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What is Process Control? Its Importance and Working Principle

Written by Partha Pratim Panja in Process

The purpose of the article is to define what we mean by chemical process control & the objective of controlling a chemical process.

What is Process Control?

Basically, process control means maintaining the desired condition in a chemical system by adjusting the selected process variable. It deals with science & technology. The process variables can be temperature (T), Pressure (P), Level (L), flow rate (F), etc.

For an appropriate design & implementation of a control system, the controller must be based on a complete understanding of the process dynamics. Process control is a control of an output variable by sensing the amplitude of the output variable from the process comparing it to the setpoint value and causing an error signal fed back to the controller to take control action through the final control element (e.g. control valve).

Why Process Control?

The main objective of process control includes many advantages including,

  • Enhanced process safety
  • Meeting environmental constraints& compliances
  • Satisfying product quality &specifications
  • Protection of Equipment & Environment
  • Enhancement of profitability
  • Smooth Operation

What is a Control System?

A control system is used to retain process conditions at their desired level by manipulating certain process variables (PV) to adjust the target variables.  A common example is the fuel gas flow to the heater (the manipulated variable). The controller compares the measurement signal of the controlled variable to the setpoint (the desired value of the controlled variable). The difference between the two values is called the error.

What is an Error?

Error is defined as follows, Error= (Setpoint value)– (Measurement signal of controlled variable). Depending upon the magnitude and sign of the error, the controller takes appropriate action by sending a signal to the final control element, which provides an input to the process to return the controlled variable to the set point.

Generalized Process Control System
Fig. 1: Generalized Process Control System

What is a Block diagram?

A block diagram is a pictorial representation that shows the flow of information around the control system and the function of each part of the process.

What is a Closed-loop?

A control loop is called a closed loop when the measured value of the controlled variable is fed back to the controller.

What is a Controlled variable?

The controlled variable is the variable of the process that we want to control at a particular value.

What is a Controller?

The controller is the heart of the control systems that can be called a decision-maker. Basically, it is a hardware element with a built-in capacity for performing the only task requiring some form of intelligence. Some examples are pneumatic controllers, electronic controllers, etc. It generates a signal to the process depending on the magnitude of the error signal. A proportional controller (P) creates a signal that is proportional to the error.

What is Disturbance Rejection?

One goal of a control system is to enable the system to “reject” the effect of disturbance changes and maintain the controlled variable at the set point.

What are Disturbances?

Disturbance can be any process variable that can cause the controlled variable to fluctuate. Generally, disturbances are those variables over which we have no control.

What is a Manipulated Variable?

Manipulated variables are those process variables that are adjusted so that the controlled variable can be brought back to the set point.

What is an offset?

The steady gap or error between the setpoint value (SP) and (PV) is called offset in process control.

What is an Open-Loop?

An open loop is just the opposite of a closed loop as the measured value of the controlled variable is not fed back to the controller.

What is a Set Point?

Setpoint the values at which we want to control the controlled variable. This value needs to be given manually to the controller.

What is a Sensor/Transmitter?

A sensor is a device that detects the process variables, such as temperature, pressure, flow rate, and level, and has the ability to give a measurable output that varies with respect to the change of the physical variable. The sensor gathers information about the status of the process variables (PV).

The transmitter converts the measured electrical or mechanical phenomenon to 3-15 PSIG pneumatic signals, a 4-20-mA electrical signal, or a 0-5 V DC voltage or digital signal that can be transmitted to the controller.

Some examples of sensors are thermocouples (for temperature measurements), differential Pressure cells (for liquid level measurements), gas/liquid chromatography (for Composition measurement), etc.

What are Signal Converters?

Signal converters in a feedback control system convert the pneumatic signal (3–15 PSIG) to an electronic signal (4–20 mA), or vice versa. This conversion is accomplished by certain hardware units called pneumatic-to-current (P/I) and current-to-pneumatic (I/P) converters. In addition to that, it is required to convert an analog signal to a digital signal by an (A/D) and a digital signal to an analog signal by a (D/A) converter. The use of an analog and/or digital filter is also quite common to get rid of undesirable processes and transducer noise. Due to the fast response of a signal converter, no dynamics are associated with these units.

What is an Actuator?

An actuator is a mechanical device that generates a motion through the conversion of energy and signals generated by the controller. The motion generated by the actuator can be rotary or linear. Linear actuators produce linear motion. So it is very apparent that linear actuators can move forward or backward direction. The flow control valve is a typical example of an actuator that controls the rate of flow of a fluid in proportion to the amplitude of an electrical signal generated by the controller.  There are different types of actuators used in industry that could be electrical, pneumatic, or hydraulic. The selection of actuator type will most likely depend on the application and -specific requirements.

TypeAdvantageDisadvantage
HydraulicCan handle loads of more than 10 kN.It requires pumps, valves, tanks, hoses & regulators.
PneumaticMovement is very fast between two points.It requires valves, tubes & compressors.
ElectricalVery simple, and causes low sound & energy savings.Lower speed than compared to others, less suitable for heavy loads.
Table 1: Hydraulic, Pneumatic, and Electrical actuators
Examples of Hydraulic, Electrical, and Pneumatic Actuators
Fig. 2: Examples of Hydraulic, Electrical, and Pneumatic Actuators

What is the Final Control Element?

The final control element is none other than the actuator that throttles the manipulated variables based on the command signal it receives from the controller. In the chemical industry, the manipulated variable is often the flow rate of a process stream (e.g., the steam or cooling water flow rate for temperature control, the flow rate of gas or liquid, the solid flow rate of a catalyst using a slide valve or a screw conveyor, etc.). The most commonly used final control element for throttling a flow rate is a control valve. Some other final control elements are a variable speed pump, a silicon-controlled rectifier (SCR), and an immersion heater.

What is Feedback Control?

Feedback control is based on the measurement of the controlled variable (process variable, PV) by a proper sensing element and transmitting the measured signal to the controller. The desired value of the controlled variable that is put manually is also made available to the feedback controller as the setpoint (SP). The controller subtracts the measured controlled variable from its set point and calculates the error signal. The error signal triggers the control law and calculates corrective action and this action is implemented by the final control element.

The steps that are performed by the feedback control strategy are as below,

  • Measurement of the desired process variable directly or indirectly by a sensor/transducer;
  • Compare the measured variable with its set point & calculate corrective action (decision);
  • Implement the corrective action, using a final control element such as the control valve.

What is the ON-OFF Controller?

The ON-OFF controller is the simplest type of feedback controller. Based on the position of the controlled variable relative to the setpoint it drives the manipulated variable from fully closed to fully open or vice versa. This means that the control element does not operate at any intermediate position between 0-100% ranges. In ON-OFF control when the process variable changes and deviates from a certain set point the output variable of the system is fully opened all of a sudden. The  ON-OFF controller is also called a Bang-Bang controller or two-step controller.

