API RP 941-2008 pdf download.Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants.
3 Operating Limits 3.1 Basis for Setting Operating Limits Figure 1 illustrates the resistance of steels to attack by hydrogen at elevated temperatures and hydrogen pressures. HTHA of steel can result in surface decarburization, internal decarburization and fissuring, or both (see Section 4). Figure 1 gives the operating conditions (process temperature and hydrogen partial pressure) above which these types of damage can occur. Figure 1 is based upon experience gathered since the 1940s. Supporting data were obtained from a variety of commercial processes and laboratory experiments (see the References to Figure 1). While temperature and hydrogen partial pressure data were not always known precisely, the accuracy is often sufficient for commercial use. Satisfactory performance has been plotted only for samples or equipment exposed for at least one year. Unsatisfactory performance from laboratory or plant data has been plotted regardless of the length of exposure time. The chemical compositions of the steels in Figure 1 should conform to the limits specified for the various grades by ASTM/ASME. Since the original version of Figure 1 was prepared for API in 1949 , further experience has enabled curves for most commonly used steels to be more accurately located. A major exception has been for C-0.5Mo steel. This edition consolidates all information relevant to 0.5Mo steels (C-0.5Mo and Mn-0.5Mo) in Annex A. The fifth edition of this RP also added three data points, which show HTHA of 1.25Cr-0.5Mo steel below the current 1.25Cr-0.5Mo curve. See Annex B for more discussion of 1.25Cr-0.5Mo steel. Annex C gives a similar discussion for 2.25Cr-1.0Mo steel. 3.2 Selecting Materials for New Equipment Figure 1 is often used when selecting materials for new equipment in hydrogen service. When using Figure 1 as an aide for materials selection, it is important to recognize that Figure 1 only addresses a material’s resistance to HTHA.
d) synergistic affects such as between HTHA and creep. Temperatures for data plotted in the figures represent a range in operating conditions of ±20°F (±11°C). Because Fig- ure 1 is based largely upon empirical experience, an operating company may choose to add a safety margin, below the relevant curve, when selecting steels. 3.3 High Temperature Hydrogen Attack (HTHA) in a Liquid Hydrocarbon Phase HTHA can occur in a liquid hydrocarbon phase if it can occur in the gas phase in equilibrium with the liquid phase. For materials selection purposes (using Figure 1), hydrogen dissolved in liquid hydrocarbon should be assumed to exert a vapor pressure equal to the hydrogen partial pressure of the gas with which the liquid is in equilibrium. Recent plant experience and testing of field-exposed specimens have shown that HTHA can occur under such conditions . HTHA has been found in carbon steel, liquid-filled piping downstream of a heavy oil desulfurization unit separator that was operating at hydrogen partial pressure and temperature conditions above the Figure 1 carbon steel curve. Testing of field-exposed test specimens showed HTHA of both chrome-plated and bare carbon steel samples which were totally immersed in liquid .
3.4.1 References 1. Shell Oil Company, private communication to API Subcommittee on Corrosion. 2. Timken Roller Bearing Company, private communication to API Subcommittee on Corrosion. 3. F. K. Naumann, “Influence of Alloy Additions to Steel Upon Resistance to Hydrogen Under High Pressure,” Technische Mitieilungen Krupp, 1938, Vol. 1, No. 12, pp. 223 – 234. 4. N. P. Inglis and W. Andrews, “The Effect on Various Steels of Hydrogen at High Pressure and Temperature,” Journal of the Iron and Steel Institute, 1933, Vol. 128, No. 2, pp. 383 – 397. 5. J. L. Cox, “What Steel to Use at High Pressures and Temperatures,” Chemical and Metallurgical Engineering, 1933, Vol. 40, pp. 405 – 409. 6. R. J. Sargant and T. H. Middleham, “Steels for Autoclaves,” Chemical Engineering Congress Transactions, June 1936, Vol. I, World Power Conference, London, pp. 66 – 110. 7. Standard Oil Company of California, private communication to API Subcommittee on Corrosion. 8. E. I. du Pont de Nemours and Company, private communication to API Subcommittee on Corrosion. 9. Ammoniawerk Merseberg, private communication to API Subcommittee on Corrosion, 1938. 10. Hercules Powder Company, private communication to API Subcommittee on Corrosion. 11. C. A. Zapffe, “Boiler Embrittlement,” Transactions of the ASME, 1944, Vol. 66, pp. 81 – 126. 12. The M. W. Kellogg Company, private communication to API Subcommittee on Corrosion. 13. German operating experience, private communication to API Subcommittee on Corrosion, 1946. 14. Vanadium Corporation of America, private communication to API Subcommittee on Corrosion. 15. Imperial Chemical Industries, Billingham, England, private communication to API Subcommittee on Corrosion. 16. T. C. Evans, “Hydrogen Attack on Carbon Steels,” Mechanical Engineering, 1948, Vol. 70, pp. 414 – 416.