Type 254 SMO Comparative

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1 Type Comparative to Other 6Mo Stainless Grades North American Version Imperial Units This brochure briefly describes the many similarities and few differences between 1 alloy and other 6Mo stainless steel alloys, such as the ATI Allegheny Ludlum AL-6XN 2 alloy. It is based on s 30+ years of experience with developing, producing, and marketing of 6% molybdenum-containing stainless steels. While extensive, this brochure does not provide all detailed information that has been published in applicable literature or observed by over the years with respect to 6Mo stainless steels. For additional details regarding such information as references, testing standards, and results, please contact. 254 SMO and Most Other 6Mo Grades are Essentially Equivalent The physical properties of 6Mo grades, including both the 1 and AL-6XN 2 alloys are essentially equivalent as described herein. Because of the similarities among the 6Mo grades, they may be used interchangeably, may be used together and the selection of a specific grade should be based on availability, price, and service. 254 SMO: The Leanest* 6Mo Stainless on the Market The 6Mo stainless steels, whether 254 SMO (S31254), AL-6XN (N08367), or 1925 hmo and 25-6Mo (both covered by N08926), are substantially similar with respect to significant performance characteristics. 3 The chemical composition of the 254 SMO stainless steel typically has a slightly higher copper content than the AL-6XN alloy (Table 1). The original Avesta Jernverk AB (predecessor to ) patent 4 on 254 SMO was based, to some extent, on data that demonstrated that % copper in a 6Mo stainless steel produced an optimal combination of resistance to reducing acids and resistance to chlorides. 4 The AL-6XN alloy contains copper only as a residual element, as do most austenitic stainless steels. Based on s experience, most austenitic stainless steels have a residual copper content of about 0.20%. * Leanest meaning lowest Ni content of all the 6Mo grades listed in reference #3. In practice, there will be only a small difference between the AL-6XN and 254 SMO alloys with respect to copper. The N08926 alloy requires a copper content of %. 5 The effect of the different concentrations of copper on corrosion resistance would be difficult to detect in laboratory corrosion tests and are not considered to be statistically significant in any application, other than reducing acid environments, such as the intermediate concentration range of pure sulfuric acid, depending on the exact exposure and evaluation criteria. 4 Composition, wt. pct Table 1 Element Carbon Chromium Nickel Molybdenum Nitrogen Copper Sulfur Phosphorus Silicon Manganese Iron (wrought products) max max max 0.80 max 1.00 max Balance ATI Allegheny Ludlum Typical AL-6XN Balance ** See producers websites for published alloy surcharges. The most notable difference in composition between the 254 SMO and AL-6XN alloys is the nickel content (Table 1). The 254 SMO alloy contains about 6% less nickel than the AL-6XN, which results in a negligible difference in performance 6, yet often achieves a significant

2 savings in cost due to the volatility in nickel prices**. The 254 SMO alloy was the first nitrogen-alloyed 6Mo grade stainless steel. 6,7 Avesta Jernverks AB was granted a patent for such composition that required various other elements. 4 When other producers decided to produce a nitrogencontaining 6Mo steel, the use of a Ni content higher than that in the 254 SMO alloy avoided conflict with the patent without substantial detrimental effects. 8 As shown in Figure 1, the most likely performance characteristic that is potentially affected by the lower 254 SMO alloy nickel content is the resistance to chloride stress-corrosion cracking. 9 However, laboratory testing has failed to demonstrate any detectable influence on the chloride stress corrosion cracking resistance due to the 6% nickel content difference. Both the 254 SMO and AL-6XN alloys will pass the wick test 10 and the boiling 25% NaCl test for SCC resistance, yet neither will pass the boiling 42% magnesium chloride test (Table 2). In the sophisticated drop-evaporation test, it is possible to make either the 254 SMO alloy or the AL-6XN alloy look superior, depending on precise conditions. However, any differences in such drop-evaporation tests are not believed to be statistically significant. 