Welding Hydrogen diffusion Cohesive zone modelling Fracture toughness abstract An API X70 pipelin... more Welding Hydrogen diffusion Cohesive zone modelling Fracture toughness abstract An API X70 pipeline steel has been investigated with respect to hydrogen diffusion and fracture mechanics properties. A finite element cohesive element approach has been applied to simulate the onset of hydrogen-induced fracture. Base metal, weld simulated heat affected zone and weld metal have been investigated. The electrochemical permeation technique was used to study hydrogen diffusion properties, while in situ fracture mechanics testing was performed in order to establish the hydrogen influenced threshold stress intensity. The average effective diffusion coefficient at room temperature was 7.60 Â 10 À11 m 2 /s for the base metal, 4.01 Â 10 À11 m 2 /s for weld metal and 1.26 Â 10 À11 m 2 /s for the weld simulated heat affected zone. Hydrogen susceptibility was proved to be pronounced for the heat affected zone samples. Fracture toughness samples failed at a net section stress level of 0.65 times the yield strength; whereas the base metal samples did not fail at net section stresses lower than the ultimate tensile strength. The initial cohesive parameters which best fitted the experimental results were s c ¼ 1500 MPa (3.1$s y ) for the base metal, s c ¼ 1800 MPa (3.0$s y ) for weld metal and s c ¼ 1840 MPa (2.3$s y ) for heat affected zone. Threshold stress intensities K Ic,HE were in the range 143e149 MPaOm.
Electrochemical hydrogen permeation measurements have been performed on pre-strained pipeline ste... more Electrochemical hydrogen permeation measurements have been performed on pre-strained pipeline steel base metal and weld simulated heat affected zone specimens. The level of plastic pre-strain was 0-3%. The effective diffusion coefficient decreased with higher pre-strain. At higher pre-strain levels the effect of plastic deformation on hydrogen diffusion is dominating the influence of microstructure. Sub-surface hydrogen concentration was found to be unaffected by plastic strain. The calculated number of traps was clearly higher than results available for alpha ferrite in literature.
In this investigation, we investigate the effects of solid state phase transformation on residual... more In this investigation, we investigate the effects of solid state phase transformation on residual stresses in welding supermartensitic stainless steels, using the Satoh experimental test approach. The results obtained clearly demonstrate that the austenite-to-martensite phase transformation has remarkable effects on the final tensile residual stress level, and stresses as low as 70 to 170 MPa were found, depending on the weld thermal program. These results may imply that unnecessary conservatism is often used when assuming residual stresses to be of the same order as the base metal yield strength.
Volume 3: Materials Technology; Jan Vugts Symposium on Design Methodology of Offshore Structures; Jo Pinkster Symposium on Second Order Wave Drift Forces on Floating Structures; Johan Wichers Symposium on Mooring of Floating Structures in Waves, 2011
Fracture mechanics SENT testing and FE simulation to establish hydrogen influenced cohesive param... more Fracture mechanics SENT testing and FE simulation to establish hydrogen influenced cohesive parameters for X70 structural steel welded joints have been performed. Base metal and weld simulated coarse grained heat affected zone have been included in the study. The base metal did not fail at net section stresses lower than 1.29 times the yield strength and reveals low sensitivity to hydrogen embrittlement. The weld simulated coarse grained heat affected zone was prone to fracture at stresses above 64% of the yield strength, which indicates hydrogen embrittlement susceptibility. The cohesive parameters best fitting the experiments are δ c =0.3 mm and σ c =1700 MPa (3.5•σ y ) for the base metal and δ c =0.3 mm and σ c =2100 MPa (2.6•σ y ) for the coarse grained heat affected zone.
Heat affected zone Pipeline steel Three-dimensional model abstract A three-dimensional finite coh... more Heat affected zone Pipeline steel Three-dimensional model abstract A three-dimensional finite cohesive element approach has been developed and applied in order to simulate the crack initiation of hydrogen-induced fracture. A single edge notched tension specimen of an X70 weld heat affected zone was simulated. The results were compared to similar two-dimensional plane strain model and the cohesive parameters were calibrated to fit the experimental results. The three dimensional simulations gave higher values in terms of opening stress at the stress peak, plastic strain levels at the crack tip and hydrogen lattice concentration when compared with two-dimensional simulations under the same global net section stress levels. Nevertheless a higher cohesive strength was needed for the 2D model for the onset of crack propagation. The best fit to the experimental data were obtained for a cohesive strength of 1840 MPa and 1620 MPa for the 2D and 3D simulation respectively. The critical opening was assigned to 0.3 mm for both models. The threshold stress intensities K IC,HE were 142 MPaOm and 146 MPaOm for the 2D and 3D models, respectively.
