These highly regarded seminars are conducted regularly in Calgary, Toronto and Montreal. We also conduct many in-house seminars. A one-day "CAESAR Refresher" course is now being offered for those who have used the software in the past but would like to get reacquainted.. Learn the latest technology at this hands-on, computer-aided pipe stress analysis course! Information below includes:.
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Notice: Unless otherwise noted herein, the information contained in these course notes is proprietary and may not be translated or duplicated in whole or in part without the expressed written consent of COADE Engineering Software, Jones Rd. Secondary Loads A system's behavior can be quantified through the aggregate values of numerous physical parameters, such as accelerations, velocities, displacements, internaI forces and moments, stresses, and external reactions developed under applied loads.
Allowable values for each of the se parameters are set after review of the appropriate failure criteria for the system. System response and failure criteria are dependent on the type of loadings, which can be classified by various distinctions, such as primary vs.
Due to the extensive calculations required during the analysis of a piping system, this field of engineering provides a natural application for computerized calculations, especially during the last two to three decades. The proliferation of easy-to-use pipe stress software has had a two-fold effect: first, it has taken pipe stress analysis out ofthe hands ofthe highly- paid specialists and made it accessible to the engineering generalist, but likewise it has made everyone, even those with inadequate piping backgrounds, capable of turning out official- looking results.
The intention ofthis course is to provide the appropriate background for engineers entering the world of pipe stress analysis. The course concentrates on the design requirements particularly from a stress analysis point ofview of the codes, as weIl as the techniques to be applied in order to satisfy those requirements. Although the course is taught using the CAESAR II Pipe Stress Analysis Software, the skills learned here are directly applicable to any means of pipe stress analysis, whether the engineer uses a competing software program or even manual calculational methods.
There are a number ofreasons for performing stress analysis on a piping system. A few of these foIlow:. Documentation typically associated with stress analysis problems consists of the stress isometric, the stress analysis input echo, and the stress analysis results output. Examples ofthese documents are shown in Figures through on subsequent pages. The stress isometric Figure is a sketch, drawn in an isometric coordinate system, which gives the viewer a rough 3-D idea of the piping system.
The stress isometric often summarizes the piping design data, as gathered from other documents, such as the line list, piping specification, piping drawing, Appendix A Figure of the applicable piping code, etc. Design data typically required in order to do pipe stress analysis consists of pipe materials and sizes; operating parameters, such as temperature, pressure, and fluid contents; code stress allowables; and loading parameters, such as insulation weight, external equipment movements, and wind and earthquake criteria.
Points of interest on the stress isometric are identified by node points. Node points are required at any location where it is necessary to provide information to, or obtain information from, the pipe stress software.
Typically, node points are located as required in order to:. The input echo Figure provides more detailed information on the system, and is meant to be used by the engineer in conjunction with the stress isometric. The analysis output provides results, such as displacements, internal forces and moments, stresses, and restraint loadings at each node point of the pipe, acting under the specified loading conditions. The output also provides a code check calculation for the appropriate piping code, from which the analyst can determine which locations are over stressed.
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The stresses calculated are not necessarily real stresses such as could be measured by a strain gauge, for example , but are rather "code" stresses. Code stress calculations are based upon specific equations, which are the result of8 decades of compromise and simplification.
The calculations reflect:. Because of this, every code gives different results when calculating stresses. A summary of significant dates in the history of the development of the piping codes is presented below:. Normal stresses: Normal stresses are those acting in a direction normal to the face of the crystal structure ofthe material, and may he either tensile or compressive in nature. In fact, normal stresses in piping tend more to tension due the predominant nature of internal pressure as a load case.
Normal stresses may be applied in more than one direction, and may develop from a numher of different types of loads. For a piping system, these are discussed below:. Longitudinal stress: Longitudinal, or axial, stress is the normal stress acting parallel to the longitudinal axis ofthe pipe. This may he caused by an internal force acting axially within the pipe:.
Replacing the terms for the internaI and metal areas of the pipe, the previous equation may be written as:. Another component of axial normal stress is bending stress. Bending stress is zero at the neutral axis of the pipe and varies linearly across the cross-section from the maximum compressive outer fiberto the maximum tensile outer fiber.
Calculatingthe stress as linearly proportion al to the distance from the neutral axis:. Hoop stress: There are other normal stresses present in the pipe, applied in directions orthogonal to the axial direction.
One ofthese stresses, caused by internaI pressure, is called hoop stress. This stress acts in a direction parallel to the pipe circumference. Radial stress: Radial stress is the third normal stress present in the pipe wall. It acts in the third orthogonal direction, parallel to the pipe radius. Radial stress, which is caused by internal pressure, varies between a stress equal to the internal pressure at the pipe's inner surface and a stress equal to atmospheric pressure at the pipe's external surface.
Assuming that there is no external pressure, radial stress may be calculated as:. Note that radial stress is zero at the outer radius of the pipe, where the bending stresses are maximized. For this reason, this stress componenthas traditionally been ignored during the stress calculations. Shear stresses: Shear stresses are applied in a direction parallel to the face of the plane of the crystal structure of the material, and tend to cause adjacent planes of the crystal to.
These shear stresses are distributed such that they are maximum at the neutral axis ofthe pipe and zero at the maximum distance from the neutral axis. Since this is the opposite of the case with bending stresses, and since these stresses are usually small, shear stresses due to forces are traditionally neglected during pipe stress analysis.
