Shakedown of Torispherical Heads Using Plastic Analysis

1998 ◽  
Vol 120 (4) ◽  
pp. 431-437 ◽  
Author(s):  
A. Kalnins ◽  
D. P. Updike
Keyword(s):  
Equivalent Stress ◽  
Applied Pressure ◽  
Material Behavior ◽  
Parameter Range ◽  
Burst Pressure ◽  
Fatigue Stress ◽  
Stress Parameter ◽  
Hardening Models ◽  
Plastic Analysis ◽  
Definition Of

The condition of shakedown is examined for torispherical heads. The reason for using plastic analysis is to account for the strengthening that heads experience when subjected to internal pressure. Cyclic pressures are considered up to an allowable burst pressure that is based on the membrane stresses of the spherical part of the head. To simulate a proof test before service cycling, cases when the applied pressure is higher for the first cycle are also included. A definition of shakedown is used that places the limit of twice the yield strength on a fatigue stress parameter range that is defined in the paper. The equivalent stress and plastic strain ranges are calculated for ten head thickness-to-spherical radius ratios. From these data, shakedown pressures are obtained as fractions of the allowable burst pressure. By giving bounds for isotropic and kinematic strain-hardening models, the results are made independent from specific cyclic material behavior. It is also shown that if an elastic, geometrically linear algorithm is used, which is unable to account for the strengthening, the fatigue stress parameter range is overestimated for the thinner heads.

Improving the Long-Term Performance of Elastomeric Seals by Material Behavior Design

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ryan B. Sefkow ◽  
Nicholas J. Maciejewski ◽  
Barney E. Klamecki
Keyword(s):  
Energy Density ◽  
Contact Pressure ◽  
Strain Energy ◽  
Applied Pressure ◽  
Material Behavior ◽  
Time Dependent ◽  
Ring Section ◽  
Stiff Material ◽  
Elastomeric Seals

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.

Failure Analysis of High Pressure Rupture Discs and Effective Counter Measures

2016 ◽  
Author(s):  
Stefan Rüsenberg ◽  
Georg Vonnahme
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Influencing Factor ◽  
Applied Pressure ◽  
Life Time ◽  
Burst Pressure ◽  
Counter Measures ◽  
Welding Joint ◽  
Rupture Disc ◽  
Geometrical Change

For the production of LDPE, high process pressures (>1000 bar up to 3500 bar and above) as well as high temperatures (>100 °C up to 300 °C and above) are required. In order to ensure a safe production process the autoclaves and compressors have to be protected against dangerous overpressure. Rupture discs are typically used to protect this high pressure process itself, as well as the employees, and the environment. Traditionally rupture discs for high pressure applications are manufactured by a weld seam which has an influence on the burst pressure. After installation the applied pressure is nearly fully-loaded on the welding joint. Additionally, the welding joint is another unwanted influencing factor. This increases the possibility of an unexpected failure which leads to an unwanted rupture disc response or, in critical cases, to a rupture disc failure recently after initial operation of the process even at lower pressures than the defined burst pressure. This, in turn, leads to a reduced life time of the disc. A special version of a rupture disc, a High Pressure Rupture Disc (HPRD) is developed specifically for this application. This long life version for high pressure applications has a lifetime which is 5–10 times higher than that of a standard rupture disc, that saves money and installation time. The differences are explained in some minor geometrical changes. This safety device allows a protection of high pressures up to 4000 bar and beyond. The HPRD is a forward acting rupture disc and the burst pressure is adjusted by a combination of material thickness, the height of the dome, and, of course, of the chosen material. An easy and simple geometrical change eliminates the welding joint as an influencing factor, thus eliminating any unwanted responding of the rupture disc. The tolerances for high pressure rupture discs are +/−3% and lower and the HPRD can be used for all kind of different high pressure applications.

scholarly journals Critical Stresses in Materials with Cracks

2019 ◽  
Vol 70 (7) ◽  
pp. 2442-2446
Author(s):  
Simona Eugenia Manea ◽  
Vali Ifigenia Nicolof ◽  
Teodor Sima
Keyword(s):  
Fracture Mechanics ◽  
Critical Stress ◽  
Crack Width ◽  
Crack Depth ◽  
Equivalent Stress ◽  
Critical Energy ◽  
Material Behavior ◽  
Experimental Results ◽  
Critical Stresses ◽  
Mechanics Concepts

The fracture mechanics concepts, as well as the concepts introduced on the basis of principle of critical energy, correlated with strength of materials with cracks is analysed. The equivalent stress method of strength was applied to cracked materials, by using the concept of local critical stress. This one depends on the material behavior and the deterioration due to crack. Experimental results have been obtained with specimens of OL304 steel with different cracks. The influence of crack depth and crack width is put into evidence.

