Recent Posts

What is HVAC Piping? Types, Materials, and Standards for HVAC Piping

Written by Adarsh in Piping Design Basics

Heating, Ventilation, and Air Conditioning (HVAC) systems are crucial for maintaining comfortable indoor environments. A key component of these systems is the piping that transports fluids—be it hot water, chilled water, or refrigerants. This blog will explore HVAC piping in detail, including types, materials, design considerations, and installation techniques.

1. What is HVAC Piping?

HVAC piping, or heating ventilation and air-conditioning piping, delivers hot water, cool water, refrigerant, condensate, steam, and gas to and from the HVAC components. These systems are vital for distributing conditioned air, heating, and cooling different areas effectively. HVAC systems provide thermal comfort for the occupants, accompanied by indoor air quality.

2. Importance of HVAC Piping

HVAC pipe systems are used in industrial, commercial, residential, and institutional buildings for different purposes, like

  • To add or remove heat from the air inside the building. 
  • Control the humidity. 
  • Filter the air in the building. 
  • Bring fresh air into the building.

So, for this process, HVAC piping systems use chilled water, hot water, condensate water, condensate drainage, refrigerant, steam, and gas to deliver from HVAC equipment using piping networks. Using HVAC piping in HVAC systems is highly efficient and affordable.

3. Cooling and Heating System of HVAC Piping

The cooling system consists of chilled water and condensate water. Chilled water systems pump water in a closed loop and never get mixed with other condensate water. Heat is absorbed and passed off at three main points in the chilled water systems. The first point is the fan coil unit located throughout the buildings. The next one is the chiller, which uses a refrigerator to cool the chilled water and act as a heat exchanger, and the next one is the condensate water system acting as an open loop, that exposes the water to the atmosphere at the cooling towers.

The heating system, which is capable of adding heat to the occupied space, adds up both the steam system and the hot water system. Which uses a boiler to produce the steam, usually fired up by natural gas or fuel oil. Boiler pressure is used to force the steam through the piping system to a heat exchanger. Inside the heat exchanger, the heat is transferred into the hot water and is carried to the occupied space. Steam traps are used to collect the condensate after the steam has given off its heat and allowed it to condense back to a liquid state. Condensate pumps are used to pump the condensed water back to the boiler to proceed again. The next one is the hot water system, which is also a closed-loop system. Which gets its heat from the heat exchanger and is pumped into the spaces within the buildings which are to be heated. These cooling and heating piping networks are collectively called HVAC piping systems.

4. Types of HVAC Piping Systems

The HVAC piping system can be classified into two parts; the piping in the central plant equipment room and the delivery piping. The central plant equipment room consists of the pipe networks connected to the rotating equipment and tanks. They are connected to different types of equipment like heat exchangers and pumps over the pump room. From these regions, the piping network transports the process liquid to the other parts of the building using the delivery piping. Again, they can be classified as follows:

4.1 Hot Water Piping

Hot water piping is used in hydronic heating systems where water is heated and circulated to provide warmth. Key considerations include:

  • Pipe Materials: Common materials include copper, PEX (cross-linked polyethylene), and steel.
  • Insulation: Insulating hot water pipes prevents heat loss and improves system efficiency.

4.2 Chilled Water Piping

Chilled water piping is used in air conditioning systems to transport chilled water from chillers to air handling units. Important aspects include:

  • Pipe Size: Proper sizing is critical for maintaining desired flow rates and efficiency.
  • Temperature Control: Maintaining chilled water temperature is vital for system performance.

4.3 Refrigerant Piping

Refrigerant piping is used in refrigeration and air conditioning systems. Key considerations include:

  • Type of Refrigerant: Different refrigerants require specific types of piping and connections.
  • Pressure Ratings: Refrigerant lines must be rated for the pressures they will encounter.

4.4 Ventilation Piping

Ventilation piping, often referred to as ducting, facilitates the movement of air in HVAC systems. While technically not piping, understanding its role is crucial for a complete picture. Considerations include:

  • Material Types: Galvanized steel, aluminum, and flexible duct materials are common.
  • Airflow Efficiency: Proper sizing and sealing are critical for minimizing energy loss.

Fig. 1 below shows a typical air duct piping.

Example of a Air Duct Piping
FIg. 1: Example of an Air Duct Piping

5. HVAC Piping Materials

The effectiveness of the piping is influenced by the materials used to make it. Copper and steel are the two major types of metals used for HVAC piping. 

  1. Copper is used mostly for smaller piping, transporting water in AC units with a maximum commercial size of about 12 “as the use of copper is more expensive than that of other materials available. So the piping used in HVAC is 3 “and smaller. 
  2. Steel, on the other hand, is much cheaper and is used for large sizes. It can also withstand higher pressure than copper and is ideal for both hot and cold water. It usually allows for a range of temperatures and pressures. Sch 40 and Sch 80 pipes of the same are acceptable for several HVAC applications.

For chilled and heating water services 8” and above, ASTM A53 or A135 (light wall black steel pipe) are used.

ASTM A120 and A53 (black steel pipe Sch. 40) are used up for services like

  1. Chilled and heated water piping
  2. Miscellaneous drains and overflows
  3. Emergency generator exhaust
  4. Safety and relief valve discharge
  5. Chemical treatments
  6. High- and low-pressure steam
  7. Steam vent

ASTM 120 and A53 Sch. 80 (black steel pipe) are used for pumped and gravity steam condensate return.

ASTM A120 Sch. 40 (galvanized steel pipe) can be used up for miscellaneous indirect wastewater pipes.

ASTM B88 (copper pipe) used for,

  1. Industrial cold water (above grade-type L) for piping 4 “and smaller.
  2. Refrigerant piping (type L, hand-drawn) below 6“
  3. Chilled and heating water (type L and hand-drawn) below 3”.

Underground pipes need to have cathodic protection to prevent corrosion from dirt. Which is coating it in a thin layer of some other metal, such as zinc, to absorb the corrosion. The flanges used are per ANSI B16.1. Cast iron or steel is used for screwed pipe and forged steel welding necks are used for welded line sizes.

Plastic piping, which is much cheaper than copper and steel, is another common material used for HVAC applications. They are thinner and weaker and won’t be able to withstand much pressure. It doesn’t get corroded, which makes it suitable for underground uses. PVC and CPVC are the two types of plastic piping commonly used. They won’t be able to withstand a wide range of temperatures as metal.

6. HVAC Piping Insulation

Depending upon the existing code conditions, they may or may not be insulated. Usually, they are insulated with closed-cell elastomeric foam pipe insulations due to their closed-cell structure and built-in vapor barrier. They range from -297°F to +220°F HVAC pipe services.

