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Richard P. Gangloff - One of the best experts on this subject based on the ideXlab platform.

  • Hydrogen Environment Assisted Cracking of Ultra-High Strength AetMet(Trademark) 100 Steel
    2020
    Co-Authors: Richard P. Gangloff
    Abstract:

    Abstract : Precipitation hardened martensitic AetMet(tradeMark) 100 is a high purity ultra-high strength steel with exceptional plain strain fractare toughness (K(sub IC) 130 MPa square root to m) and high yield strength (sigma YS 1725 MPa). The hydrogen envfronment assisted Cracking (FlEAC) behavior of this modem steel is not w#1 understood, and was characterized in neutral 3.5% NaCl solution at various applied potentials (E(sub App)) relevant to coated applications in marine environments. A novel short crack specimen was stressed under constant displacement-rate, and monitored using a high resolution electrical potential crack monitoring technique to determine the Stage II crack growth rate (da/dt(sub II)) and threshold stress intensity (K(sub TH)) typically of the chemically short crack reghne (250 to 1000 micronmeter). AerMet(TradeMark) 100 is susceptible to severe transgranular (TG) HEAC when stressed in neutral 3.5% NaCl and at near free corrosion potentials, as quantified by reduced Km, to as low as 10% of K(sub IC), and da/dt(subII) as high as 0.5 micronmeter/s. Applied electrode potential (E(sub App)) is a critical variable. As EApp increases from -1.1 volts vs. saturated calomel electrode (V(sub SCE)) to 0.625 V5CE, operationally defined Km increases from the very low level of 9 MPa square root to m to a maximum of 40 MPa square root to m, and da/dt(sub II) decreases monotonically from 500 nm/s to 1 nm/s. Additional polarization to -0.5 V(sub SCE), typical of free corrosion in aerated solution, produces a decrease in Km to l6MPa square root to m and increase in da/dt(sub II) to 100 nm/s. The mechanism for this behavior is crack tip hydrogen embrittlement. The effect of electrode potential is understood based on occluded crack acidification at the anodic conditions and cathodic polarization at lower potentials, each favoring H production and uptake.

  • Strategies for Mitigation of Hydrogen Environment Assisted Cracking of High Strength Steels
    2020
    Co-Authors: John R. Scully, B. A. Kehler, Richard P. Gangloff
    Abstract:

    Abstract : Modem ultra high strength alloy steels (UHSS) have been developed with outstanding combinations of strength and fracture toughness. Such steels are characterized by high purity and nanoscale strengthening clusters/coherent precipitates in a complex precipitation hardened, martensitic microstructure. However, the performance of such steels is degraded dramatically by internal hydrogen embrittlement (IHE) and hydrogen environment embrittlement (HEE). Thus, the development of an UHSS that is immune to hydrogen embrittlement is of seminal importance. The issues that hinder understanding of IHE/HEE center on the capability to first understand fracture process zone damage mechanisms, and second to quantify and ultimately predict crack tip hydrogen concentrations relative to critical concentrations that trigger fracture. Mitigation of the hydrogen-Cracking resistance of modem UHSS requires reduction in hydrogen uptake and/or modification of critical hydrogen concentrations for a given material by improving the intrinsic tolerance to dissolved and trapped hydrogen. Strategies for controlling and/or mitigating HEE and IHE of UHSS include control of intrinsic intergranular susceptibility governed by hydrogen-segregated impurity interactions and metallurgical alteration of H trap states. Another strategy is to exploit the strong electrochemical potential dependency of HEE Cracking by using tailored cathodic protection schemes. Lastly, coatings can be designed to release ions that% reduce H production and/or block H uptake at crack tips. A combination of a responsive coating that provides a tailored-low level of cathodic protection and active corrosion inhibition, as well as control of metallurgical purity and H trap states, provides a necessary- couple strategy to mitigate HEE of modem high strength steels.

  • Interdisciplinary multi-scale research on environment assisted Cracking: The 50 year legacy of Robert P. Wei
    International Journal of Fatigue, 2017
    Co-Authors: Richard P. Gangloff, D. Gary Harlow
    Abstract:

    Abstract Robert P. Wei died at the age of 84 in Bethlehem, Pennsylvania on September 28, 2015. The solid mechanics and materials science communities have lost a leader and visionary who dedicated five decades of his life to developing people and fundamental knowledge through world-class teaching and research. His contributions greatly advanced the broad areas of hydrogen embrittlement, stress corrosion Cracking, and Environment-Assisted fatigue crack propagation. His approach, centered on interdisciplinary integration of rigorous fracture mechanics experiments and mass transport plus reaction rate modeling, provides a roadmap for future developments. It is appropriate to recognize the large body of Professor Wei’s work in this special issue of the International Journal of Fatigue.

