Both Cast iron and Cast steel are ferrous products containing iron and carbon as the major components. Cast iron is a ferrous material containing more than 2% carbon. On the other hand, Cast steel contains less than 2% carbon. So composition-wise the main difference is the amount of carbon present in cast iron and steel. Both cast iron and steel provide very good casting properties and are therefore used for a wide range of applications. Both cast iron and cast steel have very good mechanical properties. In this article we will explore the major differences between cast iron and cast steel; i.e Cast iron vs Cast steel.
Cast Iron vs Cast Steel
The main differences between cast iron and cast steel or Cast iron vs Cast Steel are provided below in a tabular format.
Cast Iron
Cast Steel
Cast Iron is very easy to cast due to its very good flowability and low shrinkage.
Cast Steel has less flowability and more shrinkage as compared to Cast Iron.
Cast iron is better in terms of corrosion resistance and resistance to mechanical wear.
Cast steel is better in terms of impact loads.
Cast iron is cheaper.
Cast Steel is costlier as compared to cast iron.
Cast iron has very good vibration-damping properties.
In terms of vibration damping, cast steel is inferior to cast iron.
Cast iron is more Brittle in Nature.
Cast steel is Ductile in nature.
The Machinability of cast iron is lower.
Cast steel provides good machinability.
The Weldability of cast iron is lower as compared to cast steel
Cast steel exhibits Good Weldability
Cast Iron has a relatively Low melting point
Cast Steel possesses higher melting points.
The main element in Cast iron in Iron and Carbon. Other elements can be present in a negligible amount.
Other alloying elements are present in cast steel in considerable amounts.
Table: Cast Iron vs Cast Steel
Cast Iron vs Cast Steel: Which one to Select?
Even though cast iron and cast steel have their own advantages and disadvantages; the selection between cast iron vs cast steel completely depends on the end use and application of the product.
Choosing Cast Iron:
If mechanical strength is of less importance then cast iron is a great choice.
Select cast iron if heat retention is required as cast iron has higher thermal capacities.
If the more compressive strength is required, go for cast iron.
If you need an economical item then choose cast iron as grey iron is cheaper to produce.
The use of Cast iron is normally limited to low-temperature and pressure applications.
Choosing Cast Steel:
If ductile behavior along with good strength is the requirement then choose Cast Steel.
If the end product is to be used in impact loading conditions use Cast Steel as it has higher toughness properties.
If you need very good thermal and electrical conductivity, select cast steel.
Choose Cast Steel for flexibility in design.
Use Cast Steel for high-temperature and pressure applications.
Cast Iron vs Cast Steel: How to Identify
There are various methods for the identification of Cast iron vs Cast Steel. Some methods are listed below:
Chemical Analysis: This is the best method to determine if a specimen is Cast iron or Cast Steel. The analysis will specifically determine the elements and percentage of carbon present from which steel and iron can easily be distinguished.
Spark Test: One of the easier methods to check cast iron vs cast steel is by spark test. The specimen can be grinded using an abrasive wheel and looking at the spark pattern and spark color, an experienced person can inform if the material is Cast iron or cast steel. Steel will most often give off bright yellow sparks, whereas iron produces more red or orange sparks.
In cast iron, the spark color tends to be the brightest at the end of the spark whereas for cast steel the spark originates at the grinding wheel and extends outwards.
Drilling Test: Drilling cast iron vs cast steel looks completely different. In cast iron, the generated chips are of very short length and resemble graphite flakes. On the other hand, the chips of cast steel form wire-like chips.
Grain Structure: Cast iron vs cast steel can also be identified by looking at the grain structures of the broken parts. The grain structures for cast iron and cast steel are completely different and one experienced engineer can easily differentiate between the two.
What is a Globe Valve? Working, Parts, Types, symbols
Globe valves are linear motion closing-down valves used to start, stop or regulate the flow using a closure member referred to as a disc. The globe valve disk can completely close the flow path or can be removed entirely. The seat opening changes proportionately with the travel of the disc which is ideal for duties involving flow regulation. Globe valves are most suitable and widely used for throttling and controlling fluid flow and are generally employed in small-size piping.
A globe valve uses a linear motion for moving a disc (closure member) into or out of the seating surface. Globe Valves form a globular-shaped cavity around the port region and hence the name. The disc can be of various shapes and moves perpendicular to the globe valve seat. This disc movement helps in valve opening and closure. Globe valves in general are used for pipes of size 8 inches or less. In this article, we will explore the globe valve types, parts, working principles, functions, symbols, applications, advantages, and disadvantages.
In addition, depending on the design of the seat and disc, the seating load of globe valves can be positively controlled by a screwed stem. The sealing capacity of the globe valve is high. They can be used for on-off duty if the flow resistance from the tortuous flow passage of these valves is acceptable. Some globe valves are also specifically designed for low flow resistance for use in on-off duty. Because of the short travel distance of the disc between the open and closed positions, globe valves are ideal if the valve has to be opened and closed frequently. Thus, globe valves can be used for a wide range of duties.
Globe Valve Parts
A typical globe valve constitutes of the following parts:
Valve Body (6): Globular shape
Bonnet (7)
Disc or Plug (10)
Stem (9)
Yoke
Gland bushing and flange (3)
Seat ring (11)
Yoke Sleeve (2)
Gland Bolts and Nuts (4)
Handwheel (1): Mechanical Actuator
Back Seat
Pressure Seal Gasket
Packing
Typical Globe Valve
Types of Globe Valve
To meet the varied range of work duties at the lowest cost, numerous variations of globe valves are designed. The three most common types of globe valve configurations available for industrial use are
Tee Pattern (T-Type) Globe valves possess the lowest flow coefficient and a higher pressure drop. In severe throttling services, such globe valves can be used. If the pressure drop is not a concern and throttling is required, the Tee type globe valve will be a good choice.
Wye Pattern Globe valves can be cracked open for long periods without severe erosion. They offer very low resistance to flow. For start-up operations, Y-type globe valves are extensively used.
Angle Pattern Globe valves turn the fluid flow in a perpendicular direction without the use of an elbow. For pulsating flow services, angle-type globe valves are used because of their capability of handling the slugging effect.
