Pipe Class vs Pipe Specification: Key Differences

Key Distinction

Pipe class = Project-specific document defining compatible components (pipes, fittings, valves, flanges) for a given service condition. Pipe specification = Standard document (ASTM, API, ASME) defining manufacturing requirements for pipes only.

Pipe classes reference pipe specifications. For example, a pipe class might specify “A106 Gr. B per ASTM A106.”

Pipe Class and Pipe Specification

These two terms cause confusion because they sound similar but serve different purposes. Understanding the difference is essential for anyone working on piping design or procurement.

What Is a Pipe Class?

A pipe class is a project-specific document that defines which materials and components can be used together in a piping system for a given set of service conditions. Every major oil company, EPC contractor, and refinery develops their own pipe classes.

Saudi Aramco Pipe Class

Think of a pipe class as a “recipe” for a piping system. It specifies: use this type of pipe, with these fittings, these flanges, these valves, and these gaskets-all guaranteed to work together under the specified conditions.

Information in Pipe Classes

Element	What It Specifies
Material specs	ASTM/API grades for pipes, fittings, flanges, valves
P-T ratings	Maximum pressure and temperature for the class
Corrosion allowance	Extra wall thickness for expected corrosion
Size range	Applicable pipe diameters (e.g., 1/2” to 24”)
End connections	Welded, threaded, flanged-and when to use each
Component types	Elbows, tees, reducers, valves, gaskets included
Design codes	ASME B31.3, B31.1, etc.
Special requirements	Impact testing, sour service, coatings

Pro Tip

When reviewing an existing pipe class, always verify that the P-T rating on the line list matches the rating in the pipe class document. I’ve seen cases where the piping spec was upgraded mid-project but the line list wasn’t updated - resulting in materials being procured to the wrong class.

Who Issues Pipe Classes?

Pipe classes are developed by the engineering team of the EPC contractor or owner company. Key contributors:

Role	Contribution
Piping Engineer	Leads development; defines materials, P-T ratings, component types
Process Engineer	Provides fluid data, operating conditions
Materials Engineer	Advises on corrosion resistance, material compatibility
QA/QC Engineer	Reviews for standards compliance

Major operators (Shell, BP, Saudi Aramco, ExxonMobil) maintain standard pipe class libraries that get adapted for each project. ASME and API codes provide the baseline, but individual companies add their own requirements based on experience.

Do Pipe Classes Specify Pipes Only?

No-that’s the key point. A pipe class covers the entire “system” of compatible components:

piping materials

Component	What the Pipe Class Specifies
Pipes	Material (e.g., A106 Gr.B), schedule, applicable ASTM spec
Fittings	Material (e.g., A234 WPB), ratings, dimensions per ASME B16.9/B16.11
Valves	Type (gate, globe, check), class, materials, end connections
Flanges	Type (WN, SO, blind), rating, face type (RF, RTJ)
Gaskets	Type (spiral wound, ring joint), material
Bolting	Stud bolt and nut grades (e.g., A193 B7 / A194 2H)

This is why pipe classes are so valuable-they ensure all the pieces fit together mechanically, thermally, and chemically.

Common Mistake

Assuming that matching material grades means components are compatible. A106 Gr.B pipe and A234 WPB fittings are chemically similar, but if the fittings are Class 3000 forged and the pipe is Sch.40, you’ve created a pressure mismatch. Always verify that wall thicknesses and pressure ratings align across all components.

What Is a Pipe Specification?

A pipe specification (pipe spec) is a manufacturing standard issued by organizations like ASTM, API, or ASME. It defines how pipes must be made, tested, and certified-independent of any particular project.

When you see “ASTM A106 Grade B” on a mill test certificate, that’s referring to a pipe specification. The spec defines everything the manufacturer needs to know:

Information in Pipe Specifications

Element	What It Defines
Material grade	Chemical composition, mechanical properties
Dimensions	OD, wall thickness, tolerances per ASME B36.10
Manufacturing	Seamless vs. welded, ERW, SAW
Mechanical properties	Tensile strength, yield strength, elongation
Testing	Hydrostatic test, NDT requirements
End finish	Plain end, beveled, threaded
Marking	Required stenciling/stamping

The key distinction: a pipe specification applies universally to all pipes made to that standard, regardless of project. A pipe class is project-specific and references pipe specifications.

Who Issues Pipe Specifications?

Unlike pipe classes (project-specific), pipe specifications come from standards organizations:

Source	Examples
ASTM International	A106, A312, A335, A333 (material specs)
API	5L (line pipe), 5CT (OCTG)
ASME	B36.10/B36.19 (dimensions), B31.x (design codes)
EN (European)	10216, 10217 (seamless/welded tubes)

These organizations develop consensus standards through technical committees. The resulting specs are used globally-an A106 pipe from China must meet the same requirements as one from Germany.

Major Standards Organizations by Region

Region	Key Organizations	Common Pipe Specs
USA	ASTM, API, ASME, AWWA, MSS	A53, A106, A312, API 5L
Europe	CEN, DIN, BSI, AFNOR	EN 10216, EN 10217, EN 10220
Japan	JIS, JPI, JWWA	JIS G 3452, JIS G 3454
Korea	KATS (KS standards), KGS	KS D 3507, KS D 3562
China	SAC (GB standards), CISA	GB/T 8163, GB/T 9711

For cross-reference between US and European pipe specifications, see the equivalent grades article.

Specifications for Other Piping Products

Yes-every piping component has its own set of standards:

Component	Key Specs
Fittings	ASME B16.9 (BW), ASME B16.11 (forged)
Flanges	ASME B16.5 (up to 24”), ASME B16.47 (26”+)
Valves	API 6D, API 600, API 602, ASME B16.34
Gaskets	ASME B16.20 (metallic), ASME B16.21 (non-metallic)
Bolting	ASTM A193/A194 (high temp), ASTM A320 (low temp)

Summary: Pipe Class vs. Pipe Specification

Aspect	Pipe Class	Pipe Specification
Issued by	EPC contractor or owner company	Standards body (ASTM, API, EN)
Scope	All piping components (pipe, fittings, valves, flanges, bolting)	Pipes only
Purpose	Ensure system compatibility for specific service	Define manufacturing requirements
Project-specific?	Yes	No (universal standard)
Contains	Material callouts, P-T ratings, component types, connection methods	Chemical composition, mechanical properties, testing, tolerances
Used by	Design engineers, procurement	Manufacturers, QC inspectors

The relationship: A pipe class references pipe specifications. When a pipe class says “Pipe: A106 Gr. B, Sch. 40,” it’s calling out the ASTM A106 pipe specification and adding project-specific requirements (schedule, size range, corrosion allowance).

Both documents are essential-the pipe specification ensures you get quality pipe; the pipe class ensures that pipe works with everything else in the system.

Field Note

During receiving inspection, always verify that incoming materials match both the pipe specification (on the MTR) and the pipe class (on the purchase order). I’ve seen compliant A312 pipe rejected on-site because the procurement team ordered it to the wrong pipe class - same material spec, but wrong wall thickness for the application.