This article covers the design consideration of emergency response procedures and measures in petroleum refineries, chemical plants, and similar plants. This can be used in conjunction with the Job Specification, the client’s standards and intent, the licensor’s instructions, and related regulations. This article describes the emergency response design consideration of the following emergency measures.
Of the various measures for protecting a plant from the emergency situation, pressure-relieving through safety valves and rupture discs shall be examined first. This part will be covered in separate articles.
Isolation with Emergency Shut-off Valve
This section describes the installation standards of Emergency Shut-off (Block) Valves (ESV)used for isolating the equipment from the units in an emergency.
First, the following should be clarified with the client.
Client’s general philosophy for safety
Reliability for sensor(application of 2 out of 3 or not etc.)
Category of ESV (local, all shut down, etc.)
Inspection under operation (bypass or parallel installation)
The purpose of isolation by ESV is classified into the following.
Equipment Protection (Vessel, Tower)
Heat Off (Furnace, Steam supply)
Fluid or Seal gas Cut(Compressor, Pump), Leak Air Cut (Vacuum Pump)
Emergency Response Plan forVessels
ESV is not always necessary to be provided on the Vessel outlet line.
If both the vessel volume of liquid and fluid condition meet the following requirements, ESV shall be provided on Vessel outlet lines.
(a) Vessel volume-This limitation should be verified with project specifications.
Liquid both flash point below 22.8°C and boiling point below 37.8°C
LPG, Naphtha, liquid with temperature more than auto ignition temp.
A control valve with a solenoid valve may be used as ESV if the following conditions are met:
It is not equipped with a minimum stop
It will close on the failure of the air supply or power failure.
A leak amount of CV is allowable.
The client’s approval is obtained
Emergency Responses for Furnaces
Fuel lines to process furnaces and steam boilers shall be provided with remotely operated emergency valves.
In addition to the above, a manually operated block valve shall be provided in each fuel line. This includes the pilot gas supply line if it is a separate line. These valves shall be located at least 15 meters horizontally from the furnace or boiler protected.
ESV (Emergency shut-off valve) on the snuffing steam line shall be located at least 15 meters horizontally from the furnace and operable from grade.
Emergency responses for Steam Line to Reboiler
ESV will be installed on the steam inlet line to Reboiler especially in the case when the control valve is installed on the Reboiler outlet condensate line.
Emergency Measures for Compressors
ESV shall be provided in the suction and discharge lines of centrifugal compressors to prevent seal gas leakage.
(2) Other specifications for ESV installation are as below.
In case when Control Valve closing time is too slow. (Cost study is necessary)
A Balance line with ESV between suction and discharge may be requested by the client.
Emergency Response Plan for Pumps
ESV will be provided in the suction line of Pumps. (Treated as Vessel Outlet ESV)
ESV may be installed on the discharge line of high-head pumps to prevent backflow.
Emergency Response Guidelines: Vacuum Pumps
In the case of the NASH Pump, ESV will be installed on the suction line (process side) of Vacuum Pumps to prevent seal liquid from backflow into the process.
Emergency Measures: Depressurizing
When metal is exposed to fire, the metal temperatures may reach a level at which stress rupture could occur. The use of an emergency vapor depressurizing system is one method of avoiding such an occurrence.
Design Base of Vapor Depressurizing
The design base of vapor depressurizing is as follows. (Refer to API RP 520, 521)
Depressurizing Valve is of a remotely operated type.
Depressurizing initial pressure may be assumed up to design pressure.
The depressurized level should beat 7.0 kg/cm2 G or 50% of vessel design pressure, whichever is lower.
The duration time of depressurizing should be 15 minutes with a wall thickness of 25 mm, while vessels with thinner walls generally require a somewhat greater depressurizing rate.
Total Vapor Depressurizing Load:
The total vapor load will be obtained as the summation of the following.
Vapor generated from the liquid by heat input from a fire
Density change of the vapor in the equipment during pressure reduction, plus
Liquid flashing during pressure reduction
Design Consideration:
For the recycle compressor stoppage, settling out pressure should be investigated.
Excessive hot depressurizing gas should not be introduced to the flare header. Cooling should be provided in such a case.
As for the temperature effect due to hot depressurizing gas, it is not necessary to take it into account for the determination of the design temperature of each piece of equipment because of short-term conditions. However thermal stress checks of related piping should be necessary as required.
Regarding both pressure and flow rate change along with traveling time, the following tentative method may be available.
Relieving Rate Calculation
The dynamic simulation should be carried out to confirm:
Reactor mechanical bed pressure checks during Depressurizing.
H/E with differential pressure design.
Mechanical damage for Compressor Seal Oil etc.
(NOTE) In the case of Manual Depressurizing with HCV, the above is not necessary.
Emergency Response Procedure: Alarm and Trip System
(a) Alarm and trip signals are indicated on DCS or CCR panel. When the signal tells abnormal situations happened, it is expected that the operator takes appropriate countermeasure actions in accordance with the operating manual.
(b) As for compressor and other package units, alarm and trip signals are indicated on the local panel. Only common alarm and trip signals are indicated on DCS or CCR panel. It is expected that the operator explores the cause of the failure at the local panel and takes appropriate actions in accordance with the operating manual.
(c) Each ESD (Emergency Shut Down) shall be independent of the distributed control system (DCS) and may be activated either by plant transducers (eg. high pressure, low flow) or manually from CCR.
