ISO 4144:2003

Overview

ISO 4144:2003 - Pipework: Stainless steel fittings threaded in accordance with ISO 7-1 - defines the types, minimum dimensions, materials and pressure‑temperature ratings for stainless steel threaded fittings used in ordinary piping for steam, air, gas, water, oil, etc. It is a technical specification for manufacturers, designers and inspectors to ensure interchangeability, safety and performance of threaded stainless steel fittings.

Key topics and technical requirements

• Scope and use: Applies to stainless steel fittings for threaded connections made in accordance with ISO 7-1 for pressure‑tight joints.
• Types of fittings: Specifies 12 fitting types and symbols (elbows, reducing elbows, 45° elbows, male/female elbows, tees, crosses, half sockets, sockets, reducing sockets, reducing bushes, hexagon/reducing nipples, caps, plugs, and several unions).
• Dimensions and drawings: Detailed minimum dimensions, joint geometry and dimensional tables are provided (Figures 1–14 and Tables 3–16) covering nominal diameters DN (1/8 to 4 in the published tables).
• Threads: Threads must conform to ISO 7-1. External and internal threads are tapered at 1:16 (internal threads may be parallel). Union-nuts and mating threads are exceptional and may follow ISO 68‑1/ISO 228‑1/ISO 261/ISO 262/ISO 724. Thread ends should be chamfered.
• Pressure‑temperature ratings: Rated non‑shock maximum working pressures are specified across a temperature range (values provided in Table 2). The standard permits interpolation for intermediate temperatures and clarifies that internal fluid temperature is the reference.
• Materials and manufacturing: Fittings may be produced by casting, rolling or forging. Material must be austenitic stainless steel with proof stress at least equal to steel TS 47 (ISO 2604‑2) and suitably solution‑annealed per ISO 4991:1994.
• Quality provisions: Includes requirements for tests, inspections, marking and designation to support traceability and compliance.

Applications and who uses it

• Practical for piping designers, plant engineers, specifiers and procurement teams selecting threaded stainless steel fittings for HVAC, process piping, steam lines, compressed air, fuel and water systems.
• Used by manufacturers and fabricators to produce and verify fittings to internationally accepted dimensions and materials.
• Referenced by inspection and quality assurance personnel for testing, marking and acceptance criteria.

Related standards

• ISO 7‑1, ISO 7‑2 (pipe threads)
• ISO 68‑1, ISO 228‑1, ISO 261, ISO 262, ISO 724 (thread standards)
• ISO 2604‑2 (steel proof stress reference)
• ISO 4991:1994 (steel castings heat treatment)
• ISO 4990 (revision reference)

Keywords: ISO 4144, stainless steel fittings, threaded fittings, ISO 7‑1, pressure‑temperature ratings, pipework standard, austenitic stainless steel, pipe fitting dimensions.