In the below figure you can see the water level in the tank is regulated through ON-OFF installed on the water supply line. Most of the time ON-OFF valve is used as SDV (Shut down valve), and EIV (Emergency isolation valve) in a process.

Various Control Loops
Fig. 3: Various Control Loops

What is a Proportional Controller?

Proportional controllers’ output is proportional to the magnitude of the error signal. The proportionality constant, Kc, is referred to as the controller proportional gain, Pbias is the controller bias that is the output generated from the controller when the error signal becomes zero. In short, it is a linear type feedback controller through which the corrective action is implemented to the controlled variable that is proportional to the error.

P(t) =Pbias+Kc e(t), where P(t) is the controller output at time t.

What is Proportional Integral (PI) Controller?

This controller’s output is proportional to the magnitude and time integral or duration of the error signal. τ1 is referred to as the controller integral time or rest time. PI controller is a close control loop of a feedback system. It continuously detects an error signal (the difference between a measured process variable and the desired setpoint). P-controller acts as a multiplication factor to the magnitude of the error & generate output. I-controller keeps a certain value based on the difference between the reference (that we want as output) & the actual value of output. So, I- the controller is the summation of the error signal over some time that is generally moving to & fro from a setpoint.

PI controllers Loop
Fig. 4: PI controllers Loop

What is Proportional-Integral-Derivative (PID) Controller?

A PID controller is a widely used control system that is used in almost all industrial processes to regulate temperature, flow, pressure, speed, and other process variables. The PID stands for Proportional-Integral-Derivative which uses a control loop feedback system to control process variables (PV) and it is one of the most accurate and stable controllers. The output of the PID controller is proportional to the magnitude, duration (time integral), and time rate of change (derivative) of the error signal. τD is designated as the controller derivative time or rate time. Here the derivative action predicts the future as it predicts what is yet to happen by projecting the current rate of change into the future. The equation that calculates the control action of a PID controller is

PID control loop
Fig. 5: PID control loop

What is a Feed-Forward Control?

Feed-forward control is a control system that predicts the influences of the disturbances and manipulated input on the relevant process variables. This model responds in a pre-defined way without responding to how the load reacts. So it is not an error-based control system rather it depends on the mathematical model of the process. This control strategy can be highly effective and largely suppress the impact of disturbances. So in this control system, the disturbances are measured & corrective action is implemented before the disturbances have time to affect the system.

Feed-forward Control loop
Fig. 6: Feed-forward Control loop

Feed-forward Vs Feedback Control

The main advantages of a Feedback control system are as follows,

  • Corrective action is generated as soon as the controlled variable deviates from the desired set point, irrespective of the source and type of disturbance.
  • Feedback control needs very little knowledge about the process to be regulated. In particular, no mathematical model of the process is required, although it can be very needful for designing the control system.
  • The PID controller is both versatile and robust in nature. If the conditions of the process change, the controller usually produces satisfactory control.

At the same time, Feed-forward control has several disadvantages like,

  • The value of the disturbance variables must be measured online. In many applications, this is not practically feasible.
  • At least an approximate process model should be available to make effective feedforward control. Particularly, it is required to know the response of the controlled variable with respect to the changes of both the disturbance and manipulated variables. The quality of feedforward control solely depends on the accuracy of the process model.
  • Ideal feedforward controllers that are theoretically able to achieve proper control of the system may not be physically realizable.

In practical application, feedback control is preferred over feedforward control.

Example of the letters used in a P&ID

Symbols and Letters in P&ID
Fig. 7: Symbols and Letters in P&ID

Online Video Courses On Process Control

Want to have more insights into the process control fundamentals? Then the following online video courses are a must for you:

What is an RTJ Flange? | Ring Type Joint Flanges

Written by Anup Kumar Dey in Pipeline,Piping Design Basics

An RTJ flange or Ring Type Joint Flange is one of the various types of flanges used widely in piping and pipeline industries. RTJ flanges are commonly used for high-pressure and high-temperature applications in oil field valves, pipework assemblies, refineries, high-integrity pressure vessel joints, chemical and petrochemical plants, etc. In this article, we will explore more about RTJ flanges.

What is an RTJ Flange?

A Ring Type Joint (RTJ) Flange is basically a machined metallic ring having a deep groove cut into its face. Metallic RTJ gaskets sit in the groove to seal the flange pair. When the connecting bolts of the RTJ flanges are tightened, the gasket is compressed and the flange pair creates a leak-proof tight seal. RTJ flanges, in general, have a raised face with the groove into the face of the flange, but the raised face doesn’t contain the pressure similar to weld neck raised face flanges. Refer to Fig. 1, which gives an example of a typical RTJ flange assembly.

RTJ Flange Assembly
FIg. 1: RTJ Flange Assembly

The RTJ flanges are usually preferred for Class 600 and higher ratings and/or when service temperature exceeds 800°F (427°C).

Characteristics of RTJ Flanges

A ring-type joint flange is substantially different from other types of flanges used in the piping and pipeline industry. The main characteristics of an RTJ flange are:

  • Instead of the flat composite material gaskets, RTJ flanges use a steel ring. The gasket rests on the machined groove.
  • The sealing is achieved by the deformation of the soft metallic gasket which flows into the microfine structure of the hard flange material.
  • RTJ flanges provide superb metal-to-metal sealing.
  • The raised face may be present in a ring-type joint flange but it does not contain the pressure. However, while tightening the RTJ flanges if raised faces come in contact with each other, the extra load is transferred to the faces which, in turn, provides the integrity of the joint during over-tightening, vibration, and movement.
  • They are very easy to assemble and disassemble.

RTJ Flange Materials

Ring-type joint flanges are made from various engineering materials like

Codes and Standards for RTJ Flanges

The design and manufacturing of RTJ flanges are governed by the following standards:

  • ASME B16.5 up to 24″ size.
  • ASME B16.47, Series A & B for sizes 26 inches through 60 inches.
  • MSS SP-44
  • API 605
  • EN 1092
  • BS 4504, BS 1560
  • ISO 70051
  • DIN2527, DIN2576, DIN2641, DIN2642, DIN2655, DIN2656, DIN2627, DIN2628, DIN2629, DIN 2631, DIN2632, DIN2635, DIN2636,DIN2637, DIN2638, DIN2673, DIN2566, DIN2573, DIN2633, DIN2634
  • AWWA
  • ASA
  • GOST 12820
  • SABS 1123

RTJ Flange Types

Ring-type joint flanges can be classified depending on their face types and pressure classes.
Based on pressure classes, the following types of RTJ flanges are available.