11,12,13 Chloride Stress Corrosion Cracking Resistance Table 2 Grade ATI Allegheny Ludlum AL-6XN 2205 Code Plus Two Alloy 20 Alloy 904L 2 - Type Comparison Boiling 42% MgCL2 Wick Test or Boiling 25% NaCl or The time to failure in boiling magnesium chloride solution of stainless steel wire as a function of Ni content Figure 1 has observed that when one 6Mo alloy is not satisfactory for use in a particular application due to susceptibility to SCC, then selection of the other 6Mo alloys for that application would be an exceedingly risky proposition. The relative level of SCC resistance of the 6Mo alloys, which corresponds to resistance in boiling NaCl solutions, but susceptiblein boiling MgCl 2, is the same level of relative resistance for the 20Cb-3 14 alloy, 904L, the duplex grades 2205 and 2507, and any ferritic stainless steel with nickel content in the range of 1% or higher, such as the SEA-CURE 15 alloy. 10 Based on the Copson curve (see Figure 1), a minimum of 34% nickel content is required to pass the magnesium chloride test. Pitting and Crevice Corrosion Based on published results on pitting and crevice corrosion resistance 16,17 lab data give little concrete evidence to choose between these alloys. A study by NASA 18 to evaluate the resistance of the 254 SMO and AL-6XN alloys to chloride- Isocorrosion Curves 0.1 mm/year for given steels in pure sulfuric acid Figure 2 Note: While this data seems to indicate a small advantage for the AL-6XN alloy over the 254 SMO alloy in this specific environment, the data has not been produced under exactly the same conditions. Thus, small differences in test procedures and sampling may account for the minor differences in test results. bearing launch environments found both alloys performed substantially better than 304 stainless steel and the 254 SMO alloy performed slightly better than the AL-6XN alloy. Support for the similar performance comes from the very similar Pitting Resistance Equivalent number (PREn) for these alloys. The PREn employs statistical regression to relate pitting resistance to the chemical composition of a stainless steel. 19 The PREn calculations from various investigators have demonstrated that the pitting resistance depends primarily on the level of Cr, Mo, and N content. It has also been shown that nickel has very little statistically detectable effect on pitting corrosion resistance over the full range of austenitic stainless steels. 20 The sensitivity of the PREn data is such that within grade variations of Cr, Mo, and N near the nominal values for these stainless steels, the apparent PREn variation is of minor import compared to effects from surface finish, normal variations in practical annealing conditions, and variations in the corrosiveness of the environment. These effects will overshadow any apparent differences in PREn values for the nominal compositions that are available in the various 6Mo alloys. In view of the above, recommends a conservative approach to use the standardized minimums for Cr, Mo, and N for the 6Mo alloys in the PREn calculation, and concludes that there are no statistically significant differences. In oil & gas production environments, the 254 SMO, AL-X6N, and other 6Mo alloys have been extensively researched and compared and are all typically specified interchangeably. 21 Welding High amounts of nickel in lower alloyed austenitic materials have been shown to increase the tendency for hot cracking due to the mode of solidification of the weld metal. 22 Low nickel levels favor either complete solidification as primary ferrite (termed Type F), or solidification of primary ferrite followed by some austenite formation (termed Type FA). 22 Higher levels of nickel favor solidification either as primary austenite followed by the formation of some ferrite (termed Type AF) solidification, or complete Type Comparison - 3