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 3, 2005
Supermartensitic 13% Cr stainless steels have been in use in offshore satellite flowlines for sev... more Supermartensitic 13% Cr stainless steels have been in use in offshore satellite flowlines for several years. Since they contain microstructure that is susceptible to hydrogen cracking, the pick up of hydrogen in welding with subsequent transport to critical areas may be very important, also with respect to hydrogen embrittlement when hydrogen is coming from other sources than welding (e.g., cathodic protection). In the present investigation the pick up of hydrogen has been assessed using mechanized TIG welding with superduplex 25% Cr wire. The WM and HAZ hydrogen levels were analyzed. With addition of hydrogen in the shielding gas in multipass welding, the mean WM hydrogen contents were found to be approximately 10 and 6 ppm in the cap layer and root pass, respectively. The corresponding mean HAZ concentration was 3.1 ppm (scatter between 1.3 and 4.8) immediately after welding. Post weld hydrogen diffusion heat treatment showed that hydrogen diffusion was retarded at room temperature, even for 1 month storage. Limited diffusion took place at 90°C, particularly for the cap region. The results indicate that superduplex weld metal with high hydrogen content (6-10ppm) will act as a hydrogen reservoir supplying H to the 13% Cr HAZ as long as 2-3 years after welding.
Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cra... more Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25%Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25%Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 lm gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85-0.9 times the yield strength.
This is a review based on classic and recent published literature regarding hydrogen diffusion an... more This is a review based on classic and recent published literature regarding hydrogen diffusion and hydrogen assisted cracking in stainless steels. The majority of the reviewed literature is related to supermartensitic, duplex and super duplex stainless steels. Recent models for hydrogen diffusion and hydrogen assisted fracture in the presence of sharp notches are presented and discussed. New approaches in cohesive FE modelling of hydrogen assisted cracking are presented and reviewed as a possible method for building a bridge between the modelling of micro mechanisms in the fracture process zone and the global fracture response.
Laboratory experiments of repeatable full scale precision tests on reinforced concrete elements e... more Laboratory experiments of repeatable full scale precision tests on reinforced concrete elements exposed to blast loads require considerable resources, and are in many cases impossible with the test equipment available nationally and internationally. In this respect testing of scaled structural elements is advantageous. Model laws must be applied, and the effect of relaxations of a strict model law application must be well understood. The objective of this report is to give specifications for production of reinforced concrete slabs in replica scaling. Three slabs with different dimensions are included: 300 x 300 x 30 mm (P1), 1000 x 1000 x 100 mm (P2) and 3000 x 3000 x 300 mm (P3). Concrete mixes are developed for all three slabs. Concrete quality comply with C35, and similitude in the compressive strength between the mixes is required. Use of replica scaled accumulated aggregate grading curves was a part of the scope of work. Specifications for production of deformed bars with diame...
This is a review based on classic and recent published literature regarding hydrogen diffusion an... more This is a review based on classic and recent published literature regarding hydrogen diffusion and hydrogen assisted cracking in stainless steels. The majority of the reviewed literature is related to supermartensitic, duplex and super duplex stainless steels. Recent models for hydrogen diffusion and hydrogen assisted fracture in the presence of sharp notches are presented and discussed. New approaches in cohesive FE modelling of hydrogen assisted cracking are presented and reviewed as a possible method for building a bridge between the modelling of micro mechanisms in the fracture process zone and the global fracture response.
Hydrogen induced cold cracking is a critical issue for hyperbaric welding of pipelines on the sea... more Hydrogen induced cold cracking is a critical issue for hyperbaric welding of pipelines on the sea bed. The susceptibility to cracking is influenced both by the microstructure, the hydrogen content and the stress state. In order to investigate these complex phenomena a hydrogen diffusion model has been included in the FEcode WELDSIMS. Here, the hydrogen diffusion is dependent on both the temperature, the hydrostatic stress and the phase composition, and the effect of reversible traps is included. The model has been applied on a case involving 14-pass butt welding of a ferritic steel pipe. The hydrogen concentration and stress state in the vicinity of a weld root defect is investigated. The effect of possible interpass and post weld heat treatment on the hydrogen concentration is predicted. 2D simulations with a good spatial resolution and numerical accuracy are accompanied with 3D simulations on a sector of the pipe. A cohesive element model is used to predict whether hydrogen induced cracking will occur in the HAZ after welding. Residual stresses and hydrogen concentrations from the welding simulation are imported into an ABAQUS model, where the hydrostatic stress field is used as a driving force in an isothermal analysis of hydrogen diffusion. This procedure allows fracture mechanics assessment of both cold cracking and fracture due to mechanical loads, e.g. during reeling operations.