Globe Valve Patterns
Types of Globe Valves depending on Body Bonnet Connection
Based on body-bonnet connections the following types of globe valves are available:
Screwed bonnet: Inexpensive, simple design.
Bolted bonnet: most popular and widely used. Need a gasket for body and bonnet joint sealing.
Welded bonnet: popular where no disassembly is required. lighter weight.
Pressure-Seal bonnet: for high-pressure applications, this type of globe valve is used.
Flanged bonnet: Can be designed for any size and operating pressure. However, with an increase in pressure, this type of globe valve becomes heavy and bulky.
Union-ring bonnet: A separate screwed union ring is required to hold the bonnet to the valve body. This type of globe valve construction is usually limited to up to 3 inches in size.
Globe Valve Seating
Globe Valves are provided with either metal seats or soft seat arrangements. To keep the seating stresses uniform, a number of variations of seating design are made. The following figure shows the most frequently employed seating configurations in globe valves.
Common Seating Configurations in Globe Valve
The Function of a Globe Valve
The main function of a globe valve is to start, stop, or regulate the flow. As the globe valve opens the disk moves upwards allowing the fluid to flow proportionally. In an open position, the valve stem rises and popped out at the top. Globe Valve is normally used in smaller sizes; mostly 12 inches or less in sizes. With an increase in the globe valve size, the power required to operate increases. In normal practice, a globe valve works as an on-off valve, but it can be used for throttling purposes as well.
Working Principle of Globe Valve
Refer to the cross-sectional image of the globe valve shown below. A globe valve is comprised of a movable disk and a stationary ring seat in a spherical body. The seat of a globe valve is in the middle of and parallel to the pipe, and the opening in the seat is closed off with the disk. As can be seen from the image, when the handwheel is rotated manually or by an actuator, the disc movement is controlled (lowered or raised) by means of the valve stem. When the globe valve disc seats over the seat ring, the flow is completely stopped.
Globe Valve Working
But when the disk is lifted the flow begins as the upward movement of the disc creates space for the fluid.
Globe Valve Disks
The position of the globe valve disk and seat can be described schematically as follows:
Globe Valve Disc position
The Disc of a globe valve is made in three basic designs; Conventional Disc (or Ball Disc), Composition Disc, and Plug Type Disc.
Ball Disk:
In the conventional type of disc, the seat and disc construction is made of a ball-shaped metal disc. This possesses a short taper and it easily fits against a flat-surfaced seat in the body. For low-pressure services, this type of globe valve is quite popular and economical. Even though the ball disc is capable of throttling flow, but still primarily used to start and stop the flow.
Composition Disk:
A hard, nonmetallic insert ring is used on the disc of a composition disc design to create a tighter closure. For high-temperature and pressure applications, composition disks are used due to their sufficient resilience and erosion resistance. The composition disc globe valve is basically an improved version of the conventional disk-type globe valve. Composition discs can be replaced or repaired.
Types of Disks of a Globe Valve
Plug Disk:
The plug disc is the best among all three globe valve disk designs and is suitable for throttling services. A long tapered metal plug is made into a plug disc that seats into a cone generating a wide seating surface.
Disc – Stem Configuration
The stem of a globe valve can rotate or not rotate while raising or lowering the disc depending on the design. Accordingly, various disc–stem configurations are available like
Rotating Stem with Integral Disc
Rotating Stem with Non-Integral Disc
Non-Rotating Stem with Integral Disc
Non-Rotating Stem with Non-Integral Disc
Because of the simplicity of design, most globe valves incorporate a rotating stem.
Globe Valve Flow Direction
For low-temperature applications, the flow direction in a globe valve is installed so that pressure acts under the disk. This design helps in easy operation, protects the packing, and eliminates a certain amount of erosive action to the seat and disk faces. Whereas, for high-temperature steam service, globe valves are positioned such that the pressure is above the disk. This will avoid the stem contraction upon cooling that may tend to lift the disk off the seat.
Globe Valve Symbol
The following globe valve symbol is quite popular in the piping industry. These are used in P&IDs to differentiate a glove valve from other valve types.
Glove Valve Symbol
The following image shows the typical globe valve symbol used to denote a bypass valve in the control station.
Globe Valve in Control Valve By-pass
Globe Valve Patterns
Globe Valves are available in three body patterns.
Standard pattern (T-Pattern or Z-Pattern)
Angle Pattern
Oblique Pattern (Wye Pattern or Y – Pattern)
Standard Pattern or T/Z– Pattern globe valves
This is the most common globe valve body pattern. The horizontal setting of the seat allows the stem and disk to move perpendicular to the direction of the fluid flow. This design provides the highest resistance to fluid flow among all of the available patterns. This standard pattern globe valve design has the lowest flow coefficient and the highest pressure drop. For severe throttling services and applications where pressure drop is not of much concern like in bypass lines around a control valve, this type of globe valve is commonly used.
Z-type globe valve diagram
Oblique Pattern or Y–Pattern globe valve
The oblique Pattern globe valve body design is suitable for applications requiring low-pressure drop. Their oblique pattern design reduces the resistance to the flow of the globe valve to a minimum. The seat and stem being angled at approximately 45 degrees, provides a straighter flow path at full opening and offer the least flow resistance.
Y-type globe valve diagram
Angle Pattern globe valve
Angle pattern globe valve body design is manufactured by modifying the basic standard pattern globe valve. The valve ends of this type of globe valve are perpendicular or at an angle of 900, and fluid flow occurs with a single 900 turn. As compared to the oblique pattern globe valves, they have a slightly lower coefficient of flow. For applications having pulsating flow because of their capability to handle the slugging effect, angle pattern globe valves are used.
When a globe valve is required near a pipe bend, the angle pattern globe valve body offers two advantages. First, the angle pattern body provides a greatly reduced flow resistance. Second, the angle pattern design saves the requirement of a pipe fitting and joint.
Angle-type globe valve diagram
Advantages of Globe Valve
The main advantages of globe valves can be summarized as follows:
Good sealing capability.
Moderate to good throttling capability.
Shorter stroke.
