ISO 21225-2:2018

Overview

ISO 21225-2:2018 - Plastics piping systems for the trenchless replacement of underground pipeline networks (Part 2) - defines requirements and test methods for using polyethylene (PE) pipes and fittings in trenchless off‑line replacement by horizontal directional drilling (HDD) and impact moling. The standard covers manufactured PE pipes (three types), jointing methods prior to installation and the installed replacement system, and is intended to be used alongside construction standards for PE pipeline systems.

Key topics and technical requirements

• Scope and applicability
  • Applies to replacement of underground non‑pressure and pressure drainage/sewerage, water and gas supply networks by HDD and impact moling.
  • Applicable only to PE pipes and fittings (not polypropylene or other plastics) and not to push‑fit jointed discrete pipes assembled during installation.
• PE pipe types covered
  • Solid wall single‑layer PE pipes (nominal outside diameter).
  • Co‑extruded layered PE pipes (all layers with same MRS rating) - see Annex A.
  • PE pipes with a peelable thermoplastic outer coating ("coated pipe") - see Annex A.
• Jointing and fittings
  • Butt fusion joining of pipe strings prior to installation.
  • Fabricated and injection‑moulded PE fittings.
  • References to electrofusion and butt fusion equipment standards for fusion jointing.
• Design, materials and regional requirements
  • Material selection, MRS considerations and ancillary components.
• Installation practice
  • Preparatory work, storage, handling and transport.
  • Required equipment: inspection tools, lifting gear, skids/rollers, HDD rigs, impact moling equipment, fusion equipment.
  • Installation steps, process‑related inspection/testing and finishing off.
• Fitness for purpose
  • Final inspection, pressure testing, disinfection and documentation requirements to demonstrate compliance.
• Annexes
  • Annex A: layered/coated pipe details (normative).
  • Annex B: pipe design considerations specific to HDD (informative).

Practical applications and users

• Typical users:
  • Pipeline designers and engineers specifying trenchless replacement systems.
  • Contractors and HDD/impact moling operators.
  • Manufacturers of PE pipes, fittings and fusion equipment.
  • Asset owners, utilities (water, gas, drainage/sewerage) and public works authorities.
• Practical uses:
  • Specifying compliant PE piping systems for trenchless off‑line rehabilitation projects.
  • Guiding procurement, quality control, and on‑site inspection and testing during HDD or impact moling operations.
  • Ensuring fitness for purpose and compatibility with regional construction standards.

Related standards

• ISO 21225-1 (replacement on the line - pipe bursting/pipe extraction)
• ISO 11295 (complimentary information on renovation)
• Normative references cited in ISO 21225-2: ISO 4427, ISO 4437, ISO 12176 (butt fusion/electrofusion) and relevant EN standards for seals and PE systems (EN 12201, EN 1555, EN 681 series).

ISO 21225-2:2018 is essential when planning trenchless off‑line replacements with HDD or impact moling and helps stakeholders specify, install and verify PE piping systems to international best practice.