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Collar Bolts To Maintain Removable Bundles in Heat Exchangers

Written by Baher Elsheikh in Maintenance,Mechanical

What is a Collar Bolt?

Collar bolts are a type of fastener that is extensively used to hold the bundle in the exact place for removable bundle heat exchangers. This ensures the channel removal without interrupting or breaking the seal between the shell and tube sheet. Figure 0 shows a typical schematic diagram of a collar bolt assembly.

Collar Bolts Assembly
Fig. 0: Collar Bolts Assembly

Collar Bolts in Standards

TEMA Standard

The new part (RCB-11.8) was added in the tenth edition of the TEMA (Tubular Exchanger Manufacturer Association) standard, covering the recommendations of the collar bolts in the removable bundles with B-Type bonnet as shown in Figure-1.

Collar stud shall be used on units with removable tube bundles only when specified by the purchaser. Normally, It is recommended for B-Type of bonnets. The Outer Diameter (OD) of the static tube sheet should match the mating flange OD, and shall be through-bolted. It is preferable to have every fourth stud in the bolt circle (with a minimum of 4) as collar type I for type II as shown in Figure 2 below.

TEMA 10th Edition
Fig. 1: TEMA Tenth Edition 2019

Collar bolts are only used to maintain the gasket integrity and position when the channel is removed and torqued prior to pressurizing.

As an alternative to collar studs, every fourth bolt hole in the tube sheet may be drilled and tapped to the size of the stud bolt. The studs in the threaded holes shall be double nutted on the shell side or provided with machined flats to allow the tube side nut without rotating the stud.

API 660 Standard

In API 660, Para 7.5.2.4: A full-diameter stationary tube sheet shall be provided for removable tube bundle exchangers with bonnets (Figure 2). The tube sheet shall be provided with collar studs or tapped tube sheet holes for a minimum of 25 % of the bolts (4 minimum). Hydrostatic testing of the shell side shall be allowed with the bonnet removed and all bolting installed in place.

When collar bolts/drilled-and-tapped holes are used, at least four shall be provided and the location of them shall be identified on the drawings and by stamped markings on the external diameter of the tube sheet.

Type B Stationary Head as per TEMA
Figure 2: Type B Stationary Head as per TEMA

PIP VEV1100M

As per PIP VEFV1100M Vessel/Shell &Tube Heat Exchanger Standard Details, the standard arrangement and configuration for collar bolt dimensions are produced in Figure 3 below.

Collar Bolt and Locking nut for Heat Exchanger
Fig. 3: Collar Bolt/ Locking nut for Heat Exchangers

HEI

Surface condensers are designed to the requirements of HEI (Heat Exchange Institute) per the typical configuration shown in Figure 4. Here, both tube sheets are fixed. Also, without the removal of one of the tube sheets, the gasket between the tube sheet and shell flanges cannot be attended to.

Surface Condenser
Figure 4 Surface Condenser

Surface Condenser without Collar Bolts

A manual of one of the most famous and reputable surface condensers manufacturers in the world alerts the following:

“It is important not to break this seal between the tube sheet and the shell flange. The tubes are expanded into each tube sheet holding them firmly in place, and the shell seal cannot be replaced without retubing the entire condenser. To prevent breaking the joint, it is important that all nuts be removed from the water box flange side and not from the shell flange side. Do not loosen or remove the stake studs and double nuts on the shell side.”

Finding a leak in the shell side causes a huge impact on the plant as it breaks the vacuum. In such a configuration, the collar bolts must be used. 

Despite the illustrated advantages of the use of the collar bolts, there is a debate about the disadvantages as it might be a cause for trouble instead of enhancing the exchanger’s maintainability. In the following section, the main advantages and disadvantages of the use of collar bolts are summarized.

Advantages of the use of collar bolts 

The main objective and advantage of the collar bolts is better maintainability considering that each time the channel is removed, the bundle shall be removed for replacing the gasket between the tube sheet and shell to avoid leakage after pressurizing the exchanger. Bundle gasket replacement is time-consuming and increases MTTR (Mean Time To Repair/Restore). 