There are also different types of insulation, like mineral fiber insulation (glass fibers bonded with thermosetting resin), which includes

  • Preformed pipe insulation (comply with ASTM C547)
  • Blanket insulation (ASTM C553)
  • Fire-resistant adhesive
  • Vapor retarder mastics
  • Mineral fiber insulating cement (ASTM C195)

Prefabricated thermal insulating fitting covers (ASTM C450) and elastomeric cellular thermal insulations (ASTM C 534).

Buried HVAC piping parts are wrapped in accordance with AWWA C209 and C214.

The minimum thickness of the insulation can be determined using the following equation:

MInimum Insulation Thickness Equation for HVAC Piping

Here,

  • T = minimum insulation thickness (inches).
  • r = actual outside radius of pipe (inches).
  • t = insulation thickness specified in Fig. 2 below for applicable fluid temperature and pipe size.
  • K = Conductivity of alternate material at mean rating temperature indicated for the applicable fluid temperature (Btu × in/h × ft2 × °F).
  • k = the upper value of the conductivity range specified in Table 606.4 for the applicable fluid temperature.
Minimum Pipe Wall Thickness
Fig. 2: Minimum Pipe Wall Thickness

7. HVAC Piping Design Considerations

7.1 HVAC System Load Calculation

Accurate load calculations are essential for determining the appropriate pipe size and type. Factors to consider include:

  • Building size and orientation
  • Insulation levels
  • Local climate conditions

7.2 Pipe Sizing

Pipe size affects flow rates and pressure loss. The following guidelines should be considered:

  • Hydronic Systems: Follow the recommended guidelines for water flow and pipe size.
  • Refrigerant Lines: Use manufacturer specifications for proper sizing.

7.3 Layout and Routing

Proper routing minimizes bends and obstacles, reducing pressure loss and improving efficiency. Considerations include:

  • Avoiding sharp turns and excessive lengths
  • Ensuring accessibility for maintenance

7.4 Insulation Requirements

Insulating pipes is critical for energy efficiency. Key factors include:

  • Hot Water Pipes: Insulation thickness should prevent heat loss.
  • Chilled Water Pipes: Insulation prevents condensation and energy loss.

8. Analyzing HVAC Piping Systems

Analysis of the system includes checking the piping system for its compliance with code requirements in stresses under different loading conditions. Operating conditions will be design temperature, ambient temperature, operating temperature, design pressure, and hydro test pressure. Materials required are selected accordingly as per the process parameters. Sometimes, expansion compensators are used to accommodate the expansion and contraction of the HVAC piping network.

In these cases, mostly ASME B31.9 (utility service piping) is used, sometimes B31.3 and B31.4 for underground piping. 

Verifying the displacement and loads on supports in the overall systems. Usually, the plastic piping will have more displacements due to its elastic properties. Quality assurance must also be made sure. The piping material and installation shall meet the requirements of the local building codes and service utility requirements.

9. Support Spacing of HVAC Piping System

The usual support span for horizontal HVAC piping systems is provided in the table below:

Pipe SizeMaximum Support SpacingCommon Hanger Diameter if supported using Rigid hangers
1/2 to 1-1/4 inches (12.7 to 31.75 mm)6 feet 6 inches (2 m)3/8 inch (9.5 mm)
1-1/2 to 2 inches (38.1 to 50.8 mm)10 feet (3 m)3/8 inch (9.5 mm)
2-1/2 to 3 inches  (63.5 to 76.2 mm)10 feet (3 m)1/2 inch (12.7 mm)
4 to 6 inches (101.6 to 152.4 mm)10 feet (3 m)5/8 inch (15.9 mm)
8 to 12 inches (203.2 to 304.8 mm)14 feet (4.25 m)7/8 inch (22.2 mm)
14 inch (355.6 mm) and over20 feet (6 m)1 inch (25 mm)
PVC (All sizes)6 feet (1.8 m)3/8 inch (9.5 mm)
C.I. Bell and Spigot (or No-Hub)5 feet (1.5 m) at joints3/8 inch (9.5 mm)
Table 1: Support Span for HVAC piping systems

Horizontal Cast iron HVAC pipes are supported adjacent to each hub, with 5 feet (1.5 m) maximum spacing between supports/hangers. Vertical HVAC pipes are generally supported on every floor. Vertical cast iron pipes are supported at each hub.

10. Joining HVAC Piping

Usually, the following guidelines are followed for joining HVAC piping during installation:

  • HVAC piping systems are joined using the method suggested by the manufacturer in accordance with applicable codes and standards.
  • For copper HVAC piping Soldered joints are used.
  • For steel HVAC piping, Screwed, Flanged, or Welded joints are used.

11. Installation of HVAC Piping System

11.1 Pre-Installation Planning

Before installation, careful planning is essential:

  • Blueprint Review: Ensure all piping plans align with the HVAC layout.
  • Material Inventory: Confirm all materials and tools are on-site.

11.2 Pipe Supports and Hangers

Proper support is vital for preventing sagging and ensuring structural integrity:

  • Support Spacing: Follow manufacturer guidelines for spacing of hangers.
  • Material Selection: Choose hangers that can withstand the system’s weight and conditions.

11.3 Joining Techniques

Different materials require specific joining techniques:

  • Copper: Use soldering or brazing.
  • PEX: Utilize crimp or clamp fittings.
  • Steel: Use threaded or welded connections.

11.4 Testing and Commissioning

After installation, testing ensures the system operates correctly:

  • Pressure Testing: Check for leaks and ensure system integrity.
  • Flow Testing: Verify that flow rates meet design specifications.

12. HVAC Piping Standards

HVAC piping standards are established guidelines that ensure the safety, efficiency, and reliability of piping systems in heating, ventilation, and air conditioning applications. These standards cover various aspects of piping, including materials, design, installation, testing, and maintenance. Below are some key HVAC piping standards:

12.1 ASHRAE Standards

  • ASHRAE 15: This standard outlines safety requirements for refrigeration systems, including guidelines for refrigerant piping and system design.
  • ASHRAE 90.1: It provides minimum requirements for energy-efficient design in buildings, affecting HVAC system design and piping efficiency.

12.2 International Plumbing Code (IPC)

  • This code provides guidelines for the installation and maintenance of plumbing systems, including those that may interface with HVAC systems, particularly in hydronic heating and cooling applications.

12.3 National Fire Protection Association (NFPA)

  • NFPA 54: This standard governs the installation of gas piping systems, ensuring safety in HVAC systems that use gas as a fuel source.
  • NFPA 90A: This standard covers the installation of air conditioning and ventilating systems to reduce fire risks.

12.4 ANSI/ASME Standards

  • ANSI A13.1 or ASME A13.1 is recommended for identifying piping systems in industrial, commercial, and institutional settings, as well as in buildings designed for public assembly.
  • ASME B31.5 provides guidelines for “Refrigeration Piping and Heat Transfer Components.
  • ASME B31.9 provides guidelines for “Building Services Piping.”

