ISO 20723:2004

Overview - ISO 20723:2004 (Structural steels, surface condition)

ISO 20723:2004 specifies delivery requirements for the surface condition of hot-rolled structural steel sections with nominal thicknesses from ≥ 3 mm to ≤ 160 mm. The standard applies to all faces of sections except edges and defines how to measure, classify and repair surface discontinuities (imperfections and defects) to meet purchaser and manufacturing requirements.

Key topics and technical requirements

• Scope & measurement
  • Applies to hot-rolled sections (3–160 mm nominal thickness), excluding edges.
  • Depth of representative discontinuities is measured from the product surface after the discontinuity is removed (e.g., by grinding).
  • Affected area is determined by drawing a continuous line 20 mm from isolated, clustered or linear discontinuities. Aligned discontinuities and proximity rules are defined (e.g., edges closer than 40 mm considered one discontinuity).
• Classification
  • Distinguishes imperfections (within limits) and defects (exceeding limits that require repair).
  • Divides requirements into Types (Type 1 and Type 2), Classes (C - general applications; D - special applications), and Subclasses (1 grinding permitted; 2 welding only if agreed; 3 welding not permitted).
• Permissible depths and area limits
  • Class C and Class D have separate maximum permissible depths by nominal thickness (e.g., Class D limits are stricter: 0.5 mm for 3–20 mm, up to 1.5 mm for 80–160 mm).
  • Areas with remaining thickness below minimum tolerances are allowed up to 15% for Class C and 2% for Class D of inspected surface (Type 2 requires remaining thickness not be below minimum).
• Repair procedures
  • Grinding/machining: discontinuities must be removed fully; maximum grinding allowance below minimum thickness is specified by thickness range.
  • Welding: allowed only under specified conditions - removal of defect prior to welding, qualified operators/procedures, post-repair NDT verification. Welding must not reduce section thickness below 70% of nominal. Limits on total welded area mirror the ground-area limits (15% Class C, 2% Class D).
• Common discontinuities
  • Annex A lists typical surface issues: rolled-in scale, pitting, roll marks, scratches, blisters, hot tears, seams, cracks and inclusions.

Applications and who uses ISO 20723

• Target users: steel producers, structural fabricators, quality inspectors, procurement engineers, construction project managers and testing laboratories.
• Practical uses:
  • Define delivery acceptance criteria for hot-rolled profiles.
  • Specify allowable surface repair methods and documentation for purchasing agreements.
  • Guide inspection, non‑destructive testing (NDT) and quality assurance on structural steel.

Related standards

• ISO 6929 (definitions/classification of steel products)
• ISO 404 (general technical delivery requirements)
• Relevant ISO product standards for dimensional tolerances (e.g., ISO 657 series for hot-rolled sections)

Keywords: ISO 20723, structural steels, surface condition, hot-rolled sections, delivery requirements, defects, imperfections, repair procedures, welding, grinding, class C, class D.