Disadvantages of the use of the collar bolts

  1. Some field experience showed that it is nonmandatory to remove the bundle if the channel is removed. This opinion is built on some special experience in using cam profile gaskets and the application of initial proper stress to reach the desired gasket stress.
  2. In case of using tapped holes and the bolts get stuck and the attendance for the holes machining and replacement of the bolts would be time-consuming and might be beyond the readiness of the maintenance crew for the task.
  3. Marking or stamping of the collar bolts has to be adequate to avoid misleading the maintenance crew otherwise, they may remove collar bolts by mistake.
  4. Relative higher cost due to the bigger tube sheet size and the aching required for the bolt holes in the tube sheet. 

Few more resources for you..

Shell & Tube Heat Exchanger Piping: A brief Presentation
An article on Plate Heat Exchanger with Steam
A typical Check List for Reviewing of Shell & Tube Heat Exchanger Drawings
Basics of Shell and Tube Heat Exchangers: A brief presentation
A brief presentation on Air Cooled Heat Exchangers
Basic Considerations for Equipment and Piping Layout of Air Cooled Heat Exchanger Piping

References

  • [1] API Std 660 – Shell-and-Tube Heat Exchangers
  • [2] TEMA Tenth Edition, 2019 (Standards Of The Tubular Exchanger Manufacturers Association)
  • [3] PIP VEFV1100M Vessel/S&T Heat Exchanger Standard Details
  • [4] Explore The World Of Piping – EWP https://www.wermac.org/equipment/collarbolt.html)

What is FMS or Flow Metering Skid?

Written by Anup Kumar Dey in Instrumentation,Mechanical,Pipeline,Piping Interface

What is FMS or Flow Metering Skid?

A Flow Metering Skid is a framed or moduled device on which various other assemblies are fitted for the measurement (flow rates) of gas or liquid products. The major purpose of using a metering skid is for custody transfer. They are designed and manufactured to fulfill the lowest uncertainty. At the same time, they optimize operation and maintenance costs.

The metering skid includes equipment for flow conditioning, filtration, automated or manual operational sequences, draining, venting, safety, maintenance, lifting, proving, sampling, etc. Mass or Volumetric flow rates as per the client’s specification are measured by such skids or packages. Depending on the requirements for measurement, this package can also be used for other treatments like flow control and cleanliness of fluid.

Flow Metering Skid Components

The main components of a metering skid (Fig. 1) are listed below:

  • The structural framework of the skid along with supporting members
  • The piping network
  • Applicable process equipment
  • The electrical power feed including the earthing system, the MCC, and all cabling and trays
  • The local instrumentation and control system includes the flow computer, personal computers, printers, and PLC.
Flow Metering Skid
Fig. 1: Typical Flow Metering Skid

Purpose of the metering skids

Metering skids can be used for various purposes as mentioned below:

  • Pressure regulation and metering stations
  • Fuel gas conditioning systems
  • Border metering stations
  • Offshore gas and liquid metering
  • CNG filling stations
  • Biomethane grid injection systems
  • Underground gas storage metering and control skids
  • LNG metering skids
  • Calibration facilities

Application of metering skid

Offshore metering systems are used in FPSO, FSO, Platform / MOPU / TLP, and FLNG / FSRU. Onshore metering systems are used in Oil Production plants, Oil refineries, Gas Processing Plants, Petrochemical plants, Terminal, Tank farms, Pipelines, etc.

Few important considerations for FMS Design

The type and size of the FMS are based on fluid properties, required system uncertainty, flow rate, pressure drop, maintenance, proving requirements, and more. Different types of flowmeters such as the Positive Displacement meter (PD meter), Turbine meter, Ultrasonic Flowmeter (UFM), Coriolis meter, Orifice meter, V-Cone meter, and Venturimeter, etc. are used for flow metering.

A flow meter must be calibrated and validated at a certain interval of operating life to ensure the reliability and uncertainty of the system. The validation methodology and calibration intervals must be carefully decided as it plays a crucial role in the design of the metering system design.

