Evaluation of Creep Strength Reduction Factors for Welded Joints of Modified 9Cr-1Mo Steel (P91)

2006 ◽  
Author(s):  
Masaaki Tabuchi ◽  
Yukio Takahashi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Creep Rupture ◽  
Type Iv ◽  
Rupture Data ◽  
Term Creep

In order to review the allowable creep strength of high Cr ferritic steels, creep rupture data of base metal and welded joints have been collected and long-term creep strength have been analyzed in the SHC committee in Japan since 2004. In the present paper, the creep rupture data of 370 points for welded joint specimens of modified 9Cr-1Mo steel (ASME Grade 91) offered from seven Japanese companies and institutes were analyzed. These data clearly indicated that the creep strength of welded joints was lower than that of base metal due to Type IV fracture in HAZ at or above 600°C. From the activities of this committee, the master curve for life evaluation of welded joints of Gr.91 steel could be represented as follows: LMP==34154+3494(logσ)−2574(logσ)2,C=31.4 The reduction factor of 100,000 hours creep rupture strength of welded joint to base metal was concluded to be 0.75 at 600°C and 0.70 at 650°C for the Gr.91 steel.

Evaluation of Long-Term Creep Strength of Welded Joints of ASME Grades 91, 92 and 122 Type Steels

2012 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Takuaki Matsumura ◽  
Katsuaki Hoshino
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Creep Rupture ◽  
Creep Rupture Strength ◽  
Strength Reduction Factor ◽  
Rupture Data ◽  
Term Creep

Creep rupture data of welded joints of ASME Grades 91, 92 and 122 type steels have been collected and long-term creep rupture strength of the materials has been evaluated. Similar study was conducted by the SHC Committee in 2004 and 2005, therefore, the evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained after the previous study, in addition to discussion of the effects of product form, welding procedure and test temperature etc. on the creep strength. Almost the same results were obtained on the welded joint of Grade 92 as the previous study, however, the master creep life equations for the welded joints of Grades 91 and 122 were lower than the previous results, especially in the case of Grade 122. Furthermore, the creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.

A Study for Proposal of Welded Joint Strength Reduction Factors of Modified 9Cr-1Mo Steel for Japan Sodium Cooled Fast Reactor (JSFR)

2013 ◽  
Author(s):  
Takashi Wakai ◽  
Takashi Onizawa ◽  
Takehiko Kato ◽  
Shingo Date ◽  
Koichi Kikuchi ◽  
...  
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Polynomial Equation ◽  
Creep Rupture ◽  
Short Term ◽  
Type Iv ◽  
Rupture Data

This paper proposes provisional welded joint strength reduction factors (WJSRF) of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural designing of “Japan sodium cooled fast reactor (JSFR)”. In the welded joints of creep strength enhanced ferritic steels including modified 9Cr-1Mo steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. The authors had proposed provisional allowable stress for the welded joints made of the steel in PVP 2010 conference, taking creep strength degradation due to “Type-IV” damage into account. Available creep rupture data of the welded joints made of the steel provided by Japanese steel venders were collected. The temperature range was from 500 to 650°C. The database was analyzed by stress range partitioning method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). The difference in the creep failure mechanisms between short-term and long-term regions is taken into account in this method. Boundary between these regions was half of 0.2% proof stress of the base metal at corresponding temperature. First order polynomial equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. JSME (Japan Society of Mechanical Engineers) published a revised version of the elevated temperature design code in last year. Modified 9Cr-1Mo steel was officially registered in the code as a new structural material for sodium cooled fast reactors. The creep rupture curve for the base metal of the steel was standardized by employing stress range partitioning method, same as for the welded joint. However, second order polynomial equation of logarithm stress was applied in the analysis for the base metal. In addition, the creep rupture data obtained at 700°C were included in the database and data ruptured in very short term, i.e. smaller than 100 hours, were excluded from the analysis. Thus, there are some differences between the procedures to determine the creep rupture curves for base metal and welded joint made of modified 9Cr-1Mo steel. This paper discusses the most feasible procedure to determine the creep rupture curve of the welded joint of the steel by performing some case studies to focus on physical adequacy and harmonization with the determination procedure of the creep rupture curve for the base metal. Then, the WJSRF are provisionally proposed based on the design creep rupture stress intensities. In addition, the design of JSFR pipes was reviewed taking WJSRF into account.

