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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

What is Pump Cavitation? Types, Causes, Effects, and Prevention of Pump Cavitation

Written by Anup Kumar Dey in Mechanical

What is Pump Cavitation?

Pump cavitation is a destructive issue that can generate excess noise and energy usage to serious pump damage. The problems of pump cavitation are not new and ever-growing. It seriously affects the pump operation and lifespan. However, pump cavitation can be easily avoided with the right planning and troubleshooting.

Cavitation is an important term for rotating equipment engineers. The generation of vapor bubbles or cavities in a fluid flow due to low pressure and its sudden collapse causing damages in the related parts like the impeller, pump housing, etc are termed as Cavitation. It is one of the major problems for Centrifugal pumps. There are various criteria that can describe the occurrence of cavitation, its extent, and its impact of it.

Cavitation occurs when the liquid in a pump creates air bubbles because of the partial pressure drop of the flowing liquid. Insufficient net positive suction head available is the main cause of generating air bubbles. Changes in the liquid pressure in the pump turn the liquid into vapor. As the liquid moves by the pump’s impeller spinning, the air bubbles move and instantaneously implode. The collapse of vapor bubbles creates a shockwave that erodes the impeller surface. When strong cavitation occurs at the impeller inlet, the pump performance decreases, leading to even pumping failure.

Pump Cavitation is usually common with centrifugal pumps as these types of pumps work by changing the pressure inside the unit to create a vacuum, pushing the liquid into the unit as opposed to pulling it in. Cavitation in submersible pumps is less frequent.

What Causes Cavitation?

When the suction pressure drops below a certain value, the performance of the centrifugal pump deteriorates. This suction pressure that is often decided with respect to vapor pressure at suction temperature is called Net Positive Suction Head which is popular by its acronym NPSH. If this NPSH drops, impeller inlet pressure may fall below the vapor pressure which causes vapor bubbles or voids to generate. If the flowing liquid is then subjected to pressures above the vapor pressure, these voids can implode causing damage, which is called cavitation.

The most well-known causes of cavitation are:

  1. Not meeting the required NPSH
  2. The pump is installed at too high of a distance above the fluid source
  3. The suction pipe diameter is too small
  4. Pipe blockage on the suction side
  5. Clogged or obstructed filters
  6. The length of the Suction pipe is more.
  7. Excessively high suction lift.
  8. Poor piping design
  9. Flowing liquid is having a very low vapor pressure
  10. Fluid is overly heated to the point of vaporization.
  11. The pump is running too far right on the pump design curve
  12. The Pump Speed is more
  13. Due to a high-vacuum or low-pressure environment, the flow in the pump is not proper.
  14. High discharge pressure.
  15. Poorly specified pump.
Cavitation and its Effect
Cavitation and its Effect

Cavitation Types

Two types of cavitation are more prevalent in rotating equipment engineering; Vapor Cavitation and Gas Cavitation.

Vapor Cavitation

When the static pressure in a flowing fluid falls below the vapor pressure, Vapor cavitation develops. At the same time, the presence of nuclei or microscopically small vapor bubbles are required for the cavitation to form. The static pressure decreases if the local velocity is increased or the inlet conditions change.

Now, the generated vapor bubbles implode suddenly at a very high velocity, when the static pressure rises above the vapour pressure in the flow direction. This sudden implosion may lead to material erosion, a rise in noise levels, rough running of the pump, and a drop in pump efficiency and head. Normally, as the implosion begins, vapor bubbles will dent inwards, and later a water microjet is formed that is directed at the wall and strikes with a high velocity. This sequence of all events, along with with the fissured microstructure, very fine pores, indentations, and cracks in the wall surface is the main reason behind the material’s destruction, which is accelerated in the presence of mechanical stress.

Gas Cavitation

When the bubbles are generated due to the release of dissolved gases from the solution in conjunction with diffusion, Gas Cavitation occurs. When the fluid’s pressure drops below the saturated vapour pressure, Dissolved Gases come out from the solution. This mechanism is dependent on the concentration of the dissolved gases. In terms of material damage, Gas cavitation is not as destructive as vapor cavitation, because, with rising pressure, the gas diffuses into the liquid again which means that this process is much slower than the collapse of vapor bubbles.

Bubble Formation During Cavitation
Bubble Formation During Cavitation

The formation of Vapour and Gas may overlap, as well. Vapor bubbles which are generated when the fluid’s pressure reaches or drops below vapour pressure may also contain gas that can release from the solution via diffusion while the fluid approaches the suction of the pump. So both of these two cavitations together, intensify the extent of the impact on the fluid flow.