For the optimum performance and operability of an FMS, the most critical items are the Metering Control System whose design depends on various functional applications and requirements with preferences for Flow Computer, PLC, and HMI manufacturers in line with the preferred operator infrastructure.

In addition to its metering capability-related design considerations, the system has to be designed and developed in the context of various external influences like availability, maintenance possibilities, safety procedures, ATEX and Ingress Protection, etc. 

The design must strictly comply with project specifications and applicable international codes, standards, and regulations, etc.

FMS Packages, in general, contain two numbers of metering runs (2 x 100 % configuration) one-meter run as a duty or operating and another meter run as standby. Under normal operation mode, only one stream (Stream-A) shall be in operation as Duty Stream. This is calculated to be able to provide 100% flow rates required for the FMS skid. In this mode, the other stream (Stream-B) and Proving run should be fully isolated.

Caesar II image of typical FMS Skid
Fig. 2: Caesar II image of a typical FMS Skid

Operating & Control Philosophy

  • Prior to the operation of the FMS Skid, a line walk is required to ensure that all equipment is in good installed condition. 
  • Valve opening-close position shall be ensured to be as per PEFS (P&ID Drawing) requirements.
  • The stream intended to be placed in operation must be pressure-equalized with the inlet pressure.
  • All operation control of the metering stream shall be made using the operation of USV Valves in the inlet, outlet, and proving run of each metering stream. 

Few more Resources for You…

Types of Flowmeters and their Applications
What is Fluid Flow?
Piping Interface Related articles
Piping Design and Layout

Comparison between Piping and Pipeline Engineering : Piping vs Pipeline

Written by Anup Kumar Dey in Pipeline,Piping Design Basics,Piping Interface

Both Piping and Pipeline originated from Mechanical Engineering and many a time, share common activities. For example, both have piping materials, piping expansion, stress, and support problems. So, both piping and pipelines need Stress and Material engineers. Both piping and pipelines are used to transport fluids. On a broad scale, ASME B31.3/ASME B31.1 deals with piping engineering, and ASME B31.4/ ASME B31.8 deals with pipeline engineering. Refer to Figure 1, which shows the piping and pipeline demarcation for a typical plant. Through this article we will try to find out a few other differences that piping and pipeline systems have in a general sense:

Geographical Differences

Piping and Pipelines are normally demarcated by a boundary or fence. Outside the fence comes under the pipeline scope and the inside boundary falls under the piping scope. Generally, a pipeline travels a long distance (across villages or countries) whereas the length of single piping is short (equipment to equipment or pipeline to equipment).

Physical Personality or Action Performed

Piping is normally connected with various equipment and carries fluids inside a complex network that will be processed in that equipment. Whereas Pipelines supply the feed for further processing or deliver the processed fluid or end product and they normally run straight. The number of equipment connections in the pipeline is very less as compared to piping. 

Construction

Pipelines travel aboveground, underground, or sub-sea with the maximum part being buried. Whereas, piping systems are mostly aboveground.

Piping vs Pipeline
Fig. 1: Piping vs Pipeline Scope Demarcation

Pipe Diameter and Fitting Types

In piping systems, pipe size is normally less (the majority of lines in the Process or the power piping systems are less than 36 inches) but the number of pipe fittings used is very high. On the contrary, pipeline diameters are large and the number of fittings is comparatively much less.

Type of Pipe and valves:

In most cases Line Pipes i.e, API 5L code is used for pipeline material and API 6D is used for pipeline valves whereas piping material uses ASTM, BS, API 5L, or various other codes and standards and piping valves are from BS or API standard.

Design temperature

In most of cases, fluid design temperature for pipelines is normally less than 230 deg C, whereas piping systems carry fluids with different design temperatures.

Hydrotesting Pressure

For the piping system, the hydro test pressure is calculated by multiplying design pressure by 1.5 and a temperature factor whereas pipeline design pressure is 1.25 times the design pressure for liquid pipelines and (1.25 to 1.5) times the design pressure for gas pipelines. Also, pressure holding time for pipelines is normally 24 hours whereas for piping the same is generally, 2 to 6 hrs.

