What Is a Piping System (In Simple Terms)?

A piping system is a connected network of pipes, fittings, valves, and supporting components designed to transport fluids (liquids or gases) between points in an industrial facility. Most industrial piping operates as a pressurized closed conduit (the pipe is fully filled), with a few exceptions like some drains that behave like open-channel flow.

Why codes and standards matter

Codes and standards create a consistent engineering “rulebook” for safety and performance. They guide: material selection, allowable stress, design pressure/temperature, fabrication, inspection, testing, and operation.

Key Piping Design Codes: ASME B31 & EN 13480

The ASME B31 family is among the most widely used piping code frameworks. Each section targets a specific industry/application type, with similar principles but different safety factors and details.

ASME B31.1 — Power Piping

Commonly used for power plants, power generation facilities, geothermal systems, and central/district heating systems.

ASME B31.3 — Process Piping

Used in refineries, chemical plants, petrochemical plants, and many process industries (including paper, textiles, semiconductors, and more).

ASME B31.4 — Liquid Transportation

Applies to pipeline transportation of liquids (such as hydrocarbons) outside a refinery boundary, often associated with upstream or inter-facility transport.

ASME B31.8 — Gas Transportation and Distribution

Focuses on gas pipelines and related infrastructure beyond plant boundaries, addressing unique safety and regulatory needs.

EN 13480 — European Industrial Piping

EN 13480 is a major European counterpart for industrial piping design and calculation, covering materials, fabrication, installation, and testing within European regulatory contexts.

Codes vs. standards (quick difference)

• Code: broad requirements and design rules (what must be achieved).
• Standard: detailed component specs (how dimensions/materials/components are defined).

Common Piping Standards You’ll See in Specifications

Industrial piping frequently references component standards for interoperability and safety. Examples include (by topic):

Flanges, fittings, gaskets, valves

• ASME B16.5 (flanges up to 24")
• ASME B16.47 (large diameter flanges)
• ASME B16.9 (butt-weld fittings)
• ASME B16.11 (socket-weld and threaded fittings)
• ASME B16.20 / B16.21 (gaskets)
• ASME B16.34 (valves)

Pipe dimensions

• ASME B36.10 (carbon steel pipe dimensions)
• ASME B36.19 (stainless steel pipe dimensions)

Material specifications (examples)

ASTM/ASME material standards define material chemistry and mechanical properties. A common “real-world confusion” is that different components can be the “same base metal” but have different designations due to fabrication method (cast/forged/welded).

• ASTM A53 (carbon steel pipe – grades A/B)
• ASTM A106 (seamless carbon steel pipe – grades A/B/C)
• ASTM A105 (forged carbon steel flanges)
• ASTM A312 (stainless steel pipe – 304/316/321/347, etc.)
• ASTM A335 (alloy steel pipe for high temperature service)

Load Types in Piping: Sustained, Displacement, and Occasional

A safe piping design accounts for different load categories that can occur during fabrication, installation, testing, normal operation, and abnormal/transient events.

1) Sustained loads

These are the “always there” loads during normal operation, such as: pipe self-weight (dead load), contained fluid weight, and internal pressure effects. They form a baseline for integrity and support design.

2) Displacement loads

These loads occur due to movement or displacement—most often from thermal expansion. If expansion is restrained by supports, anchors, or equipment nozzles, thermal loads and stresses can rise quickly.

3) Occasional loads

These are intermittent/transient loads such as wind, seismic, vibration, pressure surges, or water hammer. Even if rare, they can be critical for safety and must be checked using code rules and allowable stress adjustments.

Design Pressure, Design Temperature, and MDMT (Minimum Design Metal Temperature)

Design pressure

Design pressure should not be lower than the pressure expected in normal operation, and it must reflect the most severe coincident conditions.

Design temperature

Design temperature represents the most severe temperature condition expected (often paired with pressure). With external insulation, it is typically based on the maximum contained fluid temperature.

MDMT

MDMT is the lowest temperature at which the selected material can safely operate without brittle fracture risk. Codes provide guidance curves based on material and thickness; impact testing may be required if conditions are demanding.

Pressure Loss & Pipe Sizing: Why Diameter Matters

Pipe diameter selection is primarily a hydraulics/fluid mechanics problem involving flow rate, velocity, allowable pressure drop, fluid properties, pipe length, and roughness—plus practical installation choices (equipment flange sizes, standardization, cost).

Laminar vs turbulent flow (Reynolds number)

Flow behavior changes based on Reynolds number: laminar flow tends to occur at low Reynolds values, while turbulent flow dominates at higher values. The transition range can be unstable and needs careful consideration.