(d) Typical set point for level alarm and level trip
– High / Low alarms at 80% and 20% of the range
– High / Low trips at 90% and 10% of the range
A dedicated level switch is provided for the level trips.
A minimum of 5 minutes will be available for the operator’s intervention after a high or low-level alarm is actuated and before gas breakthrough or liquid flooding takes place. Or an independent ESV is provided for the operator to initiate manually to close the outgoing flow. (to be confirmed by the process engineer)
(e) Setpoint for temperature and pressure alarm and trip.
– As specific to the project, contents shall be individually investigated and clarified.
Emergency Response Procedure: Failures & Trips
The failures for units and equipment, as also trip actions are summarized under the following categories.
Furnaces
Pumps including Hydraulic Power Recovery Turbine
Compressors
The trip sequence is summarized on the PID. It is necessary, however, to prepare the sequence logic diagram at the same time. Also, it is desirable to explain the outline of the trip sequence in the operation manual. Typical TRIP SEQUENCE is as follows.
Trip Sequence
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Thermowells are cylindrical pressure-tight fittings used to protect the temperature sensors such as thermocouples, thermistors, and bimetal thermometers which are inserted into a pipe or vessel in industrial applications. A thermowell is basically a tube closed at one end and mounted in the process stream. The thermowell acts as a barrier between the sensing element and the process medium. It protects the sensing element against corrosive process media and fluid pressure and velocity.
Thermowells also increase the sensor longevity, allow sensor replacement without draining the system and eliminate the probability of contamination. Thermowells are designed for both high and low-pressure applications.
Thermowells find wide applications in many industrial sectors including refining, cosmetics, petrochemical, food processing, chemicals, Power, pharmaceutical, and other process industries.
Thermowells ensure that process temperature is passed to the sensor (proper heat transfer).
Improved heat transfer, results in better accuracy.
Allow the removal of the sensing element while maintaining a closed system.
Types of thermowell
Thermowells in the piping industry can be classified based on various parameters as listed below:
Depending on the stem design shape, four types of thermowell are available:
Straight Thermowell
Stepped thermowell
Tapered Thermowell, and
Built-up thermowells
Straight Thermowell
Straight thermowell has the same diameter for the entire insertion length. They are simple to fabricate and possess good rigidity and offer protection against corrosion and erosion.
Stepped Thermowell
Stepped thermowell have stepped diameters; Normally at the tip, they have a smaller (typically 1/2″) diameter while a larger diameter (Typically 3/4″) at the top. Due to decreased thermal inertia at the process end, these thermowells allow smoother velocities and respond more rapidly to temperature changes than their straight counterparts.
Tapered Thermowell
The tapered thermowell has varying diameters (smooth continuous taper) over its full insertion length. Tapered thermowell is suitable for high-velocity heavy-duty applications and possesses a fast response time.
Built-up Thermowell
Built-up thermowells are suitable for very long process insertion lengths. They are available in all the above types but a length of pipe is welded between the tip and process connection to give the long insertion length.
Fig. 1: Types of Thermowells
Depending on material types, Two types of Thermowells can be found:
Pipe Fabricated.
Bar stock thermowells.
Depending on thermowell end connections, five types of thermowells are available. they are
Threaded thermowells
Weld-In thermowells
Socket Weld thermowells
Van Stone or Lap Joint flanged thermowells
Flanged thermowells
Threaded Thermowell
The threaded type thermowell is generally the least costly and most versatile. Threaded thermowells are normally used for non-corrosive applications. They are screwed into the pipe. Their material is such that it can be welded or brazed to provide additional strength.
Weld-in Thermowell
Weld-in thermowell connections are preferred for food and pharmaceutical industries where contaminants from threads must be avoided.
Socket Weld Thermowell
Socket Weld Thermowells are directly welded into the pipe. Its strong connection helps these thermowells to use as a permanent connection. Applications involving very high temperature and pressure use socket-welded thermowell connections.
Van Stone Thermowell
For high-pressure applications, the Van Stone thermowell is ideal. They are usually machined from a solid bar and are placed in a sandwich position between the nozzle and cover flange. Vanstone flange surface is with a phonographic spiral serration.
Flanged Thermowell
A flanged thermowell is designed with a flange at the top end. This type of thermowell is connected to the pipe using nuts and bolts. Flanged thermowell connections are mostly used in high-temperature applications that require frequent replacements.
Flanged thermowells are used in a wide range of industrial applications where temperature measurement is critical. The flange design allows for easy installation and removal of the thermowell without interrupting the process or requiring any special tools.
Some common applications of flanged thermowells include:
Chemical processing: Flanged thermowells are used to measure the temperature of various chemicals in reactors, vessels, and pipelines.
Oil and gas: Flanged thermowells are used in oil refineries, pipelines, and gas processing plants to measure the temperature of crude oil, natural gas, and other hydrocarbons.
Food and beverage: Flanged thermowells are used in food and beverage processing plants to measure the temperature of liquids, such as milk, beer, and juice.
HVAC: Flanged thermowells are used in heating, ventilation, and air conditioning (HVAC) systems to measure the temperature of air and water.
Power generation: Flanged thermowells are used in power plants to measure the temperature of steam and other fluids used in power generation.
Pharmaceutical: Flanged thermowells are used in pharmaceutical manufacturing processes to measure the temperature of various chemicals, drugs, and biological products.
Overall, flanged thermowells are used in any process where temperature measurement is critical and the protection of the temperature sensor is required from harsh process conditions.