13. HVAC Piping Specification

HVAC piping specifications detail the materials, dimensions, installation procedures, and performance requirements for piping used in heating, ventilation, and air conditioning systems. These specifications ensure the safe, efficient, and reliable operation of HVAC systems. In general, the HVAC Piping specification provides the following information:

  • Piping Material Details
  • Fitting and Valves
  • Pipe sizing
  • Insulation Requirements
  • Support Requirements
  • Testing and Commissioning Requirements
  • Maintenance Considerations
  • Documentation and Compliance Requirements

A well-defined HVAC piping specification ensures that systems operate efficiently and safely. It serves as a crucial reference for designers, installers, and maintenance personnel, facilitating proper installation and compliance with industry standards.

14. HVAC Piping Frequently Asked Questions with Answers

What is HVAC piping made of?

HVAC piping is usually made of Steel, Copper, or PVC. For smaller pipes, Copper is used. In general, copper as an HVAC piping material is selected for lines below 3 inches.

What type of pipe tubing is most common in the HVAC industry?

The most widely used HVAC pipe tubing is made up of copper. They are widely used in both refrigerant and heating systems. However, recently, PEX tubing is replacing copper tubing in cold and hot water applications.

What is a two-pipe HVAC system?

A two-pipe HVAC system is a cost-effective HVAC piping solution that uses the same piping system alternately for chilled water cooling and hot water heating.

What type of pipe is used for chilled water?

For chilled water piping systems, steel pipe is the most widely used material.

What type of copper pipe is used for HVAC?

Type L copper pipe, which is available in rigid as well as flexible forms, is used in HVAC piping systems.

What is an Ejector? Types, Parts, Datasheet, and Working Principles of Ejectors

Written by Partha Pratim Panja in Process

What is an Ejector?

An Ejector is a piece of equipment often used to eject gases and vapors or non-condensable from a system to generate a vacuum. Ejectors are used in several industries in numerous ways including chemicals, pharmaceuticals, FMCG, petrochemicals & refineries, etc.

Working Principle of an Ejector

An ejector follows Bernoulli’s Principle i.e. when the kinetic energy of a fluid increases its pressure energy decreases to maintain total energy constant & vice versa. Equation 1 clearly indicates that if velocity increases pressure energy decreases.

P+(1/2)ρV2+ρgh=Constant……….(1)

Where,

  • P= Pressure energy
  • (ρV2)/2  = Kinetic energy per unit volume
  • ρgh       = Potential energy per unit volume
  • ρ            = Density
  • V            = Velocity

The ejector has a converging section in which velocity increases to convert pressure energy into kinetic energy. This transformation results in a low-pressure region that provides the motive force to draw the process fluid. Then both the fluid is mixed & flows through the diverging section consisting of a diverging nozzle. As it propagates through the diverging section the kinetic energy converts into pressure energy by decreasing its velocity and increasing the pressure. Finally, by re-compressing the mixed fluid it meets the destination pressure.

How vacuum is created in an Ejector?

In the ejector, the velocity of the motive fluid becomes very high as it expands across the converging and diverging nozzles from motive pressure to the operating pressure of process fluid. The expansion of the motive fluid through the motive nozzle causes supersonic velocities at the exit of the nozzle. Velocity coming out from a motive nozzle is 3 to 4 times the Mach number. In the actual scenario, the motive fluid expands to a pressure lower than the suction process fluid pressure. This causes the driving force to draw the suction fluid into the ejector. High-velocity motive steam entrains and mixes with the suction fluid.

Main Parts of an Ejector

There are five main parts of an ejector which are as follows,

STEAM CHEST: This is the part of the ejector where the high-pressure motive fluid is entered into the ejector.

SUCTION CHAMBER: It is a chamber that has proper connections for the process inlet, diffuser section, and motive nozzle.

INLET DIFFUSER:  It is a properly shaped introductory section and converging diffuser zone that handles the high velocity of the fluids. In this section, entrainment and mixing of the motive and process fluids occur, and the energy of supersonic velocity is converted to pressure energy.

THROAT SECTION: This section is the transition section where the converging section ends and the diverging section begins. Basically, it is located at the junction of the converging supersonic inlet diffuser and the diverging subsonic outlet diffuser.

OUTLET DIFFUSER: It is a properly shaped diffuser section for accomplishing the conversion of velocity head to pressure head. After passing the fluid through the throat of the diffuser, the velocity becomes essentially subsonic. The outlet of the diffuser section further decreases the fluid velocity to a significant level so as to convert the kinetic energy to pressure energy.

Parts of an Ejector
Fig. 1: Parts of an Ejector

Types of Ejectors

Ejectors are mainly categorized into two types which are as follows,

  • Single-Stage ejector
  • Multi-Stage ejector

Single-Stage Ejector

Single-stage ejectors are the simplest and most frequently used in industries. They are generally recommended to use for pressures from atmospheric to 80 torrs or for compression ratio <10. A single-stage ejector discharges at or near atmospheric pressure.

Multi-Stage Ejector

A multi-stage ejector is normally used when a generation of high vacuum is required that is normally from the atmosphere to in the range of 30 torrs to 0.05 torr. For the generation of such low pressure, up to six stages of the ejector can be used.

What is Motive Fluid?

Motive fluid is the fluid that motivates the process fluid to draw into the ejector. Normally, high-pressure steam is used as a motive fluid, but compressed air or gas can also be used as the motive fluid. The choice depends on the availability of the utility, operational feasibility, etc. A minimum pressure of the motive fluid is required to maintain a stable operation & thereby to design a stable ejector system. If the pressure of the motive fluid falls below the design pressure, then the nozzle will pass less steam than required. If it happens, the ejector is not provided with sufficient energy to compress the process fluid to the design discharge pressure. A similar problem occurs when the supply temperature of motive fluid rises above its design value, which results in increased specific volume, and consequently, less steam passes through the motive nozzle.

What is a Gas Ejector?

A gas ejector is an ejector which utilizes high-pressure gas as a motive fluid. The motive gas can be compressed natural gas, nitrogen, air, etc. Normally gas ejector has three connecting points high-pressure gas, low-pressure gas & discharge. This type of ejector is used to draw flare gas & routed it to flare.

What is a Steam Ejector?

Steam ejector is the ejector which utilizes high-pressure steam as the motive fluid. It has a converging and diverging nozzle across which pressurized motive fluid is passed. In the diffuser section, the velocity of the mixed fluid is recovered to pressure energy greater than suction pressure but it is lower than the inlet pressure of the motive steam. This pressure should be greater or equal to the backing pressure for smooth operation.  For low vacuum, multiple-stage ejectors are used. Table 1 shows the probable suction pressure vs total steam consumption in an ejector.

