ISO 7788:2021

Steel - Surface finish of hot-rolled plates and wide flats - Delivery requirements

This document specifies delivery requirements applicable to the surface finish of hot-rolled plates rolled on reversing mills and wide flats, with a nominal thickness ≥3 mm and ≤400 mm.

Acier — État de surface des tôles et larges-plats laminés à chaud — Conditions de livraison

General Information

• Status: Published
• Publication Date: 14-Oct-2021
• ICS: 77.140.50 - Flat steel products and semi-products
• Technical Committee: ISO/TC 17/SC 3 - Steels for structural purposes
• Drafting Committee: ISO/TC 17/SC 3/WG 14 - Surface finish of hot-rolled plates and wide flats – Delivery requirements
• Current Stage: 6060 - International Standard published
• Start Date: 15-Oct-2021
• Due Date: 27-Apr-2021
• Completion Date: 15-Oct-2021

Relations

• Revises: ISO 7788:1985 - Steel - Surface finish of hot-rolled plates and wide flats - Delivery requirements
• Effective Date: 27-May-2017

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.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 7788
Second edition
2021-10
Steel — Surface finish of hot-rolled
plates and wide flats — Delivery
requirements
Acier — État de surface des tôles et larges-plats laminés à chaud —
Conditions de livraison
Reference number
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents  Page
Foreword .iv
1  Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  General . 3
5  Classification . 3
6  Requirements . 4
6.1 Depth and affected area of discontinuities . 4
6.1.1 Depth . . 4
6.1.2 Affected area . . 4
6.2 Repair requirements . 5
6.2.1 Class A . 5
6.2.2 Class B . 7
6.3 Repair procedures . 7
6.3.1 Grinding . . 7
6.3.2 Welding . 8
Annex A (informative) Action to undertake in function of the depth of discontinuities and
nominal thickness of the products .10
Annex B (informative) Classes and subclasses for surface conditions with their respective
requirements .13
Bibliography .14
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 17, Steel, Subcommittee SC 3, Steels for
structural purposes.
This second edition cancels and replaces the first edition (ISO 7788:1985), which has been technically
revised.
The main changes are as follows:
— updated normative reference;
— new definitions added and definitions in former Annex A added to Clause 3;
— deletion of distinction concerning boilers and pressure vessel applications (Clause 4);
— new definition of two classes and three subclasses added (Clause 5);
— new Clause 6 on depth and determination of affected areas, repair requirements and repair
procedures;
— new Annex B with classes and subclasses for surface conditions with their respective requirements;
— deletion of former Annex A.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
INTERNATIONAL STANDARD ISO 7788:2021(E)
Steel — Surface finish of hot-rolled plates and wide flats —
Delivery requirements
1  Scope
This document specifies delivery requirements applicable to the surface finish of hot-rolled plates
rolled on reversing mills and wide flats, with a nominal thickness ≥3 mm and ≤400 mm.
2  Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6929, Steel products — Vocabulary
ISO 7452, Hot-rolled steel plates — Tolerances on dimensions and shape
ISO 9034, Hot-rolled structural steel wide flats — Tolerances on dimensions and shape
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 15607, Specification and qualification of welding procedures for metallic materials — General rules
3  Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6929 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
imperfection
surface discontinuity other than cracks (3.10), shell and seams (3.11) with a depth and/or an area equal
to or less than a specified limiting value
Note 1 to entry: Discontinuities that are required to be repaired are regarded as defects.
3.2
defect
surface discontinuity with a depth and/or area greater than a specified limiting value and all cracks
(3.10), shell and seams (3.11), irrespective of their depth or/and area
3.3
rolled-in scale and pitting
marks on the rolled surface varying in shape, thickness and frequency resulting from the unsatisfactory
subsequent removal of scale from the stock before or during hot rolling and processing
Note 1 to entry: Rolled-in scale-pitting can be regarded as discontinuities.
3.4
indentations and roll marks
marks appearing at periodic intervals caused by damaged rolls or pinch rolls
Note 1 to entry: Indentations (depressions) or roll marks (protuberances) can be distributed at definite distances
apart or irregularly throughout the length and width of the stock. Indentations can be caused, among other
things, by protuberances on rolls or rollers.
Note 2 to entry: Indentations and roll marks can be regarded as discontinuities.
