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کاتالوگ نفتا صنعت ناظران- 960425.pdf
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Mechanical Vibration Analysis (Design Approach 3, API 618, 5th Edition)
While pulsation forces can be reduced through the pulsation solution (as outlined in Section 2), the remaining
forces such as gas forces, crosshead forces, mass unbalance and couples, cannot be reduced – they must be
controlled through a mechanical vibration analysis. This analysis provides recommendations on piping supports,
package design, piping, clamps, skid, and other components.
forces such as gas forces, crosshead forces, mass unbalance and couples, cannot be reduced – they must be
controlled through a mechanical vibration analysis. This analysis provides recommendations on piping supports,
package design, piping, clamps, skid, and other components.
Mechanical vibration analysis is part of a Design Approach 3 of API 618, 5th edition. The scope includes calculating Mechanical Natural Frequencies (MNFs) throughout the system and a Forced Response Analysis to predict vibration and stress amplitudes, if necessary.
The goal of the analysis is to avoid mechanical resonance in the compressor/piping system. In many situations, and especially at higher order frequencies, it may be impossible to avoid resonance.
In this case, the engineer must “manage resonance”. Vibration will exist, but through detailed mechanical modeling and Forced Response Analysis techniques, the vibration consultant can predict whether a certain mode or location will have acceptable vibration and stress amplitudes.
In this case, the engineer must “manage resonance”. Vibration will exist, but through detailed mechanical modeling and Forced Response Analysis techniques, the vibration consultant can predict whether a certain mode or location will have acceptable vibration and stress amplitudes.
The mechanical analysis starts by developing an accurate computer model of the mechanical system. The model starts at the compressor (or cylinder); includes the pulsation control devices, scrubber, and main piping, and ends, as a minimum, at the second clamp away from the discharge/suction.
this model includes a (super element) frame FE model to accurately model the boundary conditions of cylinder/piping interface. This superelement frame model is an option for our standard Mechanical Vibration Analysis.
Pig launchers and pig receivers are installed on a pipeline to launch and receive pipeline pigs and pipeline inspection tools.
Piping system must be designed in the way that connecting pipes will not over-stress launcher or receiver. Let’s start from pig launcher supports. The first support has holes that fit bolts, but the second support has slotted holes that will provide free thermal expansion for the launcher itself. Since the first support is fixed, pipeline thermal expansion will imposed thermal force on the pig launcher. The pig launcher and receiver must be arranged in relation to a pipeline in such way that thermal expansion force from pipeline is minimal. Please see the the figure below.
In the arrangement shown above, the underground pipe will be anchored by the virtual anchor that is result of soil friction. Pipeline flexibility is achieved by having elbow, allowing free thermal expansion in the direction perpendicular and parallel to launcher. If this arrangement is not suitable for your application, pig launcher can be set in direction of pipeline. Please see the figure below.
Usually, this type of arrangement will require a concrete stop block to limit pipeline thermal expansion. Only stress analysis conducted on underground pipeline can determine requirement for the stop block. In the case that stop block is used, it must be sized in such way that resisting soil pressure does not exceed allowable soil pressure. Please see the figure below.