No. of stageOperating suction pressure (Torr)Total Steam consumption per kg of air pumped (kg)
1200-1004-8
260-40015-20
320-518-25
43-0.520-100
Table 1: probable suction pressure vs total steam consumption in an ejector

The steam jet ejector capacity is directly proportional to the weight of the motive fluid. Motive gas to process gas pumped is high, especially under low vacuum, and results in the huge requirement of steam in multi-stage systems. Operating parameter of motive steam such as inlet steam pressure, and discharge pressure has a significant impact on overall ejector performance.

Different Sections of a Steam Ejector
Fig. 2: Different Sections of a Steam Ejector

Purpose of Inter-condenser

Inter-stage condensers & ejectors are staged in series with each other. The purpose of the inter-condenser is to condense hydrocarbon & steam as much as possible. The load of the downstream ejector can be reduced by condensing steam & hydrocarbon. So for proper maintaining of motive steam consumption condenser is highly recommended.

Typical tower vacuum system configuration
Fig. 3: Typical tower vacuum system configuration

Factors affecting the performance of the steam ejector

The following factors have a significant impact on the performance of the ejector’s performance

  • Motive steam
  • Cooling water
  • Dry & saturated air
  • Gas & vapor densities

Motive steam:

A steam ejector is normally designed for a motive steam pressure of 15 to 600 PSIG. Motive steam pressure must be above a minimum pressure for stable operation. This minimum pressure is called motive steam pick-up pressure. So it is very much essential to maintain motive steam pressure; otherwise, the ejector cannot give the desired performance. On the other side, excess motive steam pressure can lead to the wastage of costly steam. Steam ejectors are operated normally with saturated dry steam or superheated steam.  5–15 °C superheating is recommended, but its effect should be considered during ejector design. The use of wet steam is not at all desirable, as it erodes the ejector nozzle and interferes with the ejector performance by clogging the nozzle with droplets of water. The design pressure of the motive steam should be selected as the lowest expected pressure at the steam nozzle of the ejector. The recommended design pressure of the steam is the expected minimum pressure at the motive nozzle: 10 psi.

Cooling Water:

In the inter-condenser, the temperature of the cooling water has a significant impact on the efficiency of the ejector. If the temperature of cooling water rises more than the design condition available LMTD of the condenser decreases.  In this situation, the condenser will not condense properly and vapor & non-condensable gases are carried out as saturated fluids.

On the other hand, if the flow rate of the cooling water decreases below the design condition, a huge temperature rise across the condenser occurs. Even if cooling water is at its designed inlet temperature, an increase in temperature rise reduces available LMTD across condensers. Thus the efficiency of condensation is greatly reduced, and additional load is passed on to the downstream stage of the ejector.

Dry and saturated air

If an ejector is used for maintaining a vacuum in the condenser, the air that is extracted by the ejector is saturated with water vapor. The entrained water vapor by the dry air that leaks into the condenser depends upon the temperature of the mixture and the vacuum at the ejector suction.

Gas and vapor densities

When an ejector handles chemical gases or vapors, it is necessary that the density of the gas be known. The compression of a given weight of heavy gas requires less operating steam than the same weight of light gas e.g., one pound of air is more easily handled by an ejector than one pound of water vapor.

What is the maximum discharge pressure of an ejector?

The maximum discharge pressure (MDP) is the highest discharge pressure that an ejector can achieve with the given amount of motive steam fluid passing through the motive nozzle. If the discharge pressure of an ejector exceeds the MDP, it will become unstable and break the operation. If this occurs, an abrupt increase in suction pressure happens. Since increasing the discharge pressure more than the MDP causes a loss of performance, it seems rational that reducing the discharge pressure below the MDP should have the opposite impact. If the compression ratio (discharge pressure to suction pressure) of the ejector is higher than 2:1 then it is called a critical ejector.

Calculation of flow rate of motive steam requirement:

The flow rate of motive fluid is a very crucial parameter for the ejector operation. It can be calculated by the following method. Other than this, it can be calculated in ASPEN Hysys software as well as by graphical method.

The following equation has been developed by the Heat Exchanger Institute,

Equation for Flow Rate of Motive Steam
Fig. 4: Equation for Flow Rate of Motive Steam

Ejector Datasheet

The below figure (Fig. 5) shows a sample datasheet of an ejector.

Typical Ejector Datasheet
Fig. 5: Typical Ejector Datasheet

Eductor vs Ejector: Differences between an Eductor and an Ejector

The terms educator and ejector are used interchangeably. Their working philosophy is similar, and both of them work based on Bernoulli’s principle. However, some engineers believe there is a slight difference between the eductor and the ejector. The difference between eductor and ejector is mentioned in the table (Table-2) below:

EductorEjector
The main objective of an eductor is to take the volume of any fluid out of the system by maintaining a system pressure upstream. The main objective of an ejector is to maintain a system vacuum upstream.
Eductors usually have a high compression ratio as compared to ejectors.Ejectors simply suck the excess volume of fluid to maintain system pressure. The compression ratio is low.
The diameter of the eductor throat is larger than that of ejectors.The ejector throat diameter is smaller.
The main function of the eductor is compression. The main function of the ejector is vacuum creation.
In general, the motive fluid of the eductor is liquid.The motive fluid of ejectors is usually gas (Steam or Air).
The operation of eductor is generally silent.Noisy operation.
Eductors operate at lower velocities. Ejectors operate at higher velocities.
The motive fluid nozzle for eductors is a converging type.The motive fluid nozzle for ejectors is a converging-diverging type.
Table 2: Eductor vs Ejector

What is Cryogenic Piping? | Materials and Pipe Supports for Cryogenic Services

Written by Adarsh in Piping Design Basics,Piping Supports

Cryogenic piping refers to the piping network that operates below -290C. This temperature represents the demarcation of embrittlement for carbon steel materials. However, various literature considers the piping systems operating below -1500C (-3000F) as cryogenic piping systems in the true sense. Industrial processing and transportation of propane, butane (LPG), methane (LNG), ethylene, nitrogen, ammonia, oxygen, etc. require the extensive use of a cryogenic piping system. These piping systems must be designed with special care to work in such low temperatures. In this article, we will explore more details about cryogenic piping.

Properties of Common Cryogenic Materials

Cryogenic materials are odorless, tasteless, and colorless when vaporized. Cryogenic liquids need to be carefully handled as they may cause skin burns and frostbite. Table-1 below lists the liquid temperatures and the liquid-to-gas expansion ratio of some of the common cryogenic materials:

Cryogenic MaterialLiquid Temperature (0C)Liquid-to-gas volume expansion ratio
Oxygen-1831: 860
Nitrogen-1961: 696
Methane-1621: 579
Helium-2691: 757
Argon-1861: 847
Hydrogen-2531: 851
Fluorine-1871: 888
Table-1: Properties of Common Cryogenic Materials

Why is Cryogenic Piping Challenging?

