Effect of Material Strength on Ductile Failure of Steel in Pressure Vessel Design

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Pressure Vessel ◽  
Failure Criterion ◽  
Ductile Failure ◽  
Threshold Value ◽  
Pressure Vessels ◽  
Local Failure ◽  
Material Strength ◽  
Steel Grades

Abstract Pressure vessels and their components are commonly designed with the ASME Boiler and Pressure Vessel Codes. One of the requirements when pursuing the design by analysis route is to design these equipment against ductile local failure criterion provided in the codes. However, the ductile local failure criterion in the ASME codes only accounts for the stress triaxiality (T) as a stress state measure. Recent work has shown that ductile failure highly depends on the stress state characterized by both T and the Lode parameter L, which is related to the third deviatoric stress invariant. In this study, the effect of stress state characterized by both T and L is investigated for six different steel grades with different material strength levels. To establish the ductile failure loci for the six steel grades with respect to T and L, experiments were conducted on two different specimen geometries. The L parameter is controlled by the specimen configuration, where the round notched bar specimen corresponds to axisymmetric tensile conditions (L = −1) and the flat notched specimen corresponds to plane strain loading conditions (L = 0), whereas T is controlled by introducing a notch at the center of the specimens. A Lode sensitivity parameter (LS) is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter. The Lode sensitivity was quantified, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels. The application of the enhanced failure locus in a design analysis of a pressure vessel made of a high-strength steel grade is demonstrated, which showed that the original ASME criterion, as compared to the enhanced criterion in this study, is not capable of predicting ductile failure and hence rendering a rather nonconservative design. It is concluded that the enhanced local failure criterion is recommended to be used for the design of pressure vessels and their components made of steel grades with an ultimate strength higher than the threshold value.

Failure Strain Criterion Accounting for the Effect of Material Strength

2021 ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Failure Criterion ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength Steels ◽  
Local Failure ◽  
Material Strength ◽  
Lode Parameter ◽  
Steel Grades

Abstract The objective of this study is to investigate the effect of the Lode parameter on different material strengths. Recent work has shown that ductile failure highly depends on the stress state characterized by both the stress triaxiality T and the Lode parameter L, which is related to the third deviatoric stress invariant. Thus, for six different steel grades, two different specimen geometries were manufactured to account for two different Lode parameters (L = −1 and L = 0), whereas T is controlled by introducing different sized notches at the center of the specimens. By performing tensile experiments and running finite element simulations, the ductile failure loci of the six materials showed variations between the two specimen geometries, indicating that the failure highly depends on the stress state characterized by both T and L. This indicates the need to reassess the ductile local failure criterion in the ASME codes that only accounts for T as a stress state measure. A Lode sensitivity parameter LS is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels.

The Sensitivity to the Lode Parameter in Ductile Failure of Tubular Steel Grades

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
I. Barsoum ◽  
M. A. Al-Khaled
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength ◽  
Pressure Vessels ◽  
Electron Microscopic ◽  
Lode Parameter ◽  
Steel Grades ◽  
Failure Locus

Ductile failure in steels is highly controlled by the stress state, characterized by the stress triaxiality (T) and the Lode parameter (L). The ASME Boiler and Pressure Vessel Code requires pressure vessels to be designed to resist local ductile failure. However, the standard does not account for the Lode parameter dependence in its failure locus. In this study, the influence of the stress state, characterized T and L, on the ductility of ASME tubular product steel grades is investigated. Two seamless pipes of midstrength carbon steel SA-106 Gr. B and high-strength superduplex steel SA-790 were considered. Ring specimen geometries for plane strain (PS) stress state (L = 0) and tensile stress (TS) state (L = −1) are utilized to establish the ductile failure locus in terms of T and L for the two steels. The experimental results (EXP) show that the effect of the Lode parameter on the failure locus for the SA-106 Gr. B steel is insignificant, whereas for the SA-790 steel, the effect is rather significant. A parameter SL is introduced in order to quantify the sensitivity of the failure locus to the Lode parameter. It is found that for materials with ultimate strength lower than about 550 MPa, the sensitivity to L is insignificant (SL ≈ 1), whereas for materials with ultimate strength higher than 550 MPa, the sensitivity to L could be significant (SL > 1). Scanning electron microscopic (SEM) analysis of the fracture surfaces revealed that the sensitivity to L is closely associated with the rupture micromechanisms involved.