The present paper deals with hydrogen embrittlement (HE) susceptibility of a weld thermal simulat... more The present paper deals with hydrogen embrittlement (HE) susceptibility of a weld thermal simulated heat affected zone of X70 structural steel in high pressure hydrogen gas at 20 1C. Fracture mechanics Single Edge Notched Tension tests at various hydrogen pressures (0.1, 0.6, 10 and 40 MPa H 2 ) have been carried out. The HE susceptibility was quantified through the measurement of the fracture toughness K Q and J (the effect of hydrogen pressure was addressed through linear load increase conditions till failure was obtained). The results show that hydrogen causes a strong decrease in the fracture toughness with increasing hydrogen pressure. The critical hydrogen pressure for the onset of HE was observed to fall between 0.1 MPa and 0.6 MPa. These results were supported by Scanning Electron Microscope (SEM) investigations of the fracture surfaces which showed a clear shift in the fracture mode at 0.6 MPa H 2 . Moreover, constant load tests were carried out in order to investigate the influence of hydrogen exposure time. The results imply that fracture always occurs within 8 h and that longer time to failure is related to stronger toughness reduction. This effect is more pronounced for test at 40 MPa than at 0.6 MPa hydrogen pressure levels. 3D Finite Element calculations of hydrogen diffusion have been performed and the results are discussed in relation to the experiments, in order to attempt to identify the hydrogen populations (diffusible or trapped) which act predominantly on the embrittlement of the material.
Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cra... more Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25%Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25%Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 lm gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85-0.9 times the yield strength.
The Failure Assessment Diagrams (FAD) used in BS 7910:1999 (Guide on methods for assessing the ac... more The Failure Assessment Diagrams (FAD) used in BS 7910:1999 (Guide on methods for assessing the acceptability of flaws in fusion welded structures) represent high structural constraint applications. The standard gives literature references for constraint correction methods, based on T and Q, but none of these are included in the standard. There is evidently a need to present a framework for
Welding Hydrogen diffusion Cohesive zone modelling Fracture toughness abstract An API X70 pipelin... more Welding Hydrogen diffusion Cohesive zone modelling Fracture toughness abstract An API X70 pipeline steel has been investigated with respect to hydrogen diffusion and fracture mechanics properties. A finite element cohesive element approach has been applied to simulate the onset of hydrogen-induced fracture. Base metal, weld simulated heat affected zone and weld metal have been investigated. The electrochemical permeation technique was used to study hydrogen diffusion properties, while in situ fracture mechanics testing was performed in order to establish the hydrogen influenced threshold stress intensity. The average effective diffusion coefficient at room temperature was 7.60 Â 10 À11 m 2 /s for the base metal, 4.01 Â 10 À11 m 2 /s for weld metal and 1.26 Â 10 À11 m 2 /s for the weld simulated heat affected zone. Hydrogen susceptibility was proved to be pronounced for the heat affected zone samples. Fracture toughness samples failed at a net section stress level of 0.65 times the yield strength; whereas the base metal samples did not fail at net section stresses lower than the ultimate tensile strength. The initial cohesive parameters which best fitted the experimental results were s c ¼ 1500 MPa (3.1$s y ) for the base metal, s c ¼ 1800 MPa (3.0$s y ) for weld metal and s c ¼ 1840 MPa (2.3$s y ) for heat affected zone. Threshold stress intensities K Ic,HE were in the range 143e149 MPaOm.
Electrochemical hydrogen permeation measurements have been performed on pre-strained pipeline ste... more Electrochemical hydrogen permeation measurements have been performed on pre-strained pipeline steel base metal and weld simulated heat affected zone specimens. The level of plastic pre-strain was 0-3%. The effective diffusion coefficient decreased with higher pre-strain. At higher pre-strain levels the effect of plastic deformation on hydrogen diffusion is dominating the influence of microstructure. Sub-surface hydrogen concentration was found to be unaffected by plastic strain. The calculated number of traps was clearly higher than results available for alpha ferrite in literature.
