Overview
ISO 3306:1985 - "Plain end as-welded and sized precision steel tubes - Technical conditions for delivery" defines the delivery requirements for longitudinally welded, plain-end precision steel tubes. This second edition (1985) replaces the 1975 version and covers tube grades, dimensional series, chemical composition, mechanical properties, tests and inspection rules. The standard applies to outside diameters from 6 mm up to and including 160 mm and specifies conditions for as-welded (KM), annealed (GKM/GZF) and normalized (NKM/NZF) deliveries. For use in hydraulic piping equipment, tubes must be supplied only in the annealed or normalized condition.
Key Topics and Requirements
- Scope and designation
- Defines product naming convention: product - ISO reference - steel grade - delivery condition - D x T.
- Steel grades and chemistry
- Lists approved grades (e.g., R28, R33, R37, R44, R50) and tabulates maximum elemental limits (see table 2).
- Delivery conditions and heat treatment
- Delivery symbols: KM (as-welded/sized), GKM/GZF (annealed, descaled options), NKM/NZF (normalized, descaled options).
- Specific heat treatments and descaling requirements are defined in table 1 and related tables for mechanical properties.
- Dimensions, masses and tolerances
- Dimensions and mass per unit length referenced to ISO 4200 and given in table 8; tolerances on diameter, thickness, ovality, straightness and length are specified.
- Mechanical properties
- Tensile strength, elongation and (for normalized material) upper yield strength specified by grade and condition (tables 3, 4, 5).
- Inspection and testing
- Mandatory/optional tests: visual inspection, tensile test (ISO 6892), flattening test (ISO 8492/9492), drift expanding (ISO 8493) and, when requested, a hydraulic leaktightness test (typical 5 MPa).
- Lot acceptance rules and sampling: lots of 200 tubes; test frequency and retest rules per ISO 404.
- Purchaser information
- Purchaser must specify quantity, steel grade, delivery condition, OD/thickness, length and reference to ISO 3306.
Applications and Users
- Practical uses: precision structural and mechanical tubing where dimensional accuracy, surface finish and predictable mechanical properties are required - including instrumentation, fittings, assemblies and certain pressure piping.
- Special note: tubes intended for hydraulic piping equipment must be annealed or normalized.
- Typical users:
- Tube manufacturers and mill quality engineers
- Procurement and specification engineers in automotive, hydraulic, instrumentation and industrial equipment sectors
- Inspectors and testing laboratories ensuring compliance with delivery conditions
Related Standards
- ISO 4200 - dimensions and masses for plain end steel tubes
- ISO 404 - general technical delivery requirements
- ISO 2604/3 - product analysis tolerances (steel)
- ISO 3545 - symbol conventions for tubular products
- ISO 6892 - tensile testing of metallic materials
- ISO 8492 / ISO 9492 - flattening tests for tubes
- ISO 8493 - drift expanding test
Keywords: ISO 3306, precision steel tubes, as-welded and sized, technical conditions for delivery, hydraulic piping equipment, dimensions and tolerances, mechanical properties, chemical composition, inspection and testing.