Pipes are defined as circular tubular products used for conveying fluids (liquids, gases, and fluidized solids). Pipes are designed for a particular design pressure corresponding to the design temperature. Various parameters related to pipes are Pipe Size, Pipe Schedule or thickness, Pipe Material, Pressure withstanding capability, Temperature withstanding capability, etc. Different types of pipes are used in the industrial sector for different purposes.
Common industries that find extensive use of pipes are oil and gas, process industries, chemical and petrochemical complexes, food and beverage industries, power sectors, steel industries, HVAC industries, plumbing industries, pipeline industries, refineries, etc. Today, the use of pipes is so wide that modern industrial plants can not be thought of without pipes. Types of pipes are decided based on various factors. In this article, we will explore different types of pipes that are widely used in industries.
Pipe Types based on Material
Pipes are normally classified based on the material which is used to produce the pipe during manufacturing. In general, there are two types of pipes:
Metallic Pipes and
Non-metallic Pipes
Metallic Pipes
The pipes made of metal are known as metallic pipes. They can be grouped into two categories:
These types of pipes are stronger and heavier. These pipes have iron as their main constituent element. Common examples of pipes made from ferrous materials are
This category of pipes is suitable for higher temperature and pressure applications. Most of the pipes used in oil and gas, refineries, chemical, petrochemical, power plants, etc. are made of ferrous materials. Click here to learn more about Steel Pipes.
Type of Pipes made from Non-ferrous materials:
In this group of pipes, iron is not the main constituent element. They are usually made of copper, aluminum, brass, etc. Common pipes made from non-ferrous materials are
Non-metallic pipes are widely used for services where the temperature is not significant. Non-critical services like water industries and drainage systems make use of most of the non-metallic pipes. Common non-metallic and widely used pipes are:
The main advantages of reinforced plastic and composite pipes are that they are highly corrosion-resistant and durable. While metallic pipes are usually designed for up to 25 years of service. Composite and Reinforced plastic pipes can easily serve up to 50 years. However, their main limitation is the temperature. Non-metallic pipes are not suitable for high-temperature applications.
Cement pipes, manufactured from reinforced concrete are usually used for stormwater, gravity service, irrigation industries, and culverts.
Types of Pipes depending on the industry they are used
Depending on the type of industry there are three types of pipes.
Pipes for Chemical and Power Piping Industries.
Pipes for the Plumbing industry.
Pipes for the Pipeline industry.
Types of Pipes for Chemical and Power Piping Industries
These types of pipes are suitable for high-temperature and pressure applications. Mainly pipes made from ferrous materials are used in chemical, power, petrochemical, steel, oil, and gas industries. They are usually designed following codes like ASME B31.3, ASME B31.1, and various other international codes. They are usually selected based on their ability to sustain pressure, temperature, corrosion resistance, etc.
Types of Pipes for the Plumbing Industry
Common plumbing pipes are PVC pipes, PEX pipes, Copper pipes, ABS pipes, CPVC Pipes, HDPE Pipes, Cast Iron and galvanized steel pipes, etc. They are mainly used for water distribution purposes.
Pipes for the Pipeline Industry
Pipes used in pipeline industries are usually known as line pipes and are designed by API 5L standards. Pipes for pipeline industries are designed following ASME B31.4 and ASME B31.8 codes. There are various grades of API 5L pipes that are used to convey oil, gas, or water through pipelines. Other types of pipeline materials are SS, DSS, SDSS, GRE, FRP, etc.
Types of Pipes based on the fluid they transport
Depending on the type of fluid they transport, pipes are categorized as follows:
Pipes can also be classified based on the method of manufacture. These are again sub-categorized depending on the material of the pipe. For example, Metallic pipes can be categorized as
In general, pipes with a diameter of less than 16 inches are seamless, and larger-diameter pipes are welded. Seamless pipes are preferred due to the absence of the weld seam which is considered a weak point. However, they are costlier than welded pipes. Also, For large-diameter pipes, producing seamless pipes becomes difficult.
Carbon steel pipes (A53, A333, A106, and API 5L) have the largest market share due to the fact that they are cheaper and suitable for a wide range of applications ranging from -29 Deg C to 427 Deg C.
Finally pipes can also be classified based on connection types as follows:
Types of Pipes based on Connection Type
Threaded: Pipes with external or internal threads for screw connections.
Flanged: Pipes with flanges for bolted connections.
Welded: Pipes that are joined by welding.
Push-fit or Compression: Pipes that use fittings to join without welding or threading.
