Overview
ISO 161-1:2018 - Thermoplastics pipes for the conveyance of fluids - Part 1: Metric series - defines the nominal outside diameters (dn), nominal pressure ratings (PN) and minimum required strengths (MRS) for metric thermoplastics pipes used to convey fluids. The standard applies to smooth thermoplastics pipes with a constant circular cross-section (regardless of material or manufacturing method) and serves as a reference basis for product standard writers. It does not apply to pipes designated by nominal inside diameter (DN/ID).
Key topics and requirements
- Nominal outside diameter (dn): Values are specified in a metric table covering nominal sizes up to 3 000 mm (DN 3000 uses the R 40 series in ISO 3). For metric pipes conforming to ISO 161-1, dn equals the minimum mean outside diameter dem.min specified in the applicable pipe standard.
- Nominal pressure rating (PN): PN values are selected from the R 10 preferred-number series (ISO 3). ISO 161-1:2018 extends PN choices (including PN 25) and clarifies that PN 6 must be designed using 6.3 bar from the R 10 series.
- Minimum required strength (MRS): MRS is defined as the lower confidence limit (LPL) of long-term hydrostatic strength at 20 °C for 50 years, rounded to preferred-number series values. MRS steps from 1 to 20 MPa use R 10 increments; MRS values above 20 MPa use R 20 increments.
- Design stress and hydrostatic stress: Design stress σS = MRS / C, where C is the design coefficient (see ISO 12162). Hydrostatic stress for internal pressure p is given by σ = p·d / (2·e) (with d = outside diameter, e = wall thickness).
- Terminology and measurement rules: Definitions for outside diameter at any point, mean outside diameter, minimum mean outside diameter and other terms are provided to ensure consistency in product standards.
Applications and who uses it
ISO 161-1:2018 is essential for:
- Standards writers drafting thermoplastics pipe product standards and specifications
- Pipe manufacturers and material suppliers specifying nominal sizes and pressure ratings
- Pipeline designers, civil and mechanical engineers selecting pipe systems for pressure and non-pressure fluid conveyance
- Test laboratories and certification bodies assessing long-term pressure performance
- Procurement and regulatory authorities harmonizing technical requirements across projects
Related standards
- ISO 3 - Preferred numbers (R series used for dn, PN, MRS rounding)
- ISO 12162 - Thermoplastics materials for pipes and fittings for pressure applications (classification and design coefficient)
- ISO 497 - Guide to choice of preferred-number series
Keywords: ISO 161-1:2018, thermoplastics pipes, nominal outside diameter, nominal pressure, MRS, metric series, pipe standards, conveyance of fluids.