  • Hydrogen Environment Assisted Cracking of Modern Ultra-High Strength Martensitic Steels
    Metallurgical and Materials Transactions A, 2017
    Co-Authors: Greger L. Pioszak, Richard P. Gangloff
    Abstract:

    Martensitic steels (Aermet^®100, Ferrium^®M54™, Ferrium^®S53^®, and experimental CrNiMoWV at ultra-high yield strength of 1550 to 1725 MPa) similarly resist hydrogen environment assisted Cracking (HEAC) in aqueous NaCl. Cracking is transgranular, ascribed to increased steel purity and rare earth addition compared to intergranular HEAC in highly susceptible 300M. Nano-scale precipitates ((Mo,Cr)_2C and (W,V)C) reduce H diffusivity and the K-independent Stage II growth rate by 2 to 3 orders of magnitude compared to 300M. However, threshold K _TH is similarly low (8 to 15 MPa√m) for each steel at highly cathodic and open circuit potentials. Transgranular HEAC likely occurs along martensite packet and {110}_α′-block interfaces, speculatively governed by localized plasticity and H decohesion. Martensitic transformation produces coincident site lattice interfaces; however, a connected random boundary network persists in 3D to negate interface engineering. The modern steels are near-immune to HEAC when mildly cathodically polarized, attributed to minimal crack tip H production and uptake. Neither reduced Co and Ni in M54 and CrNiMoWV nor increased Cr in S53 broadly degrade HEAC resistance compared to baseline AM100. The latter suggests that crack passivity dominates acidification to widen the polarization window for HEAC resistance. Decohesion models predict the applied potential dependencies of K _TH and d a /d t _II with a single-adjustable parameter, affirming the importance of steel purity and trap sensitive H diffusivity.

  • Hydrogen Environment Assisted Cracking of a Modern Ultra-High Strength Martensitic Stainless Steel
    Corrosion, 2017
    Co-Authors: Greger L. Pioszak, Richard P. Gangloff
    Abstract:

    A modern martensitic stainless steel (Ferrium® PH48S™) resists hydrogen environment assisted Cracking (HEAC) in aqueous NaCl at ultra-high yield strengths (1,400 MPa to 1,600 MPa). HEAC is transgra...

A Turnbull - One of the best experts on this subject based on the ideXlab platform.

  • Issues in modelling of environment assisted Cracking.
    Environmentally Assisted Cracking: Predictive Methods for Risk Assessment and Evaluation of Materials Equipment and Structures, 2020
    Co-Authors: A Turnbull
    Abstract:

    Risk-based inspection is becoming the cornerstone of modern practice in ensuring the integrity of engineering structures and components in a cost effective manner. The approach relies heavily on experience, insight and awareness of the likelihood of crack initiation and on models to predict the evolution of crack size. Environment assisted Cracking poses a particular problem because of the sensitivity to transients and excursions in service behaviour and because models of crack growth kinetics, both empirical and deterministic, have significant limitations. A number of the existing issues in prediction are highlighted with recommendations for future development.

  • Enviornment assisted Cracking of metals - engineering challenges.
    2020
    Co-Authors: A Turnbull
    Abstract:

    A short overview is given of some of the key requirements in meeting the needs of industry with respect to testing and prediction of environment assisted Cracking of metals. The primary challenge is to bridge the gap between laboratory testing based on simplified testing conditions and actual service experience where complex variations in environment, temperature and stress often determine the likelihood of failure. Examples from the oil and gas, power and chemical process industries will be used to illustrate the progress in responding to these demands.

  • Implications of hydrogen uptake and transport for environment assisted Cracking testing and interpretation of results
    British Corrosion Journal, 2013
    Co-Authors: A Turnbull, A.j. Griffiths
    Abstract:

    Abstract Laboratory evaluation of environmental assisted Cracking (EAC) of metals induced by absorbed hydrogen atoms requires careful consideration because of the dependence of hydrogen uptake and transport on environment composition and temperature, and the need to reconcile the timescalefor hydrogen ingress with short term testing. Hydrogen permeation measurements in relevant environmental conditions can provide key information with respect to hydrogen diffusivity, concentration, and trapping parameters. Using data for three alloy types commonly used in the oil and gas industry, namely duplex stainless steel, 13Cr martensitic stainless steel, and low alloy carbon steel, examples are given of the application of such data in providing guidance in EAC testing and in interpreting the results.

