ISO 657-18:1980

Overview

ISO 657-18:1980 specifies dimensions, sectional properties and dimensional tolerances for hot-rolled steel L sections (metric series) for shipbuilding. The standard gives a designation system (L followed by web height H, flange width B, web thickness t and flange thickness T - e.g., L250 x 90 x 9 x 13), and provides tabulated dimensions, area, centroid, moments of inertia and mass per metre for commonly used L profiles.

Key topics and technical requirements

• Designation and metric series: Profiles are designated as L H x B x t x T (example shown in the standard).
• Dimensions & sectional properties: Table 1 lists standard sizes and sectional properties (area, centroid location, moment of inertia, mass per m) for shipbuilding L sections.
• Dimensional tolerances:
  • Height of web (H) and width of flange (B): tolerances are given in a millimetre table (values depend on H/B ranges).
  • Web thickness (t): tolerance specified in clause 4.2 of the standard.
  • Flange thickness (T): tolerances provided in Table 3 (by thickness ranges, with positive and negative limits).
  • Length tolerance: a standard tolerance on length is specified; tighter tolerances may be agreed between purchaser and supplier.
• Geometric tolerances:
  • Camber: maximum permissible camber measured over the full length is 0.5% of L.
  • Out-of-square: legs must be perpendicular within a maximum deviation of 2.5% of B (measured at the shorter leg end).
  • Flatness: tolerance on web flatness is subject to purchaser-manufacturer agreement and measured using a steel straightedge as shown in the standard’s figure.

Practical applications and users

• Primary users: shipbuilders, structural engineers, naval architects, steel fabricators and quality inspectors.
• Use cases:
  • Selecting standard L sections for hull framing, brackets, stiffeners and other shipbuilding structures.
  • Ensuring compatibility between supplier deliveries and shipyard design tolerances.
  • Verifying material for fabrication, welding preparation and structural calculations using the provided sectional properties.
  • Contract specification: buyers and manufacturers use the dimensional and tolerance rules to define acceptance criteria and inspection methods.

Related standards

• ISO 657 (other parts) - the broader series covering hot-rolled steel sections.
• Consult ISO TC 17 (Steel) publications for complementary guidance on steel product specifications and testing.

Keywords: ISO 657-18:1980, hot-rolled steel L sections, shipbuilding, dimensions, sectional properties, tolerances, metric series, camber, out-of-square, flatness.