In this investigation, we investigate the effects of solid state phase transformation on residual... more In this investigation, we investigate the effects of solid state phase transformation on residual stresses in welding supermartensitic stainless steels, using the Satoh experimental test approach. The results obtained clearly demonstrate that the austenite-to-martensite phase transformation has remarkable effects on the final tensile residual stress level, and stresses as low as 70 to 170 MPa were found, depending on the weld thermal program. These results may imply that unnecessary conservatism is often used when assuming residual stresses to be of the same order as the base metal yield strength.
Volume 3: Materials Technology; Jan Vugts Symposium on Design Methodology of Offshore Structures; Jo Pinkster Symposium on Second Order Wave Drift Forces on Floating Structures; Johan Wichers Symposium on Mooring of Floating Structures in Waves, 2011
Fracture mechanics SENT testing and FE simulation to establish hydrogen influenced cohesive param... more Fracture mechanics SENT testing and FE simulation to establish hydrogen influenced cohesive parameters for X70 structural steel welded joints have been performed. Base metal and weld simulated coarse grained heat affected zone have been included in the study. The base metal did not fail at net section stresses lower than 1.29 times the yield strength and reveals low sensitivity to hydrogen embrittlement. The weld simulated coarse grained heat affected zone was prone to fracture at stresses above 64% of the yield strength, which indicates hydrogen embrittlement susceptibility. The cohesive parameters best fitting the experiments are δ c =0.3 mm and σ c =1700 MPa (3.5•σ y ) for the base metal and δ c =0.3 mm and σ c =2100 MPa (2.6•σ y ) for the coarse grained heat affected zone.
Heat affected zone Pipeline steel Three-dimensional model abstract A three-dimensional finite coh... more Heat affected zone Pipeline steel Three-dimensional model abstract A three-dimensional finite cohesive element approach has been developed and applied in order to simulate the crack initiation of hydrogen-induced fracture. A single edge notched tension specimen of an X70 weld heat affected zone was simulated. The results were compared to similar two-dimensional plane strain model and the cohesive parameters were calibrated to fit the experimental results. The three dimensional simulations gave higher values in terms of opening stress at the stress peak, plastic strain levels at the crack tip and hydrogen lattice concentration when compared with two-dimensional simulations under the same global net section stress levels. Nevertheless a higher cohesive strength was needed for the 2D model for the onset of crack propagation. The best fit to the experimental data were obtained for a cohesive strength of 1840 MPa and 1620 MPa for the 2D and 3D simulation respectively. The critical opening was assigned to 0.3 mm for both models. The threshold stress intensities K IC,HE were 142 MPaOm and 146 MPaOm for the 2D and 3D models, respectively.
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 3, 2005
Supermartensitic 13% Cr stainless steels have been in use in offshore satellite flowlines for sev... more Supermartensitic 13% Cr stainless steels have been in use in offshore satellite flowlines for several years. Since they contain microstructure that is susceptible to hydrogen cracking, the pick up of hydrogen in welding with subsequent transport to critical areas may be very important, also with respect to hydrogen embrittlement when hydrogen is coming from other sources than welding (e.g., cathodic protection). In the present investigation the pick up of hydrogen has been assessed using mechanized TIG welding with superduplex 25% Cr wire. The WM and HAZ hydrogen levels were analyzed. With addition of hydrogen in the shielding gas in multipass welding, the mean WM hydrogen contents were found to be approximately 10 and 6 ppm in the cap layer and root pass, respectively. The corresponding mean HAZ concentration was 3.1 ppm (scatter between 1.3 and 4.8) immediately after welding. Post weld hydrogen diffusion heat treatment showed that hydrogen diffusion was retarded at room temperature, even for 1 month storage. Limited diffusion took place at 90°C, particularly for the cap region. The results indicate that superduplex weld metal with high hydrogen content (6-10ppm) will act as a hydrogen reservoir supplying H to the 13% Cr HAZ as long as 2-3 years after welding.
Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cra... more Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25%Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25%Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 lm gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85-0.9 times the yield strength.
This is a review based on classic and recent published literature regarding hydrogen diffusion an... more This is a review based on classic and recent published literature regarding hydrogen diffusion and hydrogen assisted cracking in stainless steels. The majority of the reviewed literature is related to supermartensitic, duplex and super duplex stainless steels. Recent models for hydrogen diffusion and hydrogen assisted fracture in the presence of sharp notches are presented and discussed. New approaches in cohesive FE modelling of hydrogen assisted cracking are presented and reviewed as a possible method for building a bridge between the modelling of micro mechanisms in the fracture process zone and the global fracture response.