Energy conservation and pressure drop

As fluid flows, friction between fluid layers and the pipe wall dissipates energy into heat. This appears as a drop in pressure along the flow direction—measured with instruments like manometers.

Darcy–Weisbach (conceptual)

A widely used approach relates pressure loss to friction factor, pipe length, diameter, and velocity. The hardest part is often the friction factor, which depends on Reynolds number and pipe roughness.

Fittings matter too

After straight-run losses, you also account for elbows, tees, valves, reducers, etc. Many engineers use established fitting-loss coefficient methods (from industry references) to calculate total system loss.

The core trade-off

• Larger diameter → lower velocity and lower pressure loss, but higher installation cost.
• Smaller diameter → lower initial cost, but higher velocity and higher pressure loss (higher energy cost).

Material Selection & Corrosion Basics

Piping materials must balance corrosion resistance, strength, temperature capability, weldability, and cost. No single material is “best for everything,” so selection is a technical-economic decision.

Common corrosion types mentioned in practice

• Uniform corrosion: general thinning over time (often managed with corrosion allowance).
• Galvanic corrosion: dissimilar metals + electrolyte cause accelerated attack of the anode metal.
• Erosion-corrosion: high velocity/particles remove protective layers and accelerate damage.
• Pitting: localized holes that can cause failure with minimal overall weight loss.

Corrosion allowance

Engineers may add extra thickness so the pipe can safely “lose” material over the equipment life. The challenge is estimating corrosion rate accurately (often using best practices, testing data, and references like NACE guidance).

Temperature capability (practical guidance)

Carbon steels are commonly used to moderate temperatures, while alloy steels (e.g., Cr-Mo) cover higher temperatures. Stainless steels are widely used where corrosion resistance is a primary requirement.

Piping Specifications (Piping Class): What They Include

A piping specification is a project document that defines the allowed components for a service: pipe material, schedule, flanges, fittings, valves, gaskets, joining method, and applicable standards. It ensures uniformity, safety, and consistent procurement across the plant.

Pipe size basics: NPS/MPS and Schedule

Pipes are typically identified by Nominal Pipe Size (NPS/MPS) and schedule (wall thickness class). For many common sizes, NPS does not equal the actual outside or inside diameter—so always reference standards tables.

Joining methods overview

• Threaded: economical for small sizes/low pressure; limited use in many process services due to leak risk.
• Welded: high strength and tightness; common for steel process piping.
• Flanged: easy disassembly for maintenance; common at equipment interfaces, valves, instruments.

Valves in Piping: Core Types and What They Do

Valves control flow, pressure, and direction—often representing a meaningful portion of piping cost in plants. Valve selection typically considers type, materials, end connections, pressure class, size, temperature, and actuation.

Common valve categories

• On/off valves: open or close flow (e.g., many gate and ball valve use cases).
• Regulating valves: throttle/control flow rate (e.g., globe valves, control valves).
• Check valves: prevent backflow automatically.
• Safety/relief devices: protect against overpressure.

Quick practical notes

• Gate valves: best for isolation (fully open/closed), not ideal for throttling.
• Globe valves: good for regulation but adds pressure drop due to flow direction change.
• Ball valves: quarter-turn isolation; fast and tight shutoff; not for fine throttling.
• Butterfly valves: light, economical, common in large diameters/low-to-moderate pressure.
• Check valves: backflow prevention; selection affects water hammer risk and pressure loss.

Watch the Full Lesson

Conclusion

Industrial piping design is a mix of code compliance, mechanical integrity, and practical engineering trade-offs. When you understand the ASME B31 family (and EN 13480), load categories (sustained/displacement/occasional), and the basics of pressure loss, materials, piping class, and valves, you can read piping specs confidently and design safer systems.

Next steps

• Review your project’s required code edition year and client specs.
• Learn how your organization calculates pressure drop and fitting losses (tools + references).
• Build a simple “piping class cheat sheet” for common services (materials, rating, joining method).

FAQ

Which ASME B31 code should I use?

It depends on the application: power (B31.1), process plants/refineries (B31.3), liquid transport pipelines (B31.4), or gas pipelines (B31.8). Your contract/client specification usually defines the required code.

What are the three main piping load types?

Sustained loads (weight + pressure), displacement loads (thermal expansion/movement), and occasional loads (wind, seismic, surges).

Why does pipe diameter affect pressure loss so much?

Smaller diameters generally increase velocity for the same flow rate, raising friction losses and pressure drop. Larger diameters reduce velocity and losses but cost more to install.

What is a piping specification (piping class)?

A document listing approved materials, schedules, components, standards, and joining methods for a specific service in a plant.