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:
Not meeting the required NPSH
The pump is installed at too high of a distance above the fluid source
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
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:
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
Lowering the pump speed.
Raise the liquid level to increase the NPSH so that a lower pressure scenario does not occur.
Lowering the operating temperature.
Reduction of Pump motor RPM. Running the pump at the ideal rpm.
Using a booster pump to feed the principal pump.
Increasing the impeller diameter.
To properly operate a pump best suited for the application
Selecting the impeller inlet geometry that ensures no vapor formation.
Using two lower capacity pumps in parallel.
Installation of an impeller inducer
Strictly following the pump’s manufacturer performance guidelines.
Increasing pump suction line size.
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.
The fluid temperature needs to be monitored to keep cavitation under control.
Avoiding pockets for air or vapor accumulation.
Keeping pipe reducers as close to the pump as possible.
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
Increased flow rate (high velocity) that results in a high level of turbulent energy
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
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.
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
DEP 31.38.01.26 V43
Energy Institute guidelines for the avoidance of vibration-induced fatigue failure in process pipework
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
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:
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.
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.
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
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
Heating: The liquid mixture is heated in a distillation flask. As the temperature rises, components with lower boiling points start to vaporize.
Vaporization: The vapor rises through the fractionating column, where it encounters a series of packing materials or trays that promote vapor-liquid contact.
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.
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
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.
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
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.
While stress analysis and supporting considerations it is always a better engineering practice to provide line stops or axial stops or pipe anchors at the neutral point of the straight portion of the piping. It is believed that at the neutral point, thermal movement is zero and frictional resistance equalizes from both sides of the piping system. In such a scenario, the frictional forces cancel out as forces are positive on one side and negative on the other. Also as there is no thermal movement, there will be zero axial loads due to the temperature effect. So, the software will show zero anchor loads in such locations.
Example of Zero Anchor Loads
For example, In the following symmetric system with two U-shape loops, as shown in Fig. 1, The leg length on both sides of the intermediate anchor is equal. Thus the intermediate anchor node 11 becomes a neutral point.
Fig. 1: Symmetrical piping system with Intermediate Anchor
As can be seen in Fig. 2, The load along the pipe in an intermediate anchor (node 11) will be zero.
Fig. 2: Zero Anchor Load for the System shown in Fig. 1
In reality, the piping heating up can be uneven, the friction forces can be different on the left and right parts of the piping, piping design can’t be ideal. Therefore, the real load on the anchor will not be zero.
How to Avoid Zero Anchor Loads?
To avoid such a situation the Anchor Factor “k” is used in piping stress engineering practice. The following method can be manually used in any pipe stress analysis software. In PASS/START-PROF piping stress analysis software this is a built-in function.
If loads from pipes to the left and right of the support (N1 and N2) are in the same direction, they are combined as N1+N2
If loads N1 and N2 are in different directions, the lower values are multiplied by k and then combined as N1+N2*k (|N2|<|N1|)
If the support is on an end node, factor k is not used
Factor k is applied only for loads in the horizontal plane: axial force, lateral force, and horizontal moment.
The common value, that is recommended by some piping stress analysis codes is k=0.8. If we use a 0.8 value the result will be as shown in Fig. 3. and Fig. 4.
Fig. 3: Actual Anchor Load in Axial Direction
Fig. 4: Intermediate Anchor with Actual Anchor Load in Start-Prof
The following training video shows how to create this model. It takes 2 minutes
Piping support plays a very crucial role in the proper functioning of piping systems. Pipe support carries the pipe weight with contents. To maintain the integrity of the piping system, A pipe must be supported following a proper pipe support span. Pipe support engineering is very critical for the success of any project as an accurate and judicious selection of piping support is required. Pipes as irregular space frames are not self-supporting so must be supported. Piping Loads are transmitted from pipe to supporting structures with the help of pipe supports. Proper pipe support knowledge during the layout stage is advantageous.
The piping system is a major part of any hydrocarbon industry. Proper pipe support knowledge during the layout stage is advantageous. Piping Loads generated due to Weight, Pressure, Temperature, or Occasional Events have to be transmitted from pipe to supporting structures with the help of appropriate pipe supports.
Difference Between Pipe Support and Pipe Restraint
The term “Restraints” is invariably used for pipe supports. However, there is little difference between pipe support and restraint. Pipe supports are used to support the piping system by carrying the vertical load whereas pipe restraints limit the movements of the pipe so take care of the horizontal loads. So from the definition, Simple Rest is pipe support but Guide and line stops are pipe restraints. Normally, All pipe restraints come in combination with piping supports. Pipe support and restraints, combined can be said pipe support systems. Henceforth, the term pipe support refers to the pipe support system.
