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