ISO 11922-2:1997

Overview

ISO 11922-2:1997 - Thermoplastics pipes for the conveyance of fluids - Dimensions and tolerances - Part 2: Inch‑based series - specifies standardized tolerance grades for inch‑based thermoplastic pipes. It consolidates prior single‑material standards into a unified system applicable to smooth, constant‑section extruded thermoplastic pipes, regardless of material or manufacturing method. The standard is intended as the source of dimensional tolerances to be referenced by product and system standards.

Key topics and technical requirements

• Scope and applicability
  • Applies to inch‑based nominal outside diameters and nominal pressures aligned with ISO 161-2.
  • Covers smooth pipes of constant circular cross‑section used for the conveyance of fluids.
• Tolerance concepts
  • Defines terms: nominal outside diameter (dn), mean outside diameter (de,m), outside diameter at any point (de,y), out‑of‑roundness, wall thickness at any point (e_y) and mean wall thickness (e_m).
  • Establishes how deviations are expressed relative to the nominal values.
• Outside diameter tolerances
  • Provides tolerance grades F, G, H for mean outside diameter. Each grade uses a formula based on dn (e.g., Grade F = 0.009·dn, Grade G = 0.006·dn, Grade H = 0.003·dn) with minimum/maximum limits and rounding rules.
• Out‑of‑roundness
  • Defines grades P, O, R with calculation factors tied to dn; Grade P is recommended for coiled pipe when a relaxation treatment is specified.
• Wall thickness tolerances
  • Specifies multiple grades for wall thickness at any point (Grades T, U, V) and for mean wall thickness (Grades W, X), with formulaic relationships and tabulated values up to specified thickness ranges.
  • Explains how to derive maximum thickness from minimum thickness using the grade tolerance.
• Measurement
  • All dimensional measurements are to follow the applicable product standard or ISO 3126 (Plastics pipes - Measurement of dimensions).

Practical applications and users

• Who uses ISO 11922-2:
  • Pipe manufacturers (extrusion tolerance control)
  • Standards writers and product specifiers (selecting appropriate tolerance grades)
  • Quality control and inspection labs (dimensional verification)
  • Designers and system engineers (ensuring compatibility with fittings and pressure ratings)
  • Suppliers of mechanical fittings (tight wall‑thickness tolerances such as Grade V are useful)
• Practical use cases:
  • Selecting tolerance grades for specific materials and applications
  • Ensuring interchangeability and fit with mechanical connectors
  • Specifying acceptable out‑of‑roundness for coiled or large‑diameter pipe
  • Harmonizing dimensional limits across product families

Related standards

• ISO 11922-1 (metric series)
• ISO 161-2 (nominal sizes and pressures for inch series)
• ISO 3126 (measurement of dimensions)

Keywords: ISO 11922-2:1997, thermoplastics pipes, inch-based series, dimensions and tolerances, outside diameter, out-of-roundness, wall thickness, tolerance grades.