Piping Design: Principles, Process, Standards & Best Practices

What is piping design? Designing an industrial piping system involves much more than simply connecting pieces of equipment. A piping system must convey process fluids safely, maintain proper flow and pressure, accommodate thermal expansion, withstand mechanical loads, allow for maintenance, and generally conform to engineering requirements.

Designing the optimal piping system requires an engineer to draw upon process, mechanical engineering, fluid mechanics, materials, plant layout, structural and safety engineering knowledge, as well as construction requirements and expertise.

Whether designing a piping system for an oil refinery, chemical plant, power facility, pharmaceutical plant, food-processing facility, or water-treatment system, engineers should understand that smart arrangement of piping and equipment can have a major impact on the success and cost of a project.

From choosing the right material and line size for a piping system to calculating expansion and designing for flexibility, everything in piping design can impact a project.

This guide examines the basics, workflow, standards, software, and best practices for engineers who must develop a piping system in an industrial setting.

Table of Contents

1. What Is Piping Design?

2. Why Proper Piping Design Matters

3. Key Inputs for a Piping Project

4. The Piping Design Process

5. Pipe Sizing and Hydraulic Considerations

6. Piping Materials and Component Selection

7. Piping Layout and Routing

8. Pipe Supports and Flexibility

9. Stress Analysis

10. Valves, Fittings, and Special Components

11. Engineering Drawings and Documentation

12. Software and 3D Modeling

13. Codes and Standards

14. Common Piping Design Mistakes

15. Best Practices for Better Piping Systems

16. FAQs

17. Conclusion

18. Key Takeaway

What Is Piping Design?

Piping design is the engineering process of developing a piping system that safely transports liquids, gases, vapors, slurries, or other process fluids from one location to another.

The process involves much more than choosing the right size for a pipe. Engineers must consider many different design elements such as fluid properties, operating and design pressure, operating and design temperature, flow rate, pipe size, appropriate materials, corrosion and erosion resistance, thermal movement, and pipe support arrangements, among many other considerations.

In a process plant, the piping system carries fluids between major equipment items, such as pumps, compressors, heat exchangers, vessels, reactors, tanks, filters, and separators.

A well-conceived piping system yields a design that will function effectively and safely during its intended service life rather than one that is simply a drawing connecting "point A" to "point B".

Why Proper Piping Design Matters

A system involving piping that is not properly designed may have unforeseen consequences.

The results might include excessive pressure loss in a system, equipment damage, accessibility or maintenance problems, leakage, excessive stresses, or even catastrophic system failure.

For projects involving hazardous chemicals, hydrocarbons, high-pressure steam, or other potentially dangerous materials, the consequences of a poorly designed piping system can extend far beyond a simple process malfunction.

The Occupational Safety and Health Administration (OSHA) has developed the Process Safety Management framework to help manage the potential hazards associated with processes involving highly hazardous chemicals.

Proper piping design can directly impact a number of critical project goals.

Safety

A piping system must be able to safely contain the process fluid under expected process and upset conditions.

Selection of materials, pipe sizes, pressure ratings, supports, relief valves, and isolation provisions will contribute to the safety of a system.

Reliability

The piping design should tolerate expected loads without causing excessive deformation, fatigue, vibration, or component failure.

Efficiency

Proper selection of line sizes and routing can lead to reductions in unnecessary pressure losses, pumping requirements, and operating costs.

Maintainability

Operators and maintenance personnel require reasonable access to valves, instrumentation, drains and vents, flanges, and equipment.

Cost Control

A seemingly short route may add costs due to the need for additional supports or restrictions. A slightly more circuitous route could offer significant advantages in terms of reduced supports, increased flexibility, ease of fabrication, or vastly improved maintenance opportunities.

Key Inputs for a Piping Project

Before beginning detailed design work, engineers must understand the requirements and specifications of the project.

Some of the primary items that should be considered before developing a piping design include:

• Process flow diagrams (PFDs)

• Piping and instrumentation diagrams (P&IDs)

• Equipment data sheets

• Process design conditions

• Line lists

• Fluid properties

• Equipment layout

• Plot plans

• Civil and structural information

• Piping material specifications

• Applicable codes

• Insulation requirements

• Corrosion allowances

• Instrumentation requirements

• Operating and maintenance philosophy

A vital document for use in piping design is the Piping and Instrumentation Diagram (P&ID), since it includes many of the main connections and requirements concerning the process, such as valves, instrumentation, and equipment relationships.