A Continued Evaluation of the Role of Material Hardening Behavior for the NeT TG1 and TG4 Specimens

2014 ◽  
Author(s):  
David J. Dewees ◽  
Phillip E. Prueter ◽  
Seetha Ramudu Kummari
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Critical Factor ◽  
Material Model ◽  
Standard Test ◽  
Material Behavior ◽  
Weld Residual Stress ◽  
Hardening Models ◽  
Elastic Plastic Material

Modeling of cyclic elastic-plastic material behavior (hardening) has been widely identified as a critical factor in the finite element (FE) simulation of weld residual stresses. The European Network on Neutron Techniques Standardization for Structural Integrity (NeT) Project has provided in recent years both standard test cases for simulation and measurement, as well as comprehensive material characterization. This has allowed the role of hardening in simulation predictions to be isolated and critically evaluated as never before possible. The material testing information is reviewed, and isotropic, nonlinear kinematic and combined hardening models are formulated and tested. Particular emphasis is placed on material model selection for general fitness-for-service assessments, as it relates to the guidance for weld residual stress (WRS) in flaw assessments of in-service equipment in Annex E of the FFS standard, API 579-1/ASME FFS-1.

scholarly journals Taking into account the non-proportional loading effect on high cycle fatigue life predictions obtained by invariant-based approaches

2019 ◽  
Vol 300 ◽  
pp. 12003
Author(s):  
Lorenzo Bercelli ◽  
Cédric Doudard ◽  
Sylvain Moyne
Keyword(s):  
High Cycle Fatigue ◽  
Equivalent Stress ◽  
Multiaxial Fatigue ◽  
Proportional Loading ◽  
Industrial Structures ◽  
Complete Chain ◽  
Stress Signals ◽  
Definition Of ◽  
Life Predictions ◽  
Fatigue Criterion

Industrial structures are often subjected to multiaxial fatigue loadings. If the multiple stress signals are not synced the loading is said to be non-proportional. Most of the multiaxial fatigue criteria give highly inaccurate lifetime predictions when used in the case of such loadings. The scalar equivalent stress defined by the criteria does not take into account the non-proportional nature of the multiaxial loading and leads to non-conservative predictions. Moreover a multiaxial fatigue criterion can only be applied on a stress cycle which has no clear definition when multiple unsynced signals are to be considered. This study addresses these issues by proposing a correction of an invariant based multiaxial fatigue criterion through the definition of a non-proportional degree indicator. A definition of multiaxial cycle is also given based on the Wang-Brown method. Finally a complete chain of invariant based lifetime prediction for non-proportional multiaxial fatigue is validated.

Theoretical and Numerical Predictions of Burst Pressure of Pipelines

2007 ◽  
Vol 129 (4) ◽  
pp. 644-652 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Equivalent Stress ◽  
Failure Criteria ◽  
Burst Pressure ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Strain Criterion ◽  
Stress Criterion ◽  
Numerical Predictions ◽  
Yield Theory ◽  
Von Mises

To accurately characterize plastic yield behavior of metals in multiaxial stress states, a new yield theory, i.e., the average shear stress yield (ASSY) theory, is proposed in reference to the classical Tresca and von Mises yield theories for isotropic hardening materials. Based on the ASSY theory, a theoretical solution for predicting the burst pressure of pipelines is obtained as a function of pipe diameter, wall thickness, material hardening exponent, and ultimate tensile strength. This solution is then validated by experimental data for various pipeline steels. According to the ASSY yield theory, four failure criteria are developed for predicting the burst pressure of pipes by the use of commercial finite element softwares such as ABAQUS and ANSYS, where the von Mises yield theory and the associated flow rule are adopted as the classical metal plasticity model for isotropic hardening materials. These failure criteria include the von Mises equivalent stress criterion, the maximum principal stress criterion, the von Mises equivalent strain criterion, and the maximum tensile strain criterion. Applications demonstrate that the proposed failure criteria in conjunction with the ABAQUS or ANSYS numerical analysis can effectively predict the burst pressure of end-capped line pipes.