Provide a wide range of capabilities as available in tee, Wye, and angle body styles.
Machining and resurfacing the seats are easy.
The globe valve can be used as a stop-check valve by modifying the design slightly.
Disadvantages of Glove Valve
The globe valve disadvantages can be listed as follows:
Higher pressure drops due to many directional changes.
Greater force or power requirement to seat the valve.
Throttling flow under the seat and shutoff flow over the seat.
Applications of Globe Valve
Globe valves can be used in a wide range of services; both low-pressure and high-pressure fluid services. The typical applications of globe valves are:
Bernoulli’s principle provides a relationship between the pressure of a flowing fluid to its elevation and its speed. The conservation of kinetic, potential, and flow energies of a fluid stream and their conversion to each other is dictated by the Bernoulli principle. This principle is widely used in the study of the flow of water, air, or any other fluids having low viscosity. Many real-life engineering problems related to fluid flow can be easily solved by applying Bernoulli’s principle. This is the reason that Bernoulli’s principle is quite popular and studied in engineering and physics. This principle is deduced by Daniel Bernoulli and as per his name, it is widely known as Bernoulli’s principle.
Bernoulli’s Equation
Bernoulli’s equation provides the mathematical basis of Bernoulli’s Principle. It states that the total energy (total head) of fluid along a streamline always remains constant. The total energy is represented by the pressure head, velocity head, and elevation head.
The pressure head signifies the height of a column of fluid and is represented by P/ρg; the Velocity head signifies the kinetic energy and is represented by V2/2g, and the Elevation head signifies the potential energy and is represented by z. So, As per Bernoulli’s equation
(P/ρg)+(V2/2g)+z=Constant
The equation explains that, if an increase in the speed of a fluid occurs, there will be a decrease in static pressure or a decrease in the fluid’s potential energy. For flow inside horizontal pipes, where elevation head z is constant; the velocity increase will cause a decrease in pressure.
Assumptions in Bernoulli’s Equation
The following assumptions are made for deriving the above-mentioned Bernoulli’s equation:
The fluid is ideal and it does not have any viscosity.
Net frictional forces are negligible.
The fluid is moving or flowing through a pipe or channel.
The flow is incompressible and steady.
The is no rotation in the flow.
There is no heat transfer in the streamline.
Derivation of Bernoulli’s Equation
Refer to the image shown below that indicates the motion of a fluid particle of length ds in the s direction.
Applying Newton’s second law in that moving fluid particles in a steady flow we get,
Now considering the assumptions mentioned above, the significant forces that will be acting in the s-direction are the pressure and the component of the weight of the particle in the s-direction.
Therefore, we can write the above equation as:
P dA − (P + dP) dA − W sin 𝜃 = mV (dV/ds );
where 𝜃 is the angle between the normal of the streamline and the vertical z-axis at that point, m = 𝜌V = 𝜌 dA ds is the mass, W = mg = 𝜌g dA ds is the weight of the fluid particle, and sin 𝜃 = dz/ds. Substituting we get,
−dP dA − ρg dA ds (dz/ds) = ρ dA ds V (dV/ds)
After simplification, we get
−dP − ρg dz = ρV dV
Now, V dV = 1/2 d(V2) and dividing each term by 𝜌 gives
dP/ρ + 1/2 d(V2) + g dz = 0
Integrating we get,
P/ρ +V2/2 + gz = constant
Dividing by g we get,
(P/ρg)+(V2/2g)+z=Constant
This is the famous Bernoulli equation, widely used in fluid mechanics for steady, incompressible flow along a streamline in inviscid regions of the flow.
Applications of Bernoulli’s Equation
The Bernoulli equation and principle find a wide range of applications in engineering fluid dynamics. This theory is applied to designing aerospace wings and for designing pipes for hydroelectric plants. Bernoulli’s equation is popularly used to:
The following examples of Bernoulli’s principle are widely popular.
Bernoulli’s Equation for Pump Sizing:
The volute in the centrifugal pump casing converts the velocity of the fluid into pressure energy by increasing the flow area. Here the conversion of kinetic energy into pressure energy is according to Bernoulli’s equation.
The pump head requirement is also decided by applying Bernoulli’s equation.
Design of Ejectors:
The conversion of the pressure energy of the motive fluid into the kinetic energy inside an ejector follows the principles of Bernoulli’s equation.
Pressure measuring instrument, Pitot Tube also works following Bernoulli’s principle.
Bernoulli’s equation to design the Automobile Carburetor:
Automobile Carburetors are a good example of Bernoulli’s equation. Bernoulli’s principle is used to meter the airflow inside the carburetor. The faster the air flows, the lower the static pressure, and the higher the dynamic pressure that decides the fuel intake into the airstream.
Working of Siphons:
Widely used Siphons also follow Bernoulli’s equation to evacuate or remove fluids from a container.
Application in Hydro-power Generation:
Hydroelectric engineers decide the water velocity from mountain reservoirs by knowing the elevation changes and using Bernoulli’s Principle.
Bernoulli’s Principle for Generating the Lift Force in Aeroplanes:
The top part of an airplane wing is curved while the bottom part is designed as a flat surface. This results in lower pressure on the top of the wing as compared to the bottom of the wing. This generated pressure difference (according to Bernoulli’s principle) creates the lift force for the plane.
Birds also fly in the sky using the same Bernoulli’s Principle.
Venturi meters are instruments for fluid flowmeasurement. It has a converging section that gives an increase in the flow velocity with a corresponding drop in pressure from which the flow rate can be calculated. The reduction in the fluid pressure that occurs when a fluid moves through a constricted passage is known as the Venturi effect. Venturi meters are widely used wherever there is a need for fluid flow measurement, specifically in water, chemical, and oil industries. Depending on the application and size requirements, industrial venturi meters are constructed in various forms. These versatile instruments are known for longevity, long performance, and reliability. In this article, we will discuss about the following:
Definition of Venturimeter
Venturimeter Diagram and Parts
Working Principle of Venturi meter
Venturimeter Formulas
Co-efficient of Discharge for Venturimeters
Venturimeter Types
Applications, Advantages, and Disadvantages of Venturimeters
Difference between Venturimeter and Orificemeter, and
Many more.
