IEC 61518:2001

Overview

IEC 61518:2001 specifies the mating dimensions and related requirements for differential pressure (type) measuring instruments and flanged-on shut-off devices (manifolds) for service up to 41.3 MPa (413 bar) at 38 °C. It applies where a manifold is directly bolted to the instrument, defining flange geometry, seal types, bolt recommendations, assembly tolerances and marking to ensure leak-tight, interchangeable connections between devices from different manufacturers.

Key topics and technical requirements

• Scope: Direct-bolted instrument–manifold assemblies; metallic flanges with yield strength ≥ 190 N/mm². Adapters or additional sealing elements are excluded.
• Mating dimensions: Detailed flange and port dimensions in millimetres, including two recommended manifold facings:
  • Type A: with extended spigot (insert)
  • Type B: without extended spigot
• Seals and gaskets:
  • Flat rings specified (materials: PTFE and graphite) with dimensional tables for Type A and B interfaces.
  • O-ring for Type A: ISO 3601-1 dimensions d1 = 20 mm, d2 = 2.65 mm; material FPM, IRHD 90 per ISO 48 and ISO 1629.
  • No ISO-standard O-ring specified for Type B - user to select per local practice.
• Fasteners and bolt details:
  • Bolt materials and minimum requirements listed (e.g., ASTM A193 Group B8, ISO 898-1 Class 8.8, ASTM A449, ISO 3506).
  • Thread engagement minimum 0.8 × thread diameter; guidance for bolt lengths for blind and through-threaded transmitters.
  • Figures show common bolt thread examples (e.g., 7/16" UNF × 20).
• Assembly and installation:
  • Clean, undamaged surfaces within 28 mm of each port.
  • Even bolt tightening; metallic flange gap after tightening < 0.2 mm.
  • Flange thickness minima: full flange 10 mm; split (2-kidney) flange 14 mm.
• Marking: Both transmitter and manifold must carry a permanent “IEC” mark visible after installation (min. 5 mm letters).

Applications and who uses IEC 61518

• Instrument manufacturers designing differential pressure transmitters, gauges and flanged manifolds to ensure interchangeability.
• Process and plant engineers specifying compatible instrument–manifold assemblies in oil & gas, petrochemical, power and chemical plants where high-pressure, leak-free connections are critical.
• Maintenance and procurement teams selecting spare parts and verifying bolting, seal and flange compatibility.
• Safety and compliance professionals reducing leakage risk with standardized mating dimensions.

Related standards

• ISO and ASTM standards referenced for O‑rings, seal hardness, and fastener properties (e.g., ISO 3601, ISO 898-1, ASTM A193, ASTM A449, ISO 3506) - consult IEC 61518 normative references for details.

Keywords: IEC 61518, differential pressure measuring instruments, flanged-on shut-off devices, manifolds, mating dimensions, seal rings, PTFE, graphite, O-ring, bolt material, 413 bar.