Creep Strength Evaluation of Welded Joint Made of Modified 9Cr-1Mo Steel for Japanese Sodium Cooled Fast Reactor (JSFR)

2010 ◽  
Author(s):  
Takashi Wakai ◽  
Yuji Nagae ◽  
Takashi Onizawa ◽  
Satoshi Obara ◽  
Yang Xu ◽  
...  
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Strength Degradation ◽  
Creep Rupture ◽  
Primary Circuit ◽  
Allowable Stress ◽  
Type Iv ◽  
Term Creep

This paper describes a proposal of provisional allowable stress for the welded joints made of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural design of Japanese Sodium cooled Fast Reactor (JSFR). For the early commercialization of the SFRs, economic competitiveness is one of the most essential requirements. One of the most practical means to reduce the construction costs is to diminish the total amount of structural materials. To meet the requirements, modified 9Cr-1Mo steel has attractive characteristics as a main structural material of SFRs, because the steel has both excellent thermal properties and high temperature strength. Employing the steel to the main pipe material, remarkable compact plant design can be achieved. There is only one elbow in the hot leg pipe of the primary circuit. However, in such a compact piping, it is difficult to keep enough distance between welded joint and high stress portion. In the welded joints of creep strength enhanced ferritic steels including ASME Gr.91 (modified 9Cr-1Mo) steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. Though obvious strength degradation has not observed at 550°C yet for the welded joint made of modified 9Cr-1Mo steel, it is proper to suppose strength degradation must take place in very long-term creep. Therefore, taking strength degradation due to “Type-IV” damage into account, the allowable stress applicable to JSFR pipe design was proposed based on creep rupture test data acquired in temperature accelerated conditions. Available creep rupture test data of welded joints made of modified 9Cr-1Mo steel provided by Japanese steel vender were collected. The database was analyzed by region partition method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). Boundary condition between short-term and long-term was half of 0.2% proof stress of base metal at corresponding temperature. First order equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. Present design of JSFR hot leg pipe of primary circuit was evaluated using the proposed allowable stress. As a result, it was successfully demonstrated that the compact pipe design was assured. For validation of the provisional allowable stress, a series of long-term creep tests were started. In future, the provisional allowable stress will be properly reexamined when longer creep rupture data are obtained. In addition, some techniques to improve the performance of welded joints were surveyed and introduced.

Re-Evaluation of Long-Term Creep Strength of Welded Joint of ASME Grade 91 Type Steel

2016 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Kaoru Nakamura ◽  
Sosuke Nakahashi
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Rupture Strength ◽  
Creep Rupture ◽  
Base Metals ◽  
Rupture Data ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

Creep rupture data of welded joints of ASME Grade 91 type steel have been collected from Japanese plants, milling companies and institutes, and the long-term creep rupture strength of the material has been evaluated. This evaluation of welded joints of Grade 91 steel is the third one in Japan as similar studies were conducted in 2004 and 2010. The re-evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained since the previous study, with durations of the new data of up to about 60000h. The new long-term data exhibited lower creep strength than that obtained from the master creep life equation for welded joints of Grade 91 steel determined in 2010, then the master creep life equation was again reviewed on the basis of the new data using the same regression method as that used in 2010. Furthermore, the weld strength reduction factors obtained from 100000h creep strength of welded joints and the base metals are given as a function of temperature, where the master creep equations of the base metals are also redetermined in this study.

Evaluation of Creep Strength Reduction Factors for Welded Joints of Grade 122 Steel

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Yukio Takahashi ◽  
Masaaki Tabuchi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Thermal Power ◽  
Strength Reduction ◽  
Creep Rupture ◽  
Piping System ◽  
Type Iv ◽  
Rupture Data

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, a type IV creep damage formed in the heat-affected zone can cause a considerable decrease in the creep strength of the weldment and a failure of large diameter piping due to this damage took place recently in a thermal power plant. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, the creep rupture data of base metal and welded joints have been collected and analyzed by the Strength of High-Chromium Steel Committee in Japan. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations are analyzed. These data clearly indicate that the long-term creep strength of the welded joints becomes weaker than that of the base metal at above 600°C due to the type IV fracture in the fine grain heat-affected zone. After the discussions on the effects of product form, welding procedure, specimen sampling procedure, etc., on the creep strength, the master creep life equation for the welded joints is developed. The so-called region decomposition technique was adopted to fit the data in both high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 h creep strength of the welded joints and the base metal is given as a function of temperature.

