Few words about piping classes (Part 1)

by Jul 21, 2018

In a nutshell, a piping class is a collection of pipe, fittings, flanges, valves and other auxiliary components and a set of rules required to design and construct a leak-free piping system. The purpose of the piping class is to standardize the components and summarize the applicable design requirements to reduce errors in the design, fabrication, construction, erection, examination, inspection and testing of the piping systems. From a code compliance point of view, a piping class is written to enforce the requirements of applicable acts, regulations, piping design industry standards (such as ASME B31.3), and company guidelines.

A piping class covers a range of pipe sizes (e.g., NPS 2 to NPS 10) required to complete a facility or a project. A piping class can theoretically contain pipe and fittings of a single size, however, this is not very useful or practical. Project P&IDs and LDTs show the applicable piping class for each logical piping line. This helps the piping designer to select the correct components while laying out the design of the physical line (corresponding to the logical line). The resulting CAD model and drawings show the layout as well as correct components and materials. The BOM from the model or drawings can be aggregated to determine the total quantities of components required to complete the project. This leads to a pain-free procurement process for piping, fittings, and valves.

A piping class contains a single material family. For the purpose of this text, materials with similar compositions, mechanical properties, welding characteristics, and notch toughness properties can be considered a material family regardless of the product form.  This leads to a few benefits as noted below.

  • When joining of pipe and components is performed using welding techniques, a piping system designed with a single piping class can be welded with a minimum number of welding procedure specifications (in most cases, with a single WPS).
  • The welds or joints can be examined and inspected using same NDE techniques.
  • There is no risk of material contamination and the whole system can be pressure tested with liquid medium together.
  • The expected life of the piping system in a given service and expected operating conditions can be easily forecasted.

For these reasons, the examination techniques, the extent of examination and pressure tests can be defined at piping class level. In addition, where welding is required, the fabricator, package manufacturer or field contractor can select one or more WPS(s) that will cover the welding on the all the piping systems designed to a given piping class. All these standardizations help reduce the quality issues in the fabrication and examination of the piping systems.

A piping class contains following commodity components made to Industry standards such as ASME B16/B36 series.

  1. Pipe
  2. Fittings
  3. Flanges
  4. Valves
  5. Other Components

In some instances, a standard component is required to complete the design of a piping system but is not available in the piping class. They can be used as “Approved Out of Spec” items in the piping class with approval from Piping Engineer and need to be tracked in a separate list for each piping class.

In other instances, a non-standard component is required to complete the piping system and has a specific use such as an injection quill. These components are designated as “Specialty Items” and are tracked in Specialty Items List. Specialty Items do not become part of the piping class.

Abbreviations used in this text are
WPS – Welding Procedure Specification BOM – Bill of Materials
CAD – Computer-Aided Drawing/Drafting
LDT – Line Designation Table 
NDE – Non-Destructive Examination
NPS – Nominal Pipe Size 
P&ID – Piping and Instrumentation Diagrams 
WPS – Welding Procedure Specification

This article was originally published on LinkedIn on October 15, 2017.

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