Assessment of Section III Appendix XIII-3230 Plastic Analysis

2020 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Strain Curve ◽  
Service Level ◽  
Reduction Factor ◽  
Collapse Load ◽  
Analysis Method ◽  
Stress Strain Curve ◽  
Primary Stress ◽  
Computational Implementation ◽  
Plastic Analysis ◽  
Definition Of

Abstract Plastic analysis according to Section III Appendix XIII-3230 may be used in lieu of satisfying primary stress limits. The associated definition of plastic collapse load is based on limiting the permanent plastic deformation to not exceed the elastic deformation using a method that is also used to determine the collapse load experimentally. The acceptable load is calculated from the collapse load using a reduction factor that depends on the Service Level. Using some simplified application examples, the strengths and weaknesses of the method are discussed relative to the objectives of primary stress limits. Proposals for modifications of the plastic analysis method in the Code are reviewed and assessed. Elements of a proposal for an updated version of Appendix XIII-3230 are discussed, including providing additional guidance for the computational implementation of the method. The representation of the material stress-strain curve is another important aspect that may require additional guidance.

Effect of Nozzle Dimensions on the Stresses in Compensated Openings in Cylindrical Shells

2015 ◽  
Author(s):  
Dipak K. Chandiramani ◽  
Shyam Gopalakrishnan ◽  
Ameya Mathkar
Keyword(s):  
Cylindrical Shells ◽  
Shell Height ◽  
Applied Pressure ◽  
Reactive Force ◽  
Area Method ◽  
Pressure Area ◽  
Section Viii ◽  
Vessel Material ◽  
Definition Of ◽  
Physical Dimensions

Clause 4.5 of ASME Section VIII Div. 2 [1] provides rules for compensation of openings in cylindrical shells having fitted nozzles. There appears to be no definition of “nozzle” in either ASME Section VIII Div. 2 or ASME Section VIII Div. 1 [2]. The rules provided in Clause 4.5.5 of ASME Section VIII Div. 2 are based on pressure area method which ensures that the reactive force provided by the vessel material is greater than or equal to the load from the pressure. The key element in applying this method is to determine the dimensions of the reinforcing zone, i.e, the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure. There appears to be no restriction on the physical dimensions of the nozzle or shell, so long as the required area AT is obtained and the stresses are within allowable limits. It is therefore possible that all of the required area AT is obtained from the nozzle or from the shell. While both these alternatives would be acceptable, the actual stresses at the shell/nozzle junction may vary considerably. The work reported in this paper was undertaken with a view to determining if there needs to be any restriction on the proportion of area contributed by shell or nozzle to ensure that actual stresses were within allowable limits.

Effects of Local Peak Stress Distribution on the Ratchet Limit

2002 ◽  
Author(s):  
Nobuyoshi Yanagida ◽  
Masaaki Tanaka ◽  
Norimichi Yamashita ◽  
Yukinori Yamamoto
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Plastic Strain ◽  
Equivalent Stress ◽  
Equivalent Plastic Strain ◽  
Peak Stress ◽  
Element Analysis ◽  
Stress Evaluation ◽  
Elastic Plastic ◽  
Plastic Analysis

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1],[2] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: (1) Evaluating variations in plastic strain increments, and (2) Evaluating the width of the area in which Mises equivalent stress exceeds 3Sm. To verify of these criteria, we selected notched cylindrical vessel models as prime elements. To evaluate the effect of the local peak stress distribution on these criteria, cylindrical vessels with a semicircular notch on the outer surface were selected for this analysis. We used two notch configurations for our analysis, and the stress concentration factor for the notches was set to 1.5 and 2.0. We conducted elastic-plastic analysis to evaluate the ratchet limit. Sustained pressure and alternating enforced longitudinal displacements which causes secondary stress were used as parameters for the elastic-plastic analysis. We found that when no ratchet was observed, the equivalent plastic strain increments decreased and the area in which Mises equivalent stress exceeds 3Sm are below the certain range.

Burst Analysis of Cylindrical Shells

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Liping Xue ◽  
G. E. O. Widera ◽  
Zhifu Sang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Cylindrical Shell ◽  
Cylindrical Shells ◽  
Three Dimensional ◽  
Computer Software ◽  
Finite Element Method Simulation ◽  
Material Behavior ◽  
Burst Pressure ◽  
Element Method

The purpose of this paper is to demonstrate that the burst pressure of a cylindrical shell subjected to internal pressure can be accurately predicted by using finite element method. The computer software ANSYS (Swanson Analysis System Inc., 2003, “Engineering Analysis Systems User's Manual”) is employed to perform a static, nonlinear analysis (both geometry of deformation and material behavior) using three-dimensional 20 node structural solid elements. The “Newton–Raphson method” and the “arclength method” are both employed to solve the nonlinear equations. A comparison with various empirical equations shows that the static finite element method simulation using the arclength method can be employed with sufficient accuracy to predict the burst pressure of a cylindrical shell. It is also shown that the Barlow equation is a good predictor of burst pressure of cylindrical shells.

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