Purpose or Functions of Piping Support
The various functions that pipe support serves are as follows:
For the proper working of the piping system, it has to be supported properly. The major purpose of pipe supports can be elaborated as follows:
Piping Supports for Carrying Weights
Pipe Supports are required to support the line during all conditions i.e. during operation as well as during testing. In the case of the vapor line, this difference will be very large due to hydro testing. Supports should be designed for this load (unless otherwise decided in the project). Sometimes the line is capable of having a longer span but the load coming on the support may be very large (especially with large-diameter pipelines). Then to distribute the load uniformly, the number of supports should be provided with a smaller span.
Notes:
It may be noted that during testing conditions there is no thermal load.
Piping Supports to Take the ‘Thermal or Expansion Load’
Whenever thermal expansion is restricted by pipe supports, it introduces additional load on the support. Support restraints must be designed to take this load in addition to all other loads.
Pipe Supports transfer the Occasional Earth Quake Loads
The earthquake is normally associated with horizontal acceleration of the order of 1 to 3 m/sec2. This is around 10% to 30% of the gravitational acceleration and introduces a horizontal force of about 10 to 30% of the vertical load (or supported mass). While designing pipe support, this should be taken care of.
When the pipe is subjected to moving machinery, pulsating flow, or very high-velocity flow, the pipe may start vibrating vigorously and ultimately may fail, particularly if the span is large. To avoid this it may be required to introduce additional supports at a smaller span apart from other requirements. It may not take axial load but must control lateral movements.
Carry the ‘Occasional Wind Load’:
Wind introduces lateral load on the line. This load is considerable, especially on large diameter pipes, and increases as line size is increased. This load tends to sway the line from its normal position and the line must be guided properly against it to avoid any kind of malfunction. In the case of large-diameter overhead lines, supported by tall support extended from the floor, wind load introduces large bending moments and should be considered critically.
Support the System during the ‘Transient Period of Plant & Standby’
Transient Condition: Transient condition refers to the start-up or shutdown condition in which one piece of equipment may get heated up faster and the other one gets heated slower. Due to this the expansion of one piece of equipment that in normal operation will get nullified, may not get nullified, and exert a thermal load on supports.
Fig. 2: Operating- Standby Condition
The standby condition is also similar. If there are two pumps, one being standby and both connected in parallel (as shown), the design and operating temperature of both connections will be the same. But the expansion of two parallel legs will not be nullified because at a time only one leg will be hot, and the other will be cold.
Noise due to pulsating flow can be reduced by using a silencer in the line. Still, if it is not below an acceptable level acoustic enclosure may be used. Piping Insulation over the line also helps in reducing the noise.
Support the System during ‘Maintenance Conditions’
When for maintenance certain equipment or components like the valve are taken out, the remaining system should not be left out unsupported.
Fig. 3: Figure showing support addition during maintenance activities
Referring to FIG-3, support ‘S1’ will be sufficient but when valve ‘V1’ is taken out for maintenance there will not be any support for the vertical leg. Therefore second support ‘S2’ may be required to take care of such conditions.
Piping Support for ‘Shutdown Conditions’
In shutdown conditions, all equipment may not be in the same condition as in operating conditions. For example, refer to the pump discharge line in Fig-4, Point A is resting, Point B & C are spring supports and Point D is the pump discharge nozzle. The springs are, designed based on weights considering the weight of fluid as well as pipeline and thermal movements. But during shutdown conditions, the fluid may be drained and the pipe becomes lighter. Hence, the spring will give an upward reaction and shall load the nozzle ‘D’ beyond the permissible limit.
Fig. 4: Use of Limit elements in spring during shut-down
In this case, a limit stop is used which will not allow Point C to move up above the horizontal level. (However, it will allow downward movement during operating conditions).
Use of Pipe Support for Erection Conditions
Erection conditions can be different than the operating conditions which should be considered while designing supports.
For example, for normal operation, a long vessel supported by three supports, S1, S2 & S3 is shown in FIG-5. If support S2 is higher then all load will act at S2 only. During an erection, if the level of S2 is lower then the entire load will be divided into two supports S1, and S3 only. Therefore the foundation of S1, S2 & S3 should be capable of taking such conditions.
Fig. 5: Vessel supported at three supports.
A pipeline supported by S1, S2 & S3 taken from the vessel is shown in above FIG – 6. During operation, there will be no weight at S2 & S3 (as it is the only guide), but wind conditions will be there. Loads due to such conditions must be considered while designing the supports.
Fig. 6: Pipe supported from vessel cleats/clips.
Codes and Standards for Piping Support Design
The following codes and standards are used for piping support design.
ASME B31.3: Process Piping Code ASME B31.3 is the base code for pipe-supporting requirements.
MSS-SP-58– Establishes the material, design, and inspection criteria to be used in the manufacturing of standard pipe supports. (USA)
MSS-SP-69- Provides recommendations for the selection and application of pipe supports. (USA)
MSS-SP-89- Provides recommendations for the fabrication and installation of pipe supports. (USA)
MSS SP-89: Provides fabrication and installation practices for Pipe Hangers and Supports.
