CAESAR II : Using FEA Results with CAESAR II designs(Part III)⬇️⬇️⬇️⬇️⬇️⬇️
CAESAR II & PV Elite : Accuracy with FEA Tools (Part I)⬇️
CAESAR II & PV Elite : Accuracy with FEA Tools (Part II) ⬇️⬇️
Piping Stress Analysis (PSA Group)
SPS-01-02.pdf
Special pipe support Design ana Analysis
Basics for Fatigue Analysis of Piping System using Caesar II ⬇️
Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Continued cycling of high stress concentrations may eventually cause a crack which propagates and results in leakages. This failure mechanism is called fatigue. Damage once done during the fatigue process is cumulative and normally unrecoverable.
Fatigue can be grouped in two classes; High cycle fatigue and low cycle fatigue.
High cycle fatigue involves little or no plastic action. Therefore, it is stress-governed. Normally, a fatigue curve (also called the S–N curve) is generated for every material by experimental tests which correlates applied stress with the number of cycles to cause failure. For high-cycle fatigue, the analysis is performed to determine the endurance limit, which is actually a stress level that can be applied for an infinite number of times without showing any failure. As a general rule no of cycles 10^5 is considered as demarcation point for high and low cycle fatigue.
Fatigue can be grouped in two classes; High cycle fatigue and low cycle fatigue.
High cycle fatigue involves little or no plastic action. Therefore, it is stress-governed. Normally, a fatigue curve (also called the S–N curve) is generated for every material by experimental tests which correlates applied stress with the number of cycles to cause failure. For high-cycle fatigue, the analysis is performed to determine the endurance limit, which is actually a stress level that can be applied for an infinite number of times without showing any failure. As a general rule no of cycles 10^5 is considered as demarcation point for high and low cycle fatigue.
The loading cycles applied in piping design are normally very few in the order of a few thousands. This type of fatigue is identified as low-cycle fatigue. For low-cycle fatigue, the applied stress normally exceeds the yield strength of the material, which causes plastic instability in the specimen under test. But when strain is used as the controlled variable, the results in low-cycle region are reliable as well as reproducible.
Sources of Fatigue:⬇️⬇️
For Piping system, Cyclic loadings are primarily due to:
* Thermal Expansion & Contraction
* Vibration due to Occasional loading
* Pressure variation within Piping system
* Motion wave.
* Due to Flow induced Vibration
The fatigue process is divided into three stages: crack initiation from the continued cycling of high stress concentrations, crack propagation to critical size, and unstable rupture of the section.
For Piping system, Cyclic loadings are primarily due to:
* Thermal Expansion & Contraction
* Vibration due to Occasional loading
* Pressure variation within Piping system
* Motion wave.
* Due to Flow induced Vibration
The fatigue process is divided into three stages: crack initiation from the continued cycling of high stress concentrations, crack propagation to critical size, and unstable rupture of the section.
Factors Affecting the Fatigue Behavior:⬇️⬇️⬇️
The factors which affect the fatigue behaviour are listed below:
*Type and Nature of Loading.
*Size of Component and stress or strain Distribution.
* Surface finish and Directional Properties.
*Stress or Strain Concentration.
*Mean stress or Strain.
*Environmental Effects.
*Metallurgical Factors and Material Properties.
*Strain Rate and Frequency Effects.
The factors which affect the fatigue behaviour are listed below:
*Type and Nature of Loading.
*Size of Component and stress or strain Distribution.
* Surface finish and Directional Properties.
*Stress or Strain Concentration.
*Mean stress or Strain.
*Environmental Effects.
*Metallurgical Factors and Material Properties.
*Strain Rate and Frequency Effects.
Characteristics of Low Cycle Fatigue:⬇️⬇️⬇️⬇️
*Characterized by high loads and a small no. of cycles before failure.
*Here failure occurs only with stress levels in the plastic range, i.e. significant plastic strain occurs during each cycle.
*The stresses which cause fatigue failure in the piping are the peak stresses.
*In piping design, most of the loading cycles encountered would be of the low cycle type
*Characterized by high loads and a small no. of cycles before failure.
*Here failure occurs only with stress levels in the plastic range, i.e. significant plastic strain occurs during each cycle.
*The stresses which cause fatigue failure in the piping are the peak stresses.
*In piping design, most of the loading cycles encountered would be of the low cycle type