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Introduction to Pipe sizes and Pipe schedule

By PMG Engineering ·

Introduction

Pipe size calculation is a critical step in food factory design and industrial piping projects. It ensures that the selected piping dimensions align with process flow, pressure conditions, and end equipment. In engineering consulting, especially for food manufacturing plants, precise pipe sizing is essential to prevent cost overruns and operational issues.

Poor pipe selection can lead to:

  • Increased project cost due to oversizing
  • Complicated designs and layout inefficiencies
  • Process disturbances and flow instabilities

Accurate pipe sizing plays a vital role in efficient communication between the piping design team and the execution team, ultimately affecting the success of food processing facility construction.

 

Pipe sizing

Pipe size is specified with two non-dimensional numbers,

a.    Nominal Pipe Size (NPS)                                         

b.    Schedule Number (SCH)

    And the relationship between these numbers determines the inside diameter of a pipe.

Nominal pipe size and its importance

Pipes are referred to using terms like:

  • Nominal Pipe Size (NPS) – North American standard based on outer diameter
  • Nominal Bore (NB) – European equivalent of NPS
  • Nominal Diameter (DN) – Metric approximation used for international standardization

These notations are frequently used in food plant utility design, especially when integrating process piping with sanitary equipment.

Nominal Pipe Size (NPS)

Defines the pipe’s outer diameter, irrespective of wall thickness. For example, 2 NPS implies an OD of 2.375 inches (60.3 mm)

       

Nominal diameter (DN): Used in metric systems, this is a rough approximation of the internal diameter, crucial in sizing pipe fittings in international projects

Nominal Bore (NB): Represents the internal diameter approximation across a pipe’s cross-section. NB is often used in food processing consultant projects for selecting compatible pipe connections and equipment..

What is schedule Number?

The schedule number indicates the wall thickness of a pipe, affecting:

  • Pipe strength
  • Pressure-handling capacity
  • Material cost

The formula is:

Schedule Number = P / S

(Where P = service pressure in psi, S = allowable stress in psi)

In food factory utility systems, pipe schedule selection must consider sanitation, CIP (clean-in-place) compatibility, and process safety.

Conclusion  

Proper pipe sizing is a foundational element in designing efficient and compliant food processing facilities. Whether it’s understanding Nominal Pipe Size (NPS), Nominal Bore (NB), or selecting the appropriate pipe schedule, these decisions significantly impact the safety, cost-efficiency, and reliability of food manufacturing operations. As a leading food processing consultant and engineering services provider, we at PMG Engineering ensure every pipeline is meticulously calculated to support high-performance processing systems. Investing in accurate pipe sizing helps prevent operational failures, supports regulatory compliance, and optimizes the overall performance of your food factory design.

Reference

1.     https://www.theprocesspiping.com/nominal-pipe-size-and-schedule/

2.     https://blog.enerpac.com/pipe-diameters-a-simple-guide-to-sizing-and-schedules/

3.     https://www.allaboutpiping.com/what-is-piping/

4.     https://anchoragegroup.com.au/pipe-sizes-schedules-materials/

Frequently asked
What actually goes wrong if we get pipe sizing wrong in a food plant project?
Poor pipe selection in food factory design leads to increased project cost due to oversizing, complicated designs and layout inefficiencies, and process disturbances and flow instabilities. Accurate pipe sizing also underpins efficient communication between the piping design team and the execution team, so errors ripple into execution and ultimately affect the success of the food processing facility construction.
How is a pipe size actually specified on a drawing?
Pipe size is specified with two non-dimensional numbers: the Nominal Pipe Size (NPS) and the Schedule Number (SCH). The relationship between these two numbers determines the inside diameter of the pipe. NPS defines the outer diameter irrespective of wall thickness, while the schedule number sets the wall thickness, so both are needed before a pipe can be procured or fabricated.
What is the difference between NPS, NB and DN?
Nominal Pipe Size (NPS) is the North American standard based on outer diameter. Nominal Bore (NB) is the European equivalent of NPS and represents the internal diameter approximation across a pipe's cross-section. Nominal Diameter (DN) is the metric approximation used for international standardisation and is a rough approximation of the internal diameter, useful when sizing pipe fittings on international food plant projects.
Does 2 NPS mean the pipe is 2 inches across?
No. Nominal Pipe Size defines the pipe's outer diameter irrespective of wall thickness, and the number is nominal rather than exact. For example, 2 NPS implies an outer diameter of 2.375 inches (60.3 mm). The actual inside diameter depends on the schedule number selected, since the schedule determines the wall thickness.
How is the schedule number determined, and what does it affect?
Schedule Number = P / S, where P is the service pressure in psi and S is the allowable stress in psi. The schedule number indicates the pipe's wall thickness and therefore affects pipe strength, pressure-handling capacity and material cost. In food factory utility systems, schedule selection must also consider sanitation, CIP (clean-in-place) compatibility and process safety.
What must pipe sizing be matched against in a food processing facility?
Pipe size calculation must ensure the selected piping dimensions align with process flow, pressure conditions and the end equipment. In food plant utility design, NPS, NB and DN notations are used when integrating process piping with sanitary equipment, and NB is commonly referenced when selecting compatible pipe connections and equipment. Accurate sizing supports safety, cost-efficiency, regulatory compliance and reliable operation.
CITE THIS

PMG Engineering. (2023). Introduction to Pipe sizes and Pipe schedule. PMG Engineering. https://pmg.engineering/Article/179/introduction-to-pipe-sizes-and-pipe-schedule/

https://pmg.engineering/Article/179/introduction-to-pipe-sizes-and-pipe-schedule/