There are two other types of thermowell connections; Scruton thermowell and Sanitary thermowell.
Scruton Thermowell
To avoid damages that can be caused due to the mechanical load and critical condition of the process, the Scruton thermowell is designed. They save time and cost on re-work at the site.
Sanitary Thermowell
A sanitary thermowell is used for isolation and protection of the sensing element of any temperature instrument. To avoid bacterial build-up, Sanitary thermowells are built with hygienic connection.
Fig. 2: Thermowell types based on End Connection
Materials of Thermowells
The right material increases the longevity of a thermowell. Material selection of thermowell will depend on the chemical, temperature, and flow rate of the process fluid. With an increase in temperature and fluid concentration, the corrosive effects of chemicals normally increase. At the same time, suspended particles of the fluid will cause erosion. So all these parameters need to be addressed while selecting thermowell material. Some of the most frequently used thermowell materials are listed below:
Carbon Steel
Brass
SS 316 / SS 304
SS316 with Teflon / Zirconium Coated or Tantalum / Titanium steathing.
However, the most widely used thermowell material is stainless steel as it is cost-effective and highly resistant to heat and corrosion. For pressurized vessels, Chromium/molybdenum steel is used. Cobalt, nickel, chromium, and tungsten constitute the Haynes alloy that is widely used for sulphidising, carburizing, and chlorine-containing environments. The use of carbon steel thermowell is only limited to low-temperature pressure applications due to its very low resistance to corrosion.
Thermowell Insertion Length
The length from the connection point to the thermowell tip is known as the insertion length of the thermowell (U dimension in Fig. 4). For better accuracy, the thermowell insertion length should be long enough. This will allow the entire temperature-sensitive portion of the measurement device to extend into the medium being measured.
For measuring the liquid temperatures using a temperature sensor, the device must be extended into the solution for the length of the temperature-sensitive portion plus a minimum of one inch (25 mm). For gaseous or air service, it should be immersed for the length of the temperature-sensitive segment plus an additional three inches. The temperature-sensitive section of a thermocouple or thermistor is short; therefore, the insertion length of the thermowell can be shorter for these devices. Whereas, the temperature-sensitive section of bimetal thermometers, RTDs, and liquid in glass thermometers is between 1″ and 2″ hence, the thermowells must be immersed at least 2½” in liquid for accurate measurements.
Thermowell Installation
Lagging is used when the thermowell is installed through an insulation media on a pipeline or equipment.
Fig. 3: Examples of Thermowells
An improperly specified thermowells, will result in:
Failure due to poor welding practices.
Poor compatibility with the temperature and media.
Inadequate temperature transfer.
Incompatibility with the process velocity leads to failure due to vibration.
The gap between the OD of the thermocouple sheath and the ID of the thermowell must be very close.
The bore of the thermowell must be uniform and linear.
Design of Thermowells
The design of the thermowell should cater to process media, pressures, temperatures, velocity, specific gravity, etc.
Proper MOC (Material of construction).
Wall thickness Vs response time.
Bore diameter, Insertion length, Taper requirements, Overall length, etc.
Vortex shedding
Calculate the Vibration using Wake Frequency methods.
Fig. 4: Details of Thermowell
Fig. 5: Various dimensions of Thermowells.
Thermowell Installation Requirements
Refer to Fig. 6 and Fig. 7
Fig. 6: Requirements during installation
Fig. 7: Installation Requirements
Selection of a Thermowell
The key parameters to consider while selecting a thermowell are:
Process connection size and type.
Process insertion length
Lagging length
Extension length
Sensor length
Interior diameter (bore) for the sensor or thermometer
Internal threads for the sensor or thermometer
The shape of the thermowell (straight, stepped, tapered, built-up)
Material of construction
Thermowell Design Code
Piping Designers follow ASME PTC 19.3 for guidelines regarding thermowells.
Thermowell Working Principle
The working principle of a thermowell is based on the concept of thermal conductivity, where heat flows from a region of high temperature to a region of low temperature. A thermowell is a protective casing that is used to house a temperature sensor, such as a thermocouple or a resistance temperature detector (RTD). The thermowell is inserted into the process being measured, and the temperature sensor measures the temperature of the process fluid or environment.
The thermowell is designed to protect the temperature sensor from harsh process conditions, such as high pressure, high temperature, and corrosive fluids. The thermowell is typically made of durable material, such as stainless steel or ceramic, and has a closed end that protects the temperature sensor from direct contact with the process fluid. The thermowell also has an opening that allows the temperature sensor to come in contact with the process fluid and measure the temperature.
The thermowell works by allowing the heat from the process fluid to flow through the wall of the thermowell and come into contact with the temperature sensor. The thermal conductivity of the thermowell material is chosen such that it allows for efficient heat transfer while also providing adequate protection for the temperature sensor. The thermowell also serves to isolate the temperature sensor from the process fluid, allowing for accurate temperature measurement even in harsh process conditions.
Overall, the thermowell working principle is based on the concept of thermal conductivity, where the thermowell material allows for efficient heat transfer while protecting the temperature sensor from harsh process conditions.