What is a Venturimeter? Venturimeter Definition
Venturimeter is a type of flowmeter that works on the principle of Bernoulli’s Equation. This device is widely used in the water, chemical, pharmaceutical, and oil & gas industries to measure the flow rates of fluids inside a pipe. The pipe cross-sectional area is reduced to create a pressure difference which is measured with a manometer to determine the rate of fluid flow. So, the venturi meter is a differential head type flowmeter that converts pressure energy into kinetic energy.
The principle of the Venturimeter was demonstrated by Giovanni Batista Venturi (Hence the name Venturimeter), But it was first used in practical metering applications by Clemens Herschel. In this article, we will explore the parts, working principles, equations, and applications of the Venturimeter.
Venturimeter Diagram and Parts
A venturimeter consists of four parts:
Cylindrical Inlet Section
Conical convergent Section
Cylindrical throat and
Conical divergent outlet
Fig. 1 below shows a typical venturimeter diagram with its parts.
Fig. 1: Typical Venturimeter Diagram with Parts
There are two tappings on the venturi meter for pressure measurement; the upstream pressure tapping is located at a distance of one-half of pipe diameter (D/2) upstream of the convergent entry, while the downstream pressure tapping is located in the throat (d/2) as shown in Fig. 1.
Cylindrical Entrance Section: Venturimeter entrance is a straight cylindrical section with a length equal to 5 to 8 times the pipe diameter.
Convergence Conical Section: In this section, the venturi meter tube diameter gradually decreases. The conical angle is normally 210 ± 20. While the liquid flows inside the venturimeter, the velocity of fluid increases at the expense of a decrease in pressure.
Cylindrical Throat: Throat consists of the minimum venturemeter diameter. In the throat section, the velocity is maximum and pressure is minimum. Normally, throat diameter = 1/3 to 1/4th of inlet pipe diameter.
Diverging Conical section: At this section of venturimeter, the tube diameter gradually increases. So, the pressure is built up again to the original inlet pressure. The cone angle is 5-70. British Standard BS-1042 specifies two conical angles, 5–70 and 14–150 for the outlet cone.
Materials for Venturimeter
Small-size venturimeter are made of brass, glass, or bronze and large venturimeters are made of cast iron, steel, or stainless steel.
Working Principle of a Venturimeter | How Does a Venturi Meter Work?
When a fluid flows through a venturimeter, it accelerates in the convergent section and then decelerates in the divergent section. The pressure difference between an upstream section and the throat is measured by a manometer. Using that differential pressure, applying Bernoulli’s Equation and Contininuity Equitation the volumetric flow rate can be estimated. In the next section, the equations of venturimeter to find the discharge value are discussed.
Venturimeter Equations | Formulas for Venturi Meters
Bernoulli’s principle states the relation between pressure (P), kinetic energy, and gravitational potential energy of a fluid inside a pipe. The mathematical formula of Bernoulli’s equation is given as:
Where,
p= pressure inside the pipe
ρ =density of the fluid
g =gravitational constant
v = velocity
z=elevation or head
a = cross-sectional area of the pipe
d= diameter of the pipe
Suffixes 1 and 2 are used to denote two different areas; 1 denotes the cylindrical inlet section and 2 denotes the throat section.
Now as the pipe is horizontal; there is no difference in the elevation of the pipe centerline; So, z1=z2. Re-arranging the above equation we get the following:
(p1-p2)/ρg = (v22-v12)/2g
(p1 – p2)/ ρg is the difference of pressure heads in sections 1 and 2 which is equal to h that can be measured in the differential manometer. So the above equation becomes
h=(v22-v12)/2g……….eqn. 1
Now applying continuity equations between the same sections 1 and 2, we get
a1v1=a2v2 or v1=(a2v2)/a1
Putting this value of v1 in eqn. 1 and solving we get,
So, the rate of flow through the throat (Q) can be calculated as Q=a2v2; Substituting the above value of v2 we get,
This Q represents the theoretical discharge of Venturi Meter in ideal conditions. But in actual practice, there will always be some frictional loss. Hence, the actual discharge will always be less than the theoretical discharge. So, to calculate the actual discharge, the above Q value is multiplied by Cd, called the Coefficient of discharge of venturimeter. So the actual flow rate through the throat of the venturimeter will be given by the following equation.
Coefficient of Discharge of Venturimeter (Cd)
The coefficient of discharge for Venturimeter, Cd is defined as the ratio of the actual flow rate through the venturi meter tube to the theoretical flow rate. So the venturi meter discharge coefficient is given by:
Cd=Qact/Q
As Qactual will always be less than Qtheoretical due to frictional losses, the value of Cd is always less than 1.0.
The typical range of the discharge coefficient of a Venturi meter is 0.95-0.99 but this can be increased by proper machining of the convergent section. The value of venturimeter discharge coefficient differs from one flowmeter to the other depending on the venturimeter geometry and the Reynolds number.
ISO-5167 code provides the values of venturimeter discharge coefficients. For accurate flow measurement, normally straight length requirement upstream and downstream of venturimeter is specified.
Types of Venturimeters
Normally three types of venturimeters are available:
Horizontal Venturimeter: This type of venturimeter has the highest kinetic energy and the lowest potential energy.
Vertical Venturimeter: This type has the maximum potential energy and the minimum kinetic energy.
Inclined Venturimeter: Both potential and kinetic energy are in between the above two types mentioned.
Applications of Venturimeter | Venturimeter Uses
Venturimeters find wide application in fluid industries. The major application of venturimeters include
Used in Engine Carburetors (Automobile Sector) to measure airflow
Used in process industries (Process and Power Piping Industries) to measure and control process flow.
In the medical industry, blood flow in the arteries is measured by venturimeters.
Measures the fluid flow inside pipelines (Oil & Gas Industries)
Broadly the use of venturimeters are versatile and widely used in the following industries:
Water treatment plant
Chemical processing
HVAC systems
Power Generation systems
Oil and gas industry
Advantages and Disadvantages of Venturimeter
Advantages of Venturimeter:
They provide accurate results.