Typical Piping System
Fig. 2: Typical Piping System

Pipe Routing

While routing pipelines large-diameter elbows (Normally, Hot bends up to 6D and Cold Bend up to 60D) are used whereas piping systems, in general, do not find such large diameter bends.

Construction Drawing

The construction drawings in the case of pipeline systems are termed as alignment sheets, but the same for piping systems are termed as piping isometric drawings.

Surveys

Various technical surveys like Topographical surveys, Soil-resistivity surveys, Cadastral surveys, Hydrological surveys, Geo-technical investigations, etc are performed to collect various data during pipeline design. On the contrary, Only wind and seismic profile studies are performed for piping systems.

Pigging

Long pipelines are cleaned or inspected by used pigs whereas piping systems are cleaned with steam or nitrogen.

Typical Pipeline System
Fig. 3: Typical Pipeline System

Miscellaneous

  • Pipelines are normally preserved using inert gas or corrosion-inhibited water.
  • Cathodic protection systems are involved with pipelines.
  • Corrosion protection coating is normally applied for pipelines whereas piping systems are painted.
  • The pipeline runs across rivers, below railroads, highways, etc. Hence, special design and constructional considerations are required.

Few more Resources for you..
Piping Design and Layout
Pipeline articles
Piping Materials
Piping Stress Analysis Basics
Piping Stress Analysis

References and Further Studies

Difference between Tee and Barred Tee

Written by Nur Hidayah Haron in Engineering Materials,Pipeline,Piping Design Basics,Piping Interface

Tee or Tee connection in piping engineering is a very important pipe fitting and is frequently used to combine or divide a flow. Two types of Tee are available, Equal Tee and Reducing Tee. However, in pigged pipelines, one special type of tee connection is widely used which is known as Barred Tee or Pigged Tee. In this article, we will try to study a few points about Barred Tee and Tee Connections.

Tee vs Barred Tee
Typical Tee and Barred Tee Connection

Tee vs Barred Tee

Tee is a type of pipe fitting that allows fluid to flow on its main pipe and branch out. The branch can be designed equally the same size as the main pipe (known as Equal Tee), or smaller size than the main pipe (known as Reducing Tee).

Barred Tee is a special type of Tee that is based on a normal tee (can be either an equal tee or a reducing tee) that at a later stage, will be added with bar plates inside the branch outlet (From inside it looks like a steel cage) to restrict the PIG (pipeline PIGGING) from flowing from the header pipe into the branch pipes.

Design Codes and Standards for Tee and Barred Tee

  1. The international standard dimension of the tee will be covered under ASME B16.9 or MSS-SP 75 (for DN16 and above). Click here to know more about Tee Connections.
  2. There is no international standard dimension for the barred tee. It is custom-made using the ASME B16.9/ MSS-SP 75 tee as a base. However, many develop their barred tee based on Shell DEP 31.40.10.13-Gen or ISO 15590-2 standard.
  3. This design can be a guideline to assess Vendor’s design.
Reduced Barred Tee (Reference: Shell DEP 31.40.10.13-Gen Figure 4)
Reduced Barred Tee (Reference: Shell DEP 31.40.10.13-Gen Figure 4)

Design Considerations for Barred Tee

The barred tee will be used when there is a requirement for pigging. Thus, many of its applications can be found in the pipeline or in the subsea field.

The bar plates that are welded internally at the branch are to avoid the pig from changing direction or getting stuck at the branch outlet.

The design of the bar plates must be in sufficient quantity, thickness, and adequately spaced to ensure the smoothness for the pig to run through the main pipe, and at the same time not affect the flow that was meant to flow through the branch. Normal practice is to ensure that the opening in the branch pipeline after guided bars is not more than 40% of the main pipeline area.

The size of the bars in the branch connection has to be small enough not to restrict the flow but large enough to sustain the pressure of the flow.

To ensure smoothness, the bar plates have to be a grind to suit the branch curvature. Any sharp edges spatter, and burs are required to be removed. This smoothness of the pigging process is important to protect the sensor of pig from damage.