Engineers should carefully review the information contained within the initial design documents since changes or updates to the equipment locations, process conditions, and line requirements can have significant implications for piping design.

The Piping Design Process

An engineering workflow typically progresses from the initial process definition and specifications through to detailed modeling, analysis, documentation, and construction.

1. Review Process Requirements

The initial step is for the designer to understand what the system is expected to accomplish.

Essential questions to ask at this stage include:

• What fluid is going to be transported?

• What is the required flow rate?

• What are the operating and design pressures?

• What are the operating and design temperatures?

• Is the fluid corrosive, toxic, flammable, abrasive, or otherwise dangerous?

• Does the system require heating, cooling, insulation, or tracing?

2. Establish Line Sizes

The size of the pipe will be selected based on flow requirements, velocity, pressure drop, and process limitations, as well as economic considerations.

A piping system that is too small will have excessive velocity and pressure loss. Oversized lines will add unnecessary capital expenditures without delivering significant benefits.

The hydraulic calculations may include considerations such as flow velocity, pressure rise or drop, elevation changes, fittings, valves, pressure requirements of connected equipment, and pumping or compressor performance characteristics.

3. Develop the Equipment Layout

Equipment items should be placed in a layout that allows the process to flow logically while also addressing safety, access, and maintainability requirements.

Arrangement of the major equipment often serves as the framework for the pipe routing.

4. Route the Piping

The routing of the piping connects the various equipment items while also balancing the need for a reasonably short length, flexibility, accessibility, constructability, and other design considerations.

Avoid unnecessary bends and fittings, but never sacrifice flexibility or access for the sake of distance.

5. Add Supports

Pipe supports provide restraint while also transferring loads to supporting structures.

Rests, guides, anchors, hangers, spring supports, shoes, clamps, and structural attachments are all examples of supports that might be considered.

Appropriate support will depend on pipe size, temperature, weight, movement, and loading characteristics.

Pipe Sizing and Hydraulic Considerations

Pipe sizing is one of the most important elements of a piping project.

By selecting the line size, engineers also determine the velocity of the fluid passing through the pipe.

For a given flow rate, the velocity will vary with the cross-sectional area of the pipe.

While there are many simplifications and assumptions made in fluid mechanics, an approximate relationship between volumetric flow rate, velocity, and pipe cross-sectional area can be represented as:

Q = V × A

Where:

• Q = volumetric flow rate, m³/s

• V = average fluid velocity, m/s

• A = pipe cross-sectional area, m²

In practice, engineers should always use appropriate fluid properties and established hydraulic calculations rather than simple approximations such as this one.

Piping Materials and Component Selection

Material considerations include pressure, temperature, corrosion resistance, erosion, fluid compatibility, fabrication requirements, and other project-specific needs.

Carbon steel, stainless steel, alloy steel, duplex stainless steel, nickel alloys, plastic piping, lined piping, and non-metallic materials are all examples of materials that might be used in piping systems.

Material selection is often recorded in the piping material specification, which defines acceptable piping, fittings, flanges, valves, gaskets, bolts, and other hardware for a given service.

Corrosion allowance may also be considered when appropriate.

The material choice does not have to be the cheapest option, since a lower initial acquisition cost can quickly be offset by additional maintenance and replacement expenses due to corrosion or contamination.

Piping Layout and Routing

Layout refers to how the lines will physically pass through the plant.

A good layout will deliver process fluid while balancing reasonable length, accessibility, maintainability, and constructability, as well as other factors such as safety, operator access, proper drainage and venting, thermal expansion, and avoidance of structures and obstructions.

Particular attention must be paid to routing around pumps and rotating equipment, as excessive loading or poor nozzle alignment will negatively impact the performance and reliability of the devices.

Engineers should also carefully consider constructability by determining how the system will be erected, welded, and supported.

Pipe Supports and Flexibility

Piping systems are subject to several loads, including the weight of the pipe itself, the weight of the fluid, insulation, pressure, thermal expansion, wind, seismic, vibration, and occasional loads.

As the temperature changes, a piping system will expand or contract. A long pipe that is heated can move considerably.

The piping designer must ensure that the system will possess adequate flexibility while also restricting undesirable movement.

Thermal Expansion

Thermal expansion is particularly important to consider in hot process lines and steam systems.

Restraining expansion will result in high forces and moments that can be transferred to pipe supports, adjacent equipment nozzles, and other components.

