An Elastic-Plastic Fracture Mechanics Study of Crack Initiation in 316 Stainless Steel

2009 ◽  
pp. II-611-II-611-21 ◽  
Author(s):  
PH Davies
Keyword(s):  
Stainless Steel ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
316 Stainless Steel ◽  
Elastic Plastic

Analysis of a Thermal Fatigue Test of a Stepped Pipe

2004 ◽  
Author(s):  
D. P. Jones ◽  
J. E. Holliday ◽  
T. R. Leax ◽  
J. L. Gordon
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Crack Initiation ◽  
Thermal Shock ◽  
Thermal Fatigue ◽  
Fatigue Curve ◽  
Low Oxygen ◽  
Steel Pipes ◽  
Elastic Plastic ◽  
Best Fit

Results from thermal-structural finite element analysis (FEA) were used to predict cycles to crack initiation in thermal fatigue tests of stainless steel pipes. The pipes were fatigued by alternately pumping hot and cold low oxygen water every four minutes through 304 stainless steel pipes. The rapid change in water temperature imparted a thermal shock to the inner wall of the pipe. The pipes were stepped to four different thicknesses to give four different values of thermal shock stress depending on thickness. The pipes were pressurized to 17.2 MPa (2500 psi) and the temperature cycled between 38°C (100°F) and 343°C (650°F) in three seconds. This was followed by holding at 343°C for 237 seconds and then quenching to 38°C in three seconds followed by another 237 second hold period. Thermal cycling continued until significant cracking was detected on the inside surface of the pipes. Measurements of fatigue striation spacing on the fracture surfaces allowed determination of cycles to the initiation of defects 0.254 mm (0.01 inch) deep. Alternating stresses and strains were calculated using both elastic and elastic-plastic finite element analyses (FEA). The analysis results were used with a best-fit fatigue curve to predict cycles-to-crack initiation for comparison to the experimental data. Using elastic analysis corrected for stresses beyond yield in accordance with the ASME B&VP Code and the best-fit fatigue curve adjusted for low oxygen water environments resulted in under-estimates of the observed cycles to crack initiation from the tests. Improved predictions of cycles to crack initiation are possible by using an elastic-plastic FEA method with a kinematic hardening model along with the best-fit fatigue curve.

Liquid-Metal Embrittlement of Type 316L Stainless Steel by Gallium as Measured by Elastic-Plastic Fracture Mechanics

CORROSION ◽  
2004 ◽  
Vol 60 (3) ◽  
pp. 254-261 ◽  
Author(s):  
D. G. Kolman ◽  
R. Chavarria
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Crack Growth Rate ◽  
Fracture Mechanics ◽  
Liquid Metal ◽  
Crack Growth ◽  
Liquid Metal Embrittlement ◽  
Intergranular Cracking ◽  
Elastic Plastic ◽  
Type 316L

Abstract In order to bound failure of austenitic stainless steel storage containers housing Ga-containing compounds, the liquid-metal embrittlement of Type 316L (UNS S31603) stainless steel (SS) by Ga was investigated. Type 316L SS compact tension specimens were exposed to liquid Ga using a depassivation technique to wet the specimen. Linear elastic and elastic-plastic fracture mechanics methods were used to compare the fatigue and fracture behavior. Mild liquid-metal embrittlement was observed, as indicated by increased fatigue crack growth rate, decreased number of fatigue cycles to failure, decreased crack initiation resistance, and increased crack growth rate. Stable cracking was observed for all test conditions. A small amount of intergranular cracking was observed following Ga exposure. No effect of test temperature on embrittlement was observed over the small temperature range examined (35°C to 75°C). Decreasing crosshead displacement rate promoted Ga embrittlement. Based on fractography, profilometry, and mechanics, it appears that both adsorption-induced decohesion and adsorption-enhanced plasticity mechanisms are operative in the Type 316L SS-Ga system.

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