  • 150 LBS,
  • 300 LBS,
  • 600 LBS,
  • 900 LBS,
  • 1500 LBS, and
  • 2500 LB

Specifications of Ring Type Joint Flanges

The edge (periphery) of each ring joint flange is usually marked with the letter R and the corresponding ring groove number. RTJ flanges are specified by the following parameters:

  • Flange Size (Connecting Pipe Size)
  • Flange material and grade
  • Design Standard
  • Pressure Class Rating (Temperature and Pressure rating)
  • Flange face type
  • Coating or Surface treatment requirements
  • Dimensional requirements
  • Application service type

RTJ Flange Dimensions

RTJ flange dimensions are usually specified in the design standard itself. For example, when the design code is ASME B16.5, the RTJ flange dimensional tables for each pressure rating class are provided for flanges up to 24 inches. For RTJ flange sizes exceeding 24 inches, the dimensions for RTJ flanges are available in ASME B16.47.

So, basically, for standard flanges, the RTJ flange dimensions are fixed and do not vary from manufacturer to manufacturer. However, Custom made RTJ flanges can also be manufactured for which the purchaser needs to specify the flange dimensions.

RTJ Blind Flange

RTJ blind flange is a solid flange used to block the flow and is used to pair with another type of RTJ flange. The RTJ blind flange must be of the same pressure class rating.

RTJ Flange Gasket

RTJ flange gaskets are metallic sealing rings and provide reliable sealing. Ring Type Joint gaskets provide sealing by the wedging action between the gasket and the mating flange. With the application of pressure on the bolts, the softer gasket metal flows into the microfine structure of the harder flange material, which creates an efficient tight seal.

Depending on the pressure-carrying capability, RTJ gaskets are available in various styles, like R, RX, and BX styles.

The common type of RTJ flange gasket style is style R. RTJ gaskets are manufactured based on ASME B1620 for ASME B16.5/16.47 flanges. Style R-type RTJ gaskets are manufactured in oval and octagonal configurations and are designed to seal pressure up to 6,250 psi in accordance with ASME B16.5 pressure ratings and up to 5,000 psi.

RTJ Gasket Styles
Fig. 2: RTJ Gasket Styles

The Octagonal ring provides higher sealing efficiency as compared to the oval counterpart and this is why octagonal rings are the preferred RTJ flange gasket.

The RX-type RTJ gaskets are suitable for pressures up to 700 bar. In this type of RTJ flange gasket, the outer sealing surfaces make the first contact with the flanges. RX style RTJ gasket is interchangeable with the standard R-models.

The BX-type RTJ gasket is used for very high pressures up to 1500 bar. This style of ring joint gasket is not interchangeable with other types and is only suited for API-type BX flanges and grooves.

Advantages and Disadvantages of Ring-Type Joint Flanges

The RTJ flange is one of the most efficient flanges used for high-temperature pressure lines of process piping systems. The ring and groove design uses internal pressures to increase the sealing capacity of the connecting flanges. With an increase in the working pressure, the sealing performance improves. RTJ flanges are also suitable for cyclic stresses and corrosive fluids.

The main disadvantage of a ring-type joint flange is the cost due to its complex configuration and precise machining control for both the metallic ring gasket and the ring-joint groove. Also, while dismantling ring joint flange connections, the flange needs to be separated forcibly to release the ring from the groove. This may call for sufficient space which limits the application of RTJ flanges in crowded installations.

Titanium Alloys: Applications, Types, Grades, and Examples   

Written by Sikandar Choudhury in Engineering Materials

Titanium alloys are highly popular in industries because of their very high tensile strength and toughness along with their very lightweight and extraordinary corrosion resistance properties. Titanium alloys are produced by combining pure titanium with other metals or chemical components. The presence of these different metals and chemical components modifies the physical properties of titanium alloy. Titanium is relatively powerful on its own — about as strong as steel — but when combined with other metals and chemical components, it becomes considerably stronger. On the other hand, titanium alloy has other advantages besides enhanced strength.

What is Titanium Alloy?

Titanium alloy is a metal or chemical alloy predominantly made of pure titanium with other metals or chemical elements dispersed. It’s made by combining titanium with other metals and chemical ingredients precisely. The mixture is allowed to cool once the correct ratio has been attained. In general, Titanium alloy contains traces of aluminum, niobium, tantalum, molybdenum, vanadium, zirconium, manganese, iron, nickel, chromium, cobalt, and copper.

Application of Titanium Alloys

Titanium alloys find wide applications in

  • Chemical processing
  • Chlorate manufacturing
  • Desalination
  • Marine applications
  • Production Equipment Components.
  • Aircraft turbines
  • Engine components
  • Aircraft structural components
  • Aerospace fasteners
  • High-performance automatic parts
  • Marine applications
  • Sports equipment
  • Orthopedic pins and screws
  • Orthopedic cables
  • Ligature clips
  • Surgical staples
  • Springs
  • Orthodontic appliances
  • In joint replacements
  • Cryogenic vessels
  • Bone fixation devices
  • Hydrometallurgical applications
  • Elevated temperature chemical manufacturing
  • Cryogenic Applications

Types of Titanium Alloy

Depending on the metallurgical structure, Titanium alloys can be classified into three broad categories as listed below:

i) Alpha Alloys:

It is alloyed with small amounts of oxygen to enhance commercially pure titanium’s hardness and tensile strength. It is feasible to manufacture a range of economically pure titanium grades with strength values ranging from 290 to 740 MPa by adjusting the amounts added.

Although minor amounts of beta phase are possible if the impurity levels of beta stabilizers such as iron are significant, these materials are nominally completely alpha in structure. While the alpha alloys cannot be heat-treated to increase strength, adding 2.5 percent copper to titanium produces a material that responds to solution treatment and aging the same way that aluminum-copper alloys do. Aluminum is an alpha stabilizer found in several commercially available alloys as an alloying additive to titanium.

ii) Alpha-Beta Alloys:

The beta phase is stabilized by vanadium, molybdenum, iron, and chromium, and various alpha-beta alloys have been created. These are typically medium to high-strength materials, with tensile strengths ranging from 620 to 1250 MPa and creep resistance ranging from 350 to 400°C. Low and high cycle fatigue and fracture toughness are increasingly important to design characteristics. Thus, thermomechanical and heat treatment processes have been developed to ensure that the alloys provide the best mechanical properties for various applications. Near alpha, alloys are employed for maximal creep resistance at temperatures above 450°C. At temperatures up to 600°C, they have sufficient creep strength.

iii) Beta Alloys:

Beta alloys are the other type of titanium substance. All-beta alloys can be made when enough beta-stabilizing elements are added to titanium. These materials have been around for a long time but have only recently gained popularity. They’re easier to hard work than alpha-beta alloys, can be heat treated to high strengths, and some have better corrosion resistance than commercially pure grades. There are international and national specifications for titanium materials used in aerospace, but none exist for materials used in non-aerospace applications. The ASTM collection of specifications is commonly utilized in this industry.