Flexibility can often be accomplished by routing the piping or adding bends, loops, or engineered expansion devices when necessary.

Support Locations

Supports should be placed based on span limitations, weight, flexibility, equipment constraints, and structural capacity.

Poorly located supports can cause excessive sagging, vibration, overstress, and other issues.

Stress Analysis

Stress analysis determines whether the piping arrangement is capable of withstanding applicable loads.

Sustained weight loads, internal pressure, thermal expansion, occasional loads, wind, seismic, relief-valve reactions, water hammer or dynamic effects, and vibration are all examples of load cases that might be considered.

For process piping, ASME B31.3 (Process Piping) is an extremely important reference, as it contains requirements related to materials, design, fabrication, examination, inspection, and testing for piping that is used in petroleum refineries, chemical, pharmaceutical, and other processing facilities.

While piping stress analysis software can be a useful tool for engineers, the results of software analysis should always be reviewed with engineering judgment. According to ASME's own resources, the real value comes from understanding the code and engineering principles rather than blindly trusting computer analysis.

Valves, Fittings, and Special Components

Piping systems include a variety of valves, fittings, and special components.

While the list of fittings is far from comprehensive, common examples include elbows, tees, reducers, flanges, valves, strainers, filters, expansion joints, spectacle blinds, orifice plates, drains, vents, instrument connections, and specialty fittings.

Selection of the valves and fittings will depend on the service and function. Valves might be needed for isolation, throttling, check, control, emergency shutdown, or pressure relief functions.

Flanges and flanged fittings must also be selected based on pressure-temperature ratings, materials, dimensions, connection requirements, and other specifications. ASME B16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and designation requirements for covered pipe flanges and flanged fittings.

Engineering Drawings and Documentation

Engineering drawings and documentation are essential since the piping will ultimately need to be fabricated, installed, inspected, tested, operated, and maintained.

Some of the most common deliverables include:

P&IDs

Piping and instrumentation diagrams convey process relationships and show major piping, valves, instrumentation, and equipment connections.

General Arrangement Drawings

These drawings show equipment and piping arrangement in plan and elevation views.

Piping Isometrics

Isometric drawings contain detailed information about individual pipe runs, including dimensions, fittings, valves, welds, supports, and material information.

MTO and BOM

Material take-offs and bills of materials help purchasing, fabrication, and construction teams understand what materials are needed.

Piping Specifications

These documents specify which components are acceptable for particular services, pressure classes, temperatures, and materials.

Software and 3D Modeling

Modern projects commonly use computer-aided design (CAD) and 3D plant design platforms to help engineers visualize piping within the context of the rest of a facility.

With a 3D model of the facility, piping and other systems can be reviewed for clashes, accessibility, routing, structural interference, valve access, insulation clearances, and a wide range of other considerations.

A visually appealing 3D model is not a guarantee of safety or correctness, however.

The review of a 3D model should always include multiple disciplines, including process, mechanical, piping, structural, electrical, instrumentation, operations, and construction.

Codes and Standards

While codes and standards play an essential role in piping design, engineers must understand that the requirements will vary based on the facility type, jurisdiction, servicing fluid, and other project-specific details.

ASME B31.3 (Process Piping) covers a wide variety of facilities and fluid services, with requirements for design, materials, fabrication, examination, inspection, and testing.

ISO 15649 specifies requirements for piping design and construction for petroleum and natural gas industries, including associated inspection and testing.

Engineers must always research the requirements and latest applicable revisions rather than making assumptions about what standards might apply to a given project.

Common Piping Design Mistakes

Even experienced teams can make the same common mistakes.

Ignoring Maintenance Access

Having a valve that can be installed but not accessed is a layout issue.

Overlooking Thermal Movement

Restraining hot piping without providing flexibility can result in excessive loads and equipment problems.

Excessive Pressure Drop

Using small pipes and fittings that unnecessarily restrict flow increases energy costs and reduces efficiency.

Poor Drainage

Low points can accumulate liquid, leading to process, corrosion, freezing, or other service-related concerns.

Inadequate Support

Long unsupported spans can sag, vibrate, and cause excessive stress.

Designing Without Constructability

If a route can't be fabricated, transported, lifted, welded, inspected, or maintained, it should be redesigned.

Treating Software as a Substitute for Engineering

Automated checks are a valuable tool but cannot replace experience, field knowledge, code awareness, or multidisciplinary reviews.