Investigation Into Applications of Local Failure Criterion for X70 Pipeline With Corrosion Defect

2018 ◽  
Author(s):  
Ji-Hee Moon ◽  
Nam-Su Huh ◽  
Ki-Seok Kim
Keyword(s):  
Internal Pressure ◽  
Failure Criterion ◽  
Large Scale ◽  
Ductile Failure ◽  
Limit Load ◽  
Local Failure ◽  
Ground Movement ◽  
Freezing And Thawing ◽  
Corrosion Defect ◽  
Longitudinal Length

In this paper, the local failure criterion using stress modified critical strain method based on annex B of API 579 is applied to evaluate the ductile failure of API X70 pipelines with a volumetric corrosion defect. Ductile failure is quantified in terms of strain, representing the tensile strain capacity (TSC) which is commonly used in strain-based assessment for fitness-for-service of pipelines installed in frozen area where large-scale ground movement can arise due to earthquakes, freezing and thawing. Based on the local failure criterion suggested for API X70 steel material, the TSCs of the corroded pipelines are evaluated by using the detailed finite element (FE) analyses. The effects of internal pressure and defect size (such as longitudinal length, circumferential width and depth in the direction of thickness) on TSC of pipelines subjected to axial displacement are systematically investigated. In addition, TSCs based on local failure criterion are compared with those based on net-section limit load. The TSCs from the present FE analyses for various defect geometries and internal pressure can be used to predict ductile failure of corroded pipelines and to build the framework for a strain-based assessment for in-service pipelines.

Ring Specimen Geometry for Determining the Ductility of Tubulars

2016 ◽  
Author(s):  
M. A. Al Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.

New Ring Specimen Geometries for Determining the Failure Locus of Tubulars

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
M. A. Al-Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus at both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L=0) condition and a generalized tension (L=-1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results (EXP).

Ductile Failure Analyses for API X65 Pipes Based on Local Failure Criteria

2006 ◽  
Author(s):  
Chang-Kyun Oh ◽  
Yun-Jae Kim ◽  
Jong-Hyun Baek ◽  
Young-Pyo Kim ◽  
Woo-Sik Kim
Keyword(s):  
Experimental Data ◽  
Failure Criterion ◽  
Hydrostatic Stress ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Failure Criteria ◽  
Local Failure ◽  
Defective Region ◽  
Api X65 Steel ◽  
X65 Steel

A local failure criterion for the API X65 steel is applied to predict ductile failure of full-scale API X65 pipes with simulated corrosion and gouge defects under internal pressure. The local failure criterion is the stress-modified fracture strain for the API X65 steel as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the effective stress). Based on detailed FE analyses with the proposed local failure criteria, burst pressures of defective pipes are estimated and compared with experimental data. The Failure of corroded pipes is governed by local necking and plastic collapse in the defective region, rather than failure. For pipes with gouge defects, on the other hand, it is found that fracture is dominant. The predicted burst pressures are in good agreement with experimental data. Noting that an assessment equation against the gouge defect is not yet available, parametric study is performed, from which a simple equation is proposed to predict burst pressure for API X65 pipes with gouge defects.

A Study of Integrity Changes in Structures During Exploitation

2002 ◽  
Author(s):  
Slavko Sebastijanovic ◽  
Milan Opalic ◽  
Nebojsa Sebastijanovic
Keyword(s):  
Stress State ◽  
Pressure Vessel ◽  
Pressure Vessels ◽  
Element Analysis ◽  
Critical Crack ◽  
Cylindrical Pressure Vessel ◽  
Before And After ◽  
Useful Life ◽  
Vessel Integrity ◽  
Main Components

