ISO 161-2:1996

Overview

ISO 161-2:1996 (second edition) is the ISO international standard that specifies inch-based nominal outside diameters and nominal pressure ratings for thermoplastics pipes used for the conveyance of fluids. It covers both pressure and non-pressure applications and sets requirements for minimum required strength (MRS) and Overall Service (design) coefficients (C) to support consistent design, manufacturing and system compatibility.

This part applies to smooth, circular-section thermoplastic pipes regardless of material or manufacturing method and is intended for use by designers, manufacturers, specifiers and testing organizations.

Key Topics

• Nominal outside diameter (dn) and nominal size (DN): Inch-based reference outside diameters (expressed as mm for tolerance application) used to define pipe size across components.
• Nominal pressure (PN): Alphanumeric values chosen from preferred-number series (R10/R20) used for reference ratings. Table values include common PN examples such as PN 1, 2.5, 4, 6.3, 10, 16 and 20.
• Minimum Required Strength (MRS): Hoop stress values (MPa) based on the lower confidence limit of long-term hydrostatic strength; MRS values are selected from permitted series in the standard.
• Overall Service (design) coefficient (C): Factor (>1) accounting for service conditions and system components; minimum values for specific materials are specified in ISO 12162.
• Standard Dimension Ratio (SDR) and pressure relationships: SDR links outside diameter to wall thickness and, together with MRS and C, determines the maximum allowable operating pressure (PPMS). The standard provides the engineering relations to calculate PPMS from MRS, C and SDR (and equivalently using design stress σ).
• Definitions and normative references: Includes cross-references to ISO 3 (preferred numbers), ISO 12162 (thermoplastics materials for pressure applications), ISO 4065 and related documents.

Applications

ISO 161-2:1996 is used where inch-based sizing remains standard practice. Typical applications include:

• Specification and procurement of thermoplastic pressure pipes for water distribution, industrial fluid systems and non-pressure tubing.
• Design validation: converting material MRS and service coefficient C into allowable operating pressures and selecting appropriate SDR or wall thickness.
• Manufacturing and quality control: ensuring nominal diameters and tolerances are compatible across systems and fittings.
• System compatibility and safety: using standardized PN and DN designations to match components and ensure predictable mechanical performance.

Benefits include improved interchangeability, repeatable pressure-rating calculations, and clearer material selection guidance for long-term hydrostatic performance.

Related Standards

• ISO 161-1:1996 - Thermoplastics pipes: Metric series (companion part).
• ISO 12162:1995 - Thermoplastics materials for pipes and fittings: MRS and design coefficients.
• ISO 4065:1996 - Thermoplastics pipes: Universal wall thickness table.
• ISO 3 / ISO 497 - Preferred numbers and series used for PN, MRS and nominal sizing.

Note: Annex A in ISO 161-2 is informative. Users should refer to the applicable product standard and ISO 12162 for specific MRS and C values when performing design calculations.