Examples of Titanium Alloys

The following table (Courtesy: azom.com) provides a list of titanium alloys along with their examples.

Types of Titanium AlloyExamples of Titanium Alloy
Alpha Titanium AlloyTi/Pd Alloys – ASTM grades 7 and 11
Alpha + CompoundTi-2.5%Cu – IMI 230
Near Alpha Titanium AlloysTi-8%Al-1%Mo-1%V
Ti-6%Al-5%Zr-0.5%Mo-0.2%Si – IMI 685
Ti-6%Al—2%Sn-4%Zr-2%Mo-0.08%Si
Ti-5.5%Al-3.5%Sn-3%Zr-1%Nb-0.3%Mo-0.3%Si – IMI 829
Ti-5.8%Al-4%Sn-3.5%Zr-0.7%Nb-0.5%Mo-0.3%Si – IMI 834
Ti-6%Al-3%Sn-4%Zr-0.5%Mo-0.5%Si – Ti 1100
Alpha-Beta Titanium AlloysTi-6%Al-4%V
Ti-4%Al-4%Mo-2%Sn-0.5%Si
Ti-4%Al-4%Mo-4%Sn-0.5%Si – IMI 551
Ti-6%Al-6%V-2%Sn
Ti-6%Al-2%Sn-4%Zr-6%Mo
Metastable Beta Titanium AlloysTi-3%Al-8%V-6%Cr-4%Zr-4%Mo – Beta C
Ti-15%Mo-3%Nb-3%Al-0.2%Si – Timetal 21 S
Ti-15%V-3%Cr-3%Sn-3%Al
Table 1: List of Titanium Alloys and Examples

Titanium alloys can also be classified based on their mechanical strength as follows:

  • Low Strength Titanium Alloy (Strength <=500 MPa): Example, ASTM grades 1,2,3,7 and 11
  • Moderate Strength Titanium Alloy (Strength 500 to 900 MPa): Example, ASTM grades 4,5, and 9, Ti-2.5%Cu, Ti-8%Al-1%Mo-0.1%V.
  • Medium Strength Titanium Alloy (Strength 900 to 1000 MPa): Example, Ti-6%Al-2%Sn-4%Zr-2%Mo, Ti-5.5%Al-3.5%Sn-3%Zr-1%Nb-0.3%Mo-0.3%Si
  • High Strength Titanium Alloy (Strength 1000 to 1200 MPa): Example, Ti-3%Al-8%V-6%Cr-4%Zr-4%Mo, Ti-4%Al-4%Mo-2%Sn-0.5%Si, Ti-6%Al-6%V-2.5%Sn, Ti-15%V-3%Cr-3%Sn-3%Al, Ti-5%Al-2%Sn-4%Mo-2%Zr-4%Cr, Ti-6%Al-5%Zr-0.5%Mo-0.2%Si, Ti-6%Al-2%Sn-4%Zr-6%Mo, Ti-11%Sn-5%Zr-2.5%Al-1%Mo, Ti-5.8%Al-4%Sn-3.5%Zr-0.7%Nb-0.5%Mo-0.3%Si
  • Very High Strength Titanium Alloy (Strength >1200 MPa): Example, Ti-10%V-2%Fe-3%Al, Ti-4%Al-4%Mo-4%Sn-0.5%Si

The Temperature of Transition

At room temperature and pressure, titanium crystallizes in a close-packed hexagonal phase with a c/a ratio of 1.587. Titanium undergoes an allotropic change to a body-centered cubic phase at around 890 °C, which is stable to the melting temperature.

Some alloying elements, known as alpha stabilizers, raise the alpha-to-beta transition temperature, while others, known as beta stabilizers, lower it. Aluminum, gallium, germanium, carbon, oxygen, and nitrogen are alpha stabilizers. Beta stabilizers are molybdenum, vanadium, tantalum, niobium, manganese, iron, chromium, cobalt, nickel, copper, and silicon.

Properties of Titanium

Due to the increased number of slip planes in the bcc structure of the beta-phase in comparison to the hcp alpha-phase, beta-phase titanium is more ductile. Alpha-phase titanium is stronger but less ductile. Titanium in the alpha-beta phase has a mechanical characteristic that is halfway between the two.

Titanium dioxide dissolves in metal at high temperatures and takes a long time to produce. Because of these two variables, all titanium, except the purest, has a large quantity of dissolved oxygen and is thus classified as a Ti–O alloy. Although oxide precipitates provide some strength (as stated above), they are not very heat resistant and significantly reduce the alloy’s toughness. Many alloys contain titanium as a small component. Still, because alloys are normally classified based on which element makes up most of the material, these aren’t regarded as “titanium alloys” in the traditional sense.

Titanium is a strong, light metal on its own. It is 45 percent lighter than ordinary low-carbon steel while being 45 percent stronger. It’s also twice as robust as soft aluminum alloys while weighing only 60% as much. Titanium is utilized in propeller shafts, rigging, and other seawater-exposed sections of boats because of its remarkable corrosion resistance. Titanium and its alloys are utilized in planes, missiles, and rockets where strength, lightweight, and high-temperature tolerance are vital.

Grades of Titanium Alloy

Titanium Alloy Grade 5, Ti 6Al-4V

Ti 6Al-4V, or Grade 5 titanium, is the most extensively utilized of all titanium alloys and is known as the “workhorse” of titanium alloys. It accounts for half of all titanium usage on the planet. Heat treatment can be used to improve the strength of Ti 6Al-4V. Grade 5 titanium is utilized in welded construction at temperatures up to 600 degrees Fahrenheit. This alloy’s excellent strength at a low weight, useful formability, and high corrosion resistance makes it a good choice. Because of its versatility, Ti 6AI-4V is the optimum alloy for usage in various industries, including aerospace, medical, marine, and chemical processing.

Titanium Alloy Grade 7

Grade 7 is mechanically and physically identical to Grade 2, except it contains the interstitial element palladium, making it an alloy. Grade 7 is the most corrosion-resistant titanium alloy, with outstanding weldability and fabricability. Chemical processes and industrial equipment components employ Grade 7.

Titanium Alloy Grade 11

Grade 11 is essentially identical to Grade 1, except that a small amount of palladium has been added to improve corrosion resistance, making it an alloy. Optimal ductility, cold formability, functional strength, impact toughness, and outstanding weldability are other beneficial qualities. This alloy can be used in the same titanium applications as Grade 1, but it is more corrosion-resistant.