Spherical and cylindrical pressure vessels are manufactured as welded structures, where cracks could be initiated/propagated during fabrication, pre-service hydro-test, service itself, service welding repair, or during the service hydro-test. In this case, fracture mechanics approach is necessary. This paper analyzes the stress state around cracks in the bottom head which is one of the main components in a cylindrical pressure vessel (radius of 1056 mm, wall thickness of 92 mm, pressure of 15.5 MPa and temperature of 454°C). Sizes of several detected cracks at the inner surface are determined by the NDE methods. Finite element analysis is performed to determine the stress zones in the vicinity of the most critical crack. Such analysis is done before and after the hydro-test. It will show the influence of the hydro-test on propagation of the existing cracks and fracture behavior of repaired cracks through the stress state analysis. Changes in material properties were analyzed. Results will be used to assess the pressure vessel integrity and estimate its useful life.

scholarly journals Calibration of the Ductile Failure Criterion for Nickel-Based Superalloys taking into Account the Localization of the Strain

2017 ◽  
Vol 2017 (9) ◽  
pp. 27-37
Author(s):  
Bartosz Madejski ◽  
Grzegorz Socha
Keyword(s):  
Plastic Strain ◽  
Failure Criterion ◽  
Tensile Testing ◽  
Elevated Temperatures ◽  
Strain Tensor ◽  
Equivalent Plastic Strain ◽  
Ductile Failure ◽  
Material Strength ◽  
Failure Behavior ◽  
Ductile Failure Criterion

AbstractStatic tension test allows characterization of material strength properties. This simple test provides input data for numerical calculation of structural components made of the tested alloy. Elastic, plastic and failure behavior of the structural component in question is simulated, using, for example, the FEM package, based on parameters obtained as the result of tensile testing. When using the results of the tensile test for modeling the material failure it is important to estimate correctly plastic strain corresponding to failure. It is common practice to use elongation of the specimen gage part for the calculation of failure strain. On the other side, the most popular ductile failure criterion used by engineers performing numerical simulation of the material’s behavior relies on the equivalent plastic strain as the criterial quantity. Those two parameters can differ significantly. In order to calculate the equivalent plastic strain correctly, we have to remember about strain localization (necking) appearing during tensile tests and take into account the fact that during tensile testing we have three non-zero strain tensor components. Ignoring this fact, and using only elongation as the criterial quantity can lead to enormous simulation error. This error is analyzed in this paper for nickel based superalloy tested at elevated temperatures.

An Experimental Setup for Determining the Failure Locus of ASME Tubular Pressure Vessel Steel Grades

2017 ◽  
Author(s):  
M. A. Al Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Pressure Vessel Steel ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality levels. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.

Validation of a Concept for Burst Pressure Prediction by Damage Mechanics

2016 ◽  
Author(s):  
Victoria Brinnel ◽  
Simon Schaffrath ◽  
Sebastian Münstermann ◽  
Markus Feldmann
Keyword(s):  
Pressure Vessel ◽  
Failure Criterion ◽  
Damage Mechanics ◽  
Ductile Failure ◽  
High Strength Steels ◽  
High Strength ◽  
Burst Pressure ◽  
Small Scale ◽  
Failure Behavior ◽  
Safety Factors

In ASME and EN pressure vessel standards the stress-based dimensioning is currently performed by either applying experience-based safety factors directly on the material’s yield or tensile strength (EN) or incorporating them in the allowable stress derivation (ASME). The current concept is penalizing modern high strength pressure vessel steels due to their yield-to-tensile ratio. The application of these steel grades is hindered despite their excellent mechanical properties. Possible benefits cannot be exploited. Probabilistic safety concepts are a suitable approach to derive adequate safety factors for high strength steels. But their application requires a large number of expensive full scale burst tests. Therefore, it is proposed to replace these by numerical simulations using damage mechanics. This paper aims at validating such a concept for the numerical prediction of burst pressures. The presented procedure uses a Gurson model to represent ductile failure behavior on the specimen scale and correlates it to an efficient strain-based failure criterion, which is more suitable for simulations on full component scale. The validation is performed on a demonstrator pressure vessel of the high strength steel P690Q. The strain-based failure criterion is derived on small scale tests and applied in simulations of the pressure vessel. The numerically predicted burst pressure only exceeds the actual burst pressure by 6% and the critical locations are correctly predicted. The approach is validated successfully. Suggestions for further improvements are made.

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