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CHARACTERIZATION OF THE EMBRITTLEMENT TENDENCY OF A CATHODICALLY POLARIZED SUPERFERRITIC STAINLESS STEEL IN SEAWATER (HYDROGEN DAMAGE, INTERGRANULAR)
Title
CHARACTERIZATION OF THE EMBRITTLEMENT TENDENCY OF A CATHODICALLY POLARIZED SUPERFERRITIC STAINLESS STEEL IN SEAWATER (HYDROGEN DAMAGE, INTERGRANULAR).
Creator
KRISHNAMURTHY, RAVI M., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
In order to investigate the cracking tendency of cathodically polarized SEACURE superferritic stainless steel, a series of potentiostatically controlled tests were conducted in flowing natural seawater. U-bend and tensile specimens were used to determine the threshold potential and limiting fracture stress. The microstructure was examined using a metallurgical microscope and a chemical analysis was conducted across the grain boundary. These results were then correlated to hydrogen assisted...
Show moreIn order to investigate the cracking tendency of cathodically polarized SEACURE superferritic stainless steel, a series of potentiostatically controlled tests were conducted in flowing natural seawater. U-bend and tensile specimens were used to determine the threshold potential and limiting fracture stress. The microstructure was examined using a metallurgical microscope and a chemical analysis was conducted across the grain boundary. These results were then correlated to hydrogen assisted cracking, by performing SEM and EDAX analyses on fractured U-bend and tensile samples. Finally a model was developed which explained the predominantly intergranular cracking in the static stress condition and also accommodated the transgranular failure during dynamic loading.
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Date Issued
1986
PURL
http://purl.flvc.org/fcla/dt/14325
Subject Headings
Steel--Fracture, Sea-water corrosion
Format
Document (PDF)
CORROSION FATIGUE OF NOTCHED 1018 STEEL IN SEA WATER
Title
CORROSION FATIGUE OF NOTCHED 1018 STEEL IN SEA WATER.
Creator
FLUET, JOSEPH E., JR., Florida Atlantic University, Hartt, William H.
Abstract/Description
A summary of some pertinent previous research by other authors is presented separately from the actual laboratory report. The report presents the results of air and corrosion fatigue tests which are. interpreted in terms of time to failure, crack growth history, and fracture mechanics techniques. In addition, the results of cathodic protection of corrosion fatigue tests are interpreted in terms of simple-design criteria, as well as relative to Critical Corrosion Rate Theory. One of the more...
Show moreA summary of some pertinent previous research by other authors is presented separately from the actual laboratory report. The report presents the results of air and corrosion fatigue tests which are. interpreted in terms of time to failure, crack growth history, and fracture mechanics techniques. In addition, the results of cathodic protection of corrosion fatigue tests are interpreted in terms of simple-design criteria, as well as relative to Critical Corrosion Rate Theory. One of the more significant results presented is the greater longevity of corrosion fatigue, as compared to air fatigue, notched specimens stressed within 10-15 KSI above the air endurance limit. Also, the potential required to cathodically protect such notched specimens is shown to be 50 mV lower than for comparable smooth specimens. Both phenomena are attributed in part to the lowering of crack pH to acidic levels in notched specimens.
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Date Issued
1976
PURL
http://purl.flvc.org/fcla/dt/13768
Subject Headings
Steel--Fatigue, Steel--Corrosion, Steel--Fracture, Notched bar testing
Format
Document (PDF)
Experimental and theoretical characterization of near-threshold fatigue crack growth for high strength steels in seawater
Title
Experimental and theoretical characterization of near-threshold fatigue crack growth for high strength steels in seawater.
Creator
Yang, Jingjun., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Near-threshold fatigue crack growth rate data were generated for six high strength steels at stress ratios of 0.5 and 0.8 under different environmental conditions, which included air, freely corroding in seawater, and cathodically polarized in seawater to -0.80v, -0.95v and -1.10v (vs SCE). The influence of stress ratio, loading frequency, magnitude of cathodic polarization and initial DeltaK on fatigue crack growth behavior for these high strength steels was experimentally characterized. The...
Show moreNear-threshold fatigue crack growth rate data were generated for six high strength steels at stress ratios of 0.5 and 0.8 under different environmental conditions, which included air, freely corroding in seawater, and cathodically polarized in seawater to -0.80v, -0.95v and -1.10v (vs SCE). The influence of stress ratio, loading frequency, magnitude of cathodic polarization and initial DeltaK on fatigue crack growth behavior for these high strength steels was experimentally characterized. The results disclosed general trends of fatigue crack growth under conditions relevant to offshore structure applications and circumscribed variables that are primarily influential with regard to service performance. The rate controlling processes and cracking mechanisms of near-threshold fatigue crack growth, particularly under cathodic polarization in seawater, were also studied in conjunction with crack mouth opening displacement measurements, fractographic observation and crack profile examination. The data and observations suggest that calcareous deposit induced closure was the rate-controlling factor for near-threshold fatigue crack growth under cathodic polarization in seawater although the cracking involved a brittle failure mechanism as a result of hydrogen embrittlement. With different FCGR determining procedures which included natural K-decreasing, enhanced K-decreasing, natural K-increasing and constant DeltaK, the FCGR under cathodic polarization in seawater was found to be time-dependent and, as such, was not a unique function of DeltaK but depended upon K-history or experimental procedures. These observations were consistent with results of a theoretical analysis which involved kinetics modeling of the interaction between fatigue crack growth and calcareous deposit thickening. The model also predicted the existence of an upper limit transition DeltaK, DeltaK Upp/T, between the Paris and threshold regions and it was found that the predicted DeltaK Upp/T was in agreement with the experimental one. The basis for applying this critical parameter (DeltaK Upp/T) to offshore structure designs was addressed in conjunction with experimental results.
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Date Issued
1995
PURL
http://purl.flvc.org/fcla/dt/12410
Subject Headings
Seawater corrosion, Steel--Fatigue, Steel--Fracture, Corrosion and anti-corrosives
Format
Document (PDF)