Section
7 Ferritic steel castings for low temperature service
7.1 Scope
7.1.1 This Section
gives the requirements for castings in carbon-manganese and nickel
alloy steels intended for use in liquefied gas piping systems where
the design temperature is lower than 0°C, and for other applications
where guaranteed impact properties at low temperatures are required.
7.1.2 Where it
is proposed to use alternative steels, particulars of the specified
chemical composition, mechanical properties and heat treatment are
to be submitted for approval.
7.2 Chemical composition
7.2.1 The chemical composition of ladle samples is to comply with the limits
specified in Table 4.7.1 Chemical composition of ferritic
steel castings for low temperature service. Carbon-manganese steels are to
be made by fine grain practice.
Table 4.7.1 Chemical composition of ferritic
steel castings for low temperature service
| Type of steel
|
Chemical composition %
|
C
max.
|
Si
max.
|
Mn
|
S
max.
|
P
max.
|
Ni
|
Residual elements
max.
|
| Carbon-manganese
|
0,23
|
0,60
|
0,70-1,60
|
0,030
|
0,030
|
0,80 max.
|
- Cr 0,25
- Cu 0,30
- Mo 0,15
- V 0,03
- Total 0,60
|
| 2
1/4Ni
|
0,25
|
0,60
|
0,50-0,80
|
0,025
|
0,030
|
2,00-3,00
|
| 3 1/2Ni
|
0,15
|
0,60
|
0,50-0,80
|
0,020
|
0,025
|
3,00-4,00
|
7.3 Heat treatment
7.3.1 Castings
are to be supplied:
-
normalised; or
-
normalised and tempered;
or
-
quenched and tempered.
7.4 Mechanical tests
7.4.1 One tensile
test and one set of three Charpy V-notch impact test specimens are
to be prepared from material representing each casting or batch of
castings.
7.4.3 The average value for impact test specimens is to comply with the
appropriate requirements given in Table 4.7.2 Mechanical properties for
acceptance purposes: ferritic steel castings for low temperature service. One individual value may be
less than the required average value provided that it is not less than 70 per cent of
this average value. See
Ch 2, 1.4 Re-testing procedures for re-test procedure.
Table 4.7.2 Mechanical properties for
acceptance purposes: ferritic steel castings for low temperature service
| Type of steel
|
Grade
|
Yield stress
N/mm2 minimum
|
Tensile strength
N/mm2
|
Elongation on 5,65 % minimum
|
Reduction of area %
minimum
|
Charpy V-notch impact test
|
| Test
temperature °C
|
Average energy J minimum
|
| Carbon-manganese
|
400
|
200
|
400-550
|
25
|
40
|
|
|
|
|
430
|
215
|
430-580
|
23
|
35
|
–60(see Note)
|
27
|
|
|
460
|
230
|
460-610
|
22
|
30
|
|
|
| 21/4Ni
|
490
|
275
|
490-640
|
20
|
35
|
–70
|
34
|
| 3
1/2Ni
|
490
|
275
|
490-640
|
20
|
35
|
–95
|
34
|
Note The test temperature for carbon-manganese steels may be
5°C below the design temperature if the latter is above –55°C, with a
maximum test temperature of –20°C.
|
7.5 Non-Destructive Examination
|
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