Section
8 Plates with specified through thickness properties
8.1 Scope
8.1.2 Through thickness
properties are characterised by specified values for reduction of
area in a through thickness tensile test.
8.1.3 Provision
is made for two grades Z25 and Z35. For normal ship applications the
Z25 grade is applicable, whilst the Z35 grade is for more severe applications.
8.1.5 The test
procedure detailed in this Section may also be used to demonstrate
that no unacceptable amount of banding of any detrimental phase, such
as sigma is present, see
Ch 3, 7.5 Metallographic examination for sigma phase.
Figure 3.8.1 Schematic of testing directions
8.2 Manufacture
8.2.1 All plates
and wide flats are to be manufactured at works which have been approved
by LR for this quality of material.
8.2.2 It is recommended
that the steel should be efficiently vacuum de-gassed. The sulphur
content is not to exceed 0,008 per cent.
8.2.3 Consideration
will be given to proposals for alternative methods of improving through
thickness properties.
8.3 Test material
8.3.1 Unless otherwise agreed, through thickness tensile tests are only required
for plate materials where the thickness exceeds 15 mm for carbon and alloy steels.
8.3.2 For plates and wide flats, one test sample is to be taken close to the
longitudinal centreline from one end of each rolled piece representing the batch,
see
Table 3.8.1 Batch size dependent on product
and sulphur content and Figure 3.8.2 Plate and wide flat sampling position. The test sample must be large enough to
accommodate the preparation of 6 specimens. 3 test specimens are to be prepared while
the rest of the sample is to be retained for possible retests. The test specimens shall
be prepared in accordance with a recognised standard, e.g. EN 10164 or ASTM A770/A770M.
Table 3.8.1 Batch size dependent on product
and sulphur content
| Product
|
S > 0,005%
|
S ≤ 0,005%
|
| Plates
|
Each piece (parent plate)
|
Maximum 50 t of products of the same
cast, thickness and heat treatment
|
| Wide flats of nominal
thickness ≤ 25 mm
|
Maximum 10 t of products of the same
cast, thickness and heat treatment
|
Maximum 50 t of products of the same
cast, thickness and heat treatment
|
| Wide flats of nominal
thickness > 25 mm
|
Maximum 20 t of products of the same
cast, thickness and heat treatment
|
Maximum 50 t of products of the same
cast, thickness and heat treatment
|
Figure 3.8.2 Plate and wide flat sampling position
8.3.4 Alternatively,
test sampling may be carried out in accordance with an accepted National
or International Standard.
8.4 Mechanical tests
8.4.1 The three
through thickness tensile test specimens are to be tested at ambient
temperature and for acceptance are to give a minimum average reduction
of area value of not less than that shown in Table 3.8.2 Reduction of area acceptance
values. Only one individual value may be below the minimum
average, but should not be less than the minimum individual value
shown for the appropriate grade.
Table 3.8.2 Reduction of area acceptance
values
| Grade
|
Z25
|
Z35
|
| Minimum average
|
25%
|
35%
|
| Minimum individual
|
15%
|
25%
|
8.4.2 If the average
value fails to comply with Ch 3, 8.4 Mechanical tests 8.4.1,
three additional tests may be made on specimens from the same test
sample. The results of these tests are to be added to those previously
obtained to form a new average, which for acceptance is to be not
less than 25 per cent for grade Z25 or 35 per cent for grade Z35.
No individual results in the re-test shall be below 25 per cent for
grade Z25 or 35 per cent for grade Z35, see
Figure 3.8.3 Diagram showing acceptance/rejection and retest criteria.
8.4.3 Where batch
testing is permitted, and failure after retest occurs, the tested
piece is to be rejected. Each remaining piece in the batch may be
individually tested and accepted based on satisfactory results.
8.4.4 If the fracture
of a test specimen occurs in the weld or in the heat affected zone
the test is to be regarded as invalid and is to be repeated on a new
test specimen.
Figure 3.8.3 Diagram showing acceptance/rejection and retest criteria
8.5 Non-destructive examination
8.5.1 All ‘Z’ grade plates are to be ultrasonically tested in the final supply
condition with a probe frequency of 2-5 MHz. The testing is to be performed in
accordance with and in compliance with either EN 10160 Level S1/E1 or ASTM A 578 Level
C.
8.6 Identification of materials
8.6.1 Products
which comply with the requirements of this Section are to have the
notation Z25 or Z35 added to the steel grade designation.
8.7 Certification of materials
8.7.1 The following
information is required to be included on the certificate in addition
to the appropriate steel grade requirements:
-
Through thickness reduction
in area (%), individual results and average.
-
Steel grade with Z25
or Z35 notation.
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