As the temperature gets extremely low during the operating condition, the material of the pipe faces different types of corrosion and deterioration issues as the chemical and physical properties of the material change. Normal piping systems can’t hold the processing gas in the form of liquid. Also, as can be seen from Table 1, cryogenic liquids generate a large volume of gases when vaporized. So, if they vaporize inside a sealed container, the container can burst due to the enormous pressure. As a result, this cryogenic piping requires a special type of materials, supports, and valves different than that of normal piping systems which makes the design of cryogenic piping systems highly critical and challenging. Some of the cryogenic piping system requirements are:

  • Sufficient flexibility as with lower temperatures the material contracts creating huge thermal stresses which must be compensated using proper flexibility.
  • All cryogenic lines are insulated to avoid heat gain from the environment and for safety. All these increase the weight of the pipe making the cryogenic systems more rigid.
  • Specially designed long-stem, extended bonnet valves are used as Cryogenic Valves.
  • The use of costly materials increases the project cost. So, every chance of optimization shall be used to minimize the project cost.

Cryogenic Piping Materials

With a decrease in temperature, materials become brittle, and impact test requirement as per code arises. Various parameters need to be considered for selecting cryogenic piping materials like

  • Suitability for different fabrication techniques
  • Corrosion resistance
  • Resistance to oxidation and sulfidation
  • Strength & ductility
  • Suitable for the cleaning process
  • Toughness, resistance to abrasion, erosion, galling, and sizing.
  • Physical property characteristics
  • Rigidity
  • Impact Resistance, etc

Materials that have established themselves as suitable cryogenic piping materials are provided in Table 2 below:

Ferrous Materials
Cryogenic Piping MaterialLowest Temperature (0C) for Application
SA-333 Grade 1-46
SA-333 Grade 7-73
SA-333 Grade 3-101
SA-333 Grade 8-196
Austenitic Stainless Steel (Grade 304, 304L, 321, 347)-254
Austenitic Stainless Steel (Grade 316, 316L, 316 Ti, 316 Nb)-196
Non-Ferrous Cryogenic Pipe Materials
Aluminum Alloy (1100, 3003, 5052, 5083, 6061, 5086)-254
Copper Alloy (C10200/C12200), Copper Nickel Alloy (70600, C71500)-198
Monel 400-198
Table-2: Common Cryogenic piping materials

Several non-metallic materials like Grafoil, Mineral wool, Fiberglass, Polyurethane, Styrofoam, Perlite, Viton, Glass reinforced Teflon, etc serve as various components in cryogenic piping applications.

Cryogenic Piping Standards and Cryogenic Piping Design Guide

ASME B31.3 is the main governing standard for designing cryogenic piping systems. The usual cryogenic piping design considerations are:

  • Pipe Sizing is done using normal pressure drop criteria. A drop in pressure can create flashing of part of the liquid which may result in a two-phase flow. So, if a similar situation arises, the two-phase flow must be considered for sizing. However, for oxygen gas piping, the fluid velocity is also considered during pipe sizing.
  • As the ambient temperature is hotter than the cryogenic liquid temperatures, there will be continuous heat leaks to the cryogenic pipeline and piping system which must be considered during the design.
  • Extended stem valves are used to keep the operator at ambient temperature.

Cryogenic Piping Insulation

All frequent-use cryogenic piping and pipeline systems are insulated using any one of the following cryogenic insulation types:

  • Expanded foams (For example, Foam glass, polyurethane)
  • Powder Insulation (Example, Perlite)
  • Vacuum Insulation
  • Evacuated powder & fibrous insulation
  • Opacified powder insulation

The main aim of the cryogenic piping insulation system is to create a vapor barrier to keep atmospheric moisture from leaking into the insulation space. This moisture permeates insulation and then condenses. Which significantly increases the corrosion changes in the lines. Also, build-up of water or ice may occur which in turn, results in lowered performance. Whenever the insulation has been compromised, the thermal efficiency is lost and energy consumption increases. So, high energy consumption can be reduced by using adequate insulation materials. the vapor barrier system must keep atmospheric moisture from entering the insulation space and freezing against the cryogenic lines.

Whenever a cold system is required, the entire system shall be fully insulated including the piping components, piping/tubing of instead instruments, drains, equipment nozzle, and supports. Cryogenic insulation is applied in multiple layers.

Cryogenic Piping Supports

As a matter of their extremely low temperature, extremely superior insulation properties, durability, and stable function are required for cryogenic pipe supporting devices. While designing the cryogenic supports we have to consider structural characteristics, design load, other requirements, and economical aspects for each shoe, guide, stop, and trunnion. We must clarify the behavior of cryogenic piping including pipe support, during normal operation they should also take warm-up and cool-down conditions into account. There are problems encountered in the system such as higher displacement due to the thermal expansion and contraction, pipe insulation, embrittlement of materials, icing around or between the supports, and rapid changes of phase due to large heat fluxes.

Cryogenic Pipe Supports shall meet the following requirements.

  • Lighter weight
  • High reliability in water & resistance to oil and corrosion
  • High weather tightness
  • They must have physical strength against compression, bending, and shearing
  • Suitable for mass production
  • Low water absorption
  • Heat and flame resistance
  • Must incorporate a molded heavy-density layer bonded with stainless steel.

Cold insulation supports are usually made from:

  • High-Density polyurethane foam
  • Phenolic foam insulation
  • Polyisocyanurate or PIR

Supports shall meet the design requirements in respect of compressive strength under sustained load, thermal conductivity, coefficient of friction, service temperature, and flammability.  Even considering the unexpected thermal bowing and fluctuations of flow rate pipe, the support span for cryogenic piping shall be much shorter than that of hot insulated piping, support shall be immediately adjacent to any change in direction of piping.

Typical Cryogenic Piping Support
Typical Cryogenic Piping Support

Cryogenic supports will be equipped with advanced temperature-resistant technology that protects pipes in extreme cold. Cold climates are critical for pipe supports they aren’t built to withstand the elements. Worse yet, pipes are fragile in frigid environments, and ice formation can wear down both pipes and supports, also must be designed to support pipes in temperatures as low as -320°F. They will encapsulate the fragile insulation used in these piping systems.

To stop the thermal transfer from the interior of pipes to surrounding structures they must be nonconductive. Foam-insulated cores are given to some shoes to naturally keep pipes from sudden temperature changes of heat transfer. By keeping heat inside pipes, can save energy and stop the ice formation that can destroy pipes.  A cold shoe is a support used for cryogenic applications where the heat transferred to the surface is not relevant and can be used for temperatures right down to -300˚ Fahrenheit.