3 Isocorrosion Diagrams, Corrosion rate 0.1 mm/yr, in hydrochloric acid Figure 3 Minimum Tensile Test Requirements for some 6Mo stainless steels according to ASTM A240-09a Table 3 Yield Strength, min (kpi) Tensile Strength, min (kpi) Elongation in 2, % 254 SMO AL 16 6XN UNS N austenitic solidification (termed Type A). 22 Ferrite formation during solidification has been shown to improve hot workability and cracking resistance. 22 The lower nickel content in the 254 SMO alloy, as compared to other 6Mo alloys, was designed to simultaneously precipitate ferrite and austenite from the melt, resulting in better hot workability. Other 6Mo grades that contain a higher nickel content than the 254 SMO alloy generally solidify entirely as primary austenite and as a result do not have the same improved hot workability. 4 This solidification mode also has the potential to increase the resistance to hot cracking during welding. 4 However, this potential advantage will only be realized with autogenous welds, which typically with 6Mo steels are only used in conjunction with a post weld solution anneal. 16 Welding the 254 SMO alloy with a nickel alloy filler would not result in any advantage over other 6Mo steels due to lower nickel. Tensile Strength There is different strength data published for the various 6Mo grades (Table 3). 5 However, the apparent differences in strength data result from an apples-to-oranges comparison. In other words, the strength data specifically relates to product form and the original data developed for the grades. The strength data for the 254 SMO alloy was originally developed for thick plate because that was the initial product of interest. The strength data for the AL-6XN alloy was originally developed for light gauge sheet and strip, because tubing was the initial product form. 7 As a result, the basis for the strength data for the AL-6XN alloy is different than the basis for the strength data of the 254 SMO alloy, and therefore not directly comparable. For many years, followed the traditional and more conservative approach that quotes a single minimum value for yield and tensile strengths at all thicknesses. However, in order to address market concerns about performance, introduced a higher strength quote for sheet gauges of the 254 SMO alloy. Physical Properties At Room Temperature Table 4 Property Modulus of elasticity psi x 10 6 Coefficient of thermal expansion (68 F to 212 F) x 10-6/ F Thermal Conductivity Btu/h ft F Heat Capacity Btu/lb F Density lb/in 3 Magnetic Permeability ATI Allegheny AL-6XN The N08926 alloy has a composition that most closely resembles the AL-6XN alloy (N08367) and continues to use the conservative single strength value for all thicknesses which is the same strength quote originally quoted for the 254 SMO alloy (S31254). 5 Designations The AL-6XN alloy was originally listed in the ASTM and ASME B-specs, rather than A-specs that listed nickel-base alloys, because ASTM formerly defined stainless steel in a way that excluded the 6Mo grades other than the 254 SMO alloy. 23 The old rule stated that in a stainless steel, iron had to be at least 50% by weight of the alloying additions. 24 In the last ten years, the ASTM has harmonized its steel definitions with the rest of the world. 23 As a result, the AL- 6XN alloy is now listed as a stainless steel in the ASTM A-specs. The new rule states that iron is the element with the largest weight percentage. 24 Basically, the ASTM grandfathered the specifications for nickel-base alloys (such as the AL-6XN alloy, the 904L alloy, and many other 6Mo stainless steels with original UNS N-numbering), stating its intent to maintain these specifications for a period of about ten years for the convenience of previous users and to withdraw these specifications or at least the grades that are now considered as stainless steels and covered in the A-specs. 23 As a result, the AL-6XN alloy has been introduced into most of the same specifications that the 254 SMO alloy has been in for over twenty years. believes that there is no significance to the original specifications or to the changes, except that it is now convenient to specify both grades using the same standard specifications, thereby facilitating the best service to the user. The knowledgeable user will specify both grades as acceptable alternatives. The physical properties of 6Mo grades, including both the 254 SMO and AL-6XN alloys, are essentially equivalent (Table 4). Because of the similarities among the 6Mo grades, they may be used interchangeably 3, may be used together and the selection of a specific grade should be based on availability, price, and service. Technical Support assists users and fabricators in the selection, qualification, installation, operation, and maintenance of the 254 SMO stainless steel. Technical personnel, supported by the research laboratory of, can draw on years of field experience with the 254 SMO alloy to help you make the technically and economically correct materials decision. is prepared to discuss individual applications and to provide data and experience as a basis for selection and application of the 254 SMO alloy. works closely with its distributors to ensure timely availability of the 254 SMO alloy in the forms, sizes, and quantities required by the user. For assistance with technical questions and to obtain top quality 254 SMO products, call at Type Comparison Type Comparison - 5

