1、STP-NU-059CORRECTIONS TO STAINLESS STEEL ALLOWABLE STRESSESSTP-NU-059 CORRECTIONS TO STAINLESS STEEL ALLOWABLE STRESSES Prepared by: Joseph M. Turek, Robert W Swindeman, Fujio Abe, William ODonnell and Carl Spaeder Date of Issuance: June 10, 2013 This report was prepared as an account of work sponso
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12、3 by ASME Standards Technology, LLC All Rights Reserved Corrections to Stainless Steel Allowable Stresses STP-NU-059 iii TABLE OF CONTENTS Foreword v Executive Summary vi 1 OBJECTIVE 1 1.1 Technical Approach 1 2 CURRENT RESTRICTIONS 2 3 RESULTS 3 3.1 Part 1 - Assess Available Data 3 3.2 Part 2 - Det
13、ermine Time and Temperature Limits 10 3.3 Part 3 - Draft Code Rules 10 3.4 Recommendations . 16 4 JUSTIFICATIONS 17 4.1 Carbon . 17 4.2 Nitrogen . 17 4.3 Silicon 17 4.4 Nickel 18 4.5 Chromium 18 4.6 Copper . 18 4.7 Molybdenum . 18 4.8 Sulfur and Phosphorous . 18 4.9 Nitride Formers . 19 4.10 Higher
14、Service Temperature Range . 19 4.11 Ferrite Number. 20 References 21 Appendix A 22 Appendix B. 24 Acknowledgments 27 LIST OF TABLES Table 1 - Chemical Composition of NIMS Heats Studies 4 Table 2 - Statistical Composition Results Showing the Average, Maximum, Minimum and Standard Deviations in Weight
15、 % for Select Residual Elements Present in the 340 Production Type 316 Heats 14 LIST OF FIGURES Figure 1 - 105 Hour Creep Rupture Results for the Type 304H and 316H NIMS heats 5 Figure 2 - Variations in Creep Rupture Strength for the Type 304H and 316H NIMS heats at 1292oF (700oC) . 6 STP-NU-059 Cor
16、rections to Stainless Steel Allowable Stresses iv Figure 3 - Plot of Aluminum vs. Nitrogen Shows a Large Variation in the Aluminum for the Type 316H NIMS Heats . 7 Figure 4 - The Effect of Elevated Copper on the Rupture Life of Similar Type 316H Heats at 1292oF (700oC) that Exhibit an NAV of Approxi
17、mately 0.007wt% . 7 Figure 5 - The Available Nitrogen Concentration and Impurity Copper were Identified as Controlling Variables Responsible for the Observed Heat-to-heat Variation in Creep Performance for Type 316H . 8 Figure 6 - TEM Micrographs Showing AlN Precipitates Associated with Sigma () and
18、 Chi (x) Phases at the Grain Boundaries in Type 304H and 316H after Extended High Temperature Exposure 8 Figure 7 - Creep Rupture Data Showing the Available Nitrogen and Impurity Niobium Explain Heat-to-heat Variability in Creep Life of Type 304H SS . 9 Figure 8 - Creep Rupture Data Showing that at
19、Short Exposure Times, the Presence of Fine Niobium Carbides Improves Strength but the Benefit Disappears after Extended Exposure Times 9 Figure 9 - Illustration Explaining the Observed Heat-to-heat Variability in Creep Performance of Type 304H at Short and Long Exposure Times 10 Figure 10 - Ellingha
20、m Diagram Showing the Free Energy of Formation for Nitrides, with the Stable Nitrides of Concern in Steel Identified 12 Figure 11 - Plots of the Distribution of Residual Elements Found in the 340 Production Heats 13 Figure 12 - Bar Graph Showing the 340 Commercial Heats Exhibited Lower Aluminum than
21、 the NIMS Heats 14 Figure 13 - Bar Graph Showing the 340 Commercial Heats Were Low in Residual Titanium while the NIMS Heats Varied Considerably . 15 Figure 14 - Bar Graph Showing the 340 Commercial Heats Exhibited Higher Nitrogen than the NIMS Heatsz . 15 Figure 15 - Minimum Stress Determination fo
22、r Proposed Table X-1 Compliant NIMS Heats at 1337oF (725oC) . 16 Figure 16 - The Susceptibility of Austenitic Chromium-nickel Steels to Solidification Cracking as a Function of Schaeffler Creq/Nieq and Sulfur and Phosphorous Contents (from Kujampaa et al., 1980) 19 Corrections to Stainless Steel All
23、owable Stresses STP-NU-059 v FOREWORD This document is the result of work resulting from Cooperative Agreement DE-NE0000288 between the U.S. Department of Energy (DOE) and ASME Standards Technology, LLC (ASME ST-LLC) for the Generation IV (Gen IV) Reactor Materials Project. The objective of the proj
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25、ation IV Reactors Integrated Materials Technology Program Plan. This report is the result of work performed under Task 14 titled “Corrections to Stainless Steel Allowable Stresses.” ASME ST-LLC has introduced the results of the project into the American Society of Mechanical Engineers (ASME) volunte
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33、n. STP-NU-059 Corrections to Stainless Steel Allowable Stresses vi EXECUTIVE SUMMARY The primary controlling variables for predictable 105 hour creep rupture properties in Type 304H and 316H stainless steel at elevated temperatures have been identified as nitrogen in interstitial solid solution (ava
34、ilable nitrogen) and copper above 0.25 wt% 1. An expression was developed to account for the varying residual strong nitride forming elements in a heat, where targeted nitrogen additions can be made to ensure sufficient available nitrogen levels without complicating the material certification proces
