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.
Open preview (PDF)Hot-rolled steel sections — Part 18: L sections for shipbuilding (metric series) — Dimensions, sectional properties and tolerances