4 References SMO is a trademark of OYJ, registered in the United States and other countries. 2 AL-6XN is a trademark of ATI Properties, Inc., registered in the United States. 3 Ralph M. Davison and James D. Redmond, Practical Guide to Using 6Mo Austenitic Stainless Steel, Material Performance, vol. 27, Number 12, December 1988, pp United States Patent Number 4,078,920, Austenitic Stainless Steel with High Molybdenum Content, Liljas et al, March 14, ASTM A240/240M, Standard Specification for Chromium, and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications, ASTM International, West Conshohocken, PA. 6 Mats Liljas, Development of Superaustenitic Stainless Steels, ACOM , Avesta Sheffield AB, Avesta, Sweden. 7 CASTI Handbook of Stainless Steels & Nickel Alloys, Stephen Lamb Technical Editor, CASTI Publishing Inc. Edmonton, Alberta, United States Patent Number 4,5,826, Method For Producing A Weldable Austenitic Stainless Steel in Heavy Sections, Thomas H. McCunn, John P. Ziemianski, and Ivan Franson, October H. R. Copson, Effect of Composition on Stress Corrosion Cracking of Some Alloys Containing Nickel, Physical Metallurgy of Stress Corrosion Fracture, T.N. Rhodin, Editor, Interscience, 1959, pp Corrosion of Stainless Steels, Second Edition, A. John Sedriks, John Wiley & Sons, Inc., 1996, pp Poul-Erik Arnvig and Wioletta Wasielewska, Stress Corrosion Behaviour of Highly Alloyed Stainless Steels Under Severe Evaporative Conditions, ACOM , Avesta Sheffield, Avesta, Sweden. 12 Helle Anderson, Poul-Erik Arnvig, Wioletta Wasielewska, Lena Wegrelius, and Christian Wolfe, SCC of Stainless Steel Under Evaporative Conditions, ACOM , Avesta Sheffield, Avesta, Sweden. 13 Unpublished work by Poul-Erik Arnvig Cb-3 is a trademark of CRS Holdings, Inc., registered in the United States. 15 SEA-CURE is a trademark of Plymouth Tube Company, registered in the United States. 16 ATI AL-6XN Alloy (UNS N08367) Sourcebook, Ed. 4, 2010 ATI Allegheny Ludlum. 17 Corrosion Handbook, Oyj, Tenth Edition, L.M. Calle, M.R. Kolody. R.D. Vinje, M.C. Whitten, and W. Li, Electrochemical Impedance Study of Alloys in a Simulated Space Shuttle Launch Environment, NASA Government Publication 153, ( 19 ASM Handbook, Volume 13A, Corrosion: Fundamentals, Testing, and Protection, Stephen D. Cramer and Bernard S. Covino, jr., Volume Editors, ASM International, Materials Park, Ohio 2003, pp Elisabet Alfonsson and Rolf Qvarfort, Investigation of the Applicability of Some PRE Expressions for Austenitic Stainless Steels, ACOM , Avesta AB, Avesta Sweden, International Standard NACE MRO175/ISO : Welding Metallurgy and Weldability of Stainless Steels, John C. Lippold and Mamian J. Kotecki, Wily Interscience 2005, pp Discussions with Ralph Davison former Chairman of the ASTM A1.17 Subcommittee. 24 ASTM A941-06, Standard Terminology Relating to Steel, Stainless Steel, Related Alloy, and Ferroalloys, ASTM International, West Conshohocken, PA. 6 - Type Comparison Type Comparison - 7

5 Working towards forever. We work with our customers and partners to create long lasting solutions for the tools of modern life and the world s most critical problems: clean energy, clean water and efficient infrastructure. Because we believe in a world that lasts forever. 12EN, Bannockburn, USA. October Edition 3 (US) Information given in this brochure may be subject to alterations without notice. Care has been taken to ensure that the contents of this publication are accurate but and its affiliated companies do not accept responsibility for errors or for information which is found to be misleading. Suggestions for or descriptions of the end use or application of products or methods of working are for information only and and its affiliated companies accept no liability in respect thereof. Before using products supplied or manufactured by the company the customer should satisfy himself of their suitability. is a registered trademark of Stainless Code Plus Two is a registered trademark of Stainless, Inc. High Performance Stainless 2275 E. Half Day Road, Suite 300, Bannockburn, IL USA Tel Fax outokumpu.com