Fatigue, Structural Alloys

Equipment improvements of the coke drum include an overhead elliptical head instead of a spherical head, thus increasing the effective volume of the coke drum. The transition section between the skirt and shell connection uses a forged piece structure instead of overlay structure, thereby extending fatigue life. Alloy steel and cladding are used instead of carbon steel, thus improving corrosion resistance. 

For structural alloys, the first-year program includes fatigue tests on alloys 21/6/9, AISI 304, and 316 initiation of multiple product and heat tensile tests on alloys AISI 304 and 316 and tensile and fracture toughness tests of a commercial heat of alloy 21/6/9. All tests will be performed at 300, 76, and 4K. In alloy 21/6/9, the fracture toughness at 4 K is marginal compared with AISI 304 and 316 therefore, more tests than are presently available are required to reliably describe the fracture behavior. 

FATIGUE CRACK GROWTH RESISTANCE OF STRUCTURAL ALLOYS AT CRYOGENIC TEMPERATURES... 

This paper summarizes the experimental results on the fatigue crack growth resistance of 14 commercial structural alloys tested at selected temperatures between 295 and 4 K. Many of the results are reported here for the first time some data were previously reported [% The comparisons made in this paper lead to generalizations showing that temperature effects on da/dN vs. AAT behavior can be correlated with alloy crystal structure. 

Fatigue Crack Growth Resistance of Structural Alloys at Cryogenic Temperatures... 

R. L. Tobler and R. P. Reed, Fatigue Crack Growth Resistance of Structural Alloys at Cryogenic Temperatures, Report NBSIR 76-848, National Bureau of Standards, Boulder, Colorado (1976). 

Note Stress ratio A = 0.1, at 20 to 28 Hz compact specimens, (a) NI - normal interstitial, LI = low interstitial, ELI = extra low interstitial. Source R. L. Ibbler and R.P. Reed, Fatigue Crack (Srowth Resistance of Structural Alloys at Cryogenic Temperatures, in Advances in Cryogenic Engineering, KD. Timmerhaus et al., EkL, Vol 24, Plenum Press, 1978, p 82-90... 

Cast magnesium alloys used for structural applications comprise a highly heterogeneous ductile matrix with several dominant types of inclusions that dictate fatigue resistance. We use the term inclusion as distinctly different from a crack, as the former occurs naturally as products of the casting process, while the latter is... 

High strength low alloy steels (line pipe, structural) and steels for fatigue intensive applications (axles, bearings, rail steels)... 

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