Refer to Shell DEP 31.40.10.13-Gen Figure 4 above; the quantity of the bar plates start with two (2) pieces and increase as the ID of the branch increase.

The bar plates ideally will be equally spaced.

For a larger tee (size 14 inches and above), there will be a bridge plate in the middle to support the bar stiffness when getting hit by the pig.

The material of the bar plates is commonly used the same as the tee material for weldability.

Standard practice is to avoid welding guide bars directly on the high-stress concentrated areas of the extrusion neck. Bar ends must be machined to fit the branch.

Weld Repairs on Parent metal are prohibited.

Difference Between Tee and Barred Tee

So from the above discussion, we can summarize the following differences:

ParameterTeeBarred Tee
DefinitionStandard Pipe FittingA special type of piping component
ManufacturingGenerally by Extrusion or forgingMostly Fabricated
UseUsed in both piping and pipeline engineering used in pipeline engineering near the pig launcher/receiver
Design Code / Standard ASME B16.9/MSS SP 75 Shell DEP 31.40.10.13-Gen or ISO 15590-2
Production QuantityLarge scale in bulkSelect small quantities (custom-made)
CostCheaperCostlier than normal Tee
Tee vs Barred Tee

Few more references for you

Piping Design and Layout
Piping Materials
Piping Stress Analysis
Piping Interface

Reference

Stub-in vs Stub-on | Differences between Stub-in and Stub-on Piping Connection

Written by Anup Kumar Dey in Piping Design Basics

Stub-in and Stub-on are methods for making a fabricated branch connection from the pipe. Both types are permitted by many international codes and standards, including ASME B31. However, both of these are weak connections on piping systems and are normally limited only to low-pressure and temperature applications. In this article, let’s explore the differences between Stub-in and Stub-on branch connections.

What is Stub-In?

In the case of a stub-in, a larger hole is drilled in the header or run pipe, and a branch pipe whose end is contoured similar to the inside diameter (ID) of the header is fitted inside the hole. Then both the stub-in branch pipe and the run pipe are welded together to form a connection similar to reducing tee. Stub-in is normally used when the branch is more than one size smaller than the main pipe. For the “stub in” connection, the branch pipe extends to the inside of the main pipe. Stub-in connection is also known as the set-in connection.

What is Stub-On?

On the contrary, In the case of a Stub-On branch connection, the hole that is cut in the run pipe is the same as the inside diameter (ID) of the branch Pipe (Not the Header). The end of the branch pipe connection is contoured the same as the outside diameter (OD) of the header pipe and is then fitted outside the hole on the header pipe. It looks like the branch is seated “onto” the header pipe. Stub-on is generally used when the branch is equal to or one size smaller than the main pipe. For “stub on,” the stub extends only to the outside of the main pipe. A stub-on connection is also known as a set-on connection.

Stub-in and Stub-on Connection
Fabricated Piping Branch Connections

Additional Features for Stub-In and Stub-On

Both stub-in and stub-on branch connections can be made with or without a reinforcing pad as per requirement. This requirement is normally governed by pressure and stress criteria.  The reinforcement pad is basically a ring that is cut from the run pipe or from a plate with the same material as the run pipe. At the center of the pad, a hole is made (the size the same as the branch pipe). When it is cut from a flat plate, it is contoured to fit around the run pipe. The width of the reinforcement pad is normally one-half the diameter of the branch pipe.

The aim of this reinforcement is to substitute the material that was removed for making the branch connection from the header. A small-diameter hole, known as a weep hole (1/4″ NPT) is normally drilled in the pad, which acts as a vent during the welding process for the weld-generated gases to escape. Using full penetration welds, The ring or pad is then welded to the branch and the run pipe. Once, the work is completed, the small hole is fitted using a plug.

Both the stub-in and Stub-on connections, in a sense, reduce the cost of pipe fittings. It saves installation time as well because only one weld is required around the stub hole instead of three welds that are needed for joining welding tee connections.

The welding strength of the Stub-in connection is as good as butt welding but welding steps are difficult in actual conditions. So Stub-in is comparatively stronger than stub-on connections.