Best Practices for Better Piping Systems

The following best practices can help engineers develop piping systems that are technically sound, practical, and economical.

1. Begin with accurate process information.

Verify design conditions, flow rates, fluid properties, equipment data, and P&I Ds before detailed routing.

2. Follow the applicable code.

Determine the governing regulations and understand how project specifications intersect with them.

3. Consider operations and maintenance.

Operators and technicians need safe access to important components.

4. Design for thermal movement.

Review hot and cold systems for expansion, contraction, and equipment considerations.

5. Communicate with other disciplines early.

Piping rarely exists in a vacuum; it interacts with structural, electrical, instrumentation, civil, and process systems.

6. Select appropriate pipe supports.

Supports should address weight, movement, vibration, and structural constraints.

7. Think about construction from the beginning.

Fabrication sequence, lifting, welding, inspection, testing, and access should be considered.

8. Review the 3D model carefully.

Clash detection is only one consideration. Access, safety, and maintainability are also priorities.

9. Document design decisions.

Proper specifications, drawings, calculations, and revision control reduce errors.

10. Review the complete lifecycle.

The best designs consider construction, commissioning, operation, maintenance, inspection, modification, and eventual decommissioning.

Frequently Asked Questions

What is the main purpose of piping design?

The main purpose of piping design is to develop a piping system that is safe, reliable, maintainable, and economical for transporting process fluids between equipment and other required destinations.

What is the difference between pipe design and piping design?

The term "pipe design" can refer to the narrow selection and engineering of a single pipe and its pressure characteristics. Piping design generally indicates the broader system, including routing, valves, fittings, supports, equipment interfaces, layout, stress, materials, and documentation.

Which code is commonly used for process piping?

ASME B31.3 (Process Piping) is widely used for process piping in facilities such as refineries, chemical plants, pharmaceutical facilities, and other processing installations. It contains requirements related to design, materials, fabrication, examination, inspection, and testing.

The governing code determines the specific requirements for a piping system based on service, location, jurisdiction, and other factors.

Why is pipe stress analysis necessary?

Stress analysis helps determine if the piping arrangement is capable of withstanding applicable loads. It can also help ensure that excessive loads are not transferred to equipment nozzles or supports.

What software is used for piping engineering?

Industrial projects may use a variety of specialized computer-aided design (CAD), 3D plant design, hydraulic analysis, and pipe stress analysis software. The right tools depend on the project's size, type, and special requirements.

What makes a good piping layout?

A good piping layout balances process requirements, safety, accessibility, maintainability, flexibility, constructability, structural constraints, cost, and space.

Conclusion

Designing a piping system involves much more than simply connecting equipment items. It requires mechanical, hydraulic, and process engineering as well as plant layout, materials selection, and structural considerations.

A good piping system should function reliably and safely under expected process conditions while also allowing operators and maintenance personnel access to key equipment and components.

The system must also address thermal expansion, pressure, and weight, as well as environmental loads, corrosion, fabrication, inspection, and future maintenance considerations.

ASME B31.3 (Process Piping), among other standards, provides an essential reference for process piping, while ASME B16.5 covers requirements for pipe flanges and flanged fittings among other components.

Finally, the best piping design practices combine sound engineering principles with practical experience and multi-disciplinary collaboration to help ensure that a piping system can be safely and effectively constructed, operated, maintained, inspected, and supported throughout its service life.

Key Takeaway

The best piping design solutions will include safety, performance, reliability, cost, maintainability, and constructability considerations. Begin with accurate process information, select appropriate materials and line sizes, develop a practical layout, and account for thermal and mechanical considerations.

Apply the appropriate engineering standards and work closely with the other disciplines involved in the project.

References

• ASME B31.3 - Process Piping: ASME's overview of this code's scope, including design, materials, fabrication, examination, inspection, and testing.

• ASME B31 - Piping and Pipelines: Overview of B31 piping standards along with other related engineering resources. 

• ASME B31.3 - Process Piping Fundamentals: Guidance related to code understanding and engineering principles in process piping.

• ASME B16.5 - Covers requirements for pipe flanges and flanged fittings, including ratings, materials, dimensions, and testing.

• ISO 15649 - Petroleum and natural gas industries - Piping: International requirements related to piping design, construction, inspection, and testing for applicable petroleum and natural gas facilities.

• OSHA - Process Safety Management: U.S. Occupational Safety and Health Administration's guidance concerning hazards associated with processes that involve highly hazardous chemicals.