Section
8 Ferritic steel forgings for low temperature service
8.1 Scope
8.1.1 The requirements
for carbon-manganese and nickel steels suitable for low temperature
service are detailed in this Section. They are applicable to all forgings
used for the construction of cargo tanks, storage tanks and process
pressure vessels for liquefied gases and, where the design temperature
is less than 0°C, to forgings for the piping systems.
8.1.2 The requirements
are also applicable to forgings for other pressure vessels and pressure
piping systems where the use of steels with guaranteed impact properties
at low temperatures is required.
8.1.3 In all cases,
details of the proposed chemical composition, heat treatment and mechanical
properties are to be submitted for approval.
8.1.4 In addition
to the steels in this Section, the austenitic stainless steels detailed
in Ch 5, 9 Stainless steel forgings may also be used for low
temperature applications.
8.2 Chemical composition
8.3 Heat treatment
8.3.1 Forgings
are to be normalised, normalised and tempered or quenched and tempered
in accordance with the approved specification.
8.4 Mechanical tests
8.4.1 At least
one tensile and three Charpy V-notch impact test specimens are to
be taken from each forging or each batch of forgings. Where the dimensions
and shape allow, the test specimens are to be cut in a longitudinal
direction.
8.4.3 The results
of all tensile tests are to comply with the approved specification.
8.5 Non-destructive examination
8.5.1 Non-destructive
testing is to be carried out in accordance with the requirements of
the approved forging drawing and specification, or as otherwise agreed
between the manufacturer, purchaser and Surveyor.
8.6 Pressure tests
8.6.1 When applicable,
pressure tests are to be carried out in accordance with the requirements
of the relevant Rules.
Table 5.8.1 Chemical composition of ferritic
steel forgings
Grade of steel
|
C %
|
Si %
|
Mn %
|
Ni %
|
P %
|
S %
|
Residual elements %
|
Grain
refiners %
|
Al
|
Other
|
LT–AH (AH40)
|
0,18 max.
|
0,50 max.
|
0,90 – 1,60
|
0,40 max.
|
0,035 max.
|
0,030 max.
|
Cu 0,35 max. Cr 0,25 max. Mo 0,08 max.
Total 0,60
max.
|
Total 0,020 min.
Acid soluble 0,015 min.
|
(See Note)
Nb 0,02 – 0,05 V 0,03 – 0,10 Ti 0,02
max.
|
LT–DH (DH40)
|
LT–EH (EH40)
|
LT–FH (FH40)
|
0,16 max.
|
0,80
max.
|
0,025 max.
|
0,025
max.
|
1 1/2Ni
|
0,18 max.
|
0,10–0,35
|
0,30 –
1,50
|
1,30 –
1,70
|
0,020 max.
|
Cu 0,35 max. Cr 0,25 max. Mo 0,08 max.
Total 0,60
max.
|
|
3 1/2Ni
|
0,15 max.
|
0,30 – 0,90
|
3,20 –
3,80
|
5Ni
|
0,12 max.
|
4,70 –
5,30
|
9 Ni
|
0,10 max.
|
8,50 –
10,0
|
Note The steel is to contain aluminium, niobium, vanadium or
other suitable grain refining elements, either singly or in any
combination. When used singly, the steel is to contain the specified
minimum content of the grain refining element. When used in
combination, the specified minimum content of each element is not
applicable.
|
|