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.
Piping Stress Analysis (PSA Group)
04e4529d2187f60f3428a113936441814e33.pdf
Analysis And Control Of Severe Vibration Of A Screw Compressor Outlet Piping System
The method used to solve a particular vibration problem depends on the type of vibration and the type of piping system. For example, adding restraints to a piping system will not solve a vibration problem caused by high acoustic energy.
It is not always possible to eliminate or isolate the source of vibration in many piping systems. Therefore, other means must be used to control vibration. Some common methods for doing this are briefly described below.
It is not always possible to eliminate or isolate the source of vibration in many piping systems. Therefore, other means must be used to control vibration. Some common methods for doing this are briefly described below.
Bracing ⬇️
One way to control piping vibration is by adding bracing (i.e., restraints) to the system. This increases the mechanical natural frequency of the piping, thus ensuring that resonance due to low frequency excitation will not occur. It also limits large deflections that could be caused by slug flow, water hammer, etc.
When bracing addition is being considered, it must be confirmed that this will not adversely affect the thermal flexibility of the piping system. Adding restraints increases the system stiffness and can cause higher pipe thermal stresses and end-point reaction loads. New thermal flexibility calculations may be required to confirm that the design is acceptable after adding the restraints.
One way to control piping vibration is by adding bracing (i.e., restraints) to the system. This increases the mechanical natural frequency of the piping, thus ensuring that resonance due to low frequency excitation will not occur. It also limits large deflections that could be caused by slug flow, water hammer, etc.
When bracing addition is being considered, it must be confirmed that this will not adversely affect the thermal flexibility of the piping system. Adding restraints increases the system stiffness and can cause higher pipe thermal stresses and end-point reaction loads. New thermal flexibility calculations may be required to confirm that the design is acceptable after adding the restraints.
Snubbers ⬇️⬇️
Vibration amplitudes can be decreased by installing hydraulic or mechanical snubbers. These devices (e.g., dashpots or other frictional devices) increase the system damping by resisting rapid displacements, such as that resulting from vibration. However, they permit movement resulting from slow displacements, such as those from thermal movement. Thus, snubbers may be used in situations where bracing must be added to reduce or prevent vibration movements, but rigid restraints would cause unacceptable thermal displacement stresses or loads.
Vibration amplitudes can be decreased by installing hydraulic or mechanical snubbers. These devices (e.g., dashpots or other frictional devices) increase the system damping by resisting rapid displacements, such as that resulting from vibration. However, they permit movement resulting from slow displacements, such as those from thermal movement. Thus, snubbers may be used in situations where bracing must be added to reduce or prevent vibration movements, but rigid restraints would cause unacceptable thermal displacement stresses or loads.
Surge Suppressers ⬇️⬇️⬇️
Surge suppressers may be used to control surge or pulsation-induced vibration. A typical surge suppresser consists of a pilot operated valve which quickly opens after a power failure through the loss of power to a solenoid, or by a sudden large pressure reduction or increase at the surge suppresser. The open valve releases liquid from the line being protected, thus smoothing and reducing the pressure fluctuation. The valve is closed at a slower rate by using a dashpot in order to limit the pressure rise as the liquid flow is shut off.
Surge suppressers may be used to control surge or pulsation-induced vibration. A typical surge suppresser consists of a pilot operated valve which quickly opens after a power failure through the loss of power to a solenoid, or by a sudden large pressure reduction or increase at the surge suppresser. The open valve releases liquid from the line being protected, thus smoothing and reducing the pressure fluctuation. The valve is closed at a slower rate by using a dashpot in order to limit the pressure rise as the liquid flow is shut off.
Accumulators ⬇️⬇️⬇️⬇️
An accumulator is a pressure vessel that is partially or completely filled with a gas (usually inert). This vessel is then connected by pipe to the main line being protected. In the simplest case, the liquid in the pipe is in direct contact with the gas. In some cases, an elastomer membrane separates the liquid from the gas but transmits pressure between them. In other cases, a rupture disk forms a more rigid barrier between the gas in the accumulator and the liquid in the pipe. For the first two configurations, the device acts instantaneously to a rise in pressure at the gas/liquid interface. In the last configuration, the rupture disk delays the reaction time from 0.2 to 2.0 milliseconds since it must rupture before pressure is transmitted between the two fluids.
An accumulator is a pressure vessel that is partially or completely filled with a gas (usually inert). This vessel is then connected by pipe to the main line being protected. In the simplest case, the liquid in the pipe is in direct contact with the gas. In some cases, an elastomer membrane separates the liquid from the gas but transmits pressure between them. In other cases, a rupture disk forms a more rigid barrier between the gas in the accumulator and the liquid in the pipe. For the first two configurations, the device acts instantaneously to a rise in pressure at the gas/liquid interface. In the last configuration, the rupture disk delays the reaction time from 0.2 to 2.0 milliseconds since it must rupture before pressure is transmitted between the two fluids.
Temporary Restraints ⬇️⬇️⬇️⬇️⬇️
Cables or chains can be used to temporarily control large deflections caused by vibration in piping systems. The cable or chain is attached to the pipe, connected back to nearby structure, and tightened to stop the pipe movement. Quite often, even blocks of wood or scrap steel are used as wedges between the pipe or its supports and nearby structure to stop pipe movement. This approach is useful in stopping large amplitude vibration before it can damage the pipe, and to determine the best locations to place permanent bracing. This technique is not a permanent solution to a piping vibration problem.