Evaluation of Creep Strength Reduction Factors for Welded Joints of HCM12A (P122)

2006 ◽  
Author(s):  
Yukio Takahashi ◽  
Masaaki Tabuchi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Thermal Power ◽  
Strength Reduction ◽  
Creep Rupture ◽  
Piping System ◽  
Type Iv ◽  
Rupture Data

HCM12A (ASME Grade 122) is used for boiler components in thermal power plants because of its high creep strength. However, type IV creep damage formed in heat affected zone brings about considerable decrease in creep strength of the weldment and a failure of large diameter piping in a thermal power plant due to this damage took place recently. In order to update the design method and develop life estimation method for this kind of piping system with axial weld, creep rupture data of base metal and welded joints has been collected and analyzed in the SHC (Strength of High-Chromium Steel) committee in Japan since 2004. In the present paper, the creep rupture data of over 400 points for welded joint specimens of HCM12A offered from six Japanese organizations were analyzed. These data clearly indicated that the long-term creep strength of welded joints becomes weaker than that of base metal at above 600C due to Type IV fracture in fine grain heat-affected zone. After discussing the effects of product form, welding procedure and specimen sampling etc. on the creep strength, the master creep life equation for the welded joints was developed. So-called region decomposition technique was adopted to fit the data both in high and low stress regimes with a reasonable accuracy. The creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.

Evaluation of Long-Term Creep Strength of ASME Grades 91, 92, and 122 Type Steels

2012 ◽  
Author(s):  
Kazuhiro Kimura ◽  
Yukio Takahashi
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Rupture Strength ◽  
Nickel Content ◽  
Creep Rupture ◽  
Tube Steel ◽  
Creep Rupture Strength ◽  
Rupture Data ◽  
Term Creep

Creep rupture data of ASME Grades 91, 92 and 122 type steels have been collected and long-term creep rupture strength of the steels has been evaluated. Similar study was conducted by the SHC committee in 2004 and 2005, therefore, the evaluation of long-term creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained after the previous study. Creep rupture strength was analyzed by means of region splitting analysis method in consideration of 50% of 0.2% offset yield strength, in the same way as the previous study. Almost the same results were obtained on base metal of Grade 92 as the previous study, however, evaluated 100,000 hours creep rupture strength of base metal of Grades 91 and 122 were lower than the previous results. For Grades 91 and 122 type steels, moreover, creep rupture strength of the plate steel were lower than those of pipe and forging steels. Tendency to decrease with increase in nickel content was observed on long-term creep rupture strength of tube steel of Grade 91 at 600°C. According to the evaluation of long-term creep strength of the steels, allowable tensile stress was reviewed and proposed revision was concluded.

Evaluation of Creep Strength Reduction Factors for Welded Joints of Modified 9Cr-1Mo Steel

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Masaaki Tabuchi ◽  
Yukio Takahashi
Keyword(s):  
Creep Strength ◽  
Welded Joints ◽  
Welded Joint ◽  
Residual Life ◽  
Strength Reduction ◽  
Life Assessment ◽  
Type Iv ◽  
Rupture Data ◽  
Residual Life Assessment

Creep strength of welded joint for high Cr ferritic heat resisting steels decreases due to Type-IV failure in heat-affected zone (HAZ) during long-term use at high temperatures. In order to review the allowable creep strength of these steels, creep rupture data of base metals and welded joints have been collected, and long-term creep strength has been evaluated in the SHC (strength of high-chromium steel) committee in Japan. In the present paper, the creep rupture data of 370 points for welded joint specimens of modified 9Cr-1Mo steel (ASME Grade 91 steel) offered from seven Japanese companies and institutes were analyzed. These data clearly indicated that the creep strength of welded joints was lower than that of base metal due to Type-IV failure in HAZ at high temperatures. From the activities of this committee, it was concluded that the weld strength reduction factor (WSRF) should be taken into consideration for the design and residual life assessment of boiler components in fossil power plants. The committee recommended the WSRF for 100,000 h creep of Gr.91 steel as 0.85 at 575 °C, 0.75 at 600 °C, 0.74 at 625 °C, and 0.70 at 650 °C. The master curve for residual life assessment of Gr.91 steel welds using Larson-Miller parameter was also proposed.