The accuracy of venturimeter is not dependent on temperature and pressure inside the pipe.
No moving part.
Very low energy loss.
Wide applicability for Water, suspended solids, gases, slurries, chemicals, dirty liquids, etc.
High discharge coefficient and very low-pressure drop.
Venturimeters can be installed in a horizontal, inclined, or vertical direction.
Very little chance of being clogged.
The pressure recovery of venturimeter is very high. The discharge pressure is almost near to inlet pressure.
Disadvantages of Venturimeter:
Venturi meters are large in size; so difficult to install where there is space constraint.
Expensive as compared to other types of flowmeters
Limited range of flow measurement
Not suitable for very small diameter pipes.
Codes and Standards for Venturi Meter
The codes and standards that provide guidelines related to venturi meters are
ISO 5167
ISO 9300
AWWA M33
ISO TR 15377
BS 1042
ASME MFC-8M
ASTM D2458
AGA 9
Installation of a Venturi Meter
Proper installation of a venturi meter is the key to the ideal operation. So, the installation of venturi meters must be performed following manufacturer guidelines. Normally, the following guidelines to be followed while installing a venturi meter in a piping or pipeline system:
The flow direction arrow in the venturi meter should be checked and installed to agree with the direction of the flow.
Flanges at the venturi meter ends should be properly aligned with the piping flanges.
Pipe Support should not be placed on venturi meters.
Installation tolerances should be within industry standards.
Pressure taps should be oriented horizontally for liquid service applications.
Fig. 2: Venturi Meter Pressure Connections
Venturi meter Upstream and Downstream Pipe Straight Leg Requirement
For proper functioning and accurate results, the flow through the venturi meters should stabilize. This calls for minimum straight pipe length requirements upstream and downstream of the venturi meter. Depending on the type of fitting, type of venturi meter, and beta ratio (the throat diameter divided by the inlet diameter) the straight leg requirement varies. The following image (Fig. 2) provides a sample table that provides typical strength leg requirements while installing a venturi meter in a piping system.
Fig. 3: Venturi meter Piping Requirements
Design of Venturimeters
Even though standard classical venturimeter designs need a bit more space, the significant benefit is that their design can easily be modified to fit any requirement. Over the last centuries, venturimeter design has undergone significant changes and two specific designs have contributed in significant impact on Venturi metering; They are:
Modifies Short form Venturimeters, and
Insert Venturi meters.
Modifies Short form Venturimeters: Patented by Dezsoe Halmi, these designed forms of venturimeters are highly accurate, have low headloss, and need no upstream/downstream straight length requirements. Modifies Short-form Venturimeters are more suitable for asymmetric flow patterns due to their overall short length.
Insert Venturi Meters: Insert venturimeter design is somewhat similar to the shape of a Classical Venturi but its profile is entirely inside the pipeline. They utilize a static low-pressure throat tap that sense pressure perpendicular to the axis of the flowing line fluid.
Difference between Venturi meter and Orifice meter | Venturimeter vs Orifice Meter
Venturi meters and orifice meters are both types of differential pressure flow meters that are commonly used to measure the flow rate of fluids in pipes. While they are similar in some respects, they differ in several important ways, including their design, performance characteristics, and applications.
Venturi meters are typically designed with a tapered throat section that gradually reduces the cross-sectional area of the pipe. As the fluid flows through the throat, its velocity increases and its pressure decreases, creating a pressure differential between the upstream and downstream sections of the meter. This pressure differential is proportional to the square of the flow rate and can be measured using pressure gauges or transducers.
In contrast, orifice meters use a flat plate or disc with a precisely measured hole in the center to constrict the flow of fluid in the pipe. This creates a pressure drop that is proportional to the square of the flow rate and can be measured in the same way as with a venturi meter.
Here are some key differences between Venturi meters and orifice meters:
Design: A Venturi meter has a gradual taper to the throat section, while an orifice meter has a sharp-edged disc or plate with a hole in the center.
Pressure recovery: The pressure recovery in a Venturi meter is better than in an orifice meter, meaning that the pressure downstream of the meter returns closer to the upstream pressure.
Accuracy: Orifice meters are generally less accurate than Venturi meters, particularly at low flow rates, where the turbulence caused by the sharp-edged orifice plate can create errors.
Applications: Venturi meters are often used for high flow rates and in systems where pressure drop is a concern, while orifice meters are used in a wider range of applications, including lower flow rates and where cost is a concern.
Installation: Venturi meters require longer straight sections of pipe upstream and downstream of the meter to achieve accurate readings, while orifice meters can often be installed with less straight pipe.
Overall, the choice between a Venturi meter and an orifice meter will depend on the specific requirements of the application, including flow rate, accuracy, pressure drop, and cost.
The major differences between a venturimeter and an orifice meter can be tabulated as follows:
Orifice meters, on the other hand, need relatively lower space.
In venturimeter, the Energy Loss is less.
Orifice meters have comparatively more energy loss.
Venturimeters are quite expensive.
Orifice meters are comparatively cheaper.
High discharge coefficient.
Low coefficient of discharge.
Venturimeters provide High-Pressure Recovery.
Pressure Recovery in the Orifice meter is relatively less.
Venturimeter vs Orificemeter
FAQ on Venturimeters
1. What is a venturi meter used for?
A venturi meter is used to measure the flow rate of fluids in a pipe. It is widely employed in various industries, including water treatment, chemical processing, oil and gas, and HVAC systems. By measuring the pressure difference between the inlet and the throat of the venturimeter, it provides accurate flow measurements, which are essential for process control and optimization.
2. How does a Venturi device work?
A Venturi device works on the principle of the Venturi effect, which states that as a fluid flows through a constricted section of a pipe, its velocity increases, and its pressure decreases. The venturimeter has a convergent section that narrows into a throat and then diverges. Pressure taps are located before and at the throat. The difference in pressure between these points is used to calculate the flow rate of the fluid using Bernoulli’s equation.
3. What is the working principle of the venturi effect?
The Venturi effect is based on Bernoulli’s principle, which states that an increase in the velocity of a fluid results in a decrease in its pressure. As fluid flows through the constricted throat of the venturimeter, its velocity increases, causing a drop in pressure. This pressure drop is measured and used to determine the flow rate of the fluid.
