Glossary

Piping class

A piping class defines suitable materials, components, pressure ratings and design requirements for a specific range of operating conditions and fluids.

Also: Pipe class · Piping material class · Pipe spec · Piping specification

Also known as

Pipe class
Piping material class
Pipe spec
Piping specification

A piping class is a kit of parts

A piping class – often called a pipe spec – defines, for a bounded range of service conditions (certain fluids, a pressure and temperature range), the components from which a line may be built. The designer assigns a class to every line; all pipes, fittings, flanges and valves of that line then come from this kit.

The benefit lies in repetition. Wall thicknesses and materials are verified once instead of for every line. Procurement, stores and prefabrication work with a limited, known range, and a CAD system can offer the permitted components for each line by itself.

What a piping class contains

The scope differs from one operator to the next; the core is the same everywhere.

Scope: fluids and the permitted combinations of pressure and temperature.
Design code and materials for pipe, fittings, flanges, bolting and gaskets.
Corrosion allowance.
Pipe dimensions: outside diameter and wall thickness for each nominal size.
Fittings with standard and type – bends, tees, reducers, caps.
Flanges, gaskets and bolting with rating and facing.
Valves by type and design.
Branch table: which type of branch connection applies to which combination of header and branch size.

What the entries are based on

Behind every line there is a verification. The wall thicknesses are calculated for the limiting conditions of the class to the chosen code – EN 13480-3 or ASME B31.3, for example – and rounded to standard thicknesses. For flanges and valves the pressure-temperature rating of their standard applies; for flanges, for instance, EN 1092-1 with PN designations or ASME B16.5 with Class designations.

The scope of the class is governed by its weakest component. Often that is not the pipe but the flange, whose allowable pressure decreases with rising temperature.

Distinction from specification, line list and bill of materials

Four documents tend to be confused in daily work. The piping specification contains the general rules of a project: codes, fabrication, testing, painting, insulation. The piping class is the kit of parts for one range of service. The line list assigns design data and a class to every single line. The bill of materials, finally, states what is actually ordered for a particular isometric – made up of components from the class.

Nor is a piping class a pressure rating. PN 16 describes the capability of a component; the piping class describes the whole system in which that component is used.

Common mistakes

Piping classes look like pure administration. Their errors only show on site or in operation.

A class is used outside its pressure-temperature range because a rating appears on the cover sheet.
Components to EN and to ASME are mixed although dimensions and ratings do not match.
The corrosion allowance is considered for pipe but not for fittings.
The branch table is missing, and every branch is decided individually.
Too many classes for almost identical conditions – stockholding and the risk of mix-ups grow.

What Entracon offers here is on the matching page.

See what we offer

Overview

Four documents, four purposes

Document	Defines	Applies to
Piping specification	Codes, fabrication, testing, painting, insulation	The whole project
Piping class	Materials, dimensions and permitted components	One range of fluid, pressure and temperature
Line list	Design data and assigned piping class	Every single line
Bill of materials	Quantity and description of the components required	One isometric or section

Frequently asked questions

Frequently asked questions about Piping class

Is a piping class the same as a pressure rating?

No. The rating – PN or Class – describes the capability of a single component. The piping class defines all components for a range of service, including material, wall thickness and type of branch connection.

How many piping classes does a plant need?

As few as possible and as many as necessary. Every additional class increases the effort in procurement and stores. Too few classes mean that simple lines are built in expensive materials.

Does a piping class have to be calculated?

Yes. The wall thicknesses are verified for the limiting conditions of the class to the chosen code, and the pressure-temperature ratings of flanges and valves are checked. Without this verification the class is merely a material list.

Can an existing piping class be reused for a new project?

Only after review. Codes and material standards change, and the conditions of the new project have to lie within the scope of the class.

Where the term appears on this site

From the term to the application

Service

Contact

Let's talk about your project.

One short conversation usually settles more than three quotations. Call or write — you will reach an engineer directly.

Get in touch +49 234 5414010

Machinery & Plant

Software

Material Handling

Services