Thermowell Vibrations
As thermowells are immersed in the process flow, a bending force will be experienced by them. Additionally, depending on the fluid velocity and thermowell diameter, a certain vibrational frequency will be generated leading to thermowell vibration. In general, such vibrations are of small magnitude and considered negligible. But, the thermowell must have sufficient stiffness and rigidity to absorb those vibrations. In such a scenario, tapered thermowells are preferred as they have more stiffness. However, if the generated frequency approaches the natural frequency of the thermowell, it can cause severe unacceptable vibrations. ASME PTC 19.3 provides formulas to determine if a thermowell is acceptable for a given application. Many thermowell manufacturers have generated a velocity rating table that recommends the maximum fluid velocity for their thermowells to avoid resonance.
Wake frequency calculation following the guidelines of ASME PTC 19.3 standard is performed to prove that the thermowell has the strength to handle hydrostatic pressure limit and dynamic static stress in relation to process conditions. Prior to the manufacturing of thermowell, these types of calculations ensure that the thermowells can cope with the stress and strain produced by any kind of process media.
Information required for Purchasing Thermowell
The following information must be supplied to the thermowell manufacturer/vendor while placing an order.
Process Connection Size
Thermowell Insertion Length
Lagging extension
Shank configuration
Process Connection type
Nominal Bore
Thermowell Material
Process Design temperature and pressure
Disadvantages of Thermowell
The main disadvantages of a thermowell are:
Compared to a naked sensor, slightly slower response to temperature changes.
Resistance to flow medium.
Increased cost for purchasing a thermowell.
Differences between a Thermowell and a Thermocouple: Thermowell vs Thermocouple
A thermowell and a thermocouple are both used for temperature measurement, but they are different in their design, function, and application. Here are some of the main differences between the two:
Design: A thermowell is a protective tube that is inserted into a process or fluid to provide a barrier between the sensor and the environment. A thermocouple, on the other hand, is a sensor that measures temperature by generating a small voltage in response to a temperature difference.
Function: The purpose of a thermowell is to protect the temperature sensor, usually a thermometer or a thermocouple, from damage or corrosion in harsh environments, high pressures, or high-velocity fluid flows. The thermowell provides a barrier between the sensor and the environment while allowing the sensor to detect the temperature of the process fluid. A thermocouple, on the other hand, is a sensor that directly measures temperature by generating a voltage in response to a temperature difference.
Application: Thermowells are typically used in process industries such as oil and gas, chemical processing, and food and beverage production. They are often used to protect temperature sensors that are installed in pipelines, tanks, and vessels. Thermocouples, on the other hand, can be used in a wide range of applications, including temperature monitoring in HVAC systems, laboratory equipment, and industrial processes.
In summary, a thermowell is a protective barrier that surrounds a temperature sensor, while a thermocouple is a temperature sensor that directly measures temperature. They have different functions and applications but can both be used for temperature measurement in various industries and applications.
Thermowell Probe
A thermowell probe is a temperature measurement device that consists of a temperature sensor, such as a thermocouple or a resistance temperature detector (RTD), housed inside a protective tube called a thermowell. The thermowell is typically made of metal and is inserted into a process or fluid, providing a barrier between the temperature sensor and the environment. The thermowell is designed to protect the temperature sensor from damage or corrosion caused by harsh process conditions such as high temperatures, high pressures, and corrosive fluids.
The thermowell probe allows temperature measurement without directly exposing the temperature sensor to the process fluid or environment. The thermowell can be removed and replaced if necessary without affecting the process or equipment, making it a useful tool in many industries, including chemical, oil and gas, and food and beverage production. The selection of a thermowell probe depends on factors such as the process conditions, the type of temperature sensor used, and the required accuracy and response time.
Thermowell Temperature Sensor
A thermowell temperature sensor is a device that measures temperature using a thermowell as a protective barrier between the temperature sensor and the process fluid or environment. The temperature sensor can be a thermocouple or a resistance temperature detector (RTD) and is typically housed inside the thermowell, which is inserted into the process or fluid being measured. The thermowell protects the temperature sensor from damage caused by harsh process conditions such as high temperatures, high pressures, and corrosive fluids.
The thermowell temperature sensor is commonly used in industries such as chemical processing, oil and gas, and food and beverage production, where accurate temperature measurement is essential for maintaining the quality and safety of products and processes. The thermowell temperature sensor can be installed directly into pipelines, tanks, and vessels, allowing temperature measurement of liquids, gases, and solids. The thermowell can be designed to meet various requirements, such as high temperature and pressure ratings, different materials of construction, and various process connections. The selection of a thermowell temperature sensor depends on factors such as the process conditions, the type of temperature sensor used, and the required accuracy and response time.
A pipe rack is a very important part of process piping. A Pipe Rack can be defined as a steel-framed structure that supports and carry pipes inside the processing plant and transfer the fluid between equipment and storage facilities or utility areas.
While designing a pipe rack, there are two main factors into which a stress engineer should look at details. Those are
The following write-up will list the considerations while designing the pipe loop and rack loading.
