Evaluation of Environmental Effects on the Fatigue of Notched Specimen of Austenitic Stainless Steel Using Modified Rate Approach Method

2004 ◽  
Author(s):  
Katsumi Sakaguchi ◽  
Yasuhide Asada ◽  
Masao Itatani ◽  
Toshiyuki Saito
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Notch Root ◽  
Notched Specimen ◽  
High Temperature Water ◽  
Approach Method ◽  
Temperature Water

Fatigue testing was conducted on notched specimens of austenitic stainless steel 316NG in high temperature water. Specimens were notched round bar with elastic stress concentration factors Kt of 1.4 and 3. For the specimen of Kt = 3, fatigue test was also performed in high temperature air. Environmental correction factor Fen recently proposed by Environmental Fatigue Tests (EFT) project in Japan Nuclear Safety Organization (JNES) was applied to the result of fatigue test to evaluate the environmental effects on fatigue life of notched specimen. Since the notch root strain varies non-proportionally to nominal strain in the elastic-plastic region, the modified rate approach method was applied to predict the fatigue life of notched specimen in the water, which was proposed to account for the environmental effect on fatigue life of nuclear component materials under varying conditions. Notch root strain and strain rate were calculated by FEM analysis. The difference between predicted and experimental fatigue lives in high temperature water was within factor of 2 for Kt = 3. The relationships between fictitious stress amplitude at notch root (= notch root strain amplitude multiplied by elastic modulus) and corrected fatigue life shows good coincidence with best fit curve for austenitic stainless steels. It is concluded that the modified rate approach method and current environmental correction factor Fen proposed by EFT project is applicable to predict fatigue life of the stress concentration when the notch root strain is adequately estimated.

Evaluation for Environmental Fatigue of Notched Specimen of Ni-Base Alloy

2007 ◽  
Author(s):  
Masao Itatani ◽  
Katsumi Sakaguchi ◽  
Toshiyuki Saito ◽  
Takahiro Hayashi
Keyword(s):  
Fatigue Life ◽  
Stress Amplitude ◽  
Base Alloy ◽  
Notch Root ◽  
Notched Specimen ◽  
Notched Specimens ◽  
High Temperature Water ◽  
The Difference ◽  
Best Fit ◽  
Temperature Water

Fatigue tests were conducted on the notched specimens of Ni-base-alloy NCF600 in high temperature water. Notch root strain was analyzed by finite element method (FEM) to calculate the notch root strain rate and the environmental fatigue correction factor Fen. Relationship between notch root fictitious stress amplitude and corrected fatigue life in water FenNwater are compared with the fatigue data of smooth specimen in air (i.e. best-fit curve) and it was found that the corrected fatigue life data in water shows a little shorter but almost agree with best-fit curve in air for the specimen with Kt = 1.4A. For the specimen with Kt = 3, corrected fatigue life in water is longer than that in air and the difference between both lives becomes larger with decreasing stress amplitude. The longer fatigue life in sharp notched specimen than that in dull notched specimen at the same notch root stain amplitude is thought to be dominated by the difference in the crack propagation life since the stress distributions on the cross section are decisively different. It is concluded that the fatigue life of notched specimen in high temperature water is adequately predicted using the modified rate approach method when the notch root strain is appropriately estimated e.g. by FEM analysis even though it gives excessively conservative prediction for sharp notch at low stress amplitude. The aspect of environmental fatigue of notched specimens are summarized on carbon steel and stainless steels with Ni-base alloy studied in Japan Nuclear Energy Safety Organization (JNES) Environmental Fatigue Test (EFT) project.

The Stress Corrosion Cracking of Austenitic Stainless Steel Heat Exchange Tubes: Three Cases Study

2010 ◽  
Author(s):  
Shugen Xu ◽  
Weiqiang Wang ◽  
Huadong Liu
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Austenitic Stainless Steel ◽  
Chloride Concentration ◽  
Tube Material ◽  
Steel Tubes ◽  
High Temperature Water ◽  
Temperature Water

In this paper, three leakage failure cases of heat exchange tubes have been introduced. The reasons of the leakage for austenitic stainless steel tubes and overlay welding layer on the tube sheet have been analyzed. Through the investigation of the operation process and histories of the equipment, and after chemical compositions analysis of tube material and corrosion products, metallographic test of specimens with cracks, and fracture surface scan with Scanning Electron Microscope (SEM), the cracking reason and mode are described as the Stress Corrosion Cracking (SCC) of austenitic stainless steel. This kind of cracking in three cases was induced by the micro chloride in the high temperature water (or steam). Moreover, sulfide and dissolved oxygen also reduced the threshold value of chloride concentration and enhanced the corrosion rate for SCC. The cracking mode of Case A and B are transgranular; and Case C is intergranular. It indicates that for this kind of in-service heat exchanger, the operators should not only control the chloride concentration in feed water, but also the sulfide and dissolved oxygen in the future. The austenitic stainless steel tubes (China steel types-1Cr18Ni9Ti and 0Cr18Ni10Ti, equal to Type 304 and Type 321 according to ASME code) used in this cases are not fit to this condition. Thus, for the new heat exchanger design, the tube material should be changed into austenitic-ferritic (duplex phase) steel, such as 2205 Series, which has an excellent performance for SCC resistance in the high temperature water (or steam) with chloride.

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