ISO 5175-2:2017

Overview

ISO 5175-2:2017 - "Gas welding equipment - Safety devices - Part 2: Devices not incorporating a flame (flashback) arrestor" defines general requirements and type tests for safety devices used with fuel gases and oxygen or compressed air that do not include a flame (flashback) arrestor. It applies to devices installed downstream of manifold, cylinder or pipeline outlet regulators and upstream of blowpipes for welding, cutting and allied processes. The standard does not prescribe specific installation locations and excludes devices covered by ISO 5175-1 (those incorporating flame arrestors).

Key topics and technical requirements

• Scope and definitions: Covers non-return valves, pressure relief valves, excess flow cut-off valves and multifunctional safety devices; terms follow ISO 15296 vocabulary.
• Design and materials: Connections per EN 560 and ISO 7289; materials must conform to ISO 9539.
• Gas tightness: External tightness testing per ISO 9090 (five samples for type testing). Internal leakage limits: ≤ 50 cm3/h for internal bores < 11 mm or 0.41 × d (cm3/h) for larger bores.
• Pressure resistance: Housings must withstand 10× the maximum operating pressure, but not less than 6 MPa (60 bar), with no permanent deformation after at least 5 minutes.
• Functional requirements:
  • Non-return valve: Must prevent reverse flow under test conditions.
  • Pressure relief valve: Opening pressure between 1.3× and 2× the manufacturer’s maximum operating pressure; closing pressure between 1× and 2× that value; manufacturer must state flow capacity to atmosphere at twice operating pressure.
  • Excess flow cut-off valve: Must stop flow when flow reaches 1.1× to 2× the nominal flow specified by the manufacturer.
• Testing: Type test methods (not production inspection) include hydraulic pressure, flow and leakage tests; allowable measurement errors: flow ±10%, pressure ±3%. Test gases normally air or nitrogen (dry, oil-free); hydrogen-device tightness may use hydrogen or helium.
• Flashback resistance: Where flashback exposure may occur, the device must retain performance after the flame-arrestor test per ISO 5175-1:2017 with the flame arrestor substituted by the device.
• Documentation and marking: Manufacturer’s instructions and marking requirements are specified (Clauses 7 and 8).

Applications and users

ISO 5175-2 is essential for:

• Manufacturers of gas welding safety devices (design, testing, CE/market compliance),
• Test laboratories conducting type testing and conformity assessment,
• Safety engineers, procurement teams and maintenance personnel specifying or selecting non-flame-arrestor safety devices for welding, cutting and allied processes,
• Certification bodies and third-party testers (Annex B provides guidance; third-party testing is not mandatory).

Related standards

• ISO 5175-1:2017 (devices with flame arrestors)
• ISO 2503, ISO 7291 (pressure regulators)
• ISO 9090 (gas tightness)
• ISO 9539 (materials)
• ISO 7289, EN 560 (connections)
• ISO 10225 (marking), ISO 15296 (vocabulary)

Keywords: ISO 5175-2:2017, gas welding equipment, safety devices, non-return valve, pressure relief valve, excess flow cut-off, gas tightness, pressure resistance, flashback arrestor, type testing.