Overview
ISO 4978:2018 - Steel sheet and strip for welded gas cylinders defines the material and delivery requirements for hot-rolled steel sheet and strip (thickness up to 12 mm) intended for welded gas cylinders manufactured in accordance with ISO 4706. The standard sets out chemical composition, mechanical properties, grain size, weldability, surface condition, dimensions, inspection and testing requirements specific to non-alloyed steel grades (Table 1: P235 to P365).
Key topics and technical requirements
- Scope and materials: Hot-rolled steel sheet and strip for welded gas cylinders, thickness ≤ 12 mm. Grades and chemical limits are given in Table 1.
- Chemical composition: Heat analysis limits for C, Si, Mn, P, S and aluminium (Alsol ≥ 0.015 %). Microalloy additions (Nb, V, Ti) permitted within specified maxima; purchaser can require product analysis and a maximum carbon-equivalent value (CEV, optional up to 0.45 %).
- Mechanical properties: Yield strength, tensile strength, elongation and impact energy requirements are specified (transverse direction). Impact testing required for thickness > 6 mm with defined sub-sized specimens; average of three specimens must meet the specified energy, allowing one to be as low as 70% of the limit.
- Grain size: Ferritic grain size Index 6 or finer (ISO 643).
- Weldability: Designed to be weldable by common fusion welding processes; CEV option addresses weldability concerns.
- Surface and internal quality: Supply options include rolled or descaled/oiled surfaces; general quality requirements referenced to ISO 404.
- Delivery and testing: Delivery condition (hot-rolled, normalized, normalizing rolling) and inspection documents must be agreed at order. Tests include chemical analysis, tensile, impact, bend, grain size and non-metallic inclusion assessment (as per referenced ISO methods).
- Additional requirements: Options such as impact testing at −40 °C, maximum yield/tensile ratio (≤ 0.8), and bend test acceptance criteria can be specified by the purchaser.
Applications and users
ISO 4978:2018 is used by:
- Steel producers specifying hot-rolled sheet and strip for cylinder service
- Gas cylinder manufacturers (welded refillable cylinders) selecting material compliant with ISO 4706
- Welding engineers and fabricators assessing weldability and CEV limits
- Quality assurance, inspection and procurement teams defining acceptance tests and inspection documents
- Regulatory and certification bodies verifying material conformity for pressure equipment
Keywords: ISO 4978:2018, steel sheet and strip, welded gas cylinders, hot-rolled steel, chemical composition, mechanical properties, weldability, material specification.
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