Depending on the location of pump cavitation on the suction or discharge side, pump cavitation can also be grouped as Suction cavitation and discharge cavitation.

Symptoms/ Effects of Cavitation

As a result of cavitation, One or a combination of the following symptoms or effects can be generated:

  • Unexpected Vibrations
  • Pump performance deterioration. Decreased or Reduced Flow or Pressure
  • Erosion of the Impeller
  • Seal and Bearing Failure
  • Erratic Power Consumption
  • Distinct Noise.
  • Mechanical damage.

How to Prevent Cavitation?

An obvious way to guarantee that there will be no pump cavitation is to restrict the void or bubble generation. This can be done in various ways like

  1. Lowering the pump speed.
  2. Raise the liquid level to increase the NPSH so that a lower pressure scenario does not occur.
  3. Lowering the operating temperature.
  4. Reduction of Pump motor RPM. Running the pump at the ideal rpm.
  5. Using a booster pump to feed the principal pump.
  6. Increasing the impeller diameter.
  7. To properly operate a pump best suited for the application
  8. Selecting the impeller inlet geometry that ensures no vapor formation.
  9. Using two lower capacity pumps in parallel.
  10. Installation of an impeller inducer
  11. Strictly following the pump’s manufacturer performance guidelines.
  12. Increasing pump suction line size.
  13. Altitude or height has a major effect on pump cavitation. At higher altitudes, special care must be taken to make sure that cavitation does not occur since liquids boil at a much lower temperature.
  14. The fluid temperature needs to be monitored to keep cavitation under control.
  15. Avoiding pockets for air or vapor accumulation.
  16. Keeping pipe reducers as close to the pump as possible.
  17. Regular pump maintenance.
  18. Installing the pump at the proper location

Few more resources for you..

MAJOR FACTORS AFFECTING THE PUMP PERFORMANCE”: A short article
NPSH for Pumps: Explanation and Effect
Water Hammer Basics in Pumps for beginners
Pumps & Pumping Systems: A basic presentation
A brief presentation on “CENTRIFUGAL PUMP WITH SPEED CONTROL”
Stress Analysis of Pump Piping (Centrifugal) System using Caesar II
Considerable points while Commissioning and starting-up a Process Pump
Considerable points while installing centrifugal pumps at site to reduce vibration

Reference and further Studies

Flow-Induced Vibration or FIV in a Piping System with Online Course

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

What is Flow-Induced Vibration or FIV?

Flow-Induced Vibration or FIV is a large amplitude, low frequency (generally <100 Hz) vibration that can occur in piping systems carrying high-velocity turbulent fluids. Flow-induced Vibration i.e, the fluid flow generates high kinetic energy that forces the piping system to vibrate (Piping Vibration is induced in the system by Fluid flow). It is more prevalent near turbulent sources such as pipe bends, reducers, branch connections (Tee connections), partially closed valves, process equipment connections, etc.

Flow-Induced Vibration in Pipes

In recent days, risk due to flow-induced vibration has increased a lot due to

  1. Increased flow rate (high velocity) that results in a high level of turbulent energy
  2. Use of thin-walled piping i.e high D/t ratio
  3. Long pipe support span which results in flexible piping
Sample Piping Displacement during FIV
Sample Piping Displacement during FIV

Effect of Flow-Induced Vibration

Flow-Induced vibration displaces the piping system in the longitudinal and transverse direction and in some cases leads to damage to the pipe supports.

Considering the momentum flux (density X velocity2), High-density Liquids are more prone to Flow-Induced Vibration as compared to gases.

Flow-Induced Vibration Analysis

DEP 31.38.01.26 (Design and Engineering Practice by Shell Global Solutions International) provides detailed steps for screening piping systems for Flow-Induced Vibration (FIV) by calculating momentum flux (density X velocity2) and categorizes failure susceptibility into three groups:

  • Negligible,
  • Medium and
  • High.

They also suggest further steps to follow when the susceptibility falls into the Medium or High Category. For High category vibration susceptibility fluids, the Likelihood Of Failure (LOF) needs to be calculated following detailed steps mentioned in Energy Institute guidelines for the avoidance of vibration-induced fatigue failure in process pipework. The aim of the piping engineer will be to keep LOF below 0.3. However, if LOF is more than 0.3 then corrective actions need to be taken to mitigate the vibration possibility.