Titanium Alloy Grade 12, Ti 3Al 2.5

Grade 12 titanium receives an “excellent” rating for its high-quality weldability. It’s a durable alloy with a lot of strength at high temperatures. Grade 12 titanium has properties equivalent to stainless steel from the 300 class. This alloy can be hot, or cold formed using press brake forming, hydro press forming, stretch forming, or the drop hammer method. It may be formed in various ways, and useful in a wide range of applications. The strong corrosion resistance of this alloy makes it ideal for use in manufacturing equipment where crevice corrosion is a problem.

Titanium Alloy Grade 23, Ti 6AL-4V ELI

Ti 6AL-4V ELI, also known as Grade 23, is a pure Ti 6Al-4V. Coils, strands, wires, and flat wires can all be formed. It’s the best option for any application that necessitates a mix of high strength, lightweight, exceptional corrosion resistance, and high toughness. It is more resistant to damage than other alloys.

Grade 23 is the ideal dental and medical titanium grade because of these advantages. Because of its biocompatibility, good fatigue strength, and low modulus can be employed in biomedical applications like implanted components.

Titanium Alloy Grade 6, Ti 5Al-2.5Sn

Ti 5Al-2.5Sn is a non-heat treatable alloy with good welding properties and stability. It also has a high degree of temperature stability, strength, corrosion resistance, and creep resistance. Creep is a term used to describe the process of plastic strain over time that occurs at high temperatures.

The titanium alloy Ti 5Al-2.5Sn is used in aircraft, airframes, and cryogenic applications.

References:

  • Titanium Alloys – an Overview | Science Direct Topics. (n.d.). Titanium Alloys – an overview | Science Direct Topics. https://www.sciencedirect.com/topics/engineering/titanium-alloys.
  • An Introduction To Titanium Alloy – Monroe Engineering. (2020, June 22). Monroe Engineering. https://monroeengineering.com/blog/an-introduction-to-titanium-alloy/.
  • Titanium Grades – Continental Steel & Tube Company. (2021, April 9). Continental Steel & Tube Company. https://continentalsteel.com/titanium/grades/.

Types of Condensers

Written by Anup Kumar Dey in Mechanical

A Condenser is a mechanical device that converts a hot vapor/steam into a liquid using heat transfer and/or compression. Condensers are widely used in Automotives, Building services, Process industries, Refrigeration industries, and Steam power turbines. Various international standards developed by ASME, HEI, AHRI, ASHRAE, etc govern the design, performance, environmental compliance, and safety of condensers. Condensers are usually made up of copper, brass, aluminum, carbon steel, and stainless steel. In this article, we will explore the basics of Condensers, their specification, types, functions, and selection.

The condenser is the ‘hot’ end of a refrigeration system and can be used as a heat source when heat is required at low temperatures, such as for washing water. The ramifications of raising the condenser temperature to enhance the usability of the available heat, on the other hand, should be carefully evaluated. The oil cooler is another potential heat source—higher temperature heat recovery is achieved by desuperheating the compressor discharge gas. Energy recovery from oil coolers can be useful when large compressors are used (ICAEN, 1998). Before specifying heat recovery from a refrigeration facility, a full inspection is needed

The Function of a Condenser

Every condenser has three distinct phases. The desuperheating phase is the initial step. The vapor entering the condenser has already been superheated and pressured in the evaporator and compressor. Desuperheating is removing the heat from vapor and converting it to a liquid. The next phase is the changing or condensation state when we lose additional heat and reach a point where 10% of the refrigerant is vapor, and 90% is liquid. A sub-cooling condition is the third and final phase. The sub-cooling condition ensures that the liquid refrigerant does not become vapor again even if the temperature rises.

Condenser Specification

Condenser specification is usually set by the client in the form of a condenser datasheet. All those requirements or specifications of the condenser are included on the manufacturer’s design and selection sheet. In general, the following details constitute the specification of a typical condenser:

  • Design and Operating Temperature
  • Design and Operating Pressure
  • Flow rate
  • Allowable pressure drop
  • Condensing Capacity
  • Coolant or Refrigerant Capacity
  • Condenser Material

Types of Condensers

Condensers are classified depending on various parameters like condensing medium, method of heat transfer, applications, etc.

Depending on methods of heat transfer, condensers are classified as

  • Direct Contact Condensers: Heat transfer takes place through direct contact between the gas and liquid.
  • Indirect Contact Condensers: Heat exchange happens through a thermally conductive boundary medium like a plate, shell, or tube.
  • Surface Condensers: These are basically shell and tube heat exchangers used in large thermal power plants and refrigeration systems. They are again classified as tube-side condensation and shell-side condensation.

Depending on application condensers are classified as:

  • Refrigeration and HVAC condensers
  • Car or Automotive condensers
  • Process Condensers like distillation column condensers.
  • Marine Condensers

However, the major classification of condensers is based on condensing media. Three types of condensers are based on the condensing medium used to extract heat from the system. None of the three condensers offers a significant advantage over the others. Each one should be used wisely, depending on the situation.

1. Air-cooled Condenser:

A finned constant tube coil is used in this type of condenser. The vapor from the compressor discharge enters the top of the coil and leaves the bottom, where it flows into receivers beneath the base. The condenser coil is blown across by a fan positioned on the compressor motor pulleys. The unit should be kept in a well-ventilated, cool environment. The lower the ambient air temperature, the less power is required for a given capacity.

The main benefit of this type of condenser is its ease of installation and inexpensive cost. The most common uses are self-contained units, such as residential refrigerators, freezer cabinets, display cases, water coolers, and air conditioners. This condenser uses air as the external fluid to reject heat from the system. The refrigerant travels through copper coils in air-cooled condensers. But that’s not the whole picture; natural convection and forced convection are two subsets of this type.

Examples of typical Air-Cooled Condenser
Fig. 1: Examples of typical Air-Cooled Condenser (PC: pmengineer.com)

The air-cooled condenser has two categories:

i) Natural Convection Type:

Heat is transferred from the condenser through buoyancy-induced natural convection and radiation in the natural convection type. The total heat transfer coefficient in these condensers is minimal because the airflow rate is low, and the radiation heat transfer is likewise low. As a result, a comparatively large condensing surface is required to reject a given quantity. As a result, these condensers are employed in low-capacity refrigeration systems such as refrigerators and freezers in homes.