As noted above, a number of the stress components described above have been neglected for convenience during calculation ofpipe stresses. Most V. During operation, pipes are subject to aIl ofthese types of stresses. Examining a small cube ofmetal from the most highly stressed point of the pipe wall, the stresses are distributed as so:. There are an infinite number oforientations in which this cube could have been selected, each with a different combination of normal and shear stresses on the faces.
For example, there is one orientation of the orthogonal stress axes for which one normal stress is maximized, and another for which one normal stress is minimized - in both cases all shear stress components are zero. In orientations in which the shear stress is zero, the resulting normal components of the stress are termed the principal stresses. For 3-dimensional analyses, there are three of them, and they are designated as SI the maximum , S2, and S3 the minimum. Note that regardless of the orientation of the stress axes, the sum of the orthogonal stress components is always equal, i.
The converse ofthese orientations is that in which the shear stress component is maximized there is also an orientation in which the shear stress is minimized, but this is ignored since the magnitudes of the minimum and maximum shear stresses are the same ; this is appropriately called the orientation of maximum shear stress.
The maximum shear stress. The values of the principal and maximum shear stress can be determined through the use of a Mohr's circle. The Mohr's circle analysis can be simplified by neglecting the radial stress component, therefore considering a less complex i.
A Mohr's circle can be developed by plotting the normal vs. The infinite combinations of normal and shear stresses around the circle represent the stress combinations present in the infinite number of possible orientations of the local stress axes.
A differential element at the outer radius of the pipe where the bending and torsional stresses are maximized and the radial normal and force-induced shear stresses are usually zero is subject to 2-dimensional plane stress, and thus the principal stress terms can be computed from the following Mohr's circle:.
Therefore, the principal stresses, SI and S2, are equal to the centerofthe circle, plus or minus the radius, respectively. To be useful, calculated stresses must he compared to material allowables. Material allowable stresses are related to strengths as determined by material uniaxial tensile tests, therefore calculated stresses must also be related to the uniaxial tensile test. This relationship can he developed by looking at available failure theories.
Strain Tensile Test Results. There are three generally accepted failure theories which may he used to predict the onset of yielding in a material:. These theories relate failure in an arbitrary three dimensional stress state in a material to failure in a the stress state found in a uniaxial tensile test specimen, since it is that test that is most commonly used to determine the allowable strength of commonly used materials. Failure of a uniaxial tensile test specimen is deemed to occur when plastic deformation occurs; i.
The maximum tensile stress is the largest, positive principal stress, SI. By definition, SI is always the largest of the principal stresses. Plastic deformation occurs in a 3-dimensional stress state whenever the maximum principal stress exceeds SYield. Mostofthe CUITent piping codes use a slight modification ofthe maximum shear stress theory for flexibility related failures. Multiplying both sides arbitrarily by two saves the time required to do two mathematical operations, without changing this relationship.
Multiplying by two creates the stress intensity, which is an artificial parameter defined sim ply as twice the maximum shear stress. Note that when calculating only the varying stresses for fatigue evaluation purposes as discussed in the following section , the pressure components drop out of the equation. If an allowable stress based u pon a suitable factor ofsafety is used, the Maximum Stress In tensity criterion yields an expression very similar to that specified by the B Calculation of stress intensity may be illustrated by returning to our 6-inch nominal diameter, standard wall pipe for which longitudinal, shear, and hoop stresses were calculated.
The psi is the calculated stress intensity in the pipe wall, while the is the allowable stress intensity for the material at the specified temperature. In this case, the pipe would appear to be safely loaded under these conditions.
However, piping and vessels were also found to suffer from sudden failure following years of successful service. The proposed explanation for this phenomenon was fatigue failure ofthe material, resulting from propagation of cracks on the material crystal structure level due to repeated cyclic loading.
Steels and other metals are made up of organized patterns ofmolecules, known as crystal structures. However, these patterns are not maintained throughout the steel producing an ideal homogenous material, but are found in microscopic isolated island-like are as called a grains.
Inside each grain the pattern ofmolecules is preserved. From one grain boundary to the next the molecular pattern is the same, but the orientation differs.
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COADE Pipe Stress Analysis Seminar Notes
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Pipe Stress Analysis (Seminar Notes)
Last edited by vinay; at PM. Plz forward me aur share link on egpet. I specialy need the chapters 5 to 8 talking about piping dynamic analysis. Chemical Process Simulation and the Aspen Computer Software for Project Management Computer.
Notice: Unless otherwise noted herein, the information contained in these course notes is proprietary and may not be translated or duplicated in whole or in part without the expressed written consent of COADE Engineering Software, Jones Rd. Secondary Loads A system's behavior can be quantified through the aggregate values of numerous physical parameters, such as accelerations, velocities, displacements, internaI forces and moments, stresses, and external reactions developed under applied loads. Allowable values for each of the se parameters are set after review of the appropriate failure criteria for the system. System response and failure criteria are dependent on the type of loadings, which can be classified by various distinctions, such as primary vs. Due to the extensive calculations required during the analysis of a piping system, this field of engineering provides a natural application for computerized calculations, especially during the last two to three decades. The proliferation of easy-to-use pipe stress software has had a two-fold effect: first, it has taken pipe stress analysis out ofthe hands ofthe highly- paid specialists and made it accessible to the engineering generalist, but likewise it has made everyone, even those with inadequate piping backgrounds, capable of turning out official- looking results.