4. Why is it called a venturi?
The device is named after Giovanni Battista Venturi, an Italian physicist who first described the principle in the 18th century. Venturi’s research on the effects of fluid flow through constricted sections of pipes led to the development of this flow measurement device.
5. What is the ratio of venturi meter?
The ratio of a venturi meter typically refers to the area ratio between the pipe’s diameter at the inlet and the throat. This ratio is crucial for determining the meter’s accuracy and performance.
6. What is the ISO standard for venturi meter?
The ISO standard for venturi meters is ISO 5167. This standard specifies the requirements for the design, installation, and testing of venturi meters used for measuring the flow of liquids, gases, and steam. It ensures that the venturi meters meet international standards for accuracy and reliability.
7. What size is a Venturi pipe?
The size of a Venturi pipe varies depending on the specific application and flow rates required. Venturi meters can be designed for a wide range of pipe sizes, from small laboratory setups with diameters of a few millimeters to large industrial pipes with diameters exceeding several meters. The size is typically chosen based on the fluid flow rate and the accuracy requirements.
8. What is the coefficient of Venturi?
The coefficient of a venturi meter, often referred to as the discharge coefficient (Cd), accounts for losses and deviations from the ideal flow. It is a dimensionless number that varies with the design of the venturi meter and the characteristics of the fluid. It is used to adjust the theoretical calculations to match the actual flow measurements. The value of Cd is usually determined through calibration and testing.
9. What is the advantage of venturimeters?
Venturi meters offer several advantages:
High Accuracy: They provide accurate flow measurements with minimal pressure loss.
Durability: They have no moving parts, which reduces maintenance and wear.
Wide Range: They are suitable for measuring a broad range of flow rates.
Versatility: They can measure various fluids, including liquids, gases, and slurries.
Minimal Pressure Loss: Compared to other flow measurement devices, venturi meters exhibit relatively low-pressure drops, which is advantageous for maintaining system efficiency.
Video Tutorial on Venturimeters
The above contents are explained in the following video tutorial on Venturimeters titled “What is a Venturimeter?”
Pipe Weight Calculation is a very important process in piping engineering. Pipe weight is directly related to its thickness (Pipe Schedule). The more the pipe thickness or pipe schedule, the more will be the pipe weight. The more the pipe weight, the more will be its rigidity and less flexibility. More pipe weight means more cost of procurement. More pipe weights add more loads on the pipe supports requiring more robust structural member requirements. So, we can say pipe weight is related to overall plant cost in some way. In this article, we will explore pipe weight calculation formulas and methodologies.
Calculating pipe weight is quite simple and fast. The mathematics behind the pipe weight is very easy. The steps and formula for pipe weight calculation are explained below:
Pipe Weight Calculation Formula
To calculate the mass of any object we can use the following formula
Mass (M)= Density (D) X Volume (V) …(eqn. 1)
Pipe weight is also calculated using the same equation. Pipe weight is normally expressed in Pipe Weight per meter of length or Pipe Weight per foot of length. Also, there are two other terms associated with pipe weight calculation. These are
Empty Pipe Weight Calculation and
Water-Filled Pipe Weight Calculation.
Empty Pipe Weight Calculation
Empty pipe weight means pipe weight without any content inside it. So, it is the weight of the metal present in the pipe. Refer to Fig. 1 below:
Fig. 1: Reference image for Pipe Weight Calculation
So following eqn. 1 above we have to calculate the volume (V) of the pipe first and then we have to multiply the calculated volume by pipe material density (D) in a consistent unit. To calculate the volume of the pipe we need the following parameters:
Pipe Thickness (T) (Obtained from ASME B36.10M / ASME B36.19M), and
Length of Pipe (=1 as pipe weight is expressed in pipe weight per unit length)
The inside diameter (ID) of the pipe can easily be calculated as ID=OD-2T
Pipe Metal Cross Section is calculated as Π (OD2-ID2)/4
The volume (V) of the pipe is calculated as V=Pipe metal cross-sectional area X length of pipe = {Π (OD2-ID2)/4} * 1
CS Pipe Weight Calculation in Kg/m
Let’s calculate the weight of a 6-inch CS pipe with Sch. 40 as pipe thickness. From ASME B 36.10M
Pipe OD=168.3 mm
Pipe Thickness=7.11 mm
Hence, ID=168.3-2*7.11=154.08 mm
Metal Cross Sectional Area=(Π)*(168.32 – 154.082)/4=3600.4565 mm2
So volume for a unit length of pipe=3600.4565 * 1= 3600.4565 mm3 =(3600.4565/1000000) =0.0036004565 m3
So now we have to multiply this volume by CS pipe density (7850 kg/m3) to get the actual weight of 1 m of pipe length.
So the Metal weight of 1 m of Pipe length=0.0036004565*7850=28.26358356 Kg.
To calculate the pipe weight for lengths more than 1 meter, simply multiply the above value by the actual length of the pipe.
Similarly, we can calculate an empty pipe weight per foot of length by considering all the above values in a consistent FPS unit system.
Water-Filled Pipe Weight
Water-filled pipe weight is required to calculate the loads during hydro testing. For the structural supporting design of non-critical lines, pipe loads are calculated or approximated based on water-filled pipe weight.
To calculate the content (water) weight inside the pipe we have to multiply the water density (1000 Kg/m3) with internal pipe cross-sectional volume 1*(Π * ID2)/4.
For the above pipe under consideration, the internal pipe cross-sectional area=Π*154.082/4=18645.86008 mm2=18645.86008/1000000=0.01864586006 m2
So the weight of water content inside the pipe per meter of length=1000*0.01864586006=18.64586 Kg/m.
Now add this content weight with the metal pipe weight to get the total water-filled pipe weight. So,
Water-filled Pipe Weight (Kg/m)=Weight of empty pipe (Kg/m)+ Weight of Content (Kg/m)
In the above example, Water filled pipe weight=28.26+18.65=46.91 Kg/m
By simply multiplying the above value (46.91 Kg/m) by the actual pipe length you can calculate the water-filled pipe weight in Kg.