The Welded Joint Strength Reduction Factors of Modified 9Cr–1Mo Steel for the Advanced Loop-Type Sodium Cooled Fast Reactor

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Takuya Yamashita ◽  
Takashi Wakai ◽  
Takashi Onizawa ◽  
Kenichiro Satoh ◽  
Kenji Yamamoto
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Welded Joint ◽  
High Stress ◽  
Strength Degradation ◽  
Creep Rupture ◽  
Analysis Method ◽  
Type Iv ◽  
Region Splitting

Creep strength enhanced ferritic (CSEF) steels including ASME Gr.91 are widely used in fossil power plants. In the advanced loop-type sodium-cooled fast reactor (SFR), modified 9Cr–1Mo steel (ASME Gr.91) is going to be adopted as a structural material. Modified 9Cr–1Mo steel was registered in the Japan Society of Mechanical Engineers (JSME) code as a new structural material for SFRs in the year 2012. The creep-rupture curve of the base metal of this steel was standardized using region splitting analysis method. According to this method, creep-rupture data were divided into two regions, high-stress and low-stress regimes, and those regions were individually evaluated by regression analyses with the Larson–Miller parameter (LMP). The difference in the creep failure mechanisms between the high-stress and low-stress regions was considered in this method. The boundary between these regions was half of the 0.2% proof stress of the base metal at the corresponding temperature. In the modified 9Cr–1Mo steel welded joint, creep strength may markedly degrade, especially in the long-term region. This phenomenon is known as “type-IV” damage due to creep voids and cracks in the fine-grained heat-affected zone (HAZ). There is no precedent for indicating the obvious creep strength degradation of welded joints under SFR temperatures (550 °C or less). Although obvious strength degradation of the welded joints has not yet been observed at 550 °C, it is fair to assume that the strength degradation will occur due to very long-term creep. Therefore, considering strength degradation due to “type-IV” damage is necessary. This paper proposes the creep-rupture curve and the welded joint strength-reduction factor (WJSRF). The creep-rupture curve of the welded joint was proposed by employing a second-order polynomial equation with LMP using region splitting analysis method, which is used for the base metal as well. The WJSRFs were proposed on the basis of design creep-rupture stress strength. The resulting allowable stress was conservative compared with that prescribed in ASME code and the Japan domestic regulation for thermal plants. In addition, the design of the hot-leg pipe in SFR was reviewed considering the WJSRFs.

Microstructural Evaluation of 9Cr-3W-3Co-Nd-B Heat-Resistant Steel (SAVE12AD) After Long-Term Creep Deformation

2017 ◽  
Author(s):  
Tomoaki Hamaguchi ◽  
Hirokazu Okada ◽  
Shinnosuke Kurihara ◽  
Hiroyuki Hirata ◽  
Mitsuru Yoshizawa ◽  
...  
Keyword(s):  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joints ◽  
Rupture Strength ◽  
Large Diameter ◽  
Creep Rupture ◽  
Martensite Lath ◽  
Creep Rupture Strength ◽  
Term Creep

The new ferritic heat-resistant steel composed of 9Cr-3W-3Co-Nd-B, registered as ASME Code Case 2839, has been developed for large diameter and heavy wall thickness pipes and forgings of fossil-fired power boilers. The steel, which contains 0.01 mass% boron, a small amount of neodymium, and optimized amounts of nitrogen, is characterized by the superior long-term creep strengths of both the base metal and welded joint. P92 had equiaxed subgrain structures changed from martensite lath structures and coarsened M23C6 type carbides after long-term creep. In contrast, the developed steel, SAVE12AD, maintained martensite lath structures with fine M23C6 along the boundaries even after the long-term creep stage. The addition of high amounts of boron suppressed the coarsening of M23C6 along the boundaries, thereby stabilizing the martensite lath structure in the base metal of the steel. Consequently, SAVE12AD had higher creep rupture strength than other high chromium ferritic steels. To investigate the creep rupture strength of welded joints, two welded joints with Ni-based alloy and Grade 92 welding filler wires were prepared by automatic gas tungsten arc welding. The creep rupture strength of each welded joint showed small degradation compared with the base metal in the long-term creep stage over 10,000 hours. These were ruptured 1.5 mm away from the fusion line, which was the same area as Type IV cracking. Microstructural observations were carried out by electron back scatter diffraction analysis using simulated heat-affected zone samples at different peak temperatures from 750 °C to 1350 °C in order to clarify the microstructure in the heat-affected zone. No fine grain area was observed in the microstructure after the simulated heat-affected zone at 910 °C just above AC3 transformation temperature, although there were fine grains along prior austenite grain boundaries, which seemed to form with the diffusion transformation. The creep cracks seemed to have initiated from the fine grain structures, resulting in the rupture at the same area as Type IV cracking. However, the creep rupture strength degradation of the welded joints against the base metal was significantly smaller than that of conventional steel welded joints owing to the suppression of fine grains found in the heat-affected zone heated around AC3 temperature. The developed 9Cr-3W-3Co-Nd-B steel (SAVE12AD) will be used for large diameter and heavy wall thickness pipes and forgings in 600 °C ultra super critical power plants.

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