35、s. Appendix A shows the current 2010 Subsection NH, Appendix X, Table X-1 restrictions for service up to 1100oF (595oC), with Appendix B presenting the new proposed restrictions in Table X-2 for long-term service at temperatures between 1100oF (595oC) and 1337oF (725oC). It is recommended that these
36、 proposed Table X-2 restrictions be mandatory for long term service at these temperatures to take advantage of the demonstrated creep performance improvements associated with these restrictions. A review of 340 recent Type 316 SS heat compositions identified residual titanium, aluminum, boron, niobi
37、um and vanadium at sufficient levels to impact the amount of available nitrogen necessary for optimum creep properties. These elements were targeted for restrictions in the proposed Table X-2 nitrogen calculation due to their presence as residuals in steel, their low free energy of nitride formation
38、 2 and the stability of these nitrides in steels at the anticipated service temperatures. Zirconium and tantalum were excluded from the calculation because they are typically present only at trace levels; however, these elements will be reported for future use and control if necessary. It is anticip
39、ated that the reporting of zirconium and tantalum could be eliminated if these elements continue to be at trace or less than minimum detection levels (MDL). It is proposed that the copper control be accomplished using a minimummaximum composition range, with a nominal composition typically found in
40、production heats. This approach of determining the residual nitride forming elements, and adjusting the nitrogen on a heat basis, has been reviewed by a major stainless steel producer and it has concurred that the proposed Table X-2 restrictions are acceptable for production quantities, and would no
41、t compromise the material certification process. This study examined 105 hour creep rupture data from the Japanese National Institute for Materials Science (NIMS), and consisted of nine Type 304HTB and nine Type 316HTB heats that exhibited considerable scatter in creep results. The compositions of t
42、he NIMS heats indicate that they were likely produced to requirements similar to the conventional Type 304H (UNS# S30409) and Type 316H (UNS# S31609) requirements. Given that several of the NIMS heats did not meet the current Subsection NH, Appendix X, Table X-1 composition restrictions, they noneth
43、eless exhibited significantly reduced scatter in the creep results, and, in fact, were the best performers. These data indicate that a review of the applicability of the current Table X-1 restrictions is warranted given the strong correlations established between available nitrogen and creep propert
44、ies. The proposed Table X-2 is an attempt to further reduce scatter in creep data by using targeted restrictions mostly for copper and nitride forming species, as presented herein, to modify the conventional UNS alloy composition requirements for Type 304H and 316H SS. A potential economic benefit m
45、ay be realized by re-establishing the conventional H grade composition ranges for non-restricted species, by providing suppliers some leeway to achieve the desired creep rupture properties. After eliminating the Type 316H heats in the NIMS database that did not satisfy the proposed Table X-2 restric
46、tions, and then extrapolating the remaining compliant heat creep results to 1337oF (725oC), the data suggests that these compliant heats represent a minimum creep rupture strength of approximately 2553 psi (17.6 MPa) vs. the Section III, Division 1, Subsection NH allowable of 2321 psi (16 MPa) at 13
47、37oF (725oC). Given that only three relevant data points from the NIMS study satisfy the proposed Table X-2 restrictions, additional confidence in the 1337oF (725oC) upper temperature limit could be realized by including additional 105 hour creep rupture data from other sources. An additional benefi
48、t of evaluating additional Table X-2 compliant heat creep data may Corrections to Stainless Steel Allowable Stresses STP-NU-059 vii allow a more definitive upper service temperature limit that the NIMS data suggests may, in fact, be slightly above 1337oF (725oC). Regardless of whether the proposed T
49、able X-2 is adopted or not, it is recommended that additional available 105 hour plus creep rupture data be screened for compliance to the proposed Table X-2 restrictions, and the minimum stress to rupture be recalculated for comparison to the current Section III, Division I, Subsection NH allowables. This approach is expected to allow a more accurate determination of the acceptable upper service temperature limits for Type 304H and 316H materials, and improve the confidence for designers of high temperature components. Additional recommendations include considering if ongoing creep