Pipe Weight Calculator
I have prepared one Pipe weight Calculator in kg/m using the above-mentioned steps and attached it here for your consideration. The metric unit system is used in the Pipe Weight Calculator excel-sheet. Simply, input your data in yellow highlighted boxes and get the actual calculated values at ease.
You can download the pipe weight calculator by clicking the download button shown below.
The following inputs will be required for using the above pipe weight calculator or any other online pipe weight calculator:
Pipe Outer Diameter
Pipe Thickness
Density of Pipe Material
This Pipe Weight calculator can be used to calculate the weights of any piping material by changing the pipe density to the corresponding pipe material density. So Steel pipe weight, Cast iron pipe weight, PVC pipe weight, Copper pipe weight, GRE Pipe Weight, Aluminum Pipe Weight, etc. can easily be calculated using the attached Pipe Weight calculator.
The above-mentioned pipe weight calculation steps are suitable for round pipes. However, as pipes are available in square and rectangular shapes, the methodology for pipe weight calculation for square or rectangular pipe will be different in the way the metal cross-sectional area will be calculated. However, the basic pipe weight calculation equation as mentioned in Equation 1 will still be valid.
Density of Common Pipe Materials to Use in the Pipe Calculation Formula
As you can see, pipe density is one of the most important parameters used in the calculation of pipe weight. Table 1 below provides the density of some of the common pipe materials as a ready reference
Pipe Material
Approx. Density (Kg/m3)
Pipe Material
Approx. Density (Kg/m3)
Carbon Steel
7850
Bronze
8800
Stainless Steel
7700
Titanium
4540
Aluminum
2700
Cast Iron
7000
Brass
8600
Nickel
8900
Copper
8920
PVC
1450
Table 1: Density of Common Pipe Materials in Kg/m3
Pipe Weight Calculation for Square and Rectangular Pipes
For a square pipe with a length of side A and thickness t, the metal cross-sectional area will be {A2-(A-2t)2}. Once you calculate the metal cross-sectional area, multiply it by the pipe material density to find the weight per unit length of the square pipe.
In a similar way, the metal cross-sectional area for a rectangular pipe with length A, width B, and thickness t can be calculated as [A*B-{(A-2t)*(B-2t)}]. So, once it is found, multiply with pipe density to get pipe weight per unit length of rectangular pipe.
Steel Pipe Weight Chart
For Carbon Steel and Stainless Steel pipes, the pipe weight per foot or pipe weight per meter of length can easily be taken directly from the Steel Pipe Weight Chart Provided in ASME B36.10M (For Carbon Steel) or ASME B36.19M (For Stainless Steel).
Those two ASME codes provide the Steel pipe weights directly in their tables as pipe weight per foot or pipe weight per meter of length. Part of the table from ASME B36.10M for a 6-inch line that we considered above as an example is produced here to explain the chart.
Fig. 2: Pipe Weight Chart from ASME B 36.10M
As you can see, the empty pipe weight that we calculated for the 6-inch Sch. 40 pipes matches exactly the value provided in the above ASME Code.
However, the above steel pipe weight chart provides only the empty pipe weight value directly. Water-filled pipe weight you have to manually calculate using the above procedure.
Pipe Weight Calculation using Pipedata-Pro
Both Empty pipe weight and Water-filled pipe weight can easily be obtained if you have Pipedata-Pro software. That software directly gives the pipe weight values of all pipe sizes corresponding to pipe thicknesses. Fig. 3 shows the sample pipe data-Pro Screenshot for the 6-inch Sch. 40 pipes that we considered in our pipe weight calculation.
Fig. 3: Pipe Weight Data as per Pipedata-Pro
The above values show the pipe weight in Kg/m. However, You can easily change the unit if you need data for Pipe weight per foot.
Video Tutorial on Pipe Weight Calculation
The following video tutorial clearly explains all the steps required for pipe weight calculation
How do you find what is the weight of your round pipe?
To calculate the weight of your round pipe, Follow the below-mentioned steps
Step 1. Find the volume of the pipe using the following equation; volume = 0.785398 × [(Pipe Outer diameter)² – (Pipe Outer diameter – 2*thickness)²] × length Step 2. Multiply the pipe material’s volume calculated in step 1 by the pipe material density. Hence, Pipe weight = volume × density
Scaffolding Definition: Types, Parts, Design, Materials, and Hazards of Scaffolding
The term Scaffolding is related to construction and education. In education, scaffolding means breaking the complete learning into small chunks and learning easily using various tools, techniques, and structured ways. However, in the context of this article, we are interested in exploring the term scaffolding with respect to the construction industry. Let’s start with the scaffolding definition.
Scaffolding Definition
During construction, maintenance, or repair work, to support the work crew and materials, temporary structures are built. These temporary structures are called Scaffolding. Scaffolding helps in access at heights and is widely used in all types of construction works. This impermanent structure works as a platform to support the working class to perform its construction activities. As scaffolding involves work at height, it is designed following safety regulations to reduce hazards. Surveys show that a major percentage of accidents in construction industries are directly or indirectly related to scaffolding. So, the scaffolding contractor and scaffolding workers should perform their duties with the utmost care. High-quality materials should be used for scaffolding design.
Scaffolding for Tank Construction and Erection
Scaffolding Parts or Components
The major components of scaffolding are as follows:
Standards: Perpendicular tubes that transfer the weight load to the baseplates. To increase the height of scaffolding, standards are connected using pins and socket joints.
Ledgers: Flat horizontal tubes that join between the standards. Ledgers connect multiple bays. Ledgers decide the height of the working platform.
Transom or Bearer: Transoms are used to support standards and they are at the right angles to the ledgers. Transoms define the bay width
Scaffolding Tubes: Steel or Aluminium tubes are used in scaffolding.
Couplers: Fittings to hold tubes together. They are of three types; Putlog Coupler, Swivel Couplers, and Right Angle Couplers.
Diagonal Braces: Strengthen the basic structure to carry more loads.
Boards: Steel, Aluminium, or wooden boards that provide the working area.
