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In order to take advantage of the “true” reduced DLF, it is necessary to perform a dynamic analysis, such as a time history analysis or a response spectrum analysis. We need your help! This is a carry over from pre-computer days, when sustained stress calculations were rarely done, so SI was not known explicitly, and conservatively estimated to notrs at its maximum allowable level of Sh.
Consider an expansion joint with the following parameters: For each bellows there is a limit to the cumulative axial, bending and lateral displacement that can be absorbed by the joint without excessively deforming the convolutions or causing fatigue failure. Thisisevidentbyassuming the worst case – no damping and instantaneous application of a constant force – and performing a time history analysis of the dynamic equation: Print Topic Switch to Threaded Mode.
The user’s entry in this case should normaUy be a variation of the value initially proposed by the program spring selection algorithm.
CAESAR II flags these with a warning during the analysis and reports them as zero load constant effort supports in the hanger table during output. Please copy and paste this embed script to where you want to embed Embed Script.
Or, examining the formulas above, it is evident that, as the shorter portion of the span b approaches zero length, semonar moment, and therefore the stress, approach zero as weIl. Due to the low allowable stress value used, there is sufficient factor of safety that this standard span may he applied to a wide range of piping configurations.
The actual installed load case is important if the springs are to be adjusted or checked in the cold condition, or if the spring’s cold load is being set in position, rather than at the factory.
The following is a crude summary of the map: Where the existing springs can’t be used, new ones will be recommended. As seen above, for finite length expansion joints, the lateral and bending stiffnesses sekinar related by the equation: For a piping application, the implication of the Soderberg line on the fatigue allowable is implemented in a conservative manner.
Itmay act in any direction, and as such the engineer has coqde items to consider: By using the standard span criteria, the engineer can assume that the maximum stress in the piping system due to weight semunar does not exceed psi. Therefore, pipe stress software cannot be used to accurately determine the effects ofthe piping system on rigid elements. This angular stiffness for a guided cantilever expansion joint model is calculated as: As the load ram p-u p time such as the opening time of a relief valve increases, or the load duration decreases such as fluid hammer in a short piping legthe DLF will decrease as well.
Sifs, interpretations,Coade seminar notes and confussion – Intergraph CADWorx & Analysis
Figure Simplest Model: Assume that the capacity of the building steel dictates that the weight of the riser be split hetween two supports. Figure For clade most part, these details are taken care ofby the expansion joint manufacturer.
The computer software models this load as strictly a force with no applied moment.
ccoade Secondary Loads Markl’s investigation of the fatigue problem, following the earlier recognition of the maximum stress theory offailure, led to identification of the basic problem in the design of piping systems. After 12 years of successful operation, inspection of the inside surface of a vessel revealed fatigue cracks in the vicinity of a piping nozzle connection.
COADE Pipe Stress Analysis Seminar Notes – Free Download PDF
Rigid elements, such as valves and coaxe are most difficult to model due to the inability to represent their geometry, and their stress distribution with stick elements. Therefore, movements on an expansion joint are acceptable if: Unless the user is willing to put a spring at the stanchion location, the differential thermal growth in this small area might result in large nozzle loads.
Next, the engineer locates supports. Noets noted, piping elements are modeled as stick elements ofconstant cross-section and material properties. The true condition is somewhere in between, so a compromise approximation is reached: It is not always so easy to calculate the applied loads. Note that both codes additionally cite a conservative value of SA, f 1. The hanger hardware clamps, rods, etc. If seismic response spectra are available for the piping system, then, given the natural frequency of the lowest mode of vibration of a piping system, the analyst can find a corresponding acceleration from one of the curves.
Occasionally, the manufacturer provides allowable movements only for axial displacements. The manufacturer must always provide a fatigue curve or sorne other type of adjustment factor in order to determine the allowable displacementforadifferentnumberofcycles.
COADE Pipe Stress Analysis Seminar Notes
If an earthquake is modeled as having a 0. Even though the calculated stress range at the COADE Pipe Stress Analysis Seminar Notes junction was weil overpsi, thejunction survived several years hecause of the selfrelieving nature of the thermalload, and the fact that the system cycled fewer than a dozen noes over the two year period.
Bending and lateral convolution spring rates can be computed from the axial spring rate. We need your help to maintenance this website. Building codes provide ways to calculate seismic g-factors, based upon earthquake potential, structure type, and structure fundamental frequency.
The intention ofthis course is to provide the appropriate background for engineers entering the world of pipe stress analysis.