Fig. 1: A typical Pipe rack in a Process Plant
Expansion Loop design and placement
In most organizations, there are no defined criteria for designing and placing an expansion loop in a pipe rack. So most of the time the expansion loop is designed and located based on user experience. The important parameters which govern the design of the expansion loop are listed below:
A. Design/Maximum operating temperature of the line
B. Allowed Displacement or movement (Normally allowed thermal displacement is 250-300 mm inside a loop and 75-100 mm in outside turns)
C. Allowed Expansion stress (normally within 80% of code allowable)
D. Line size (Bigger sizes require more leg to absorb expansion)
E. Loop Supporting Requirements (locations at which the loop will be supported)
F. Fluid type (Normally Flare and condensate lines require a 2D loop)
G. Line sagging criteria from Project specification (Sometimes Steam, Condensate, Two-Phase flow lines, and Flare lines require sagging limited within 3-5 mm for others it can go up to 15 mm)
H. Rack length and width
After having the above-mentioned parameters ready one can proceed to locate the loops over the rack. Follow the below-mentioned steps as a preliminary guideline:
a. Select an elevation of the pipe rack and check what the lines running over that rack.
b. Select the line with maximum temperature first. Check the allowed maximum movement outside loop (say 75 mm) and place the first anchor at a distance that will be nearer to the allowed thermal movement (75 mm) as mentioned above.
c. Now as one anchor is fixed one can easily calculate the thermal displacement at design temperature towards the other end/turn. If the displacement is within the allowed displacement (75mm) then an expansion loop is not required. But if the calculated displacement is more (>75mm) then the expansion loop is required. From this displacement, you can decide how many expansion loops are required for the straight run allowing a maximum of 250-30 0mm displacement inside the loop. (Care should be taken for expansion leg requirement as sometimes allowing 300 mm displacement may cause expansion failure or huge anchor load. In that case, increase the number of expansion loops.)
d. It is better to place lines with high temperatures outside of the rack so that a longer loop length can be achieved on the other side.
e. It is better to nest the loops in a single location (the same structures can be utilized for supporting)
f. Don’t mix lines that required 2D loops with lines that required a 3D loop in the same elevation.
g. It is better to place anchors in similar locations for deciding anchor bay.
Fig. 2: Typical Expansion Loop
h. After deciding the loops check the loop length requirements from Pipe-Data-Pro, Caesar modeling (most optimized approach), Nomograph, Manual calculation, etc.
Rack loading is provided to CSA for the economic design of the pipe rack. Providing pipe rack loading is a very difficult task for a stress engineer as most of organizations do not have any guidelines. Normally Pipe rack loads are transferred in 3 stages:
a. Initial rack loading for rack foundation design (before piling): The project has just started and very little data is available. The piping design places the lines over the rack based on preliminary P&ID. Rack loads are provided mostly based on assumption/experience. Conservative loads are to be provided.
b. Rack loading for member sizing (after 30% model review): Most of the data has started arriving. Loads are to be provided based on actual analysis.
c. Rack loading for final member checking (after 60% model review): All vendors are decided. Line size and locations are finalized. All critical lines are fixed. Loads are provided for checking designed members again. Loads are to be provided based on Software analysis.
Few points to keep in mind while providing Rack loading:
1. Operating, Water filled, and Occasional loads for big-size lines (> 16-inch NPS) are to be provided separately. For guides and anchors, loads with and without friction should be provided.
2. For the Flare line 1/3rd water-filled weight can be considered.
3. Proper directions to be marked.
4. After the long run doesn’t provide a guide in the immediate first possible location after the bend.
5. Consider concentrated loads of inline valves, flanges, equipment, etc.
6. Sometimes large equipment is placed over the pipe racks (Air Fin Fan Cooler, Heat Exchangers, etc). So take the operating weight of equipment from the mechanical group.
7. Cable tray loads are to be taken from the electrical/instrumentation group. (In absence of data a uniformly distributed load of 1.0 KPa for a single level and 1.9 KPa for a double level of cable trays can be considered)
8. Include the forces of PSV reactions if applicable.
In the absence of data, the following guidelines can be used as preliminary piping loads:
a. A uniformly distributed load of 1.9 KPa for piping, product, and insulation can be considered for line size (for each line)
b. For line size larger than 12-inch nominal diameter actual concentrated load including the weight of piping, product, valves, fittings, and insulation shall be used.
Piping insulation is a crucial aspect of any industrial, commercial, or residential piping system. It serves multiple purposes, from conserving energy and reducing heat loss to preventing condensation and protecting pipes from extreme temperatures. The choice of insulation material is critical and depends on several factors, including the operating temperature of the pipes, environmental conditions, and specific industry requirements. In this article, we’ll try to provide in-depth knowledge about all aspects of piping insulation.
Pipe Insulations are materials or combinations of materials wrapped around the pipe which retard the flow of heat energy. Pipe insulation reduces energy losses to a great extent and thereby reducesthe energy cost. Piping shall be insulated as per the insulation class, operating temperature, and insulation thickness stated in the P&ID.
Functions of Pipe Insulation | Why is Piping Insulation Important?
A piping insulation system serves three principal purposes:
The significant reduction in heat transfer of thermal energy to and from the surface of the piping system (Heat Conservation). So, piping insulation conserves energy and improves system efficiency.
The prevention of moisture formation and collection on the surface of the piping system due to condensation on cold surfaces (Cold Insulation).
The prevention of potentially injurious personnel contact with the surface of the exposed piping system (Personal Protection).
However, there are various other benefits of piping insulation as listed below
Piping insulation facilitates temperature control of the process.
Prevent vapor flow and water condensation on cold surfaces.
Increase the operating efficiency of heating/cooling, power, and process systems.
Reduce major damages in the piping during fire or accidents.
Prevent pollutant emissions to the atmosphere to a great extent.
In colder climates, insulation prevents water in pipes from freezing, which can cause bursting and significant damage.
Some insulation materials can dampen sound, reducing noise levels in a facility.
Fireproofing, fire protection, and acoustic insulation (to control noise and absorb vibration) are provided based on project specifications/ ITB requirements.
