ASME B31.3 Process Piping | Expansion Stress - Liberal stress & others. ⬇️⬇️⬇️⬇️
Piping Stress Analysis : Stiffness of Rigid body
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his refinery utilizes large centrifugal compressors. The piping system is shown below (left). Vibration problems occurred on the piping header feeding three dryers (right).
Normally the gas flow travels through two dryers and no vibration issues occur but under regeneration, the operators use only one dryer. When flowing to one dryer, the operator measured high vibrations in the header as shown by the red arrows (above, right).
One solution was to eliminate flow-induced excitations by changing the length of the inlet header and the distance between Dryer A and B inlet valves. This was determined to be too expensive, so BETA designed supports to be installed at specific locations in order to shift the mechanical natural frequency away from resonance.
PIPING VIBRATION ON SALES GAS LINE (GAS PLANT EXAMPLE) ⬇️⬇️⬇️
The 30 inch (75 cm) sales gas line had high vibration at this Asian Gas Plant. High vibration became evident on the main sales gas line under high flow / high pressure drop conditions following the installation of a new whisper trim pressure control valve. BETA’s staff conducted a site vibration assessment to determine the cause of and possible solutions to piping vibration and integrity concerns.
Based on the field analysis, the vibration upstream of the control valve is caused by Flow-Induced Excitation (FIE, also called FIV) which is created when gas flows past a dead leg. The dead leg creates vortices, which are amplified by the standing wave in the dead leg. These pulsations travel through the pipe and cause it to shake.
Three solutions were identified to reduce the excitation forces. These options included: modifications to the operation of the bypass valve; a minor modification at the mouth of the dead leg; or modifying the piping geometry by moving the recycle valve.
Three solutions were identified to reduce the excitation forces. These options included: modifications to the operation of the bypass valve; a minor modification at the mouth of the dead leg; or modifying the piping geometry by moving the recycle valve.
Under some flow condition the piping at the expansion loops was observed to exhibit very high vibration. The piping in this area is very loosely supported and any unbalanced force in the piping system will result in high vibration on these lines. If the FIV created by the dead leg near the control valve cannot be controlled, then increasing the stiffness of the expansion loops will help control vibrations. BETA provided recommendations on adding beams to support the elbows. In addition to these piping support recommendations, a pipe stress analysis is required to ensure the additional supports do not create thermal stress problems.