Assessment of Creep Rupture Strength for New Martensitic 9% Cr Steels

Abstract

The application of new heat resistant steels in power plants requires reliable long term creep rupture strength values as basis for design. Modern martensitic 9% Cr-steels have complex microstructures that change with service exposure. That is why extrapolations of long term strength properties will be most difficult. Due to new long term test results, re-assessments became necessary for grades 911 and 92. Different methods have been used. Good agreement was obtained between a graphical and the numerical ISO 6303 method. In both cases a two-step assessment procedure was used. First the raw data was prepared in a suitable way, which was followed by mathematical averaging procedures. For comparison a Larson-Miller analysis on the raw data was performed, too. The results turned out to be too optimistic at temperatures higher than 575°C (1050°F). It is shown that a suitable preparation of data can improve the Larson-Miller assessment. As a result of the new assessments the design values had to be reduced for both grades. With respect to previous assessments the new values are up to almost 10% lower. In the case of grade 92 the difference from the former ASME values are even higher. Consequences concerning design and service operation are discussed.

Analysis of Multi-Axial Creep–Fatigue Damage on an Outer Cylinder of a 1000 MW Supercritical Steam Turbine

“…Subsequently, Viswanathan et al [2,3] recommended 9-12%Cr martensitic stain less steel as the casting material for steam turbine cylinders. Hald [4] and Bendick et al [5] experimentally studied 9-12%Cr mar tensitic stainless steel, containing W, and confirmed that this mate rial met the design requirements for these steam turbine cylinders. Ernst [6], adding B and Co elements to 9-12%Cr martensitic stainless steel, found that the creep rupture strength of 9-12%Cr martensitic stainless steel after 1 x 105 h could reach 90-100 MPa under 6200 °C.…”

A Review & Assessment of Current Operating Conditions Allowable Stresses in ASME Section III Subsection NH

“…Efforts included testing sponsored by the Metals Properties Council and the U.S. Atomic Energy Commission for all of the materials in the Class 1 components nuclear construction code cases. Further, collection of data from overseas sources was undertaken by Booker and co-workers, among others [11,12]. Booker performed an evaluation of newer data for 304H stainless steel, 316 stainless steel, and alloy 800H [12].…”

“…Further, collection of data from overseas sources was undertaken by Booker and co-workers, among others [11,12]. Booker performed an evaluation of newer data for 304H stainless steel, 316 stainless steel, and alloy 800H [12]. He produced a table that summarized the database that produced the ASME III Code Case N-47 stress allowables and compared the database with a new database as shown in Table 6.…”

“…There is a need to re-visit the methods and procedures of data analysis. Here, an assessment of procedures used in Europe, Japan, and elsewhere [8][9][10][11][12] should be reviewed with respect to the special requirements and criteria for setting stress allowables in BPV III-NH.…”

The Microstructure Stability of the 10Cr9MoW2VNbBN Heat Resistant Steel

“…A series of studies have already been carried out to investigate creep behavior, and oxidation resistant properties of T/P92 steel [3,4,5]. But there has been few information of Proceedings of the ASME Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries March 25-27, 2014…”