ISO 7268:1983

Overview

ISO 7268:1983 - "Pipe components - Definition of nominal pressure" specifies how the term nominal pressure (PN) is to be used for components of metallic piping systems. The standard defines PN as a numerical designation relating to pressure that provides a convenient round-number reference. It establishes the intent that equipment sharing the same nominal size (DN) and PN designation will have matching mating dimensions for their end connections.

Key topics

• Definition of nominal pressure (PN): PN is a rounded numerical designation for reference to pressure ratings of pipe components.
• Mating dimensions: Components with the same DN and PN are intended to have compatible mating dimensions appropriate to the type of end connection.
• Permissible working pressure: The actual allowable working pressure depends on material, design and working temperature and must be selected from the pressure/temperature rating tables in the corresponding standards.
• Two PN series for flanges: The standard states two series of PN ratings to be used with flanges. As published in ISO 7268:1983:
  • Series 1: PN 2.5, PN 16, PN 20, PN 50, PN 100, PN 150, PN 250, PN 420
  • Series 2: PN 10, PN 6, PN 25, PN 40
• Standards management note: Series 1 ratings are the basic set; Series 2 ratings are to be monitored for possible deletion, with PN 40 noted as having limited application.

Applications

ISO 7268:1983 is practical for professionals involved in design, manufacture, specification and maintenance of metallic piping systems:

• Piping and flange manufacturers - to ensure dimensional compatibility across components specified by PN and DN.
• Mechanical and piping engineers - to reference nominal pressure when selecting components and verifying mating dimensions.
• Procurement and specification writers - to standardize purchases and written specifications using PN designations.
• Inspection and quality assurance - to confirm that fitted components with the same PN/DN are compatible and meet prescribed pressure/temperature selections.

Related standards

• Pressure/temperature rating tables referenced in corresponding ISO standards (used to determine permissible working pressure for a given material, design and temperature).
• Standards on DN (nominal size) and specific flange dimensional standards (for detailed mating dimensions).

Keywords: ISO 7268:1983, nominal pressure, PN, pipe components, metallic piping system, flanges, DN, pressure rating.