Flow-Induced Vibration Steps

The steps for detailed flow-induced vibration analysis based on the Energy Institute Guidelines (Use this guide for equations) are provided in the image below:

Flow Induced Vibration Steps
Flow-Induced Vibration Steps

Mitigation of Flow-Induced Vibration

Flow-Induced Vibration or FIV normally takes a long time to cause metallic fatigue failure. Hence,  it is usually resolved when vibration is observed physically after commissioning the plant. The most common mitigation is to add supports or restraints. By adding the appropriate guide and line stop supports, i.e by increasing system rigidity, the damaging effect of FIV can be reduced a lot. These added supports will minimize the shaking tendency of the pipe, thus reducing the tendency of pipe failure. Other mitigations against Flow-Induced Vibration in Piping Systems could be

  • Reduce fluid velocity by increasing pipe size or by changing process conditions.
  • Increase system rigidity by increasing pipe wall thickness.
  • Install viscous damper, shock arrestor, snubber, etc in the piping system
  • Reduce the number of turbulent sources like elbows, reducers, etc.
  • Tighten the clearances in between pipes and supports.
  • Stress concentration at branches can be reduced by contoured pipe fittings and gussets on Smallbore connections

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
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

Online Course on Flow-Induced Piping Vibration Study

To learn more about flow-induced piping vibration study, I recommend the following online video course:

  • Flow-Induced Vibrations for Piping Systems: FIV or Flow-Induced Vibration is a serious problem that has the potential to cause pipework and support failure thus impacting the structural integrity of the piping system. So, FIV study has become more important in recent times and many organizations made it mandatory to perform FIV assessment during the detailed design phase. In this course, You will learn the basic theory of Flow-induced vibration, Steps for FIV Analysis, and Finally some mitigative options.

References and Further Study

Piping Thermal Bowing Consideration in Caesar II with an Example

Written by Anup Kumar Dey in Caesar II,Piping Stress Analysis,Piping Stress Basics

What is Piping Thermal Bowing?

Piping Thermal Bowing or Bowing is an effect that occurs in horizontal piping run due to large circumferential temperature gradients which have the potential to cause large unacceptable local thermal stresses in the pipe walls leading to fatigue failure and high loads at pipe supports and connected equipment. The pipe may bend like a bow in such a situation and hence the name bowing effect. Because thermal bowing is very damaging, it is important to avoid the occurrence rather than to analyze the effect after the occurrence. This article will provide some guidance on how thermal bowing problems are considered in piping stress analysis using Caesar II software.

Which lines are prone to piping thermal bowing?

Pipe thermal bowing is a serious problem for

  • partially filled cryogenic lines like LNG, LPG, etc or
  • Uninsulated pipes which are exposed to the hot sun
  • pipes carrying the stratified flow of low-temperature fluid in horizontal lines
  • Steam lines in presence of external or internal water (Condensate)
  • Stagnation of the flow which causes stratification

In such lines, the flow inside the pipe is such that one part of the pipe cross-section is hot and the other part is cold. For example in a partly filled LNG or LPG line, the upper part of the pipe cross-section will be in hot condition (so, the pipe will expand in the upper part) and the lower part will be in cold condition (so the pipe will contract in the lower part). A similar situation arises, where one side of the pipe is heated by the hot sun exposure and the other side is in the shade. So this simultaneous expansion and contraction or uneven temperature distribution will force the pipe to produce pipe curvature.

Piping thermal bowing problems are normally not addressed in pipe stress analysis or design books. But the share of operational difficulties due to thermal bowing is very high. Therefore, it should be properly treated in the design.

What is the thermal bowing temperature?

The diametrical temperature difference across the cross-section is called the bowing temperature. The bowing temperature occurs mostly in top and bottom directions and is mainly generated by stratified flow created by rapid quenching of high-temperature gas engaged in petrochemical production, emergency cooling injection, cold re-circulation, start-up of a liquefied natural gas transfer line, rapid deployment of cryogenic liquid fuel, and so forth. It can also be generated by the startup of a large steam pipe.

For considering piping thermal bowing in Caesar II this thermal bowing delta temperature is the additional input. Thermal Bowing Delta Temperature Specifies the diametrical temperature differential between the top and bottom of the pipe. This differential temperature is used to calculate an elemental load that is added to each temperature case. This temperature will be received from the Process engineering team.

Piping Thermal Bowing Assumptions for Stress Analysis in Caesar II

For stress analysis, it is assumed that

  • the temperature distribution across the piping cross-section is linear and
  • the same thermal gradient or temperature change is applied to the complete pipe and cannot specify different thermal bowing temperatures for different pipes.