Fig. 1: Hot and Cold Pipe Insulation
Pipe Insulation Types
Piping insulation can be classified based on various parameters like
Based on the Pipe Insulation Function
Hot Insulation
Cold Insulation
Personal Protection Insulation
Acoustic Insulation
Based on Insulation Material Types
Fibrous Insulation
Cellular Insulation
Granular Insulation
Piping Insulation Types Based on the Function of Pipe Insulation
Hot Insulation
Hot insulation is applied on the hot surfaces of the piping system to prevent the energy flow from flowing fluid. So, the main aim of hot piping insulation is heat conservation. Mineral Wool, Glass Wool, Calcium Silicate, etc. are normally used as Hot insulating material. Hot Piping Insulation is typically applied for process temperatures above 60°C.
Cold Insulation
Cold Insulation is the insulation used on cold surfaces of the piping system to avoid heat gain from outside (Cold Conservation) or to avoid Condensation. Polyurethane Foam, Expanded Perlite Foam, Expanded Polystyrene Foam, etc. are the widely used cold insulating materials.
Personal Protection Insulation
Personal Protection insulation is provided to avoid personal heat injury. All exposed piping surfaces that exceed 60 degrees C are provided with personal protection insulation. The areas that are not accessible by construction or operating personnel can be left exposed. An open mesh metal guard (Fig. 2), mineral wool, etc. are used as personal protection insulation material.
The criteria for personal protection is that the exposed surfaces located within 600 mm horizontally or 2100 mm vertically of a normal access, walkway, or work area are to be insulated.
Acoustic insulation
Acoustic Insulation is provided for all piping that is considered a potential sound source. The main purpose is to reduce the noise (vibration) to an acceptable limit. The minimum thickness for acoustic insulation is normally 75 mm. Acoustic Foam, fiberglass, polyester/polyurethane foams, rock wool, Mass Loaded Vinyl, etc. are used as Acoustic Insulating material.
Fig. 2: Personal Protection Insulation in Operating Plant
Piping Insulation Types based on insulation material types
Fibrous Insulation
Fibrous insulation consists of small diameter fibers which finely divide the air space. The fibers may be perpendicular or parallel to the surface being insulated, and they may or may not be bonded together.
Common fibers used in piping insulation are Silica, slag wool, rock wool, and alumina-silica. Among these, Glass fiber and Mineral Wool are the two most widely used piping insulations of this type. Their fibers are normally bonded with organic binders for structural integrity.
Cellular Insulation
Cellular pipe insulation material comprises small individual cells separated from each other. Common cellular materials used as pipe insulation are glass or foamed plastics such as cellular glass, phenolic foam, or nitrile rubber.
Fig. 3: Typical Piping Insulation for Bends
Granular Insulation
Small nodules containing voids or hollow spaces constitute granular insulation. As gas can be transferred between the individual spaces, It is not considered a true cellular material. This type is manufactured as loose or pourable material or combined with a binder and fibers. Sometimes they undergo a chemical reaction to form rigid insulation. Calcium silicate and vermiculite are examples of these types of insulations.
Pipe Insulation Material
Low-temperature insulation is frequently made of expanded cellular plastic or foam rubber material.
Moderate temperature insulations are made from grass fiber products.
High-temperature insulation is made of preformed cementations or refractory materials or blankets made from ceramic fibers.
Insulation and accessory materials have to be 100% asbestos-free.
Normally mineral fiber, cellular glass, ceramic fiber, glass fiber, polyisocyanurate, polyurethane foam, Rockwool, Glass Wool, Expanded Perlite, Flexible Elastomeric Foam (FEF), Flexible aerogel blanket, Calcium magnesium silicate wool (CMS), Alkaline earth silicate wool (AES), Calcium Silicate, etc. are used as pipe insulation material.
The following table provides details of some commonly used insulation materials:
Pipe Insulation Material
Density (kg/m3)
Temperature Limitation
Mineral Glass Fibre
up to 535°C
Mineral Wool
140
up to 700°C
Rock Wool
140
up to 550°C
Glass Wool
80
up to 450°C
Calcium Silicate
200-280
up to 815°C
Expanded Perlite
192
up to 550°C
Expanded Silica
up to 535°C
Refractory Fiber
150
up to 1750°C
Polyurethane Foam
40
from -150°C to 110°C
Polyisocyanurate
40-64
from -150°C to 125°C
Cellular Glass
147
up to 350°C
Ceramic Fibre
250
up to 760°C
Table 1: Pipe Insulation Material Table
Some Typical Pipe Insulation materials are described below:
Fiberglass Insulation: Fiberglass is one of the most common and widely used insulation materials. It is made from fine glass fibers and is available in pre-formed sections, blankets, or wraps.
Mineral Wool (Rockwool) Insulation: Mineral wool, also known as rockwool or slag wool, is made from molten rock or industrial waste products spun into fibers. It is known for its excellent fire-resistant properties. It can withstand temperatures up to 700°C.
Cellular Glass Insulation: Cellular glass insulation is made from crushed glass that is heat-treated to create a closed-cell structure. This material is highly resistant to moisture and chemicals. ASTM C552 gives the Standard Specification for Cellular Glass Thermal Insulation.
Foam Glass Insulation: Foam glass is another form of cellular glass insulation but is produced using a different process that results in a lighter, more flexible material.