Conclusion
So, the subject types of pipes are very broad and there are various parameters that contribute to the classification of pipes. However, the most widely accepted pipe classification is based on the material used to manufacture the pipe.
Determination of Design Pressure & Design Temperature
This document covers the requirements for the determination of design pressure and design temperature of the equipment like pressure vessels and piping that are used in petroleum refineries, petrochemical plants, and other similar plants.
The following summary of input data needs to be prepared prior to the determination of design conditions.
Operational data
-Service for identification
-Operating temperature & pressure under normal operation
The design pressure for the pressure vessel is determined in the following way,
-Unless otherwise specified, this indicates gauge pressure. If design pressure<Atmospheric pressure, then absolute pressure may be used in place of gauge pressure.
-Design pressure shall be based on the expected maximum pressure drop at the top of the vessel under normal operation.
-When maximum pressure under normal operation can’t be estimated, the design pressure should be determined as per the table (Table 1) below.
-When the vessel is venting to the atmosphere, the minimum design pressure shall be ‘’Full of Water’’ or “Full of Liquid” (whichever is greater).
-When the vessel is connected to a flare, the minimum design pressure shall be 3.5 kg/cm2-g.
Design Pressure Estimation
Operating Pressure
Design Pressure
The operating pressure is less than 18kg/cm2g
Design Pressure= operating pressure+1.8 kg/cm2g
Operating Pressure 18-40 kg/cm2g
Design Pressure= operating pressure x 1.1
Operating pressure 40-80 kg/cm2g
Design Pressure= operating pressure+4 kg/cm2g
Operating pressure is greater than 80 kg/cm2g
Design pressure= operating pressure x 1.05
Table-1 Design Pressure estimation
-The design pressure should be indicated in the specification as “Design Pressure at Top”.
-The maximum pressure at the bottom of the vessel is calculated by the mechanical design department to determine the wall thickness of the vessel.
-It is thus necessary to represent the height and specific gravity of the liquid and also the pressure drop through the internals.
Example 1:
Operating Pressure Design Pressure
Pressure at the top (kg/cm2g) 2 3.8
Pressure drop (kg/cm2) 0.3 0.3
Bottom liquid head (kg/cm2g) 0.2 0.2
Pressure at the bottom (kg/cm2g) 2.5 4.3
As a practice, while a vacuum condition is likely to occur due to malfunction during steam purge or emergency shutdown of reboilers (all condensable vapor service), etc, the vessel should be designed to withstand full vacuum. If the vacuum design is an uneconomical solution, vacuum protection devices such as breather valves can be installed by employing vacuum design, keeping in mind the types, location, and response time of devices, flow rate, availability of inert gas is used as well as it should be ensured that the devices are functioning properly even under abnormal conditions.
When the vessel is located on the discharge side of the pumps and is not protected by relief devices, the design pressure shall be determined as the larger of the following criteria,
Design pressure= Differential pressure under normal flow rate + design pressure of suction vessel+ head between the tangential line of the suction vessel and the centerline of the pump impeller.
Design pressure= Pump shut off head +normal operating pressure of suction vessel+ head between the tangential line of the suction vessel and the centerline of the pump impeller. The pump shut-off head can be calculated as Maximum suction pressure + 1.25 x Normal differential pressure.
For the centrifugal compressor, the design pressure of the compressor discharge shall be at least equal to the specified relief valve setting, if the relief valve setting is not specified, the design pressure shall be at least 1.25 times the maximum specified discharge pressure (refer API RP 617). A safety valve must be used on the discharge of each stage of a reciprocating compressor to avoid possible damage to the machine from excessive pressure due to overloading.
Design Pressure of Heat Exchanger
The cause of the over-pressurization of the heat exchanger should be known before determining the design condition of the heat exchanger. The causes are as follows,
The below points are a measure for the protection of the heat exchanger due to over-pressurization,
-Install a Pressure safety valve to limit over-pressure
-Raise the design pressure to eliminate or mitigate one or more overpressure cases. For example, design the exchanger for pump shut-in pressure to eliminate the blocked outlet case or design the low-pressure side for ten-thirteen (10/13) of the design pressure of the high-pressure side to mitigate the tube failure case.
Equipment Design Pressure
The below table (Table 2) can be used to determine the design pressure of the vessel/columns/Reactors.
Maximum Operating Pressure (PSIG)
Design Pressure (Standard) PSIG
Design Pressure (Fit-for-purpose) PSIG
Design Pressure (Revamp) PSIG
Full or partial vacuum
-0.3
-0.3
-0.3
0-35
50
50
50
36-100
M.O.P+15
M.O.P+15
M.O.P+15
101-150
M.O.P+25
M.O.P+25
M.O.P+25
151-250
M.O.P+25
M.O.P+25
M.O.P+25
251-500
110% of M.O.P
110% of M.O.P
110% of M.O.P
501-1000
M.O.P+50
M.O.P+50
M.O.P+50
>1000
105% of M.O.P
105% of M.O.P
105% of M.O.P
Table-2 Design Pressure for Vessel/Columns/Reactors
The below table (Table 3) can be used to determine the design pressure of the casing & discharge piping of a compressor (ref API RP 617).
Maximum Operating Pressure (PSIG)
Standard Design Pressure (PSIG)
Fit-for-purpose Design Pressure (PSIG)
Revamp Design Pressure (PSIG)
For centrifugal compressor
125% of the maximum discharge pressure
125% of the maximum discharge pressure
125% of the maximum discharge pressure
Reciprocating Compressor
0-150
M.O.P+15
M.O.P+15
M.O.P+15
151-2500
110% of M.O.P
110% of M.O.P
110% of M.O.P
2501-3500
108% of M.O.P
108% of M.O.P
108% of M.O.P
3501-5000
106% of M.O.P
106% of M.O.P
106% of M.O.P
>500
Note 1
Note 1
Note 1
Table-3 Design Pressure for piping & casing of the compressor
Note 1: As per API RP 617, for a reciprocating compressor with a rated discharge pressure above 5000 PSIG, the relief valve setting shall be as agreed to by the purchaser and the vendor.
The below table (Table 4) can be used to determine the design pressure of the heat exchanger.
Maximum Operating Pressure (PSIG)
Standard
Fit-for-purpose
Revamp
Full or partial vacuum
-0.2
-0.3
-0.3
0-35
75
50
50
36-50
75
M.O.P+15
M.O.P+15
51-150
M.O.P+25
–
–
151-250
M.O.P+25
110% of M.O.P
110% of M.O.P
251-500
110% of M.O.P
110% of M.O.P
110% of M.O.P
501-1000
M.O.P+50
M.O.P+50
M.O.P+50
>1000
105% of M.O.P
105% of M.O.P
105% of M.O.P
Table-4 Design Pressure for heat exchanger
The below table (Table 5) can be used to determine the design pressure of the fire heater
Maximum Operating Pressure (PSIG)
Standard
Fit-for-purpose
Revamp
Full or partial vacuum
-0.1
-0.1
-0.3
0-135
150
150
110% of M.O.P
136-1000
110% of M.O.P
110% of M.O.P
105% of M.O.P
>1000
M.O.P+100
M.O.P+100
105% of M.O.P
Table-5 Design Pressure for fire heater
The below table (Table 6) can be used to determine the design pressure for the Relief and Flare system
Maximum Operating Pressure (PSIG)
Design pressure (PSIG)
Design pressure (PSIG)
Design pressure (PSIG)
Standard
Fit-for-purpose
Revamp
PSV discharge piping to Flare K.O.D
Min.100
Min.100
Min.100
Flare K.O.D & downstream piping
Min.50
Min.50
Min.50
Table-6: Design Pressure for Relief & Flare system
Design Temperature:
Design temperature is determined based on the maximum normal operating temperature and the addition of a design margin. If temperature fluctuation is expected during normal operation, the maximum value of the fluctuating temperature must be considered. If the design temperature at the bottom of a pressure vessel is significantly different from that at the top, both temperatures should be specified. The design temperature shall be calculated as follows,
Minimum Metal Design Temperature (MDMT):
A minimum design metal temperature is the lowest temperature caused by depressurization. It should also be specified in the vessel data sheet. For most of the vessels, heat exchangers, pumps, and compressors, the ASME Boiler & Pressure Vessel Code, Section VIII, Division 1, or Division 2 is used. The division 2 code is normally used only for vessels of heavy wall construction, such as the reactors in hydro-treating plants.
The MDT in Division 1 is called the “Minimum Design Metal Temperature” (MDMT), while the term “Minimum Permissible Temperature” (MPT) is used for Division 2.
Steam out Design Temperature
It is recommended that a minimum design temperature of 120ᵒC accommodate the steam out temperature.
Equipment
Standard Design Temperature
Fit-for-purpose Design Temperature
Revamp Design Temperature
Vessels/Columns/Reactors
MOT+50
MOT+25
MOT
Compressors
MOT+50
MOT+25
MOT
Heat Exchanger
MOT+50
MOT+25
MOT
Fired Heaters
MOT+50
MOT+25
MOT
Atmospheric Tankage
MOT+50
MOT+25
MOT
Pressurized Tank
MOT+50
MOT+25
MOT
Refrigerated Tank
MOT+50
MOT+25
MOT
-10ᵒF to Ambient Temperature
MOT-25
MOT-10
MOT
-80ᵒF to -10ᵒF
MOT-10
MOT-5
MOT
<-80ᵒF
MOT
MOT
MOT
Piping
MOT+50
MOT+25
MOT
Table-7 Design Temperature of Equipment & Piping
Difference between Design Pressure and Maximum allowable Working Pressure
The difference between the design pressure and Maximum allowable working pressure can be described as below,
Design Pressure
Maximum allowable working pressure (MAWP)
It is the maximum pressure that a system faced & it is imposed on the equipment’s internal & external parts.
It Is the maximum pressure that can be defined based on design code & standard data and it is related to a specific temperature that a system can withstand.
Design Pressure is normally less than the maximum allowable working pressure (MAWP).
MAWP is normally equal to or greater than the design pressure
Design pressure calculation depends on the amount of water, steam, or any liquid in a vessel.
MAWP depends on size, shape & metal’s physical properties.
It is normally calculated during designing the equipment
Maximum allowable Working Pressure is calculated after the completion of the design.
Design pressure cannot be modified once the vessel is completed.
Maximum allowable working pressure can be rechecked and corrected.
A water pipe can be defined as any pipe that is used to transport water. The applications of piping systems are very vast from the power industry to the process industry, utility services, and so on. Piping is used for transporting different states of material like liquids, gases, slurries, etc. Depending on the function of served water, there are three types of water pipes that are widely familiar:
Water piping is used for transporting treated drinking water to consumers.
Water piping systems used for firefighting operations and
Water pipes are used as sewer piping systems which is a wastewater treatment process.
The materials and conditions of these three systems are entirely different as per their respective conditions. Water piping networks, used for transporting drinking water consist of large-diameter main header pipes, which connect entire towns and smaller supply lines that supply a street or group of buildings from the header pipes. With a size range generally between 3.65 m. giant mains or header lines to small 12 mm pipes used for individual outlets in the buildings. Consuming water can be transported through gravity and the quality of water can be preserved using these piping systems.
Materials for Water Piping
Water Pipes come in several types and sizes as per their applications which include 3 main categories of materials such as metallic, cement, and plastic pipes. Metallic pipes include galvanized iron pipes, steel pipes, and cast-iron pipes. On the other hand, PVC and HDPE pipes are the main categories of plastic pipes used in water piping systems.
Steel pipes
Comparatively, they are expensive but they make the strongest and most durable for all water supply pipes. They can withstand high water pressure. They have longer lengths than most of the other pipes and thus reduce installation and transportation costs. They can also be welded easily.
Galvanized steel or iron pipes
It is the common piping material for the conveyance of water and wastewater. It’s still used throughout the world but its popularity is getting declined. Whenever the water flow is slow or static for periods, it causes rest from internal corrosion and also gives an unpalatable taste and smell to the water under corrosive conditions.
Cast iron pipes
These pipes are very stable and well applicable for high water pressure conditions. They are considerably heavy which also makes them unsuitable for inaccessible places due to transportation problems. As they are having more weight they will generally come in shorter lengths. Which increases the cost of layout and joining.
Copper
They are mainly used for the distribution of hot and cold water. Works in both underground and above-ground applications, but to use underground they require a protective sleeve as copper can be affected by some soils. Highly expensive comparing other piping materials.
Concrete cement and asbestos cement pipes
They are expensive but non-corrosive. They are extremely strong and durable. As they are bulkier and heavier the installation, handling, and transportation costs are very high.
Plasticized polyvinyl chloride (PVC) pipes
They are non-corrosive, extremely light, and thus easy to handle and transport. Even though highly flexible they are strong and come in long lengths which lowers the installation and transportation costs. But when exposed to overground they are prone to physical damage and when exposed to ultraviolet lights make it more brittle. Expansion and contraction of the PVC should be the main consideration. The material will soften and deform if it is exposed to temperatures over 65° C.
PVC piping systems, are used for many industrial applications like the transport of process cooling water, and hazardous chemicals. PVC can also meet the high demand in terms of safety, economic factors, and subsequent maintenance during industrial applications.
CPVC
Chlorinated polyvinyl chloride is often cream-colored or off-white plastic. This type of pipe can withstand temperatures up to about 180 degrees Fahrenheit or so (this depends on the schedule), so it can be used for both hot and cold-water lines.
Water Piping PEX
Cross-linked polyethylene is sometimes known as XLPEl. It has good resistance to both hot and cold temperatures, they are commonly used in hot and cold water lines for domestic service, and also for hydronic heating systems (such as radiant under-floor systems).
Cost consideration for Water Pipes
The installation costs of water pipes make up the major part of the total cost of the project. The following factors are considered.
Weight of the pipe: a pipe that is light in weight can be handled easier and faster.
Ease of assembling: methods of joining the piping like bolting, welding, threads, etc.
Pipe strength: some pipes may require special bedding to withstand external pressure. While other pipes won’t. The choice can have a big impact on cost management.
Water piping networks can run above ground or can be buried below the ground. In most situations, the majority of the water pipe network is underground.
How Deep Should You Bury Water Lines?
It depends upon the geographic conditions also. Always have to consider the municipality’s building codes. Generally, Waterlines should always be kept below the frost line to ensure that they water line will not freeze.
Water Piping in Sewage network
Another application in water piping is the sewage lines which will be mostly buried on the ground horizontally. These pipes are usually of large diameters (160 mm to 650 mm) and they consist of many pipes for the long run. Most sewage lines are cast iron and they are usually heavy. They can be made of compact PVC and HDPE materials.
Cast iron pipes are highly vulnerable to condensation and acidic gases. They may show a single penetration failure due to internal stresses.
The presence of hydrogen sulfide gas is the main cause of pipe corrosion. This gas produced from sulfates is found in both raw water sources and water treatment plants. This corrosion due to the accumulated sulfates is known as crown corrosion. Sewage pipes will get affected by corrosion which reduces the lifespan of the pipe.
To avoid corrosion in sewage piping
Inert materials can be used
Usage of sacrificial lining
Using acceptable linings
Providing ventilation for removing moisture condensation
The main European Standards followed for Water pipes in Sewage Networks are EN 1401 and EN 13476.
Water Piping in Fire protection systems
Another important application of water piping is the fire protection system which is used in industries as well as building services. Fire protection water pipes use a normal carbon steel pipe to convey fire suppression agents common water or even gas sometimes. ASTM A795 is a steel pipe for fire protection use. As per the standards, the pipe can be welded or seamless, black or galvanized. The minimum size for the fire sprinkler system is usually 1“. In general, water pipes for the firefighting network are painted red in color.
These pipe systems are lightweight so that the fabrication in the field will be easy and won’t corrode or scale up in service. C-PVC piping systems are frequently used for fire sprinkler systems installed in public spaces.
Black steel is used as the common material for traditional fire protection systems due to its strength, durability, and extreme resistance to heat exhibited. A melting point between 2600 °F and 2800 °F so that the steel pipes can withstand the heat of burning buildings and keep water flowing onto the fire. They are suitable for all fire protection systems, they can be easily formed, bent, and fabricated, enabling them to manufacture in various sizes, shapes, and configurations. It also has the lowest coefficient of thermal expansion among fire sprinkler system pipe materials. Even extended exposure to ultraviolet rays also has no impact on its mechanical properties or even performance. Painting can be done with no adverse effects.
Rigidity is a key factor during installation as it determines the distance between hangers. As more flexible materials require more hangers. It also exerts high forces on anchors.
The major drawback of the material is the corrosive issues. They are more susceptible to corrosion than any other material and even damages can begin from the installation because of the presence of water and oxygen.
The servicing becomes very costly for obstructed water pipes, repairing leaky holes, and removing loose scales or rust due to corrosion. It degrades the system flow characteristics also.
What is Process Flow Diagram (PFD)? Purpose, Symbols, Examples, & Development of Process Flow Diagram
A Process Flow Diagram (PFD) is a simplified diagram that shows the process flow of a manufacturing process in proper sequence. This diagram should consist of every essential detail like main equipment, Heat, Material, & Energy Balance, tag number, chemical composition, etc.
Also popular as Process Flow Chart, a Process Flow Diagram (PFD) describes the relationships between major components at any chemical, process, or power plant. Process Flow Diagrams or PFDs are developed using a series of symbols and notations to convey information for a process. The concept of PFD or process flow diagram was first introduced to ASME by Frank Gilbreth, Sr. in the year 1921.
Purpose of PFD or Process Flow Diagram
The purpose of the process flow diagram is to define the design of the process. A PFD is a fundamental representation of a process that schematically shows the conversion of the raw materials to the final products. Also, PFD is a basic document of a project as it is required by the project design team during the developmental stages of a project. At these stages, feasibility studies, and scope definition activities are undertaken before commencing detailed design. PFD is very closely associated with H & MB. For a project to proceed, they are used to decide if there are enough raw materials & utilities. The PFDs are documents that are used by plant-wide design groups and site management in a manufacturing organization. On completion of a PFD, detail engineering starts. Some engineering contractors or owners use a process flow diagram as a base for designing the instrumentation & control scheme. Other benefits that a process flow diagram serves are
PFDs show the plant design basis indicating feedstock, product, and main stream flow rates and operating conditions.
A PFD documents a process for training, quality control, and simpler understanding.
It standardizes a process for optimal efficiency and repeatability.
The scope of any process can easily be found in its PFD diagram.
It provides an overall idea of the complete process without detailing much on the minute details.
It helps to study the process in a simple way for better communication and brainstorming.
PFDs serve as the input document for the creation of P&IDs.
PFD diagram also provides information regarding the utility services that will be continuously used in a process.
Development of Process Flow Diagram
A PFD is most likely developed in multiple steps. The plant owner may develop a preliminary PFD, as a first step that sets down on paper a proposed process or a process change that is under consideration. But nowadays a PFD is generated by computerized simulator software using a library of indicating symbols like follows,
For a standard process, there are several licensors like UOP, Axens, Lummus, etc. & they are responsible for developing the PFD. Process flow diagrams of open art process units like CDU (Crude distillation unit), and VDU (vacuum distillation unit) can be found in the literature and encyclopedia of chemical technology. Some of them may be obsolete. After that, the PFD is reviewed by the engineering contractor’s process engineer & planning team before the release of the detailed design. So there is enough information in the PFD like material balance information, main equipment, etc. PFD undergoes several revisions based on the review, cost optimization, HAZOP study, opinion of the expert team, etc.
What are the basic information that a PFD contains?
The depth of information furnished in a process flow diagram may vary from organization to organization. However, in general, the following information is added in a PFD.
For batch process, indicate batch capacity & batch cycle time. For continuous process indicate design production rate.
Material balance:
Composition & quantity of material in process for each unit operation & each important pipeline. For batch process indicate equipment capacity & pipeline flow per batch basis. Continuous processes show flow rates in weight or volume units per hour.
Energy balance:
Indicate heat balance or heat transfer data for each unit operation.
Physical data:
Indicate operating pressure and temperature, specific gravity, molecular weight, viscosity, specific heat, and other important data.
Equipment information:
Represent all the unit operations involved in the process. Spare equipment, duplicate parallel lines, and bypass lines don’t need to show unless necessary. Arrange all the unit operations properly so that maximum simplicity can be achieved. Indicate the correct relative position so as to gravity flow, seal loop, and other requirements can be represented correctly. Represent the proper name, tag number, and capacity of each equipment item involved in the unit operations. Important features of the equipment like agitators, trays, and jacket coils are to be indicated in PFD.
Piping information:
Major process lines associated with the process are to be shown with proper directions. Other important piping items like sampling point, inline filter static mixture, etc as well as control valves to be shown in a process flow diagram. Show the major service or utility line that is essentially required for the process.
Instrument Information:
Show all the critical instruments which are involved in the control loop like the mass flow meter, temperature transmitter, etc. Along with the proper control scheme the instruments participated in the control scheme to be shown in the process flow diagram.
Size and Scale:
Use the standard scale ratio set by project standards for drawing the PFD. Generally, arrange the flow for trimming to 11” or 22” height. If an absolute scale is not used the process flow diagram should show the relative size and elevation of the components.
Drawing Instructions:
Use the standard symbol of the equipment, sketch, etc, set by the project standard. It should be represented in the legend sheet. Use the applicable data in a tabulated format and show it at the bottom of the process flow diagram for each unit operation and process line. Define the steam numbers of each process line shown in the process flow diagram whose operating condition should be represented in the process flow diagram. Indicate the proper arrow for showing the correct flow of the process so that the process flow diagram can be easily understood. Mention the process lines which carry the two-phase flow.
Flow summary:
Process flow data & conditions are provided on the process flow diagram (ref Table 5). As the process flow diagram is related closely to the material balance, mass flow units are normally used. Additionally, pressure & temperature conditions are provided as well. Flow summary is shown on the process flow diagram which contains all the necessary information. The below-tabulated format (Table-1) that contains the following information about the process should be represented in the process flow diagram.
Essential information
Optional information
Stream number
Component Mole Fraction
Operating temperature
Component Mass Fraction
Operating pressure
Individual Component Flow rates
Vapor fraction
Volumetric Flow rates
Mass flow rate
Density, Viscosity, Heat Capacity, etc.
Molar flow rate
Stream Name
Individual component flow rate
K-Values
Flow Direction
Stream Enthalpy
Table 1: Information contained in Flow Summary
As already informed that PFD is not detailed drawings of the process. So It does not provide the following information, in general:
Equipment dimensional information and requirement of spare equipment
Code class information, etc
Symbols for Process Flow Diagram
The process flow diagram shall use symbols & letter designation to represent the equipment on the process flow diagram. It is not at all necessary to add more details to the equipment shown on a process flow diagram. For example, a heat exchanger can be represented as a simple line representation of the main process flow and heat transfer medium flow, without implying a particular type of exchange. For a process flow diagram, the only information required is that a piece of equipment transfers heat at that point of the process rather than showing specifically the mechanism for heat transfers.
Stream Identification
Fig. 1: Stream Identification
Conventions used for identifying process equipment
The below tables (Table 2) contain the symbolic letters which are generally used to identify the process equipment in a process flow diagram.
Process flow diagram Symbols for Equipment | PFD Equipment Symbols
The process flow diagram symbols for equipment are shown in Fig. 2 below.
Fig. 2: Typical Symbols used in PFD
Equipment Description for PFDs and PIDs
Equipment Type
Description of Equipment
Towers
Size (height & diameter), Pressure, Temperature Number and Type of Trays Height and Type of Packing Material of Construction
Heat Exchanger
Type: Gas-Gas, Gas-Liquid, Liquid-Liquid, Condenser, vaporizer Process: Duty, Area, Temperature, Pressure for both streams No. of shell & Tube passes Material of Construction
Tanks/Vessel
Height, Diameter, Orientation, Pressure, Temperature, Material of Construction
Pumps
Flow, Discharge Pressure, Temperature, Driver type, Shaft Power, Material of Construction
Compressors
Actual Inlet Flow Rate, Pressure, Temperature, Driver type, Shaft Power, Material of Construction
Heaters
Type, Tube Pressure, Tube temperature, Duty, Fuel, Material of construction
Table 3: Description of Equipment in PFD
Example of Process Flow diagram
Fig. 3: A Simplified Process Flow Diagram
As per Fig-3, it is clearly showing that there is a flow in the process line, stream number (1) of 10000 lb/hr of wet gas with a temperature between 90 F and 180 F and a pressure of 20 Psi. The variation in temperature is caused by a process upset at the upstream of PFD. Note that, only a stream number, (1),(2),(3) identifies the pipeline. Not included is the line size, the material of construction, or the pressure rating (ANSI 150, ANSI 300, etc) for any of the piping shown on the PFD. Also, note that there is no symbol or data shown for the pump driver. Only the equipment number, G-005 identifies the pump. So it is very clear that the PFD represents the relationship between the main equipment of a process plant and at the same time, it does not show minute details like piping details and designations, etc.
Fig. 4: Sample of Process flow diagram
Fig. 5: Process flow diagram (PFD) for the Production of Benzene via Hydrodealkylation of Toluene
Flow summary table:
Stream Number
1
2
3
4
5
6
7
8
Temperature (ᵒC)
25
59
25
225
41
600
41
38
Pressure
1.90
25.8
25.5
25.2
25.5
25.0
25.5
23.9
Vapor Fraction
0.0
0.0
1.0
1.0
1.0
1.0
1.0
1.0
Mass Flow (ton/hr)
10.0
13.2
0.82
20.5
6.41
20.5
0.36
9.2
Molar Flow (Kmol/hr
108.7
144.2
301.0
1204.4
758.8
1204.4
42.6
1100.8
Component Mole Flow (Kmol/hr)
Hydrogen
.0.0
0.0
286.0
735.4
449.4
735.4
25.2
651.9
Methane
0.0
0.0
15.0
317.3
302.2
317.3
16.95
438.3
Benzene
0.0
1.0
0.0
7.6
6.6
7.6
0.37
9.55
Toluene
108.7
143.2
0.0
144.0
0.7
144.0
0.04
1.05
Table 4: Representation of Flow summary of Benzene Production from Toluene.
Codes and Standards for Process Flow Diagrams
The following codes and standards can be used for developing process flow diagrams for the process industry.
ISO 15519
ISO 10628
SAA AS 1109
ISA 5.7
Are PFD and P&ID different?
Yes, both PFD and P&ID are two different process documents. P&ID provides more detailed information about the process steps. The main differences between a PFD and P&ID are provided here.
Pipe Flushing is a pre-commissioning activity. Piping and pipeline systems are flushed before commissioning the line or put into action. Pipeline or Pipe Flushing can be defined as the activity where a sufficient quantity of fluid is pumped through the piping or pipeline section with sufficient velocity to forcibly remove construction debris, dust, rust, mill scale, oil, grease, or any other kind of impurities. The section of piping or pipeline system requiring flushing is defined beforehand and then a detailed pipe flushing plan is made for execution.
Pipe flushing is usually done for pipes with sizes 10 inches or less. For larger pipes, the fluid quantity requirement becomes so large that it slowly becomes impractical. So, full-bore pipe flushing is usually not done for pipes of size 12 inches or larger.
Types of Pipe Flushing
Depending on the fluid used for the operation, pipe flushing can be of two types:
Chemical/Water flushing and
Oil flushing
Chemical flushing is the most common method used to remove garbage elements from the piping and pipeline systems using plain water and water with chemicals. On the other hand, oil flushing is carried out after chemical flushing to ensure the fluid that will flow through the pipelines are free from any kind of contamination. Oil flushing is used for lube oil systems.
Working Principle of Pipe Flushing
Pipe flushing removes the unnecessary elements from the piping system by the force of flushing fluid which passes through the system at high velocity. The force applies to the foreign elements and becomes loose which then flows along with the flushing fluid making the pipe and pipeline surface clean.
So, the important factor for pipe flushing operation is the fluid velocity. The velocity required for pipeline flushing operation is decided in one of the following two ways:
the velocity is decided such that it achieves a Reynolds Number (NR) of 4000 for Piping and of 3000 for Tubing 1/2″ and below, or
the velocity must be equal to or more than the normal operating velocity of the actual fluid.
Pipe Flushing Criteria
A detailed pipe flushing plan should provide details of pipeline flushing criteria. Some of the basic guidelines for pipe flushing criteria are listed below:
Flushing Medium: Stainless steel pipes shall be flushed with potable or demineralized water having a chloride content of less than 20 ppm. However, for normal carbon steel or alloy steel, plant water, potable water or any other approved flushing medium can be used.
Flushing Duration: Once the pipe flushing is started in open-ended systems, It is usually stopped after 5 minutes of clear water discharging started. For closed circuit loops, flushing can be stopped once the pump strainer is found to be free from foreign materials and the circulating water is clean.
Flushing Liquid Volume: Sufficient volume of water should be available such that the complete pipe is full and exert sufficient force at high velocity on foreign matters. In normal cases, the water from the fire water distribution network is used for pipe flushing. Separate pumps shall be used for generating the required velocity.
Pipe Flushing Standards
The common industry standard governing the procedure of pipe flushing is ASTM D4174. Other considerable pipe-flushing standards are ISO 5910, ISO 28521, ISO 5911, SHELL DEP 31405030, etc.
Basic Pipe Flushing Guidelines
Some of the considerable pipe-flushing guidelines are listed below:
A detailed flushing plan should instruct about the types, steps, and duration of flushing.
Pipe flushing should be done using normal operation flow direction.
Pipeline flushing should preferably be done from the highest to the lowest elevation.
The pipe flushing activity should be supervised and inspected by a commissioning engineer.
Flushing should be performed through fully open flanges/ open pipe ends and never be carried out through smaller openings such as drains or vents.
The proper capacity of the pump shall be selected for pipe flushing activity.
All required temporary fittings like a hose, blind flange, strainer, gasket, etc must be fitted before flushing and shall be removed immediately after completion of pipe flushing.
To avoid corrosion potential, the system shall be de-watered immediately after flushing and make it dry.
What is HVAC Piping? Types, Materials, and Standards for HVAC Piping
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.
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.
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.
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
Chilled and heated water piping
Miscellaneous drains and overflows
Emergency generator exhaust
Safety and relief valve discharge
Chemical treatments
High- and low-pressure steam
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,
Industrial cold water (above grade-type L) for piping 4 “and smaller.
Refrigerant piping (type L, hand-drawn) below 6“
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
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:
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.
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 Size
Maximum Support Spacing
Common 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 over
20 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 joints
3/8 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.