Cryogenic Piping Stress Analysis

Cryogenic pipelines are a special case where the operating temperature used is extremely lower than the installed ambient temperatures. There should be a degree of rigor that is relevant for the safety of operations and potential hazards and therefore accurate flexibility analysis is very important to manage thermal forces, stresses, and displacements. Some of the Cryogenic piping stress analysis considerations are provided below:

  • Cryogenic piping systems may have a thermal-bowing effect. So it must be considered. Click here to know more about the use of pipe thermal bowing effect.
  • If it’s vacuum-insulated piping the two pipes having different displacements are to be considered and connected. The main pipe which is at cryogenic temperature contracts and the jacketed pipe usually at a temperature bit above ambient expands.
  • Equipment nozzle loads are usually qualified using Finite Element Analysis or FEA.
  • Expansion bellow or Flexible hoses may be required in the analysis.
  • Cryogenic pipe systems behave completely opposite to high-temperature piping systems. Due to the contraction of the cryogenic piping system, the supports that are usually lifted off in high-temperature piping carry the load in cryogenic-temperature piping.

LNG Piping and Cold Box Piping systems are typical examples of cryogenic piping systems.

What is Material Selection Diagram? Its Purpose, Development, and Example

Written by Partha Pratim Panja in Engineering Materials,Process

What is a material selection diagram?

A material selection diagram often called MSD in engineering terminology is basically an engineering drawing that shows the basic scheme of a process along with the information for material selection & specification of all the equipment, and lines associated with the process as well as utilities & offsite.

What is the purpose of the material selection diagram?

As we know, in a project, the cost of the materials contributes a major part to the overall project cost. So selection of proper material is a very important parameter. Besides, the important parameter of a project like the overall design, stability, and sustainability also depends on material selection.

As MSD summarizes the related information that is required for material selection of the equipment & piping in process industries so MSD is a necessary document for developing piping material specification (PMS). The piping material specification is an important document by material engineers and it is used for assigning line class/ specification to each line on the P&IDs.

How to develop a material selection diagram?

In the simplest form, an MSD is a drawing that consists of a marked-up or overlaid version of a PFD (process flow diagram). So to develop an MSD you need to have the following documents,

  • a) Basic Engineering Design Data (BEDD)
  • b) Simplified Process Flow Diagram (PFD),
  • c) Material selection information developed by the process team,
  • d) PFD marked up with proper operating pressure, temperature, design temperature, and pressure.

The content, format, use, and updating philosophy of a material selection diagram must be in agreement with the client and contractor/fabricator/licensor in the preliminary phase of the project.

Besides the above, all main documents and some other suitable standards like API, NACE, corrosion curves, and company standards shall be used as necessary documents for developing MSD

Who develops the material selection diagram?

In general, MSD is prepared by a material engineer or metallurgist in collaboration process engineer. The material engineer responsible for developing MSD must be familiar with the corrosion mechanism of the material, particularly the type of unit being designed.

Information to be shown on MSD

  1. Material of construction used for the equipment & its component, piping network (as per material legend), normally recognized by name or by tag. (See Table: 1),
  2. Chemical injection, corrosion inhibition points,
  3. Corrosion allowances,
  4. Corrosion-resistance cladding of alloy with minimum thickness & side of the components,
  5. Linings/coating for specific internal corrosion consideration,
  6. Prefabricated equipment as “Manufacturer’s Standard”,
  7. A special section of materials, prevention of corrosion, testing requirements in the form of notes (e.g. thermal stabilization, stress-relief [SR] requirements, maximum hardness requirements, velocity limits, etc. The equipment components whose material of construction to be shown are as below,
TYPE OF EQUIPMENT OR PIPINGCOMPONENTSMandatory/Optional (M/O)
Heat Exchanger (Plate and Frame)Plates  
Frame
Gaskets		M
O
O
Heat Exchanger (Shell and Tube)Shell
Channels
Baffles/Cages
Tubes
Tube sheet		M
M
O
M
M
TankShell (includes fixed roof and bottom)
Floating roof
Linings
Seals		M  
O
M
O
TowersShell
Trays/ Packing
Distributors		M
M
O
Centrifugal PumpsAPI material Class(if applicable)
Casing
Impeller		O
O
O
DrumsShell
Boot (if present)
Internals		M
M
O
PipingPipe
Control Valve
Valve trim		M
O
O
ReactorsShell
Internals		M
O
HeaterRadiant tubes
Convection tubes
Hangers		M
M
O
Air CoolerHeaders
Tubes
Plugs (if different)		M
M
O
Table: 1 List of Equipment Components

MOC for supplementary components like special gaskets, seals, etc should be identified on MSD. Additional components like bolting, impingement plates, and vessel trims may be included based on factors such as whether the materials are covered in other sites, projects, or company work practices.

Material Designations

Materials should be designated by standard formats e.g. CS or UNS (unified numbering system), 316 SS. Another specification is ASTM (e.g. A516, A351), DIN (Deutsches Institut fur Normung), etc. Generally, using specific material specifications (e.g., ASTM, ASME, and DIN) is acceptable in agreement with the client and contractor. There is a legend that should be used in each MSD. A typical example of a legend is tabulated in Table: 2.

MSDUNS DesignationFull Designation
CI Cast iron
DI Ductile iron
CSK02504, K02401, K03006Carbon steel
LTCS Low-temperature Carbon steel
1-1/4 CrK11562, K117561 ¼ Cr- ½ Mo
2-1/4 CrK215902 ¼ Cr-1 Mo
5 CrK215905 Cr- ½ Mo
9 CrK815909 Cr-1 Mo
12 CrS40500 (405 SS), S41000 (410 SS), or S41008 (410S SS12-13 Cr steel
304LS30403304L SS
316LS31603316L SS
321S32100321 SS
347S34700347 SS
310S31000310 SS
2205S32205/S3180322% Cr Duplex SS
Alloy 20N08020Alloy 20
6% MoS31254, N08367, N08926Super austenitic SS with 6% Mo
800N08800 (alloy 800), N08810 (alloy 800H), or N08811 (800HT)Alloy 800
825N08825Alloy 825
625N06625Alloy 625
276N10276Alloy 276
400N04400Alloy 400
AdmC44300, C44400, C44500Admiralty brass
NRBC46400, C46500, C46700Naval rolled brass
70/30C7150070/30 Cu-Ni
90/10C7060090/10 Cu-Ni
Ti-2R50400Titanium grade 2
Ti-12R53400Titanium grade 12
Table: 2 Material Designations

Format of Notes & Contents

General Notes: These are the notes which are applicable to the whole process unit & must be labeled with a discrete letter on all MSDs. These should be repeated in a similar order using the same letter on all MSDs.

Specific Notes: These notes are specific to the specific equipment, piping component, or location on the MSD. This note should be identified with a discrete identifying letter and generally follow the general notes on the corresponding MSD page (if MSD is more than one page).