Condensers with natural convection are either plate surface or finned tube types. The refrigerant-carrying tubes of plate surface condensers used in compact refrigerators and freezers are attached to the refrigerator’s outer walls. Except for the door, the entire body of the refrigerator functions as a fin. Insulation is given between the outside cover, which functions as a fin, and the refrigerator’s inner plastic cover. The outer body of the refrigerator is always heated due to this. Because the surface is heated, moisture condensation on the refrigerator walls is not an issue in these systems. Flat-back condensers are another name for these condensers.

ii) Forced Convection Type:

A fan or a blower maintains air circulation across the condenser surface in forced convection condensers. For efficient heat transfer, these condensers usually have fins on the airside. Fins can be plate-shaped or annular-shaped. The compressor, induction motor, condenser with condenser fan, accumulator, HP/LP cut-out switch, and pressure gauges are installed on a single chassis in the chassis-mounted type. It’s known as a condensing unit with rated capacity components that are matched to condense the required refrigerant mass flow rate to rate cooling capacity.

Window air conditioners, water coolers, and packaged air conditioning plants use forced convection condensers. These can be put on the chassis, or they can be mounted remotely. The remote-mounted kind can be vertically or horizontally put on the roof. For economical design, air velocity is typically between 2 and 3.5 m/s, with airflow rates of 12 to 20 cm per tonne of refrigeration (TR). The air density is 1.2 kg/m3, and its specific heat is 1.005 kJ/kg-K. With an average airflow rate of 16 cm, the temperature rises ta = 3.5167/(1.2×1.005 x 16/60) = 10.9°C for 1 TR. As a result, the air temperature rises 10 to 15 degrees Celsius, compared to 3 to 6 degrees Celsius for water in water-cooled condensers.

2. Water-cooled Condenser:

With compressors of one horsepower and up, water-cooled condensers are utilized. They are typically the most cost-effective option for condensers when there is an adequate supply of clean, inexpensive water with minimal corrosion and an adequate and inexpensive means of water disposal. Water is used to cool the hot refrigerant and turn it into a liquid in this sort of condenser. The components are matched to condense the required refrigerant mass flow rate for calculating cooling capacity. the lesser the amount of water utilized in a water-cooled condenser, the higher the condensing temperature and the greater the electricity cost.

Water-cooled Condenser
Fig. 2: Water-cooled Condenser (PC: blog.drakechiller.com)

A water-cooled Condenser has three different kinds:

i) Double Tube Condenser:

The cold water passes through the condensers’ inner tube, while the refrigerant passes through the annulus in the opposite direction.  Headers are utilized at both condenser ends to shorten their length and reduce pressure loss. By free convection and radiation, the refrigerant in the annulus loses some of its heat to the environment. If the tubes are long, the heat transfer coefficient is frequently low due to poor liquid refrigerant drainage. Double pipe condensers are commonly utilized up to 10 TR capacity.

ii) Shell and Coil Condenser:

A welded shell houses a coil of finned water tubing in a shell-and-coil condenser. The hot refrigerant flows in the shell while the cooling water circulates inside the coils and condenses the refrigerant in this type of water-cooled condenser.

iii) Shell and Tube Condenser:

This is the most common form of condenser, with capacities ranging from 2 TR to thousands of TR. The refrigerant travels through the shell of these condensers, while water runs through the tubes in single to four passes. At the bottom of the shell, the condensed refrigerant gathers. The coldest water makes contact with the liquid refrigerant, allowing for some sub-cooling. The liquid refrigerant is discharged to the receiver from the bottom. For smooth liquid refrigerant drainage, there may be a vent linking the receiver to the condenser for smooth liquid refrigerant drainage. In addition to being a transmitter, the shell also serves as a receiver.

Furthermore, the refrigerant rejects heat from the shell to the environment. The horizontal shell type is the most typical. Vertical shell-and-tube condensers are commonly employed with ammonia in large-capacity systems so that the tubes are cleaned from the top while the plant is operating.

3. Evaporative Condenser:

Finally, the evaporative condenser is the final form of the condenser. It’s a condenser that’s both air-cooled and water-cooled. The condensing medium in evaporative condensers is air or water. The water is sprayed over the coils by a sump in the condenser. Air is blown into the condenser by a fan. The sprayed water evaporates across the coils, and the required heat for the vaporizing water is drawn from the refrigerant’s heat. Some water circulated by descending into the sump, but additional water is provided to the sump’s water supply to compensate for the amount evaporated.

Comparison of three types of condensers is as follows:

Air-cooled condensers are easier to make than those that are water-cooled. Furthermore, there is constant access to air. Air-cooled systems are less expensive to maintain than water-cooled systems. Evaporators are frequently less expensive than water-cooled units that require a cooling tower. Evaporators are utilized in areas where water is scarce. Because the evaporator sits outside, the water pump is shut off in cold weather to prevent the water from freezing.

Selection of Condensers

Condenser selection is governed by application and various parameters like:

  • Condensing Capacity, Full or Partial condensing, Heat rejection calculation
  • Industry type
  • Temperature (Design, operating, Dry bulb, wet bulb)
  • Condenser material
  • Pressure drop criteria
  • Space availability
  • Types of condensing medium
  • Corrosion
  • Fouling factor, etc

References:

  1. W. (2019, April 3). What Are the Different Types Of Condensers And What Type Of Condensers Is the Most Efficient? – Wikihubs24. Wikihubs24. https://www.wikihubs24.info/2019/04/what-is-condenser-and-their-types-in.html.
  2. 3 Main Types Of Condensers, How Does It Work? | Linquip. (2020, July 13). Industrial Manufacturing Blog | linquip. https://www.linquip.com/blog/different-types-of-condensers/.

Spiral Welded Pipes: Applications, Manufacturing, Advantages, and Disadvantages

Written by Anup Kumar Dey in Piping Design Basics

Spiral steel pipe or spiral welded pipe are other terms for spiral pipe. Steel strip coil is used as the raw material, then extruded at room temperature and welded using an automatic double wire double-sided submerged arc welding technique—the outer diameter. The wall thickness formula defines the requirements of spiral welded pipe, which is utilized for oil and natural gas pipelines. The weld joint’s hydrostatic test, tensile strength, and cold bending performance must all be in line with the regulations for the spiral welded pipe. Spiral welded pipes are available in various sizes. However, they are mostly used for sizes in excess of 20 inches NPS.

