Pipe Class vs Pipe Spec: Key Differences

Quick Answer

A pipe class is a project-specific document that defines all compatible piping components (pipes, fittings, flanges, valves, gaskets, bolting) for a given service condition. A pipe specification (pipe spec) is a manufacturing standard issued by ASTM, API, or EN that defines how a pipe must be made, tested, and certified. Pipe classes reference pipe specifications—they do not replace them.

Comparison Table

Aspect	Pipe Class	Pipe Specification
Issued by	EPC contractor or owner (Shell, Aramco, ADNOC)	Standards body (ASTM, API, EN, JIS)
Scope	All piping components for a service	Pipes only (one product type)
Purpose	System compatibility at project level	Manufacturing and quality requirements
Project-specific	Yes	No—universal standard
Example	”Class A1A: CS, 150#, RF, hydrocarbon service”	ASTM A106 Grade B seamless pipe
Contains	Material callouts, P-T ratings, component types, connection methods	Chemical composition, mechanical properties, testing, tolerances
Used by	Design engineers, procurement, construction	Manufacturers, QC inspectors, mills
Design code	References ASME B31.3, B31.1, etc.	N/A (product standard, not design code)

How They Relate

A pipe class calls out pipe specifications by name. For example, a pipe class might state: “Pipe: ASTM A106 Gr. B, seamless, SCH 40, ASME B36.10.” Here, ASTM A106 is the pipe specification governing chemical composition (max 0.30% C, 0.29-1.06% Mn) and mechanical properties (min 240 MPa yield, 415 MPa tensile). The pipe class adds project-specific requirements such as schedule, corrosion allowance, and compatible fittings.

This distinction matters during procurement. The purchase order references both documents: the pipe class defines what to buy; the pipe specification defines what the manufacturer must deliver.

Common Sources of Confusion

“Piping specification” vs “pipe specification.” Some companies use “piping specification” as a synonym for pipe class. Technically, a piping specification covers an entire piping system, while a pipe specification covers only the pipe product. Context determines meaning—always clarify which document is being discussed.

Supplementary requirements. Pipe classes frequently add requirements beyond the base pipe specification: impact testing at -46 degrees C per ASTM A333 Gr. 6, NACE MR0175 compliance for sour service, or 100% ultrasonic examination. These supplementary requirements appear in the pipe class (or a referenced project specification) and must be included in the purchase order.

Common Mistake

Sending a purchase order that references only the pipe specification without the pipe class supplementary requirements. The mill delivers compliant material that fails the project’s additional testing requirements. Always attach both documents to the PO.

Practical Example

Component	Pipe Class Callout	Underlying Specification
Pipe	A106 Gr. B, Sch 40, SMLS	ASTM A106
Elbow	A234 WPB, BW, LR	ASTM A234, ASME B16.9
Flange	A105, WN, 150#, RF	ASTM A105, ASME B16.5
Gate valve	API 600, Class 150, RF	API 600, ASME B16.34
Gasket	Spiral wound, CGI/316, RF	ASME B16.20
Stud bolts	A193 B7 / A194 2H	ASTM A193, ASTM A194

The pipe class ties these six specifications into one system. Without it, a procurement engineer could order flanges rated for 300# while the line design pressure only requires 150#—wasting budget—or worse, order 150# components for a 300# service.

Both the pipe class and the P&ID reference each other. The line designation on the P&ID symbols includes the pipe class code, which the procurement team uses to generate material take-offs and RFQs.

Read the full guide to pipe classes and specifications