The below table (Table: 3) is the list of commonly used nomenclature that is generally used in the process industry,

NomenclatureActual Meaning
BBaffles
CCasing
CACorrosion allowance
CHChannel
HHeader
IMPImpeller
INJInjection point (e.g. wash water, chemical)
INTInternals
PWHTPost-weld heat treatment for service or material. (Design code requirements for PWHT based on thickness must also be met, but are not typically identified on the MSD.)
SHShell
SRStress relief
TTubes
TSTube sheets
Table: 3 List of Nomenclature

Requirements of special materials shall be shown in MSD, normally in the specific note region. The typical example of special requirements is as follows,

  • -Alloy 20 or alloy 825 drains in SS reactor,
  • -Higher content (>2.5%) of molybdenum for type 316L SS in cold, used in seawater, naphthenic acid service,
  • -Maximum limit of strength on CS used in LPG sphere,
  • -Welds & thermal stabilization of base materials for type 321 SS or 347 SS that is operated more than 427ᵒC,
  • -Seals & gaskets used for MTBE (methyl tert-butyl ether) service, etc.

Corrosion Allowance

Corrosion allowance is a driving parameter for material selection for construction, especially for the equipment which is operated at high pressure. So defining the CA plays a very important role. A certain acceptable CA shall be shown on the MSD for every component excluding pump casing or when the client defines only a minimum CA for a specific material that must be written as a general note.

Process data to be shown on MSD

The process data used for materials selection must be indicated on the MSD. These process data may vary unit-wise. Examples of some typical process data (as applicable), including contaminants & corrosive agents which have the potential ability to affect materials selection, include:

  • –  Operating temperature
  • –  Operating pressure;
  • –  Hydrogen partial pressure
  • –  MDMT
  • –  H2S, CO2 concentration, or partial pressures
  • –  Sulfur, Free water, Ammonia, Chloride concentrations
  • –  Water dew point
  • –  Phase (Liquid, vapor, or mixed phase)
  • –  Amine type, strength, and acid gas loading
  • –  Total acid number (TAN) or neutralization number
  • –  pH
  • –  Critical corrosion velocity limits
  • –  Short-term operating conditions that could affect materials selection.

The source of the process data e.g. pH, hydrogen partial pressure, H2S concentration, etc, may be found in heat & mass balance. These data can be represented in a separate sheet. If so, the page number & revision of information shall be shown in MSD.

Guideline on completing Material Selection Diagram

MOC & CA should be decided on the basis of predicted corrosion rate or material degradation rate under influence of all process variables e.g. stream composition, velocity, temperature & pressure, and the design life of the specified component.

  • -Most cases the maximum normal operating condition is used to decide the materials. Design temperatures & pressures are not usually used to calculate predicted corrosion & degradation mechanism.
  • -In some environments, huge corrosion or degradation of materials can occur when normal operating condition is exceeded. So the effect of short-term conditions on MOC needs to be considered. Examples are Alternate operations (presulfiding, catalyst regeneration), No flow (power failure, steam-out, cleaning, etc), Start-up & shut down, Upsets & emergency conditions, start of run (SOR) & end of run (EOR) conditions.

Material Selection Diagram Sample

The below figures (Fig. 1, Fig. 2, and Fig. 3) show a sample of the material selection diagram examples:

Material Selection Diagram Sample
Fig. 1: Material Selection Diagram Sample
Sample Legend Sheet for MSD
Fig. 2: Sample Legend Sheet for MSD
Typical Material Selection Diagram
Fig. 3: Typical Material Selection Diagram

Underground Piping Insulation

Written by Adarsh in Engineering Materials,Piping Design Basics

In refineries, chemical, and petrochemical industries we frequently find that pipes are insulated. All of these pipes are aboveground. So, sometimes a question arises in mind “does the underground pipe need to be insulated?”. Underground or buried pipes sometimes require insulation and sometimes do not. In this article, we will explore more regarding underground piping insulation.

Examples of Underground Piping Systems

Underground pipes are laid below the grade line. Common examples of underground pipes are:

  • – Cooling water (with line sizes normally ≥18″ NB)
  • – Fire-Water
  • – Contaminated Rainwater Sewer from the process catchment area. (CRWS)
  • – Oily Water Sewer (OWS)
  • – Liquid Effluent that runs to the Effluent Treatment Plant.
  • – Closed Blow Down system (CBD)
  • – Sanitary system
  • – Storm Water
  • – Equipment drainage to slop tank
  • -Fuel oil piping
  • -Water, Crude, Gas, or Oil Pipelines

The following materials are used commonly for the construction of piping systems & their advantages over the fabrication of underground pipe are listed below:

  • Carbon steel—closed-drain systems, cooling water, and fire water
  • Stainless steel—closed drains—chemical and corrosive service
  • Cast iron—used for oil-water drains and stormwater (hub and spigot fittings)
  • Ductile iron—used in Process water (its stress value is higher than that of cast iron) (hub and spigot fittings)
  • Concrete pipe—surface drainage, and for 15″ and bigger pipes
  • Fiberglass-reinforced plastic pipes— These mostly are used for low-temperature, corrosive service, and pressure systems.
  • PVC—corrosive service
  • Vitrified clay pipe- These gravity drain systems can’t be used under roads or even when subjected to significant loads (the maximum operating temperature for them will be 200°F/93°C)
  • Glass Pipe—used main for floor drains in process plants, usually acid service

Most of the above-mentioned lines are normally low-temperature lines. They do not carry fluids that are either cryogenic or have very high temperatures similar to above-ground piping systems. So, in principle, buried or underground pipes do not need to be insulated similarly to aboveground piping systems.

However, moisture and corrosion are constantly threatening the underground piping. Even though corrosion-resistant coatings are applied on the pipe surfaces, still the exposure to water and chemicals in the soil creates many problems in the buried system. Insulating the underground pipe with the correct materials can provide an additional measure of protection for them. This is one of the main reasons for insulating underground piping. Also, sometimes chilled district cooling systems and steam networks are laid underground which needs insulation.

Purposes of Underground Piping Insulation

The major benefits that an insulated underground piping system provides are:

  • It keeps the system safe. A properly insulated underground piping can prevent condensation, energy loss, vapor leaks, and temperature regulation.
  • Underground piping insulation preserves the pipes by restricting direct contact from moisture and corrosion. It increases the operating life span of buried pipes.
  • As the buried insulation faces the soil and corrosive environment, the main pipe does not suffer major problems. Hence, the maintenance and repair action reduces. The underground insulation gets damaged but they are cheaper as compared to the primary pipe. So, there is a huge saving in the budget over the complete span of the pipe.
  • Reduces heat loss from pipes.
  • Prevents the freezing of the liquid it carries through the pipe.
  • Prevents direct contact with unlike metals that would cause electrolyte action.
  • Prevents contact with concrete and other materials that can damage the parent pipe surface.