Applications of Spiral Welded Pipes

Spiral Welded Pipes are commonly used to convey liquids (oil, water, etc.), gases (air), steam, etc in

  • Chemical Industries
  • Petrochemical industries
  • Water and Wastewater engineering
  • Electrical power industry
  • Construction industry
  • Agricultural industry
Spiral Welded Pipe
Fig. 1: Spiral Welded Pipe (PC: dmitube.com)

The Spiral Welded Pipe Manufacturing Process

  • Steel strip coil, welding wire, and flux are the raw ingredients. Before being used, it must pass stringent physical and chemical tests.
  • After the steel pipe is rolled, use automatic submerged arc welding to repair welding using single-wire or double-wire submerged arc welding.
  • The strip is leveled, cut, planed, surface cleaned, and pre-bent before forming.
  • Control the pressure of the cylinder on both sides of the conveyor with an electric contact pressure gauge to ensure that the strip is conveyed smoothly.
  • Roll molding is controlled externally or internally.
  • The amount of misalignment and the weld gap are rigorously regulated using the weld gap control device to ensure that the weld gap fulfills the welding standards and the spiral welded pipe diameter.
  • Single-wire or double-wire submerged arc welding using Lincoln welding equipment from the United States is used for internal and external welding.
  • In non-destructive testing, the final welds were evaluated by an online continuous ultrasonic automatic defect detector, ensuring 100 percent coverage of the spiral welds. If there are any problems, an automatic alarm will sound, and a spray mark will appear, allowing the production worker to alter the process parameters at any time to eliminate the errors as quickly as possible.
  • An air plasma cutting machine sliced the spiral welded pipes into individual pieces.
  • The spiral welded pipe was tested for mechanical properties, chemical composition, and bonding conditions.
  • After manual ultrasonic and X-ray inspection, the part of the weld with continuous acoustic fault detection marks, If the spiral welded pipe has a flaw, must be subjected to nondestructive examination following repair until the defect is proven to remove.
  • X-ray television or film is used to inspect the spiral welded pipe where the butt weld of strip steel and the t-joint intersecting the spiral weld are located.
  • A hydrostatic pressure test is performed on each spiral welded pipe, and the pressure is radically sealed.

Spiral Welded Pipe Surface Treatment Method

1.  Cleaning:

Solvent and emulsion are used to clean the spiral welded pipe surface, removing oil, grease, dust, smoothing agents, and other organic matter. However, it cannot remove rust, oxide skin, flux, or other organic matter from the steel surface. It is used as an additional measure in spiral welded pipe anti-corrosion production.

2. Rust Removal Tool:

The spiral welded pipe is polished using wire brushes to remove loose or elevated scale, rust, welding slag, and other contaminants. The hand tool’s rust removal can reach the Sa2 level, while the power tool’s rust removal can reach the Sa3 level. The rust removal result of the tool is not ideal if the spiral welded pipe surface is attached with a strong iron oxide scale.

3. Pickling:

Chemical and electrolytic procedures are commonly used for pickling disposal. Only chemical pickling can remove oxide scale, rust, and old coatings and is applied as sandblasting following rust removal. Chemical cleaning can achieve the necessary cleanliness and roughness, but the anchor pattern is shallow, making the situation simple to contaminate.

4. Blasting with abrasive materials:

Abrasive blasting uses a high-powered engine to spin the spray (throwing) blade at high speed, allowing abrasives like steel grit, steel shot, wire segment, and mineral to be sprayed (throwing) on the surface of the steel tube under the influence of centrifugal force. Not only can rust, oxides, and dirt be fully removed, but under the influence of abrasive impact and friction, the spiral welded pipe may also achieve the needed average roughness.

After spraying (polishing) and eliminating rust, as well as the mechanical adhesion between the anti-corrosion layer and the spiral welded pipe’s outer surface. As a result, spray (polishing) rust removal is an excellent approach for removing rust from pipes. Sandblasting descaling is mostly utilized for internal and exterior pipe treatment, while shot blasting (sand) descaling is primarily used for pipe surface treatment.

Advantages of Spiral Welded Pipes

(1) Steel pipes of the same width can be utilized to make steel pipes of different diameters, especially when using narrow strip steel to make big-diameter steel pipes.

(2) The spiral weld is subjected to less stress than the straight seam, which is 75 percent to 90 percent of the straight seam welded pipe, and hence can bear immense pressure under the same pressure settings. The wall thickness can be lowered by 10% to 25% under the same pressure as a straight seam welded pipe of the same outside diameter.

(3) The size is precise, with a general diameter tolerance of less than 0.12%, a deflection of less than 1/2000, and an elasticity of less than 1%. In most cases, the size and straightening process is straightforward.

(4) It can be created indefinitely. In theory, it can make infinitely long steel pipes with a minimal cutting head and tail cutting losses, increasing the metal utilization rate by 6% to 8%.

(5) It is more flexible in operation and easy to modify the variety than straight seam welded pipe.

(6) The equipment is lightweight and requires a minimal initial cost. It can be built into a piece of trailer-type portable equipment, and the welded pipe can be produced on-site at the pipeline installation site.

(7) Mechanization and automation are simple to implement.

Disadvantages of Spiral Welded Pipes

Because the raw material is coiled steel, there is a crescent bend, and the welding point is in the elastic strip edge area. Aligning the welding torch is problematic, affecting welding quality. Set up complex weld tracking and quality inspection devices to accomplish this.

Spiral Welded Pipe vs Longitudinal

  • As the name suggests, the manufacturing processes of spiral welded pipe and longitudinal welded pipe are distinctly different. While Spiral-weld pipes are rolled and welded according to a preferred helical angle, the longitudinal welded pipes are created by bending and forming metal, and finally welded together down the length of the pipe to create a straight, longitudinal seam.
  • Spiral welded pipes are produced using a continuous process under stable working conditions. On the other hand, the manufacturing of longitudinal welded pipes is carried out in stages.
  • Longitudinal pipes are normally preferred for smaller-diameter applications whereas spiral welded pipes are best for applications requiring large-diameter pipes with thinner walls.

Spiral Welded Pipe Specification

Spiral welded pipes are also known as helical welded pipes. Common industrial spiral welded pipes are available in the following specifications:

  • Materials: Carbon Steel, Alloy Steel, Mild Steel (IS 3589, API 5L, A53, A572, DIN 2458, IS 1239, BS 1387, EN10217, etc)
  • Outer Diameter Range: 14″ to 100″
  • Wall Thickness Range: 4.8 mm to 25 mm
  • Typical Length: Fixed Length of 6m or 12 m, Also manufactured in random length as per requirements.
  • Test Certificates: As per EN10204

Common Defects of Spiral Welded Pipes

i) The main cause of the bubbles in the center of the weld bead is hydrogen is concealed within the weld metal as bubbles.  Thus, to eliminate this defect, remove the wire and weld the rust, oil, water, moisture, and other things, and then fully dry the flux to remove moisture. Furthermore, a higher current slows the solidification rate of liquid metal, limiting welding speed.

ii) Cracking of sulfur (crack caused by sulfur). The sulfide in the sulfur segregation zone enters the weld metal and causes cracks when welding plates with a strong sulfur segregation zone (particularly soft boiling steel). The explanation for this is the existence of hydrogen in steel and low-melting iron sulfide in the sulfur segregation zone. As a result, using semi-ballasted or ballasted steel with a lower sulfur-containing segregation zone is an effective way to avoid this. Cleaning and drying the weld surface and the flux is also required.

iii) Thermal cracking is a type of cracking caused by heat. Thermal cracks in the weld bead can form in submerged arc welding, particularly at the arc initiating and extinguishing arc craters. Backing plates are installed at the arc starting and arc extinguishing sites to eliminate such cracks. The spiral welded pipe can be reversed and welded into the overlap welding after the coil butt welding. When the weld stress is high, hot fractures are more prone to form.

iv) The presence of welding slag. Welding slag involvement refers to the amount of welding slag that remains in the weld metal.

v) There is a lack of penetration. The overlap between the inner and outer weld metals is insufficient, and the weld is not penetrated. Insufficient penetration is the term for this condition.