3.5
scratches and grooves
mechanical damages varying in width, depth and length at the surface, mostly parallel or at right angles
to the rolling direction
Note 1 to entry: They can be slightly rolled over and seldom contain scale. These damages are caused by friction
between the stock and parts of the equipment due to relative movements.
Note 2 to entry: Scratches and grooves can be regarded as discontinuities.
3.6
spills and slivers
minute surface discontinuities of an irregular and flake-like nature
Note 1 to entry: Spills and slivers are elongated in the direction of rolling, their extent depending on the degree of
reduction. They are still connected – as minute particles of shell – to the base metal at certain points.
Note 2 to entry: Spills and slivers can be regarded as discontinuities.
3.7
blisters
blow holes of varying size and shape located closely beneath the surface and appearing during hot
rolling
Note 1 to entry: Blisters can be regarded as discontinuities.
3.8
hot tears
variably orientated material discontinuities in the surface region varying in length, width and depth
and occurring in preferred directions and/or distributed over a limited area
Note 1 to entry: Hot tears arise in the processing of slab ingots, roughed slabs and continuously cast slabs and are
associated with the steel, with stresses in the initial material or with adverse forming conditions.
Note 2 to entry: Hot tears can be regarded as discontinuities.
3.9
sand patch
non-metallic inclusion in the surface that varies in size and shape, elongated in the direction of rolling,
randomly localized and distinctly coloured, standing out from its background
Note 1 to entry: Sand patches can be regarded as discontinuities.
3.10
crack
localized discontinuity of varying length and varying orientation related to the rolling direction in the
region of the surface, and which can less frequently occur as crazing
Note 1 to entry: Cracks are due mainly to material stresses that arise during the cooling process.
Note 2 to entry: Cracks are always considered as defects, see 6.2.1.2.3.
3.11
shell and seams
overlapping material being irregularly distributed over areas of the rolled product and being only
partially connected with the base material
Note 1 to entry: The overlapping portions of the surface varying in shape and extent. There is a preponderance of
non-metallic inclusions and/or scale among the shell. Shell can originate during casting or because of the shifting
or sliding of layers of the material during hot rolling. Seams are caused mainly when defects in the semi-product
parallel to the rolling direction, for instance, flame-cutting burrs, are overlapped during rolling.
Note 2 to entry: To get information about other surface of defects on the flat products, refer to valid references,
including Reference [3].
Note 3 to entry: Shell and seams are always considered defects, see 6.2.1.2.3.
4  General
For plates with a nominal thickness greater than 400 mm and for special applications for which a
different surface condition is required, special agreements shall be made at the time of enquiry and
order.
Responsibility for the required surface condition, whether the product is delivered descaled or not,
rests with the material producer, who has to take the necessary precautions. The producer can only
take account of discontinuities that are visible to the naked eye. Rolling or heat-treatment scale can
conceal surface discontinuities.
If the purchaser needs to be sure that all discontinuities visible to the naked eye have been identified,
assessed and where necessary, repaired before delivery, products should be ordered descaled.
If, during the subsequent descaling or working operations by the user, the material is found to
be defective because of faulty rolling or processing by the producer, the producer shall be given
opportunity to repair the product, provided that this is not in conflict with the appropriate material or
product standard.
5  Classification
The surface requirements and repair conditions are subdivided into 2 classes. Each class is further
subdivided into 3 subclasses (see also Annex B):
Class A: The surface condition shall conform to the requirements of 6.2.1 and 6.3.1.1. The remaining
thickness of the affected area (see 6.1.2) under the discontinuities and of the repaired ground areas
may be less than the minimum thickness as specified in the appropriate tolerance standard.
Class B: The surface condition shall conform to the requirements of 6.2.2 and 6.3.1.2. The remaining
thickness of the affected area under the discontinuities and of the repaired ground areas shall not be
less than the minimum thickness as specified in the appropriate tolerance standard.
Subclass 1: Repair by chipping and/or grinding followed by welding is permitted in accord
...