Since the temporary restraints are installed while the system is in operation (and hot), their presence could restrict pipe thermal movement when the system is shut down. This should be considered when locating the restraints to determine if they would cause excessive thermal stresses or loads when the system is shut down. In extreme cases, it might be necessary to remove the restraints before or as the system is shutting down in order to permit free thermal movement.
Cables or chains can be used to temporarily control large deflections caused by vibration in piping systems. The cable or chain is attached to the pipe, connected back to nearby structure, and tightened to stop the pipe movement. Quite often, even blocks of wood or scrap steel are used as wedges between the pipe or its supports and nearby structure to stop pipe movement. This approach is useful in stopping large amplitude vibration before it can damage the pipe, and to determine the best locations to place permanent bracing. This technique is not a permanent solution to a piping vibration problem.
Since the temporary restraints are installed while the system is in operation (and hot), their presence could restrict pipe thermal movement when the system is shut down. This should be considered when locating the restraints to determine if they would cause excessive thermal stresses or loads when the system is shut down. In extreme cases, it might be necessary to remove the restraints before or as the system is shutting down in order to permit free thermal movement.
1. Why to use a Spring Support?
⬇️ Any line operating at high temperature moves upwards/downwards (depending on the pipe configuration) due to thermal expansion. Any rigid support provided on such a line tends to lift pipe up/down and hence remain inactive during operating conditions. In such a case a flexible support (springs) is provided which is capable of taking the load in all the operating and cold conditions.The spring supports provides continuous support during expansion or contraction of the pipe.The spring support basically employs a spring element, which can get compressed or stretch-out depending upon the thermal movement of pipe and the corresponding loads.
⬇️ Any line operating at high temperature moves upwards/downwards (depending on the pipe configuration) due to thermal expansion. Any rigid support provided on such a line tends to lift pipe up/down and hence remain inactive during operating conditions. In such a case a flexible support (springs) is provided which is capable of taking the load in all the operating and cold conditions.The spring supports provides continuous support during expansion or contraction of the pipe.The spring support basically employs a spring element, which can get compressed or stretch-out depending upon the thermal movement of pipe and the corresponding loads.
2. Types of Spring Supports
⬇️ Depending on the loads to be accommodated and the magnitude & direction of the thermal displacement to be supported, spring supports are broadly classified as:
Variable effort springs
Constant effort springs
Some of the common terminology associated with the selection and procurement of any Springs are listed below:
Cold Load
Hot Load
Spring RateSpring
Travel
Load Variation or Variation
Pre-compression Length
⬇️ Depending on the loads to be accommodated and the magnitude & direction of the thermal displacement to be supported, spring supports are broadly classified as:
Variable effort springs
Constant effort springs
Some of the common terminology associated with the selection and procurement of any Springs are listed below:
Cold Load
Hot Load
Spring RateSpring
Travel
Load Variation or Variation
Pre-compression Length
3. Terminology
Cold Load:
This refers to the load on the spring hanger when the system is in standby or non-operating condition.
Hot Load:
This refers to the actual load on the spring hanger during operating conditions
Spring Rate/ Stifness:
This refers to the spring rate, force per unit length in N/mm, kg/mm, etc. determined from flexibility analysis.
Spring Travel:
(Installed to operating): This refers to the maximum vertical movement of the spring due to piping loads at operating conditions determined from flexibility analysis.
Load Variation or Variation:
This refers to the allowed variations between the hot load and cold loads.
Pre-Compression Length:
It is the initial compressing of the spring for sustained load.
Installation Height = loaded length – Pre-compression length
Cold Load:
This refers to the load on the spring hanger when the system is in standby or non-operating condition.
Hot Load:
This refers to the actual load on the spring hanger during operating conditions
Spring Rate/ Stifness:
This refers to the spring rate, force per unit length in N/mm, kg/mm, etc. determined from flexibility analysis.
Spring Travel:
(Installed to operating): This refers to the maximum vertical movement of the spring due to piping loads at operating conditions determined from flexibility analysis.
Load Variation or Variation:
This refers to the allowed variations between the hot load and cold loads.
Pre-Compression Length:
It is the initial compressing of the spring for sustained load.
Installation Height = loaded length – Pre-compression length
4. Variable effort spring
VES basically consist of a spring which can get compressed or expanded according to thermal movement of the pipe. However, this movement causes increase or decrease in supporting force depending on its stiffness & this differential load is transferred to the pipeThis load is less than that would be with the rigid support.In VES load variation is maintained generally within 25%.
In VES the loads increases with pipe movement.
VES basically consist of a spring which can get compressed or expanded according to thermal movement of the pipe. However, this movement causes increase or decrease in supporting force depending on its stiffness & this differential load is transferred to the pipeThis load is less than that would be with the rigid support.In VES load variation is maintained generally within 25%.
In VES the loads increases with pipe movement.
5. Types of VES/CES
Hanger type:
In hanger type spring support, the pipe is hung from the secondary support using hanger type spring, as shown. Clevis, Hanger rod, turn-buckle, pipe clamp, etc. are some other attachments associated with such a support.
Hanger type:
In hanger type spring support, the pipe is hung from the secondary support using hanger type spring, as shown. Clevis, Hanger rod, turn-buckle, pipe clamp, etc. are some other attachments associated with such a support.