Underground Pipe Insulation Materials

The leading product under underground use is the Armaflex Tuff coat as it has high water vapor diffusion resistance and low thermal conductivity. Armaflex class o nitrate foam – this insulation is the industry-leading underground insulation. That consists of an additional wrap-around self-seal plastic coating.

Mineral powder insulation, perlite insulating concrete, gilsulate, and cellular glass insulation are some of the other examples of excellent insulating materials for underground piping systems.

In general, all underground piping insulation materials should possess the following properties:

  • Good mechanical strength for direct burial.
  • High corrosion resistance (Resistance against soil moisture and soil acids)
  • Long-term insulation efficiency

Factors affecting the selection of Underground Piping Insulation System

The design and selection of an ideal underground pipe insulation system depend on factors like:

  • Type of piping or pipeline system: hot or chilled water, steam, or other
  • Operating temperature of the fluid that the main pipe will carry
  • Pipe OD and length
  • Depth of pipe cover
  • Soil type, bearing strength, electrical potential
  • Location of water tab
  • Road Crossing and Traffic load, etc

Some piping systems in the ground are required to be double-walled or secondarily contained. There will be a primary pipe and there will be a secondary pipe over the primary pipe and the purpose of that is to if the primary pipe systems fail, they are a backup plan or another layer of pipe to contain it.

Sometimes, underground pipe jacketing is also widely used in place of buried insulated piping.

Can pipe insulation be buried?

Placing the insulated piping and pipeline systems underground is one of the most practical methods of underground piping system installation. The need for costly tunnels is eliminated by this process which in turn, speeds up the buried piping installation.

What is a Pre-insulated underground pipe?

Pre-insulated underground piping systems provide a better solution by avoiding the challenges of installing insulation. There are various options available for pre-insulated underground pipe systems. They are strong and durable and can work over a variety of temperature ranges.

What is a Fire Hydrant? Its Types, Working, Components, and Color Coding

Written by Anup Kumar Dey in Health & Safety

A fire hydrant is a visible connection point placed in defined locations for firefighters to tap into a water supply. All buildings, parking areas, roadsides, mines, industrial areas, etc. must have fire hydrants with a connection to a water service network. They are designed to provide the water required by firefighters instantly to fight and extinguish a fire. Till the 18th century, underground fire hydrants were used. However, from the 19th century onwards, above-ground pillar-type fire hydrants become popular and mostly used. A fire hydrant is basically a pipe with the control of a valve through which water flows from a water main in order to put out a fire.

Purpose and Uses of Fire Hydrants

The primary purpose of fire hydrants is to supply water for suppressing fire. However, they can be used for several secondary purposes like:

  • Line Flushing: Due to their high flow capability and easy operation, fire hydrants can be used to flush main distribution system lines.
  • Testing System: To test the hydraulic capacity of the distribution system, fire hydrants can be used.
  • Other Common uses: Fire hydrants are also frequently used as a water source for commercial construction work, sewer cleaning, street construction, street cleaning, etc.

Working of a Fire Hydrant

Fire hydrants with a variety of valves and connection points are seen in many places. In the event of a fire breakout, firefighters locate the fire hydrants, connect their hoses and then pump a large volume of pressurized water to put out the fire. A special pentagonal wrench is used to remove the valve cover of the hydrant. Then after attaching the hoses, the firefighters open the valve for the water to flow.

They usually have a connection point to hook up a fire hose and a nut or bolt to turn on which will start the flow. Every fire hydrant is essentially just an attachment to the main water line. Underneath that connects the hydrant valve through a pipe called a riser. However, normal hydrants don’t change the water pressure or flow in any way. They function as valves so firefighters can utilize the already present pressure in the water pipes. While all of this may sound simple the internal mechanics of a fire hydrant are a little more complex and can vary by region.

Types of Fire Hydrants

There are two types of Fire Hydrants; Wet hydrants and Dry hydrants.

Wet Hydrant

Wet hydrants are widely used in places where there is no problem of freezing. In such types of fire hydrant systems, the water in the main supplies the hydrant close to the surface. So, in cold weather conditions, it is susceptible to freezing.

Dry Hydrant

A dry hydrant system stores the water below the ground. The Earth’s temperature is usually higher than the cold environment temperature in cold regions. So, the possibility of freezing can be prevented by this arrangement. When the dry hydrant system is required to be used, firefighters open a valve on top of the hydrant and engage their hose in it. This causes the drain valve to open inside the hydrant. This allows the water to come through which the firefighters use against the fire.

Difference between Wet barrel Hydrant and Dry barrel Hydrant

The main differences between a wet hydrant and a dry hydrant are mentioned below:

Wet Hydrant or Wet Barrel HydrantDry Hydrant or Dry Barrel Hydrant
Wet Hydrants are used where water-freezing issues are not presentDry barrel hydrants are used in cold regions where the temperature routine drops below water freezing temperature.
In the wet hydrant design, the water is placed abovegroundThe water in the dry barrel design is kept below ground to avoid freezing.
A wet Hydrant is easier to construct and cheap.On the other hand, dry barrel hydrants are costlier and difficult to construct.
Maintenance of wet barrel hydrants is easier due to easy access.Maintenance is comparatively difficult.
Table 1: Wet Barrel Hydrant vs Dry Barrel Hydrant

Components of a Fire Hydrant System

The main components that constitute a fire hydrant system are:

  • Fire Fighting Pumps & Accessories
  • Piping
  • Panels
  • Landing Valves
  • Hoses
  • Couplings
  • Hose Reel
  • Branch Pipes & Nozzles
  • Fire Brigade Connections
  • Wiring & Instrumentations
  • Maintenance Valves

Color Coding of Fire Hydrants

Following NFPA standards, all fire hydrants are color-coded. These colors indicate the expected flow during the operation. Usually, the top caps of the fire hydrants are painted. The following table provides the common colors according to the flow.

Color-CodingFlowMeaning
Light Blue/Blue>1500 GPMVery good flow, suitable for industrial applications.
Green1000-1500 GPMgood for residential purposes
Orange500-999 GPMmarginally adequate
Red<500 GPMLow flow, inadequate
Table 2: NFPA color coding of fire hydrants

Codes and Standards of Fire Hydrants

The codes and standards that are used as guidelines for designing fire hydrant systems are:

  • NFPA 1
  • NFPA 25
  • NFPA 291
  • AWWA
  • A112.21.3M
  • BS EN 14384
  • BS 750
  • DIN 3222
  • DIN EN 14339
  • AS 2419
  • FP-009
  • IS 3844
  • IS 13039

Fire Fighting System Online Courses

To learn more details about fire fighting systems, their operation, application, etc you can join the following online in-depth video courses: