What is Piping? | Basics of Piping and Pipelines Explained
Introduction
Piping systems form the backbone of fluid transportation in industries such as oil & gas, power generation, water treatment, and chemical manufacturing. Whether you’re dealing with steam, oil, gas, or chemicals, a well-engineered piping network ensures safe, efficient, and uninterrupted flow of materials. This page provides a detailed look at piping fundamentals, classifications, materials, sizing standards, and how piping systems differ from pipelines — making it an essential guide for engineers and technical professionals.
What is a Piping?
Piping refers to the complete system of pipes and connected components that convey fluids within industrial facilities. A piping system includes not just the pipes, but also:
- Valves
- Flanges and gaskets
- Pipe supports and hangers
- Special devices like strainers, traps, and instrumentation
Piping systems are engineered to meet specific temperature, pressure, and corrosion conditions, governed by codes like ASME B31.3 (for process industries).
Types of Piping Systems
Piping systems can be categorized based on the type of fluid they transport, their application, and the materials used in their construction. Common types include:
- Water piping – For potable, cooling, and wastewater
- Oil piping – Transports crude oil and refined hydrocarbons
- Gas piping – Includes natural gas, propane, and process gases
- Steam piping – High-temperature and high-pressure applications
- Slurry piping – Used in mining and material transport
- Chemical piping – Handles corrosive or toxic fluids
- Cryogenic piping – For ultra-low temperature fluids like LNG
- Compressed air and vacuum – For industrial automation and process requirements.
Materials range from carbon steel, stainless steel, and alloys to non-metals like PVC and HDPE, selected based on the fluid’s properties and system pressure/temperature.
Core Components of a Piping System
A typical industrial piping system consists of several key components, each serving a specific function:
- Pipes: The main conduits for fluid flow, available in various materials and sizes to handle different pressures and substances.
- Pipe Fittings: Used to connect pipes, change direction, branch lines, or alter pipe diameters. Common fittings include elbows, tees, reducers, couplings, and unions.
- Valves: Control, stop, or divert fluid flow. Types include gate, globe, ball, butterfly, and control valves, chosen based on the application.
- Flanges and Gaskets: Provide leak-proof connections between pipes and equipment.
- Supports and Hangers: Maintain alignment and bear the weight of the piping, preventing sagging or vibration.
- Special Items: Such as strainers, steam traps, expansion bellows, and instrumentation for monitoring and control.
Classification of Piping in Process Industry
Key Classifications According to ASME B31:
- ASME B31.1 – Power Piping:
Covers piping systems typically found in electric power generating stations, industrial and institutional plants, geothermal heating systems, and central/district heating and cooling systems. These systems handle high-pressure steam, water, and auxiliary services essential for power generation. - ASME B31.3 – Process Piping:
Applies to piping in petroleum refineries, chemical plants, pharmaceutical facilities, textile and paper plants, semiconductor manufacturing, and cryogenic plants. Process piping systems are designed to safely convey chemicals, hydrocarbons, and other process fluids under varying pressures and temperatures within complex industrial plants. - ASME B31.4 – Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids:
Governs the design, construction, operation, and maintenance of pipelines transporting liquid hydrocarbons (such as crude oil and refined products) and other liquids between plants, terminals, pumping stations, and metering stations over long distances. - ASME B31.5 – Refrigeration Piping and Heat Transfer Components:
Specifies requirements for piping systems carrying refrigerants and secondary coolants, ensuring safety in refrigeration and cooling applications. - ASME B31.8 – Gas Transmission and Distribution Piping Systems:
Covers pipelines that transport gaseous products (such as natural gas) from sources to terminals, including transmission, distribution, and storage systems. This section addresses the unique safety and operational challenges of high-pressure gas pipelines. - ASME B31.9 – Building Services Piping:
Focuses on piping systems within buildings that provide services such as heating, cooling, and water supply. - ASME B31.12 – Hydrogen Piping and Pipelines:
Addresses the design and construction of piping and pipelines specifically for hydrogen service, reflecting the growing importance of hydrogen as an industrial and energy resource
In the oil and gas sector, piping and pipelines are classified according to their function, design standards, and the materials they transport. The main classifications include:
Piping Materials
The choice of piping material depends on the fluid, pressure, temperature, and environment:
- Carbon Steel: Most common; strong, affordable, but prone to corrosion unless protected. Used in oil, gas, and steam applications.
- Stainless Steel: High corrosion resistance; used in corrosive or hygienic environments (e.g., chemical, food, pharmaceutical).
- Alloy Steel: Enhanced strength and heat resistance; used in high-temperature, high-pressure environments.
- Copper and Copper Alloys: Excellent thermal conductivity; used in plumbing, refrigeration, and HVAC.
- Ductile Iron: Used for water and sewer systems; strong and tough.
- Nickel Alloys: Exceptional corrosion and heat resistance; used in chemical and nuclear industries.
- Plastics (PVC, PVDF, PTFE, etc.): Lightweight, corrosion-resistant; used in low-pressure, corrosive, or high-purity system.
Pipe Sizing: Definition, Reading and Standards
Pipe sizing is a critical engineering process that determines the appropriate diameter and wall thickness of pipes to ensure safe, efficient, and cost-effective transport of fluids or gases within a piping system. The sizing process involves two main aspects:
Fluid Flow Design: Establishes the minimum inside diameter required to achieve the desired flow rate while keeping pressure drops and velocities within acceptable limits.
Pressure-integrity Design: Determines the minimum wall thickness needed to withstand the system’s operating pressure and ensure mechanical integrity.
How Pipe Size is Defined
Pipe size is most commonly defined using the Nominal Pipe Size (NPS) system, especially in North America and industries following imperial standards. NPS is a dimensionless designation that refers to the approximate (not exact) inside diameter of a pipe. However, as pipe wall thicknesses changed over time (with the introduction of pipe schedules), the actual inside diameter may differ from the nominal size.
- NPS (Nominal Pipe Size): A standardized, dimensionless number (e.g., NPS 2, NPS 6) that loosely refers to the pipe’s internal diameter, but is actually tied to a fixed outside diameter for each size.
- Pipe Schedule (SCH): Indicates the wall thickness of the pipe. Common schedules include SCH 40, SCH 80, etc. As the schedule increases, the wall becomes thicker, which reduces the internal diameter for the same NPS.
- Outside Diameter (OD): For a given NPS, the OD remains constant, regardless of schedule, while the internal diameter varies depending on the schedule.
- Inside Diameter (ID): The inside diameter represents the open passage within the pipe through which the fluid flows. Its value depends on both the pipe’s material and the wall thickness, so even pipes with the same nominal size (NPS) may have different IDs.
- Wall Thickness: Pipe wall thickness is indicated by a schedule number (SCH). The schedule is an indirect way of showing how thick the wall is. Examples of commonly used schedules are SCH 40, SCH 80, and SCH 160. A higher schedule number corresponds to a thicker wall capable of withstanding greater internal pressure.
- Pipe Length: Pipes are manufactured in standard lengths, though cutting or threading can be done based on project needs and the material type. Typical lengths may be around 20 feet for many sizes, but actual dimensions vary by specification and application.
- End Finish: The end preparation of a pipe is called the end finish, which ensures proper connection to fittings or other piping. Typical end types include plain end (PE), beveled end for welding (BE), threaded end (TE), and grooved end for mechanical jointing.
Example:
An NPS 3 pipe has an OD of 3.5 inches, not 3 inches. If you select SCH 40, the wall thickness is 0.216 inches, so the actual internal diameter is about 3.068 inches3.
How Pipe Size is Read
When reading or specifying pipe size, it is typically presented as:
- NPS x Schedule (e.g., 6″ NPS SCH 40)
- For metric systems, the DN (Diameter Nominal) system is used, which is based on millimeters and closely matches the NPS system for reference.
Associated Pipe Sizing Systems
- IPS (Iron Pipe Size): An older system, now largely replaced by NPS, but still referenced for certain legacy systems.
- DN (Diameter Nominal): The international metric equivalent of NPS, used mainly outside North America. For example, DN 50 is roughly equivalent to NPS 2.
- Pipe Schedule: As noted, this defines wall thickness and is essential for pressure rating and mechanical strength.
Why Proper Pipe Sizing Mater
- Ensures energy efficiency by minimizing pressure losses and pump requirements.
- Maintains system performance by preventing excessive velocities, erosion, and noise.
- Balances cost by avoiding oversized (expensive) or undersized (inefficient, unsafe) pipes.
- Supports safety by ensuring pipes can handle the required pressure and flow without risk of failure.
Pipelines
What is a pipeline?
A pipeline is a system of connected pipes designed for the long-distance transportation of fluids-such as oil, natural gas, water, or refined products-typically from one facility to another, often spanning hundreds or thousands of kilometers. Pipelines are engineered to move large volumes of liquids or gases efficiently and reliably across regions, countries, or even continents, and can be installed underground, above ground, or underwater (as with subsea pipelines)
Key Characteristics of Pipelines
- Function: Pipelines are primarily used to transport bulk quantities of fluids over long distances, such as moving crude oil from offshore platforms to refineries or delivering natural gas from production fields to distribution networks.
- Size: They typically use large-diameter pipes to accommodate high flow rates and minimize pressure loss over extended distances.
- Components: A typical pipeline system includes injection (supply) stations, pump or compressor stations, block valve stations for isolation, regulator stations for pressure control, and delivery stations at the endpoint.
- Fittings: Pipelines use a minimal number of fittings-mostly long-radius bends and valves-to reduce flow resistance and maintenance needs.
- Construction: Most pipelines are constructed from welded steel, though materials like concrete or plastics may be used for specific applications.
- Codes and Standards: Design and operation are governed by standards such as ASME B31.4 (for liquid transportation) and ASME B31.8 (for gas transmission)9.
Typical Applications
- Oil and Gas: Transporting crude oil, natural gas, and refined products over long distances.
- Water and Sewage: Moving potable water, irrigation water, or wastewater between treatment plants and distribution points.
- Industrial Uses: Conveying chemicals, slurries, or other industrial fluids
Difference Between Piping and Pipeline
| Feature | Piping (Oil & Gas Facilities) | Pipeline (Long-Distance Transport) |
|---|---|---|
| Location | Within plant/facility boundaries | Across cities, regions, or countries |
| Function | Transfers fluids between equipment/process units | Transports bulk fluids over long distances |
| Size Range | Typically ½” to 80” (varied as per plant design) | Large diameter, optimized for high-volume flow |
| Fittings | Extensive use (elbows, tees, reducers, valves) | Limited, mostly long-radius bends and valves |
| Design Codes | ASME B31.3, B31.1 | ASME B31.4 (liquid), ASME B31.8 (gas) |
| Construction | Complex, with many branches and connections | Straight runs, minimal branches |
| Materials | Wide variety (steel, alloys, plastics) | Primarily steel, designed for durability |