ISO 7788:2021

Overview

ISO 7788:2021 - "Steel - Surface finish of hot-rolled plates and wide flats - Delivery requirements" specifies delivery requirements for the surface finish of hot-rolled plates (rolled on reversing mills) and wide flats with a nominal thickness ≥ 3 mm and ≤ 400 mm. The standard defines how to identify, measure and classify surface discontinuities, sets permissible limits for imperfections, and describes required repair procedures and responsibilities between producer and purchaser.

Key Topics

• Scope and responsibility
  • Applies to hot-rolled plates and wide flats within the specified thickness range.
  • The material producer is responsible for the required surface condition and for taking precautions when delivering descaled or not-descaled products.
• Terms and definitions
  • Clear definitions for discontinuities (imperfection vs defect) and common surface faults: rolled‑in scale, pitting, indentations, roll marks, scratches, spills/slivers, blisters, hot tears, sand patches, cracks, shell and seams.
  • Cracks, shell and seams are always classified as defects.
• Classification
  • Two main classes: Class A and Class B, each subdivided into Subclass 1, 2, 3:
    • Class A: allows certain repairs that may reduce local thickness below tolerance standards.
    • Class B: repaired areas must not be less than the minimum thickness specified in the appropriate tolerance standard.
    • Subclasses define permitted repair methods (welding allowed, restricted or prohibited).
• Measurement rules
  • Depth of discontinuities is measured from the product surface after grinding out the discontinuity.
  • Affected area determination rules for isolated, clustered or aligned discontinuities - normally using a 20 mm margin and clustering rules (discontinuities closer than 40 mm are a cluster).
• Limits and repair requirements
  • Table of maximum permissible depths for imperfections by nominal thickness (e.g., 3 ≤ t < 8 mm → 0.2 mm; 80 ≤ t < 250 mm → 0.7 mm; up to 250–400 mm → 1.3 mm).
  • Clauses on permitted repair procedures: grinding, welding (subject to subclass and order agreement), and repair acceptance criteria.

Applications

• Used by steel producers, quality inspectors, procurement/specification engineers, fabricators and purchasers to:
  • Specify contractual delivery conditions for hot-rolled plates and wide flats.
  • Inspect and accept delivered steel based on defined surface‑finish classes.
  • Decide whether to order descaled material when complete surface inspection prior to delivery is required.
  • Guide allowable repair methods (grinding, welding) and limits for product acceptance.

Related Standards

• ISO 6929 (vocabulary)
• ISO 7452 (tolerances for hot‑rolled plates)
• ISO 9034 (tolerances for wide flats)
• ISO 9606-1 (welder qualification - steels)
• ISO 15607 (welding procedure specification and qualification)

Keywords: ISO 7788:2021, hot-rolled plates, wide flats, surface finish, delivery requirements, surface discontinuities, repair requirements, Class A, Class B, affected area, depth of imperfections.