Stress Considerations for Stub-in and Stub-on Connections

From the piping stress analysis considerations, the calculated SIF of stub-in and stub-on connections is much higher than weldolet fittings and ASME tees, which is significant when a detailed stress analysis is done on the system. While analyzing, extra caution needs to be considered as the stress generated will be higher. The use of this type of branch connection is not preferred for severe cyclic applications, high-pressure temperature applications, or category M fluid service applications.

Stub-in vs Stub-on Piping Connection | Differences between Stub-in and Stub-on

The main differences between a stub-in and stub-on branch piping connection are tabulated below:

Stub-in pipe ConnectionStub-on branch connection
As explained above, Stub-in is used when the run pipe and branch pipe have a difference of more than one size.On the contrary, a stub-on pipe branch connection is applicable when the branch pipe is equal to the run pipe or only one size lower than the header pipe. 
In the case of the stub-in branch connection, the pipe welding between the branch and header is of butt-weld type.
This welding is quite difficult.		Stub-on branch connections are made using fillet welds. 


Welding is easier as compared to the stub-in welding method.
A stub-in piping connection is able to withstand more pressure.Stub-on branches are comparatively weaker than the stub-in branch connection and hence handle less pressure.
The branch edge of a stub-in connection matches the internal pipe diameter of the header.For stub-on branch connection, the branch edge lies on the outside diameter of the header.
Stub-in pipe connections usually have more weld strength value than sub-on branch connections.Stub-on pipe branches possess comparatively less weld strength value.
Table 1: Stub-in vs Stub-on

Few more Resources for you..

Briefing about Reinforcement Pad
Piping Design and Layout
Piping Materials
Piping Stress Analysis
Piping Interface

What is Acoustic-Induced Vibration or AIV?

Written by Anup Kumar Dey in Mechanical,Piping Design Basics,Piping Stress Analysis,Piping Stress Basics

What is Acoustic-Induced Vibration or AIV?

Acoustic-Induced Vibration or AIV is a severe high-frequency vibration that the piping systems carrying vapor or gases may experience near the high-pressure-reducing devices. Due to high-pressure drops of vapor/gas services in this pressure-reducing device like a relief valve, orifice plate, control valve, depressuring valve, Choke Valve, Blow Down valve, etc, a high-frequency sound wave in the range of 500–2,000 Hz is generated. This wave energy induces vibration (and stress) and excites the pipe wall in the circumferential direction causing radial pipe displacement and eventually acoustic fatigue failure within a very short period of time (A few minutes or hours). Piping components with high-stress concentration zones like pipe fittings, small-bore pipe connections, Fabricated tee, welded pipe supports, etc are prone to such acoustic-induced vibration failures. 

Since the high viscosity of liquid or two-phase fluid dampens the circumferential pipe displacements, Acoustic Induced Vibration or AIV is not a concern for such systems.

Cause of Acoustic Induced Vibration

There are two main causes for Acoustic Induced Vibration (AIV), they are:

  • high-pressure drops and
  • high flow rates in vapor/gas services

Mechanism of Acoustic Induced Vibration (AIV)

In Acoustic Induced Vibration, the high-velocity fluid impingement on the piping wall, turbulent mixing, and shockwaves downstream of the flow restriction give rise to a high level of noise. This noise level is a function of pressure drop across the pressure-reducing device and gas/vapor mass flow rate. The noise is transmitted downstream of the flow restriction losing energy to friction, work is done by vibrating the pipe, and heat is lost to the surroundings. A noise or sound level of 155 dB is considered a safe level when the circumferential vibration is no longer a concern. Industry standards and experience show acoustic energy attenuates 3 dB for every 50D of piping from the source. The response caused by high-frequency acoustic excitation affects the piping downstream of the source to the first major vessel, i.e, the Separator, KO drum, etc.