MSS SP-90: Explains guidelines on the terminologies for Pipe Hangers and Supports.
MSS SP-77: Provides guidelines for Pipe Support Contractual Relationships.
BS-3974- Specification of pipe supports 1, 2, 3. (UK)
VGB-R-510 L- Standard supports guidelines. (Germany)
RCC-M- Specifications for pipe supports. (France)
MITI 501- Technical regulations (Japan)
Piping Support Design and Selection
The complex requirements of today’s piping support design are reliable functioning, maintenance-free operation, economical and easy installations, quick delivery of components, and low unit prices.
Major Criteria (Parameters) governing the pipe support hardware selection are
Pipe Support function,
Pipe Material for construction
The magnitude of expected operational and occasional load,
1. Types of Piping Supports based on the attachment with Pipes
Primary Piping Support
Pipe Supports that are directly attached to the pipe are called Primary pipe Supports. For example, Shoe support, Clamp Support, Guide Support, Line Stop Support, Trunnion Support, etc. The design and selection of primary pipe support (Fig. 1) is the responsibility of the piping team.
Secondary Piping Support
Pipe supports that are not directly attached to the pipe are called secondary piping supports. Support Brackets, Secondary Steel members on which pipe or primary supports rest, Tee Posts, Goal Posts, sleepers, racks, etc. are examples of secondary pipe supports. The design and selection of secondary pipe supports (Fig. 7) are the responsibility of the civil team.
Fig. 7: Primary vs. Secondary Support
2. Types of Pipe Supports based on Hardware Rigidity
Rigid Supports
Rigid supports provide rigidity at least in any one direction to restrict the pipe displacement in those direction(s) without any flexibility in that direction. Rigid pipe supports can serve as a Rest, Guide, Line Stop, or any combination of these. A fixed anchor is also a rigid support that provides rigidity in all six degrees of freedom. Typical examples of rigid supports are pipe shoe support, Rigid Strut Support, Trunnion Support, Saddle Support, etc.
Resilient Supports
Resilient or elastic supports use an elastic member for carrying pipe load and allow the pipe movement in the desired direction. Spring Hanger Supports which use a compression spring are known as Resilient Supports.
Adjustable Support
An adjustable support (Fig. 9) can be adjusted at the site during plant operation. These supports are normally provided for pipe and equipment alignment purposes. The first support from a pump suction and discharge pipe is provided with an adjustable pipe support. Sometimes the first support from a storage tank pipe system is also provided as adjustable support to adjust the support length in case of tank settlement.
3. Pipe Support Types Based on Piping Insulation
For hot insulated pipes, piping shoe/saddle supports are used for support. For cold insulated pipes, cold shoes (cradles) are used while supporting the pipes. For piping systems having acoustic insulation, special arrangements are made to isolate the vibrating pipe and supporting structure.
4. Types of Pipe Supports based on Weldng Requirements
Based on welding requirements, the supports may be welded or clamped. Welded pipe supports (shoe supports) are used on piping systems where welding is permitted. However, for certain piping systems, where welding is difficult or not allowed, clamped types of piping shoe supports are used.
5. Piping Supports based on the Function of the Support
Depending on the pipe support function, piping supports may be known as Rest, Guide, Hold Down, Anchor, Axial Stop, etc. These mentioned terms are defined in the pipe support terminology section.
6. Piping Supports Based on Pipe Orientation
Again, pipe supports can be differentiated based on the orientation of the pipe run. The support types and functions may be different when using the same support in a piping system of vertical or horizontal orientation. For example, a hold-down and guide support in a horizontal pipe will act as a hold-down and guide but the same in a vertical pipe may act as an all-around guide.
Piping Support Rules/Guide for Optimization
The following points need to be followed for optimized pipe support.
Group pipelines so as to minimize the number of structures needed solely to pipe supports.
Route lines close to the possible point of supports ( i.e. grade or structure which is provided for other purposes.)
Supports or braces are to be located at or near neutral points. (thermal null points)
Supports to be located as near as possible to concentrated loads such as valves, flanges, heavy actuators, etc.
Piping susceptible to vibration such as compressor connected lines to be supported independently. The use of hold-down or similar supports offers resistance to motion and provides some damping capacity to be used rather than hanging-type supports.
Piping connected to the top of the vessel to be advantageously supported from the vessel to minimize relative movement between supports and piping.
Always maintain the distance between supports as per the project specification recommended support span table. ( it is applicable to straight-run pipe length only.) When a change of direction in a horizontal plane occurs, it is suggested that the spacing be limited to ¾ times the standard pipe span.
Sufficient space to be provided to facilitate support assembly installation, inspection, and maintenance.
Fig. 8: Typical Piping Supports in Operating Plant
Piping Support Terminologies and Definitions
Brace or Bracing Support- A device primarily intended to resist displacement of piping due to forces other than thermal expansion and gravity.
Anchor Support or Fixed Support- A rigid restraint providing substantially full fixation is termed an anchor. Anchor support restricts all six degrees of freedom (three translational and three rotational) and does not allow the pipe to move in any direction. Normally Full-Welded or Bolted supports are called anchor supports. Full Anchor supports (Fig. 10) are rarely used in piping systems.
Stop- A device that permits rotation but prevents translatory movements of piping. A line stop or axial stop (Fig. 9) prevents pipe movement in the axial direction of the pipe. It is also known as a stopper.
Guide- A device that prevents the rotation of one or more axes is called a guide (Fig. 10). Guide supports (Fig. 8) prevent Lateral pipe movements.
Hold Down Support- A device that holds the pipe in position disallowing vertical upward movement or allowing decided upward movement. Hold-down supports prevent pipe disengagement from the Support structure.
Hanger- A support by which piping is suspended from a structure that functions by carrying the piping load in tension.
Rest Support or Sliding support- A device that is provided below piping to take gravity loads, offering no resistance other than frictional to horizontal motion. Rest supports (Fig. 8) do not allow the pipe to sag or move downward.
Damping element- A device that increases the damping of a system offering high resistance against rapid displacement, caused by dynamic loading while permitting essentially free movement.
Dummy Leg – Basically an extension pipe welded to an elbow, to provide support either as a resting, anchor, etc.
Fig. 9: Line Stop and Adjustable Trunnion Support
Popular Types of Piping Supports
The following types of piping supports are most popular in the oil and gas, and petrochemical industry.
Typically piping is supported at regular intervals on steel supports embedded in concrete foundation or directly on the steel structure. The distance between supports is the supporting span.
The basis for the calculation of the maximum support span
There are three main factors that affect the support span.
Supporting Criteria for Critical Lines: The support location is usually decided by piping designers. The type of support is decided by stress engineers. Primary attachments and secondary supports are selected by the designers whereas Line stop/Guide supports and gaps are informed by stress engineers.
Supporting non-critical lines
Senior designer to decide on support type and location based on
Support span
Guide span
Concentrated loads e.g. valves, instruments, etc
For the Long piping legs, the stress engineer is to be consulted
Supporting Insulated Pipes
No direct resting, pipe shoe to be provided
Minimum clearance between the insulation and the supporting structure shall be at least 50 mm.
Supporting of Non- Insulated Pipes
Directly rested except following
Pipes with sizes larger than DN 600
CS pipes with less than SCH 20
SS pipes with less than SCH 10S
The pipe that requires a slope
Dissimilar material to avoid galvanic corrosion
The pipe is to be supported on a pipe shoe to avoid damage to the pipe wall
Supports to be located on the upper half of the portion (i.e. above C.G. of pipe)
The vertical guide spacing is normally lower than the horizontal guide spacing
Clamped supports with weld-on shear lugs to avoid the pipe slipping under the clamp
Special Pipe Supports or SPS
The pipe supports that do not fall in the above category are called special pipe supports. Various kinds of special pipes are required for critical lines. The design is normally slightly complicated and a separate drawing is prepared for each special pipe support. For example
Spring hanger along with Guide
Hanger along with guide and line stop
Normal primary support requiring additional strengthening due to increased load, etc
The drawing is normally prepared by the pipe stress or pipe support engineer and checked by a civil engineer to ascertain the structural member load-carrying capability.
Differences Between Piping Support and Pipeline Supports
The main function of supports in both piping and pipeline systems is usually the same. However, there are certain distinct differences between the piping support and pipeline supports that are specified in the table below:
Feature/Aspect
Piping Supports
Pipeline Supports
Scale and Length
Used within facilities, handling shorter lengths.
Used for long-distance pipelines (hundreds or thousands of miles).
Environment
Controlled environments like plants and refineries.
Varied and often harsh environmental conditions (deserts, mountains, etc.)
Design Considerations
Managing weight, thermal expansion, and vibrations of pipes within a facility
Addressing large-scale thermal expansion, ground movement, and environmental factors over long distances.
Common Support Types
Hangers, saddles, guides, anchors, spring hangers, rigid hangers, and various complex arrangements.
Pipeline supports are usually simpler as compared to piping supports. Typical examples are sleeper supports, anchor blocks, above-ground piers, etc
Operational Context
Industrial facilities, refineries, power plants, processing complexes, etc
Long-distance pipelines, transporting fluids or gases across vast distances.
Support Span/Spacing
Usually less due to high temperature.
The support span in pipelines is comparatively large due to low-temperature applications.
Table 1: Piping Support vs Pipeline Supports
This table provides a clear comparison between piping supports and pipeline supports, highlighting
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