Overview
ISO 4991:2024 - Steel castings for pressure purposes is the fourth edition international standard that specifies requirements for steel castings used in pressure-containing parts. It applies to unalloyed and alloyed cast steels characterized by the chemical composition (Table 1) and mechanical properties (Tables 2–5). The standard covers castings manufactured for components that are both subject to pressure‑vessel codes and components not subject to codes. Annex D links ISO grade designations to similar UNS numbers.
Keywords: ISO 4991:2024, steel castings, pressure purposes, pressure vessel, chemical composition, mechanical properties.
Key technical topics and requirements
- Scope and materials: Defines grades of cast steel for pressure service (composition limits in Table 1) and associated mechanical property requirements (Tables 2–5).
- Heat treatment: Specifies required heat‑treatment types and symbols (for example +N normalized, +QT quenched and tempered, +AT solution treated) and refers to Table 6 for guidance.
- Welding: Welding is permitted with requirements for procedure and welder qualification; welding procedures follow ISO 11970 and welders shall be qualified per ISO 9606‑1. Annex B provides welding conditions.
- Inspection and testing:
- Manufacturing sampling and test‑block procedures (test blocks heat treated with the casting).
- Mechanical testing: tensile tests per ISO 6892‑1 (room temperature) and ISO 6892‑2 (elevated temperature) when required; impact testing per ISO 148‑1 where specified.
- Non‑destructive testing (NDT): purchaser specifies NDT method, area and acceptance criteria (as per ISO 4990).
- Marking and traceability: heat numbers/serials and manufacturer identification required.
- Supplementary requirements: Additional inspections/tests available when individually specified by purchaser (see Annex A). Ferrite content determination for austenitic/duplex grades via ISO 13520.
- Special additions: This edition adds a higher‑temperature cast steel grade (550 °C–700 °C range) and two duplex grades suitable up to 250 °C; welder qualification requirements were expanded.
Practical applications and users
ISO 4991:2024 is used to specify and procure steel castings for pressure components such as pressure‑vessel parts, valves, pump casings, flanges and other pressure‑containing cast components. Typical users include:
- Foundries and casting manufacturers
- Pressure‑vessel designers and fabricators
- Procurement and quality engineers specifying material and inspection requirements
- Welding supervisors and qualified welders
- Third‑party inspectors and certification bodies
Related standards and annexes
ISO 4991:2024 provides a comprehensive framework for specifying, producing and inspecting steel castings intended for pressure service, ensuring material traceability, mechanical performance and appropriate testing for safe pressure‑containing components.