Screening for Acoustic Induced Vibration

Design Engineering Practice (DEP) by Shell Global Inc provides rules for screening the systems for Acoustic Induced Vibrations (AIV). To study the effect of AIV on the piping system it is required to calculate the sound power level at the concerned pressure-reducing device based on the following equation:

Sound Power Level formula for AIV
Sound Power Level Calculation

Where: 

  • P1 is upstream pressure (bara)
  • P2 is downstream pressure (bara)
  • W is the flow rate (kg/s)
  • T is the upstream temperature (K)
  • Mw is molecular weight (grams/mol)
  • SFF is a correction factor to account for multiple occurrences of sonic flow in a line. If consecutive sonic conditions exist, then SFF=6; otherwise SFF = 0.

All the above-mentioned data can be received from the Process engineering team. If the calculated Sound power level is less than (or equal to) 155 dB, then there is no concern from the AIV viewpoint. However, if the calculated Sound power Level is more than 155 dB, then the LOF (Likelihood Of Failure) value needs to be calculated following the steps provided by Energy Institute guidelines for the avoidance of vibration-induced fatigue failure in process pipework.

Mitigation of AIV

Considerations for Acoustic Induced Vibration mitigation must be done during the design stage of the project as failures in AIV can happen within minutes of operation. There are various options for AIV mitigation. However, the following options are the most common:

  • Using a higher pipe schedule or lowering the D/t ratio.
  • Decreasing flow velocity by increasing pipe diameter.
  • Using smoother pipe fittings ensures a smooth transition from the branch to the main header.
  • Using Clamp-on supports and stiffening rings.
  • Using a full wrap-around pad on welded pipe supports. Full wrap-around is more commonly accepted in industry standards than partial reinforcing.
  • Using Multi-Stage Pressure Drop Internal Trim (Low noise trim) to reduce noise levels at the valve.
  • Using In-line Acoustic Silencer downstream of a pressure-reducing valve will reduce the acoustic energy near its origin point and prevent its further propagation. However, as silencers themselves are susceptible to mechanical damage from high acoustic energy exposure, this is not suggested.
  • Increasing line length between acoustic-induced vibration source and high-risk stress concentrated locations

Attenuation of acoustic energy at the source is the most preferred approach to achieve acceptable sound power energy in a piping system if the same is physically and economically feasible. Two types of devices can accomplish this:

Low Noise Control Valves:

As the acoustic energy generated due to turbulent fluid stream is highly sensitive, valve manufacturers design valves to generate lower levels of acoustic energy, known as low noise control valves. Depending on the sound power energy attenuation requirement of the system various design options are available:

  • Multipath Design with special low-noise trim.
  • Staged Trim design
  • Labyrinth Disk design

Restriction Orifice:

The acoustic energy generated at the source can be controlled by a multi-stage restriction orifice. One-stage pressure let-down systems operate at choked flow conditions generating extremely high levels of acoustic energy. This causes increased turbulence and shock waves downstream. Installing a series of restriction orifices (multi-stage) downstream of the let-down valve will attenuate this acoustic energy. Using multiport expansion plates in restriction orifice design is also an alternate option for mitigating acoustic-induced vibration.

If reducing the generated acoustic energy is not feasible, finding options to reduce the level of resonant response can be considered. Steps must be considered to dampen the vibration amplitude or to improve the mechanical integrity of the piping system by reducing stress concentrations.

System damping can be increased by using anti-vibration materials (elastomer). Stress concentrations can be reduced by

  • increasing pipe thicknesses
  • using full-wrap reinforcements
  • using standard branch connections (Welding Tee, Olets, etc) in place of un-reinforced fabricated connections
  • Removing screwed fittings
  • eliminating branches 2 inches and smaller
  • avoiding abrupt geometric changes in line.

Comparison of FIV and AIV

The following image shows the comparison between Flow Induced and Acoustic Induced Vibrations in a Piping System

FIV AIV differences
FIV and AIV Comparison

Few more related Resources for you.

What is Acoustic-Induced Vibration or AIV?
What is Flow-Induced Vibration (FIV) in a Piping System
Basics of Vibration Monitoring: A Presentation
Motion Amplification Technology (MAT) for Piping Vibration Visualization
Common Causes and Effects of Piping Vibration
Solving vibration problems in a two-phase flowline by Dynaflow Research Group
Considerable points while installing centrifugal pumps at the site to reduce vibration

References and Further Study