ISO 3305:1985

Overview

ISO 3305:1985 - Plain end welded precision steel tubes - Technical conditions for delivery - specifies the delivery requirements for precision welded steel tubes with plain ends. This second edition (1985) replaces the 1976 edition. The standard covers tubes with outside diameters from 4 mm up to and including 160 mm, and sets requirements for chemical composition, mechanical properties, dimensions, tolerances and acceptance tests. For hydraulic piping equipment, tubes must be supplied only in the annealed or normalized condition.

Key topics and requirements

• Scope and designation
  • Applies to precision welded tubes selected from ISO 4200 dimensional series.
  • Typical designation format: Steel tubes ISO 3305-<grade>-<delivery condition>-<D> x <T> (example: Steel tubes ISO 3305-R37-GBK-25 x 2).
• Delivery conditions
  • Defined conditions include BK (cold‑finished/as‑drawn), BKW (lightly cold‑worked), GBK/GZF (annealed, descaled variants) and NBK/NZF (normalized, descaled variants).
• Chemical composition
  • Composition limits are tabulated (table 2) by steel grade (e.g., R28, R33, R37, R44, R50). Product and ladle analyses are addressed; deviations follow ISO 2604/3 where applicable.
• Mechanical properties
  • Mechanical property tables (3–6) specify tensile strength, elongation and, for normalized tubes, upper yield strength-values depend on delivery condition.
• Dimensions, masses and tolerances
  • Outside/inside diameters, wall thicknesses and mass per unit length are referenced from table 9 and ISO 4200. Tolerances account for annealing distortion; straightness limits: for D ≥ 16 mm, total bend ≤ 0.2% of overall length and bend on any 1 m ≤ 1.5 mm.
• Tests and acceptance
  • Essential tests: visual inspection, tensile test (ISO 6892), and either drift‑expanding (ISO 8493) or flattening (ISO 8492) tests (tables 7–8). Default hydraulic leaktightness test at 5 MPa (50 bar) unless otherwise agreed.
  • Acceptance sampling: lots of 200 tubes; one tube per lot for destructive tests unless otherwise specified.

Applications and users

ISO 3305 is relevant for:

• Tube manufacturers and steel mills producing precision welded tubes.
• Engineers and OEMs specifying tubing for hydraulic systems, instrumentation, mechanical assemblies and applications requiring tight dimensional tolerances and surface finish.
• Purchasers, quality engineers and third‑party inspectors defining delivery conditions, acceptance testing and certification.
• Designers concerned with weldability, heat treatment condition (annealed/normalized) and mechanical performance.

Related standards

• ISO 4200 - dimensions and masses for plain end steel tubes
• ISO 404 - general technical delivery requirements (documentation)
• ISO 2604/3 - steel products for pressure purposes (chemical analysis deviations)
• ISO 6892 - tensile testing of metallic materials
• ISO 8492 / ISO 8493 - flattening and drift‑expanding tests
• ISO 3545 - symbols for circular cross-section tubes

Keywords: ISO 3305, plain end welded precision steel tubes, technical conditions for delivery, chemical composition, mechanical properties, dimensions, tolerances, annealed, normalized, hydraulic piping, acceptance testing.