIHAL V., BELKO J., REK A., STRANSKY K., The Thermodynamical Causes of the Cracking on the Internal Surface of the Pressure Vessel at the 40C"VC Tempera-ure and 17 MPa Pressure, Proc. VTtli seminar. "Difuze a Termodynamika kovu a slitin" Ćeska vedecka spolecnost pro nauku o kovech, duben 1993, 121-1,24.