Overview
ISO 11922-1:2018 - Thermoplastics pipes for the conveyance of fluids - Dimensions and tolerances - Part 1: Metric series - establishes standardized tolerance grades for metric thermoplastics pipes. It applies to smooth, constant circular cross‑section thermoplastic pipes (regardless of material or manufacturing method) used for the conveyance of fluids. The standard links to nominal outside diameters and pressures in ISO 161‑1 and nominal wall thicknesses in ISO 4065.
Key technical topics and requirements
- Tolerance grades: Defines groups of tolerances for mean outside diameter, out‑of‑roundness and wall thickness. Grades (e.g., A, B, C, D for diameter; K, L, M, N for out‑of‑roundness; T, U, V for wall thickness) let product standards select the appropriate accuracy for the material and application.
- Mean outside diameter (dem): Measured as the circumference divided by π (π taken as 3.142), rounded to 0.1 mm. For pipes conforming to ISO 161‑1, nominal outside diameters are minimum mean diameters and tolerances are expressed as +x/−0 mm.
- Out‑of‑roundness: Specified tolerance grades and calculation factors for different nominal diameters. Notes include the measurement timing (e.g., at extrusion, on leaving factory or at time of use) and a recommendation (Grade K) for coiled pipe with relaxation treatment.
- Wall thickness: Covers wall thickness at any point (emin) and mean wall thickness (em). Mean wall thickness is the arithmetic mean of at least four regularly spaced measurements including the minimum and maximum, rounded up to 0.1 mm. Specific formulae and tabulated tolerances are provided for different wall thickness ranges and grades (T, U, V).
- Measurement rules: Rounding rules (nearest 0.1 mm or rounded up), minimum measurement counts and how to convert tolerances into limit deviations are specified to ensure consistent inspection and verification.
Practical applications and users
ISO 11922‑1 is used by:
- Pipe manufacturers and extrusion shops to set production tolerances and quality control limits.
- Product standards committees to select appropriate tolerance grades for particular pipe systems and materials.
- Design engineers and specifiers ensuring dimensional compatibility with fittings and mechanical connectors.
- Inspection and testing laboratories implementing measurement procedures and reporting tolerances.
- Procurement and quality assurance teams verifying supplied pipe conforms to required dimensions and tolerances.
Practical benefits include consistent interchangeability, reduced assembly issues with fittings, clearer supplier specifications, and harmonized quality control across thermoplastic piping products.
Related standards
- ISO 161‑1 - Nominal outside diameters and nominal pressures (metric series)
- ISO 4065 - Universal wall thickness table
- ISO 3126 - Determination of dimensions for plastics piping components
- ISO 11922 series (other part(s) in the series) for complementary tolerancing guidance.
Keywords: ISO 11922-1:2018, thermoplastics pipes, dimensions and tolerances, metric series, outside diameter, out-of-roundness, wall thickness, tolerance grades, pipe manufacturing, extrusion.
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