Laboratory experiments of repeatable full scale precision tests on reinforced concrete elements e... more Laboratory experiments of repeatable full scale precision tests on reinforced concrete elements exposed to blast loads require considerable resources, and are in many cases impossible with the test equipment available nationally and internationally. In this respect testing of scaled structural elements is advantageous. Model laws must be applied, and the effect of relaxations of a strict model law application must be well understood. The objective of this report is to give specifications for production of reinforced concrete slabs in replica scaling. Three slabs with different dimensions are included: 300 x 300 x 30 mm (P1), 1000 x 1000 x 100 mm (P2) and 3000 x 3000 x 300 mm (P3). Concrete mixes are developed for all three slabs. Concrete quality comply with C35, and similitude in the compressive strength between the mixes is required. Use of replica scaled accumulated aggregate grading curves was a part of the scope of work. Specifications for production of deformed bars with diame...
This is a review based on classic and recent published literature regarding hydrogen diffusion an... more This is a review based on classic and recent published literature regarding hydrogen diffusion and hydrogen assisted cracking in stainless steels. The majority of the reviewed literature is related to supermartensitic, duplex and super duplex stainless steels. Recent models for hydrogen diffusion and hydrogen assisted fracture in the presence of sharp notches are presented and discussed. New approaches in cohesive FE modelling of hydrogen assisted cracking are presented and reviewed as a possible method for building a bridge between the modelling of micro mechanisms in the fracture process zone and the global fracture response.
Hydrogen induced cold cracking is a critical issue for hyperbaric welding of pipelines on the sea... more Hydrogen induced cold cracking is a critical issue for hyperbaric welding of pipelines on the sea bed. The susceptibility to cracking is influenced both by the microstructure, the hydrogen content and the stress state. In order to investigate these complex phenomena a hydrogen diffusion model has been included in the FEcode WELDSIMS. Here, the hydrogen diffusion is dependent on both the temperature, the hydrostatic stress and the phase composition, and the effect of reversible traps is included. The model has been applied on a case involving 14-pass butt welding of a ferritic steel pipe. The hydrogen concentration and stress state in the vicinity of a weld root defect is investigated. The effect of possible interpass and post weld heat treatment on the hydrogen concentration is predicted. 2D simulations with a good spatial resolution and numerical accuracy are accompanied with 3D simulations on a sector of the pipe. A cohesive element model is used to predict whether hydrogen induced cracking will occur in the HAZ after welding. Residual stresses and hydrogen concentrations from the welding simulation are imported into an ABAQUS model, where the hydrostatic stress field is used as a driving force in an isothermal analysis of hydrogen diffusion. This procedure allows fracture mechanics assessment of both cold cracking and fracture due to mechanical loads, e.g. during reeling operations.
The present paper deals with hydrogen embrittlement (HE) susceptibility of a weld thermal simulat... more The present paper deals with hydrogen embrittlement (HE) susceptibility of a weld thermal simulated heat affected zone of X70 structural steel in high pressure hydrogen gas at 20 1C. Fracture mechanics Single Edge Notched Tension tests at various hydrogen pressures (0.1, 0.6, 10 and 40 MPa H 2 ) have been carried out. The HE susceptibility was quantified through the measurement of the fracture toughness K Q and J (the effect of hydrogen pressure was addressed through linear load increase conditions till failure was obtained). The results show that hydrogen causes a strong decrease in the fracture toughness with increasing hydrogen pressure. The critical hydrogen pressure for the onset of HE was observed to fall between 0.1 MPa and 0.6 MPa. These results were supported by Scanning Electron Microscope (SEM) investigations of the fracture surfaces which showed a clear shift in the fracture mode at 0.6 MPa H 2 . Moreover, constant load tests were carried out in order to investigate the influence of hydrogen exposure time. The results imply that fracture always occurs within 8 h and that longer time to failure is related to stronger toughness reduction. This effect is more pronounced for test at 40 MPa than at 0.6 MPa hydrogen pressure levels. 3D Finite Element calculations of hydrogen diffusion have been performed and the results are discussed in relation to the experiments, in order to attempt to identify the hydrogen populations (diffusible or trapped) which act predominantly on the embrittlement of the material.
Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cra... more Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25%Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25%Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 lm gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85-0.9 times the yield strength.
The Failure Assessment Diagrams (FAD) used in BS 7910:1999 (Guide on methods for assessing the ac... more The Failure Assessment Diagrams (FAD) used in BS 7910:1999 (Guide on methods for assessing the acceptability of flaws in fusion welded structures) represent high structural constraint applications. The standard gives literature references for constraint correction methods, based on T and Q, but none of these are included in the standard. There is evidently a need to present a framework for
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