Adjustable Base Plates
Guard Rails
Decks or planks
Toe Boards
Putlogs: Putlogs are transverse members that are placed on one end on ledgers and the other ends at right angles on the wall.
Basic Scaffolding Parts
Scaffolding Types
Depending on the type of construction and its requirements to meet various job applications, the Scaffolding structure varies. Broadly, the following scaffolding types are used in the construction industry:
Cantilever Scaffolding
Trestle Scaffolding
Single Scaffolding
Double Scaffolding
Steel Scaffolding
Suspended Scaffolding
Kwikstage Scaffolding
Cantilever Scaffolding
Cantilever scaffolding is widely used where the ground surface is not suitable for setting up conventional scaffolding. Cantilever Scaffolding or needle scaffolding is highly effective when maintenance or construction is needed at great heights or when the project has space constraints. A group of cantilever or needle beams is used to reinforce cantilever scaffolding. Cantilever scaffolding is also known as Single frame scaffolding.
Typical Cantilever Scaffolding
A cantilever scaffolding normally constitutes of the following components:
A Platform
Toe Boards
Protective rails
Trestle Scaffolding
Trestle Scaffolding is a highly popular movable scaffolding that can be used up to a height of 5 m. They are fitted with wheels and can be transferred from one place to another very easily. They are used for light-duty work, normally for indoor work.
Trestle scaffolding
Single Scaffolding
Single Scaffolding is made of only one row. A series of vertical members are fixed into the ground parallel to the structure being made. Normally, a single scaffolding is used for building construction. This is also known as the brick layer’s scaffolding.
Double Scaffolding
Double scaffolding is much stronger than single scaffolding. They are also popular as independent scaffolding as two rows of scaffolds is put together that create an independent strong structure. Double Scaffolding is commonly used in stone masonry.
Single and Double Scaffolding
Steel Scaffolding
Steel scaffolding is costly scaffolding but provides greater strength and durability and more resistance. In the process and power piping industries, steel scaffolding is widely used. As the name denotes, the material used is steel in steel scaffolding which can be erected and dismantled quickly. Steel scaffolding is suitable and safe for working at great heights. For big construction works steel scaffolding is preferred over other types.
Suspended Scaffolding
As the name says, these scaffoldings are suspended using ropes or chains from overhead structures. Mainly used for repair and painting works, suspended scaffolding provides a greater range of mobility as their working height is adjustable depending on height requirement.
Suspended Scaffolding
Kwik-stage Scaffolding
This Scaffolding system uses galvanized steel and is very easy to assemble or disintegrate. They provide a strong and safe scaffolding system and are hence highly popular in both big and small construction works.
Types of Scaffolding OSHA
As per Occupational Health and Safety Administration(OSHA) Scaffolding is classified into two groups. They are:
Supported Scaffolding supported by rigid load-bearing members: Supported scaffolds are elevated platforms supported by legs, uprights, posts, frames, outrigger beams, brackets, poles, or similar rigid support. Suitable bracing should be provided to prevent swaying and excessive displacement of these structural members.
Suspended Scaffolding which is suspended by non-rigid members from overhead structures.
Scaffolding Design
As Scaffolding involves the safety of working professionals it must be designed with utmost care. The design of the scaffold should consider the following:
The supporting structure should be sufficient in strength, stability, and rigidity;
The safety of personnel associated with the erection, alteration, and dismantling of the scaffold; the safety of persons using the scaffold; and the safety of persons in the vicinity of the scaffold
The following information is required for designing the scaffold.
The location of the Site.
Time Period for the scaffolding to be erected.
Intended use of the scaffolding.
Length and Height.
Maximum working loads.
Nature of surrounding supporting structure; etc.
The following codes and standards are used for the design of scaffolding: OSHA scaffolding standard (1926.451), NZS 3404.1, NZS 3603, AS 1538, AS 1664, AS 1554.1, AS 1665 or NZS 4701, as appropriate.
Scaffolding design should consider the worst load combination expected during its service period. Dead (Weight of Structural members), Live loads (Weight of Persons), and Occasional loads (wind, earthquake, snow, etc) are to be considered.
To avoid cracking the floor the beam deflection must be limited to 1/360 of the span. Scaffolding where heavy loads are expected must be checked for this deflection criteria.
As per OSHA Scaffolding guidelines, the following considerations should be taken into account for scaffolding design:
Each scaffold and scaffold component should be designed to support its own weight and at least four times the maximum intended load applied or transmitted to it.
Loads in excess of their maximum intended loads or rated capacities shall not be applied on scaffolds and scaffold components.
Guardrails along all open sides and ends shall be installed before releasing the scaffold for use by employees, other than the erection and dismantling crews.
Scaffolding Materials
The widely used materials for scaffolding are Steel and Aluminum.
Steel is the most preferred material for scaffolding due to its great strength and durability. Also, Steel as Scaffolding material provides a certain amount of elasticity to prevent cracks. Steel can support high loads, and workers can use it for transporting heavy equipment and supplies. For tall scaffolding structures, steel material is a necessity from the strength requirement point that only steel can provide.
However, Aluminum is a good alternative for less demanding conditions with short heights.
Scaffolding floors are normally made of wooden boards or decking made from steel or aluminum. When wooden boards are used as scaffolding floor material, their ends are protected by metal plates known as hoop irons or nail plates.
Scaffolding Hazards and Risks
Working in scaffolding is full of risks. Scaffolding hazard increases with an increase in height. Studies represent that more than 65% of the construction workforce needs to work on scaffolds. Various incidents confirm the high frequency of scaffolding hazards. The major scaffolding hazards are:
Falls from scaffolding due to improper guardrail installation.
The collapse of the scaffold due to improper erection.
Falling Material from scaffolds makes the nearby region vulnerable to hazards.
Electrical hazards due to improper planning.
Slips and falls from planks
Overloading platforms.
Rolling scaffolds.
That’s why it is always suggested to inspect the scaffolding each day before starting the construction work. Many organizations use a standard checklist to ensure the scaffolding is suitable for working before work begins. The Occupational Safety and Health Administration (OSHA) provides guidelines for such checklists.