Example Problem for Piping Thermal Bowing Stress Analysis in Caesar II

LPG Line Caesar II model for Thermal Bowing Consideration
Fig. 1: LPG Line Caesar II model for Thermal Bowing Consideration

In this example, an 18-inch LPG line is considered (As shown in Fig. 1). The analysis parameters are as follows:

  • Maximum Design Temperature: 82 Deg. C
  • Minimum Design temperature: -46 Deg. C
  • Operating Temperature: -42.4 Deg. C
  • Thermal Bowing Delta Temperature: 50 Deg. C
  • Design Pressure: 2900 Kpa
  • Hydrotest Pressure: 4440 Kpa
  • Pipe Material: A333-6
  • Pipe OD: 457.2 mm
  • Pipe Thickness: 11.91 mm
  • Corrosion Allowance: 3 mm
  • Fluid Density: 600 Kg/m3
  • Cold Insulation Thickness: 80 mm
  • Insulation density: 40 kg/m3

The pipe is to be modeled in the normal method which we do for other piping analyses. Additional input is thermal bowing delta temperature that has to be entered inside the special execution parameter as shown in the image (Fig. 2) below:

Thermal Bowing Delta Temperature in Caesar II
Fig. 2: Thermal Bowing Delta Temperature in Caesar II

Next prepare all the required load cases for Analysis. Thermal bowing stress will automatically be considered for all thermal load cases. The following image (Fig. 3) shows the stress difference with thermal bowing and without thermal bowing effects.

Output Result with and without Thermal Bowing
Fig. 3: Output Result with and without Thermal Bowing

So it is clear from the above output results that there are changes in stresses. The same is true for support loads and thermal displacements.

Some more Resources for You…

Thermal Bowing Methodology Using Start-Prof
Stress Analysis using Start-Prof
Stress Analysis using Caesar II
Stress Analysis Basic Concepts
Piping Layout and Design

References and Further Studies

Types of Fractional Distillation Process

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

Fractional distillation is a fundamental separation technique widely used in various industries, including petrochemicals, pharmaceuticals, and food production. This blog post aims to provide an in-depth understanding of fractional distillation, covering its principles, equipment, applications, and advantages. By the end, you’ll have a thorough grasp of how this process works and why it’s essential in modern chemistry.

What is Fractional Distillation?

Fractional Distillation or Distillation or Fractionation is the process of separation of components from a product or mixture (Crude Oil) by heating the mixture to a temperature at which several fractions of the compound will vaporize.  It is a physical process. Normally, when the mixture is heated, the component with the lowest boiling point will vaporize first and will separate out from the mixture. With further increases in temperature, other components will start to vaporize and separate.

Fractional Distillation is the most widely used form of separation technology and finds uses in petroleum refineries, petrochemical, and chemical plants, natural gas processing, and cryogenic air separation plants. It is one of the most important separation processes.

Fractionation Towers or Distillation Columns in Process Plants
Fractionation Towers or Distillation Columns in Process Plants

Principles of Fractional Distillation

Vapor-Liquid Equilibrium

At the heart of fractional distillation is the concept of vapor-liquid equilibrium. When a liquid mixture is heated, some components will vaporize before others, depending on their respective boiling points. When these vapors condense back into liquid form, the composition of the liquid phase changes, allowing for the separation of different components over repeated cycles.

Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the atmospheric pressure. In a mixture, each component has a unique boiling point. By carefully controlling the temperature during distillation, one can selectively vaporize the component with the lowest boiling point.

Raoult’s Law and Dalton’s Law

Raoult’s Law states that the partial vapor pressure of each component in a mixture is proportional to its mole fraction in the liquid phase. This principle is essential for understanding how components interact during distillation.

Dalton’s Law of partial pressures complements Raoult’s Law by stating that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each individual gas. These laws together provide a framework for predicting the behavior of mixtures during fractional distillation.

The Fractional Distillation Process

Step-by-Step Process

  1. Heating: The liquid mixture is heated in a distillation flask. As the temperature rises, components with lower boiling points start to vaporize.
  2. Vaporization: The vapor rises through the fractionating column, where it encounters a series of packing materials or trays that promote vapor-liquid contact.
  3. Condensation: As the vapor cools, it condenses back into liquid. The composition of this liquid will be richer in the component with the lower boiling point.
  4. Collection: The condensed liquid, or distillate, is collected in receiving flasks, and the process can be repeated to achieve higher purity.

What are the alternatives to the fractional distillation process?

There are a few alternatives to distillation as mentioned below but require higher investment costs. This is the main reason that distillation remains the main choice in the hydrocarbon industry, especially in large-scale applications.

  • Liquid-Liquid Extraction or Solvent Extraction,
  • Hydrophilic Pervaporation
  • Multi-membrane Permeation Separation
  • Adsorption process.