References:

  • https://www.nucorskyline.com/globalnav/products/pipe/spiralweld.
  • https://www.dmitubes.com/spiral-welded-pipes.html.

What is a Vibration Sensor? Its Application, Working, Types, and Selection

Written by Anup Kumar Dey in Instrumentation,Maintenance,Mechanical

Vibration Sensors are vibration monitoring equipment used widely by plant maintenance teams to find insight regarding equipment or piping performance. Using vibration sensors and studying the data from these devices, engineers can predict possibilities of equipment failure and they can safeguard major equipment from breakdown by taking proper action. Vibration Sensors are also known as vibration transducers. In this article, we will explore the importance of vibration sensors, their types, working, and selection procedures. Let’s dive into the subject starting with the definition of vibration sensors.

What are Vibration Sensors?

A vibration sensor is a measuring device. As the name implies it senses the vibration or to-and-fro movement of any equipment or system at the location where it is applied. It measures the amplitude and frequency of vibration of the system under study. The most widespread application of vibration sensors is found to measure the vibration of rotating equipment and machines like pumps, compressors, steam turbines, and connected lines. These measured outputs are then studied to detect any imbalance or issues in the asset or equipment under investigation to predict the condition of the system. Vibration sensors are very important components of a vibration-measuring tool.

As vibration impacts the reliability and durability of the system in working conditions it must be measured. Industrial vibration sensors can help in monitoring the vibration issues of systems. Monitoring and measuring the vibration of equipment or systems provide several benefits like:

  • Root cause analysis of any problem.
  • Deciding repairing needs.
  • Checking the overall plant or equipment condition.
  • Overall it reduces plant operating costs by avoiding costly shut-downs in advance.

Applications of Vibration Sensors

Vibration sensors are very useful in all industries wherever there is a possibility of vibration and need to monitor the same for improved asset performance. In general, the following industries find a wide application of vibration sensors:

  • Oil and gas
  • Mining
  • Aerospace
  • Food and beverage
  • Pulp and paper
  • Refining, chemical, petrochemical, and other processing industry.
  • Metalworking
  • Automotive & Transportation
  • Power generation
  • Certain manufacturing industries
  • Wind power and other renewable power
  • Cement
  • Research and Development

There are several industry standards that govern vibration measurement for industries. Some of those are:

  • ISO 4866
  • ISO 20816
  • AS 2625.1

Working of Vibration Sensors

Vibration sensors or vibration transducers can be used either directly mounted on the equipment or used wirelessly to monitor the system. When it is placed in service, the sensors will start working and measure the displacement, velocity, or acceleration of vibration depending on the types of vibration sensors used.

Vibration sensors operate based on mechanical, electromagnetic, or optical principles to detect equipment vibration. Depending on the application requirement, the sensitivity of these vibration sensors may vary, the usual range is from 10 mV/g to 100 mV/g.

Vibration sensors consist of a crystal of piezoelectric material to which is attached a seismic mass. When the crystal is stressed, an electric signal is produced which is measured as output data. They are robust in construction and provide high reliability and long-term stability. Fig. 1 below provides the major components of a typical vibration sensor.

Vibration Sensor Components
Fig. 1: Vibration Sensor Components

If the vibration sensors are placed for a longer duration of time, it will provide the following information:

  • How frequently vibration occurs and
  • The intensity of vibration.

These data then can be compared with standard acceptable data as specified by equipment manufacturers or various codes and standards to find out if that vibration needs attention or not.

Types of Vibration Sensors

The vibration sensors used in industries can be grouped into the following three primary types:

  • Accelerometers or Acceleration Transducers
  • Velocity sensors, and
  • Displacement sensors or Displacement transducers

Accelerometers:

Accelerometers measure the acceleration of motion of a system. This type of vibration sensor converts the mechanical forces of vibration into an electrical signal using the piezoelectric effect. Accelerators are of two types; High impedance accelerometers and Low impedance accelerometers.

Accelerometers as industrial vibration sensors have a more extended high-frequency capability as compared to other types of vibration transducers. Accelerometers are used specifically for rolling element bearing and gear fault detection, detecting unbalance, misalignment, bent shaft, loose or broken parts, component resonances, etc, and are available in various sizes with an extended temperature range of applications.

Velocity Sensors:

Velocity sensors are good for monitoring rotating and reciprocating equipment and for general vibration measurement. This type of vibration sensor is used for medium-frequency measurements. The main advantage of velocity sensors is that they are electrodynamic and do not require external power.

Displacement Sensors:

Displacement Transducers are also known as proximity sensors, eddy current sensors, or proximity transducers and measure displacements. Displacement sensors are suitable for measuring radial vibration, axial movement, eccentricity, internal clearances, differential expansion, etc. This type of vibration sensor is suitable for low-frequency ranges.

Selecting a Vibration Sensor

The selection of a specific type of vibration sensor or vibration transducer is dictated by the application. The main factors that contribute to the selection of vibration sensors are:

  • Range and accuracy of the vibration transducer
  • Environmental conditions where it will be mounted
  • The shape of the measuring surface

In general, displacement sensors are suitable for vibration frequency ranges of 0 to 10 Hz, velocity sensors are suitable for 10 to 100 Hz, and accelerometers are suitable for greater than 100 Hz. The following table provides the selection of vibration transducers based on the frequency of vibration.

Frequency RangeType of Vibration Sensor
0 to 10 HzDisplacement Sensors
10 to 100 HzDisplacement or Velocity Sensors
100 to 1000 HzDisplacement, Velocity, or Acceleration sensors
1000 to 2000 HzVelocity or Acceleration sensors
Greater than 2000 HzAccelerometers.
Table 1: Selection of Vibration Sensors based on the frequency range

Will you be interested to learn more about sensors, their working, and fundamentals in more detail? Then the following two online video courses are just for you: