The current eecFatigueAnalysis Suite focuses on damage assessments, data analysis, and probability of failure based on methods found in API 579/ASME FFS-1 Fitness-For Service and ASME Section VIII Div 2 Design codes and methods. This suite of products includes:

Pricing

These tools are offered on a variety of levels. To purchase a subscription, please contact webtools@equityeng.com for more information.


Fatigue Damage

Estimate cumulative fatigue damage for a user specified stress-strain history. Fatigue damage is caused by repeated stress or strain cycling of a material and leads to damage such as incremental crack growth and plasticity. The methods employed here involve elastic and elastic-plastic analyses, plasticity correction methods, uniaxial and multiaxial cycle counting methods, and fatigue damage assessment procedures for both smooth bar and welded joint specimens. The available methods are those found in both API 579-1/ASME FFS-1 Fitness-For-Service and ASME Section VIII Div 2 Design codes, as well as our own customized procedures based on the popular and widely accepted strain-life fatigue methods. The API 579-1/ASME FFS-1 Fitness-For-Service and ASME Section VIII Div 2 Design methods include Level 2 smooth bar assessments using alternating stress and a Level 2 welded joint method using structural stress. The API 579 approach also includes a Level 3 assessment method that uses a critical-plane, strain-life approach for either elastic or elastic-plastic stresses. The “Fatigue by E2G” methods determine both uniaxial and multiaxial strain-life for both elastic and elastic-plastic stress solutions and also provide the option of using the structural stress method for welded joint specimens.

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Fatigue Data Analysis

Fit strain-controlled, constant-amplitude, cyclic fatigue data to the most popular strain-life, stress-life, and cyclic stress-strain models currently available. The statistical methods are based on a log-linear, least-squares regression analysis that determines both the fitting coefficients and the statistics of the fit that are necessary for generating customized design curves. The models currently available are the stress-life power law, total strain-life, Smith-Watson-Topper, Brown-Miller, and Cyclic Ramberg-Osgood Stress-Strain model. Additionally, the Uniform Material Law, API 579-1/ASME FFS-1 smooth bar, and ASME Section VIII, Div. 2 smooth bar curves are provided for comparison with the statistical fits. Graphs and tables are also generated to help the user assess the goodness of the fit and to provide the model coefficients and calculated statistics.

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Fatigue Data Explorer

Access E2G’s continually-expanding fatigue database that is based upon the extensive material library of Baumel and Seeger. Test data from strain-controlled and constant-amplitude fatigue tests are provided for many different material groups. Statistical methods are used to fit this data to several strain-life, stress-life, and cyclic stress-strain models that are common in the industry. The fits that are currently provided are the stress-life power law, total strain-life, Smith-Watson-Topper, Brown-Miller, Cyclic Ramberg-Osgood Stress/Strain, Uniform Material Law, API 579-1/ASME FFS-1 smooth bar, and ASME Section VIII, Div. 2 smooth bar. For each material, graphs of the fits overlaid with the test data are provided for simple comparison and validation, and the statistics of the fits are also displayed in order to select the appropriate design curve for the intended application and desired level of conservatism.


Lot Centered Analysis

Fit creep test data to the Omega creep model of API 579/ASME FFS-1, Part 10. The test data can be in the form of either rupture time, initial strain rate, or strain versus time. Users providing rupture or strain rate data can produce custom fits of the initial strain rate and Omega parameters as functions of temperature and stress in the Larson-Miller form. If the data comes from multiple material lots, the scatter between them is accounted for with lot-centered analysis and both the weighted-average statistics and uncertainty are returned. Alternatively, users providing strain-time data for tertiary creep under constant conditions may calculate the best-fit values of the parameters specific to the particular conditions and material provided.


Material Explorer

Access to E2G’s extensive material database for materials typically used in the construction of pressure vessels, piping and tankage is provided. The database includes:

  • Material physical properties – Young’s Modulus’s, thermal expansion coefficient, thermal conductivity and thermal diffusivity as a function of temperature
  • Strength parameters – yield and tensile strength as a function of temperature
  • Allowable design stresses as a function of temperature, allowable stress may be determined based upon a specific year of the code shown below.
    • ASME Boiler and Pressure Vessel Code Sections I, Section VIII, Divisions 1 and 2
    • ASME B31 Piping Codes B31.1, B31.3, B31.4 and B31.8
    • API 620, API 650, API 653

The above properties are determined for a specified input temperature. Supplemental output including tables and graphs of material properties as a function of temperature is also provided.


Smooth Bar Fatigue Life

Predict the probability of fatigue failure for smooth bar specimens under known or relatively constant operating conditions. The calculations are based on the smooth bar methods that are included in both API 579-1/ASME FFS-1 Fitness for Service and ASME Section VIII Div. 2 codes. The smooth bar fatigue life is predicted using an alternating stress that is calculated from either linear elastic stresses (API 579-1 Method 2A and ASME Section VIII Div. 2 Equivalent Stress Method) or elastic-plastic strains (API 579-1 Method 2B and ASME Section VIII Div. 2 Equivalent Strain Method).

A Monte-Carlo sampling method is used to estimate the probabilistic fatigue life using a default of 10,000 random samples of the input random variables. All input parameters are assumed to be normally-distributed random variables, while all calculated variables and the resulting fatigue life distribution make no assumptions about the distribution type (empirical pdfs and cdfs are determined). From the probability of fatigue failure distribution, more confident decisions can be made about extending the life cycle of smooth bar components with different levels of confidence.


Welded Joint Fatigue Life

Predict the probability of fatigue failure for welded joint specimens under known or relatively constant operating conditions. The method is based upon the “Structural Stress Method” that is included in both API 579-1/ASME FFS-1 Fitness for Service and ASME Section VIII Div. 2 or 3 codes. A linear elastic stress solution is used to calculate the structural stress from the through-wall linearized membrane and bending stresses at the weld toe or root/throat failure locations, normal to the hypothetically assumed crack plane. The equivalent structural stress is then further calculated to reduce the statistical variance in the fatigue-life data by incorporating additional effects that are not accounted for in the elastic model. These include environmental and manufacturing improvement factors, weld improvement techniques, initial flaw size, notch effects, thickness effects, crack growth, and residual stress. The resulting welded joint fatigue curve is log-linear and correlates all steels or aluminum/titanium alloys into a single curve. The structural stress method is referred to by many as a “Hot Spot Method”.

A Monte-Carlo sampling method is used to estimate the probabilistic fatigue life using a default of 100,000 random samples of the input random variables. All input parameters are assumed to be normally-distributed random variables, while all calculated variables and the resulting fatigue life distribution make no assumptions about the distribution type (empirical pdfs and cdfs are determined). From the probability of fatigue failure distribution, more confident decisions can be made about extending the life cycle of welded joint components with different levels of confidence.

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E2G Help Desk Services


Our Help Desk IT specialists and engineers are available for questions about all E2G products. Our goal is to facilitate upgrades and conversions, quickly answer your questions, and help you benefit from our state-of-the-art software products.

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