  • comparative evaluation of environment induced Cracking of conventional and advanced steam turbine blade steels part 1 stress corrosion Cracking
    Corrosion Science, 2010
    Co-Authors: A Turnbull, S. Zhou
    Abstract:

    A prerequisite for the introduction of a new high strength steel blade in steam turbines is to ensure that its resistance to environment assisted Cracking is at least no worse than that of existing materials. To that end a series of stress corrosion tests has been conducted to assess the performance of the candidate material, PH13-8, relative to that of conventional blade steel, represented typically by FV566. Fracture mechanics tests using compact tension specimens have been undertaken in aerated and deaerated simulated condensate solution in order to determine the threshold stress intensity factor, KISCC, and the crack growth rate. Under normal water chemistry conditions, typically containing 300 ppb Cl- and 300 ppb SO42- but with the solution aerated, KISCC was significantly higher for the more highly alloyed PH13-8 steel (79-85 MPa m1/2 compared to 42-53 MPa m1/2 for FV566) but in aerated 35 ppm chloride solution KISCC was reduced dramatically for both alloys to near 20 MPa m1/2 with the FV566 steel showing a similar or slightly lower threshold value. However, the growth rate for the higher strength steel was about an order of magnitude greater. Also, the effect of an excursion in chloride concentration to 35 ppm was to reduce the KISCC value for the PH13-8 steel when returned to normal, but aerated, water chemistry whereas there was little change in the KISCC for the FV566 steel following an excursion. Importantly, for both steels, deaeration of the solution to reflect continuous on-load conditions in service caused the growing crack effectively to arrest.

  • 2009 W.R. Whitney Award Lecture: Local Hydrogen Generation and Its Impact on Environment-Assisted Cracking and Crevice Corrosion
    Corrosion, 2010
    Co-Authors: A Turnbull
    Abstract:

    Abstract An overview is given of the key role for reduction of hydrogen ions and water in determining the local chemistry and electrochemistry in crevices and cracks. Thus, the ability to cathodica...

Shahin Khoddam - One of the best experts on this subject based on the ideXlab platform.

S. Zhou - One of the best experts on this subject based on the ideXlab platform.

  • Environment assisted Cracking of 316L stainless steel in acetic acid environments.
    Corrosion, 2020
    Co-Authors: Alan Turnbull, S. Zhou, Anthony Willetts
    Abstract:

    The effect of a chloride incursion on the environment assisted Cracking of stainless steel in acetic acid solutions containing bromide has been investigated.

  • comparative evaluation of environment induced Cracking of conventional and advanced steam turbine blade steels part 1 stress corrosion Cracking
    Corrosion Science, 2010
    Co-Authors: A Turnbull, S. Zhou
    Abstract:

    A prerequisite for the introduction of a new high strength steel blade in steam turbines is to ensure that its resistance to environment assisted Cracking is at least no worse than that of existing materials. To that end a series of stress corrosion tests has been conducted to assess the performance of the candidate material, PH13-8, relative to that of conventional blade steel, represented typically by FV566. Fracture mechanics tests using compact tension specimens have been undertaken in aerated and deaerated simulated condensate solution in order to determine the threshold stress intensity factor, KISCC, and the crack growth rate. Under normal water chemistry conditions, typically containing 300 ppb Cl- and 300 ppb SO42- but with the solution aerated, KISCC was significantly higher for the more highly alloyed PH13-8 steel (79-85 MPa m1/2 compared to 42-53 MPa m1/2 for FV566) but in aerated 35 ppm chloride solution KISCC was reduced dramatically for both alloys to near 20 MPa m1/2 with the FV566 steel showing a similar or slightly lower threshold value. However, the growth rate for the higher strength steel was about an order of magnitude greater. Also, the effect of an excursion in chloride concentration to 35 ppm was to reduce the KISCC value for the PH13-8 steel when returned to normal, but aerated, water chemistry whereas there was little change in the KISCC for the FV566 steel following an excursion. Importantly, for both steels, deaeration of the solution to reflect continuous on-load conditions in service caused the growing crack effectively to arrest.

  • overview steam turbines part 1 operating conditions and impurities in condensates liquid films and deposits
    Corrosion Engineering Science and Technology, 2003
    Co-Authors: S. Zhou, A Turnbull
    Abstract:

    AbstractA review of the literature and discussions with plant operators have provided the basis for this overview of present knowledge and understanding of the chemistry of the condensates formed on steam turbines and the link to system operation. This has been supplemented by Part 2 of this study: a review of the effect of test variables on environment assisted Cracking, which is to be published in Corrosion Engineering, Science and Technology. Steam turbine operating conditions are described including the steam cycle, chemical control of the steam/water circuit and the distribution of temperature, pressure and steam wetness in the turbine. Service experience indicates that Cracking occurs mainly in regions where condensates form. The saturation temperature, at which condensation occurs, varies from station to station, depending on the turbine design and operating conditions. Calculations based on thermodynamic data under steady flow conditions show that the concentration of non-volatile species (e.g. ch...