Polyurethane Foam (PUR) Insulation: Polyurethane foam is a versatile insulation material known for its low thermal conductivity and high resistance to water. It is available as spray foam or pre-formed sections. It can operate effectively between -150°C to 110°C.
Elastomeric Foam Insulation: Elastomeric foam insulation is a flexible, closed-cell material made from synthetic rubber. It is particularly effective in preventing condensation on cold pipes.
Calcium Silicate Insulation: Calcium silicate is a high-temperature insulation material made from lime and silica. It is widely used in industrial applications due to its durability and thermal stability. It is effective up to 815°C. ASTM C533 provides the Standard Specification for Calcium Silicate Block and Pipe Thermal Insulation.
Aerogel Insulation: Aerogel is a cutting-edge insulation material known for its ultra-low thermal conductivity. It is one of the lightest solid materials available and offers superior insulation performance. Its effective temperature range is from -268°C to 650°C.
Piping Insulation System
The main part of the Piping insulation system is the insulating material. Other elements that constitute the pipe insulation system are
Insulations are manufactured in a variety of forms to suit specific applications and functions. The installation method is decided by the combined insulation form and type of insulation. The most widely used insulation forms are:
Rigid boards, sheets, blocks, and pre-formed shapes: Cellular, granular, and fibrous insulations are produced in these forms.
Flexible sheets and pre-formed shapes: Cellular and fibrous insulations are produced in these forms.
Flexible blankets: Fibrous insulations are produced in flexible blankets.
Cement (insulating and finishing): Produced from fibrous and granular insulations and cement, they may be of the hydraulic setting or airdrying type.
Foams: Poured or froth foam used to fill irregular areas and voids. The spray is used for flat surfaces.
Fig. 4: Mineral Wool Piping Insulation
Normally, Rock and Glasswool are pre-formed in two halves; Polyisocyanurate, Polyurethane, and Cellular Glass are supplied in preformed cylindrical shapes to slit in half lengthwise, and ceramic fiber is supplied in blanket strips.
Piping Insulation Standards
The following codes and standards provide guidelines for industrial piping insulation:
Fig. 5: Insulated and Non-insulated piping in the Operating plant
Piping Insulation System Design Considerations
Some important design considerations related to piping insulation (May vary from project to project):
All insulating materials need to be free from harmful products affecting human health and the environment. To be more specific, the piping insulation material needs to be free from known carcinogens, asbestos, Chlorofluorocarbon (CFCs), Hydrochlorofluorocarbon (HCFCs), heavy metals such as lead or cadmium, and PCBs.
Insulation thickness is determined based on pipe size, normal operating temperature, temperature controlling requirement (extent of heat loss/gain), etc. At a minimum 25 mm pipe insulation thickness is to be used.
If the insulation thickness is more than 75 mm then insulation is provided in two or more layers (multi-layer).
Insulation shall not be applied until hydrostatic/ pneumatic testing is performed.
Insulation up to 12-inch NPS pipe shall be held with SS-304 tie wire and for > 12-inch NPS SS-304 bands are used.
All flanges will be insulated other than hydrogen service or high health hazard material services.
Certain piping items like vents, steam-out and snuffing steam systems, flare and blow-down systems; Piping supports; Steam Traps; Expansion joints, hinged joints and hose assemblies; Instrument connections; Sight flow indicators, etc. are usually not insulated.
Each pipe must be insulated separately except where the second pipe is for heat tracing.
Piping Insulation Thickness Chart
A piping insulation thickness chart is a reference chart for piping engineers, designers, and insulation installers when determining the appropriate insulation thickness for various piping systems. The insulation charts are made by economic pipe insulation thickness calculation and presented in a tabular format for easy reference. The piping insulation thickness chart typically includes information on pipe insulation thickness corresponding to the operating temperature range and pipe sizes. A separate table for each type of piping insulation (Hot, cold, or personal protection) is prepared.
The following Image (Fig. 6) shows a typical pipe insulation thickness chart for Heat Conservation Insulation. Note that the image only provides a sample reference for the piping insulation thickness chart, for actual values you must refer to your project-specific data.
Fig. 6: Typical Pipe Insulation Thickness Chart for Hot Insulation
Choosing the right type of piping insulation depends on various factors, including the temperature range of the system, environmental conditions, and specific industry requirements. Proper installation and maintenance of insulation are also crucial to achieving the desired performance.
Frequently Asked Questions: Piping Insulation
How does pipe insulation work?
Pipe insulation works by creating a barrier that reduces the transfer of heat between the pipe and its surroundings. This barrier minimizes heat loss in hot pipes and prevents heat gain in cold pipes. Additionally, insulation prevents condensation on cold pipes and provides a layer of protection against extreme temperatures, which can prevent freezing or overheating.
How thick should pipe insulation be?
The thickness of pipe insulation depends on several factors, including the temperature of the fluid inside the pipe, the ambient temperature, and the type of insulation material used. For most applications, insulation thickness ranges from 1/2 inch to 2 inches. Higher temperatures or more extreme environments may require thicker insulation for optimal performance. The thickness of piping insulation is calculated during the detailed design phase of a project as explained here.
How do I select the right pipe insulation?
Selecting the right pipe insulation involves considering several factors:
Temperature Range: Ensure the insulation can handle the operating temperature of your system.
Moisture Resistance: If the pipes are exposed to moisture or humid environments, choose insulation with good moisture resistance.
Fire Resistance: For high-temperature or fire-rated systems, select a material with excellent fire resistance.