Types of Distillation Processes

There are various types of distillation processes that are popularly used in various industries for separating different products. Those are

  • Fractional Distillation
  • Extractive Distillation
  • Reactive Distillation
  • Simple distillation.
  • Steam distillation.
  • Vacuum distillation.
  • Air-sensitive vacuum distillation.
  • Short path distillation.
  • Zone distillation
  • Azeotropic Distillation
  • Distillation under Reduced Pressure
  • Destructive Distillation
  • Industrial Distillation

When the physical properties (mainly boiling point) of the components in a mixture are very close to one another (For example an azeotropic mixture), the separation method becomes difficult.

Out of the above types, Fractional, Extractive, Reactive and Industrial distillation are the most frequently used ones.

Fractional Distillation

Fractional Distillation is the separation of key components from the product mixture by the difference in their relative volatility or boiling points by heating the product.

Extractive Distillation

In this type of distillation, an external solvent is introduced to the system that increases the separation. The external solvent changes the relative volatility between two close components by extracting one of the components, which forms a ternary mixture with different properties. Once, the extracted component is separated, the solvent is recycled into the system.

Reactive Distillation

In this method, a catalyst bed is used and the targeted component reacts when it is in contact with the catalyst. This separates the targeted component from the rest of the components in the mixture. The column where similar distillation is performed is termed a reactive distillation column.

Extractive and Reactive Distillation
Extractive and Reactive Distillation

Industrial distillation

Industrial distillation is performed inside a large, vertical, tall cylindrical column. These columns are popularly known as “fractionation towers” or “distillation columns” or “Distillation Towers” and can be found in most process plants. The diameter of such Columns can range from about 65 centimeters to 6 meters and heights can range from about 6 meters to 60 meters or more.

Vacuum Distillation

Vacuum distillation reduces the pressure above the liquid mixture, lowering the boiling points of components. This technique is beneficial for thermally sensitive materials that might decompose at higher temperatures.

Steam Distillation

Steam distillation is a method used for extracting essential oils and volatile compounds from plants. By passing steam through the material, the desired components are vaporized and then condensed back into liquid form.

Role of the Fractionating Column

The fractionating column is critical in the fractional distillation process. It provides a large surface area for the vapor to interact with the liquid, promoting efficient mass transfer. The design and height of the column can significantly impact the separation efficiency, as a taller column generally allows for better separation due to increased theoretical plates.

Equipment Used in Fractional Distillation

Distillation Apparatus

The basic setup for fractional distillation consists of:

  • Distillation Flask: Where the mixture is heated.
  • Heat Source: Such as a heating mantle or a Bunsen burner.
  • Thermometer: To monitor the temperature of the vapor.

Fractionating Column

The fractionating column can be packed with materials like glass beads, ceramic rings, or structured packing to enhance surface area and promote vapor-liquid interaction. The design varies based on the specific separation needs.

Reboiler and Condenser

  • Reboiler: Heats the liquid mixture, converting it into vapor.
  • Condenser: Cools the vapor, converting it back into liquid for collection.

Receiving Flasks

These flasks collect the separated components as they condense from the vapor phase.

Applications of Fractional Distillation

Petroleum Refining

Fractional distillation is a cornerstone of the petroleum industry. Crude oil is separated into various fractions, including gasoline, kerosene, diesel, and lubricating oils. Each fraction can then be further refined for specific applications.

Alcohol Production

In the production of alcoholic beverages, fractional distillation is employed to concentrate alcohol and separate different types of spirits. For instance, distilling fermented mash can yield vodka or whiskey, depending on the raw materials used.

Purification of Chemicals

Fractional distillation is used in laboratories and industries to purify solvents and chemicals. It enables chemists to isolate compounds for research or manufacturing processes.

Advantages and Disadvantages

Pros of Fractional Distillation

  • High Purity: Capable of achieving high levels of separation, yielding pure components.
  • Scalability: Can be scaled up for industrial applications or used in smaller laboratory settings.
  • Versatility: Applicable to a wide range of mixtures and industries.

Limitations

  • Energy Intensive: Requires significant energy input for heating and cooling.
  • Complexity: The equipment can be complex and costly to operate.
  • Sensitivity to Conditions: Performance can be affected by factors like pressure and temperature control.

In Conclusion, fractional distillation is an essential technique in both laboratory and industrial settings, enabling the effective separation of components in a mixture. Its principles are grounded in fundamental physical laws, making it a reliable and efficient process.

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Reference

https://en.wikipedia.org/wiki/Fractional_distillation