  • Overview Steam turbines: Part 1 – Operating conditions and impurities in condensates, liquid films and deposits
    Corrosion Engineering Science and Technology, 2003
    Co-Authors: S. Zhou, A Turnbull
    Abstract:

    AbstractA review of the literature and discussions with plant operators have provided the basis for this overview of present knowledge and understanding of the chemistry of the condensates formed on steam turbines and the link to system operation. This has been supplemented by Part 2 of this study: a review of the effect of test variables on environment assisted Cracking, which is to be published in Corrosion Engineering, Science and Technology. Steam turbine operating conditions are described including the steam cycle, chemical control of the steam/water circuit and the distribution of temperature, pressure and steam wetness in the turbine. Service experience indicates that Cracking occurs mainly in regions where condensates form. The saturation temperature, at which condensation occurs, varies from station to station, depending on the turbine design and operating conditions. Calculations based on thermodynamic data under steady flow conditions show that the concentration of non-volatile species (e.g. ch...

  • Steam turbine operating conditions, chemistry of condensates and environment assisted Cracking - a critical review.
    2002
    Co-Authors: S. Zhou, A Turnbull
    Abstract:

    A review of the literature and discussions with plant operators has been undertaken to establish present knowledge and understanding of the chemistry of the condensates formed on steam turbines and the link to system operations. This has been supplemented by an overview of the effect of test variables on environment assisted Cracking. In Section 1, steam turbine operating conditions are described including the steam cycle, the chemical control of the steam/water and the distribution of temperature, pressure and steam wetness in the turbine. Service experience indicates that Cracking occurs mainly in regions where condensates form. The saturation temperature, at which condensation occurs, varies from station to station, depending on the turbine design and operating conditions. Calculations based on thermodynamic data under steady flow conditions show that the concentration of non-volatile species (e.g. chloride, sulphate, sodium, etc.) in the liquid phase can be 100 times higher tan that in the steam. Much higher concentrations of the species may be present in deposits in the regions where the steam is dry or dry/wet cycles occur. On the other hand, the concentration of volatile species (e.g. oxygen, carbon dioxide) in the liquid phase is usually less than 1 ppb under normal operating conditions. However, concentrations of oxygen and carbon dioxide in the condensates can be as high as several ppm under transient conditions (forced condensation, air leakage and start-up). In section 2, stress corrosion Cracking (SCC) data for disc steels are reviewed critically. The effect of material properties (steel cleanliness, yield strength), environment (oxygen, carbon dioxide, chloride level), temperature and stress conditions, on the initiation and growth of stress corrosion cracks assessed. For long cracks, growth rate are claimed to be independent of oxygen and CO2 concentration, and steel cleanliness, but there are some exceptions that suggest that the apparent independence of these variables may be linked partly to the spread in growth rate data, Unquestionably, the variables having the most dramatic effect are strength level and temperature. Dissolved gases and steel cleanliness have a more profound influence on 'initiation' of stress corrosion cracks for medium strength disc steels, certainly in relation to pit development and growth but the impact on short crack growth is less well established.

S. Torkamani - One of the best experts on this subject based on the ideXlab platform.

  • Environment-Assisted Cracking of cast WE43-T6 magnesium
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Thomas James Marrow, A. Bin Ahmad, Irfan Khan, S. Torkamani
    Abstract:

    Abstract Environment-Assisted Cracking of WE43 cast magnesium (4.2 wt.% Yt, 2.3 wt.% Nd, 0.7% Zr, 0.8% HRE) in the T6 peak-aged condition was induced in ambient air in notched specimens. The mechanism of fracture was studied using electron backscatter diffraction, serial sectioning and in situ observations of crack propagation. Cracks initiated at the intergranular brittle intermetallic, and propagated by transgranular cleavage. These observations imply that a microstructural model for the static fatigue limit in cast magnesium alloys may be developed which includes the effects of notch-like defects such as porosity.

  • Environment-Assisted Cracking of cast WE43-T6 magnesium
    Materials Science and Engineering A, 2004
    Co-Authors: T. James Marrow, A. Bin Ahmad, I. N. Khan, S. M A Sim, S. Torkamani
    Abstract:

    Environment-Assisted Cracking of WE43 cast magnesium (4.2 wt.% Yt, 2.3 wt.% Nd, 0.7% Zr, 0.8% HRE) in the T6 peak-aged condition was induced in ambient air in notched specimens. The mechanism of fracture was studied using electron backscatter diffraction, serial sectioning and in situ observations of crack propagation. Cracks initiated at the intergranular brittle intermetallic, and propagated by transgranular cleavage. These observations imply that a microstructural model for the static fatigue limit in cast magnesium alloys may be developed which includes the effects of notch-like defects such as porosity. © 2004 Elsevier B.V. All rights reserved.