Cost and Availability: Consider the cost and availability of the insulation material.
Specific Application: Different environments and applications may require specialized insulation types, such as cryogenic systems or underground piping.
What is the best insulation material for pipes?
The best insulation material depends on the specific application. Fiberglass is popular for general use due to its affordability and effectiveness. Mineral wool is preferred for high-temperature applications, while elastomeric foam is ideal for preventing condensation on cold pipes. For extreme environments, materials like cellular glass or aerogel may be the best options.
How do I install pipe insulation?
Installing pipe insulation typically involves the following steps:
Measure and Cut: Measure the length and diameter of the pipe and cut the insulation material to fit.
Wrap or Slip On: Depending on the material, either wrap the insulation around the pipe or slip pre-formed sections over it.
Seal the Joints: Use appropriate adhesive, tape, or fasteners to seal any joints or seams to prevent heat loss or moisture ingress.
Protect and Finish: In some cases, especially outdoors or in high-traffic areas, you’ll need to apply a protective jacket or coating over the insulation.
Can pipe insulation be used on hot pipes?
Yes, pipe insulation is commonly used on hot pipes to reduce heat loss, improve energy efficiency, and prevent burns from accidental contact. Materials like fiberglass, mineral wool, and calcium silicate are particularly suited for insulating hot pipes.
Can pipe insulation be used on cold water pipes?
Yes, pipe insulation is effective on cold water pipes. It helps prevent condensation, which can lead to mold, corrosion, and water damage. Elastomeric foam and fiberglass are often used for cold water pipes due to their moisture-resistant properties.
What is the most effective pipe insulation?
The most effective pipe insulation in terms of thermal performance is aerogel insulation. It has an exceptionally low thermal conductivity, meaning it provides superior insulation with thinner layers compared to other materials. However, aerogel is also more expensive and may be overkill for standard applications.
Gas hydrates are ice-like crystalline minerals normally formed from methane and water. When Low molecular weight gases solidify at low temperatures and moderate pressure conditions, gas hydrates are formed. In marine sediments and permafrost, gas hydrates can occur naturally. It is believed that gas hydrates are present on other planets, too.
As exploration and development activities have moved into deeper water, gas hydrates are an increasingly important concern. This presentation gives an overview of gas hydrates including what they are, why there is so much interest in them, and ends with what areas are of interest to MMS, both in the short term and long term.
What are Gas Hydrates?
Gas hydrates are crystalline or ice-like structure that forms a cage around a molecule of gas, as you can see from Fig. 1. The water molecules are bonded to form the structure and, in this case, a methane molecule is trapped inside. The gas that is trapped can be methane, carbon dioxide, hydrogen sulfide, and some smaller hydrocarbon molecules like ethane, butane, and propane.
Fig. 1: Structure Gas Hydrate
The cage can take several forms as seen in Fig. 2. All three have been observed in nature, but they can also be synthesized in the laboratory. The interest in methane hydrates as a potential resource result from the trapping capability of the hydrate structure. Essentially, hydrates concentrated gas by a ratio of 1:160. What this means, is that in one cubic foot of hydrate, about 160 cubic feet of gas is trapped. This would be 160 cubic feet at standard temperature and pressure.
Fig. 2: Various Hydrate Structures
Elements for Gas Hydrate Formation
The formation of gas hydrates needs the following five Ingredients
Water
Gas – CH4, CO2, C2H6, H2S, etc.
Pressure
Temperature
Nucleation Site
How are gas hydrates formed?
For gas hydrates to form, several ingredients are necessary. Of course, you need water to form the cage and gas to fill the cage. The reason that hydrates are of interest in deep water is that they also need high pressures and low temperatures. In addition, a nucleation site is required. The nucleation site would be a surface such as a grain of clay or a pipeline or a piece of the platform. This is why you don’t find hydrates floating around in seawater.
Fig. 3: Examples of Gas Hydrates
Fig. 3 shows some examples of hydrates that have been recovered. In the top picture, you can see the white banding, which is the hydrate. The lower left picture is a nodule of hydrate and on the right is a hydrate recovered from the Gulf of Mexico, which is coated with oil. As you can see, hydrates from within the sediments and you would not expect to find huge blocks of hydrate in the sediments, there isn’t room for them to form.
Disadvantages of Gas Hydrates
There are several reasons for the interest in gas hydrates. The safety issues include the plugging of flowlines and geohazards. Methane hydrate is considered a potential resource. And of environmental concern, sensitive biological communities exist on outcrops. Hydrates may also contribute to global warming.
Scale Inhibitor- To reduce the scale formation due to the precipitation of mineral compounds present in water
Gas Hydrate- Inorganic salts/ crystals containing water molecules
Demulsifier– Emulsion breaker (Use to separate emulsion e.g. water in oil)
Corrosion Inhibitor–To reduce the rate of corrosion ( Anodic Inhibitor / Cathodic Inhibitor / Oxygen scavenger)
Microbicides – Antiseptics used to counter microbial corrosion
Scale Inhibitor:
Scale is a hard crystalline deposit resulting from the precipitation of mineral compounds present in water.
Oilfield scales typically consist of one or more types of inorganic deposits along with other debris organic precipitates, sand, corrosion products, etc.
Carbonate and Sulfate scales – Add to pressure drop
Cause of scale deposits
formation damage (near well bore)
blockages in perforations, gravel packs, or screens
