5.4.1 The requirements of this
section apply to piping inside and outside the cargo tanks. Relaxations
from these requirements may be accepted, in accordance with recognized
standards, for piping inside cargo tanks and open-ended piping.
5.4.2 The following direct
connection of pipe lengths, without flanges, may be considered:
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.1 Butt welded joints with complete penetration at
the root may be used in all applications. For design temperatures below -10°C,
butt welds should be either double welded or equivalent to a double welded butt
joint. This may be accomplished by use of a backing ring, consumable insert or
inert gas back-up on the first pass. For design pressures in excess of 10 bar and
design temperatures of -10°C or lower, backing rings should be removed.
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.2 Slip-on welded joints with sleeves and related
welding, having dimensions in accordance with recognized standards, should only be
used for open-ended lines with external diameter of 50 mm or less and design
temperatures not lower than -55°C.
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.3 Screwed couplings complying with recognized
standards should only be used for accessory lines and instrumentation lines with
external diameters of 25 mm or less.
5.4.3.1 Flanges in flange
connections should be of the welded neck, slip-on or socket welded
type.
5.4.3.2 Flanges should comply
with recognized standards as to their type, manufacture and test.
In particular, for all piping except open ended, the following restrictions
apply:
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.1 For design temperatures lower than -55°C, only
welded neck flanges should be used.
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.2 For design temperatures lower than -10°C, slip-on
flanges should not be used in nominal sizes above 100 mm and socket welded flanges
should not be used in nominal sizes above 50 mm.
5.4.4 Piping connections, other
than those mentioned in 5.4.2 and .3, may be accepted by the Administration
in each case.
5.4.5 Bellows and expansion
joints should be provided to allow for expansion of piping.
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.1 If necessary, bellows should be protected against
icing.
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.2 Slip joints should not be used except within the
cargo tanks.
5.4.6 Welding, post-weld heat
treatment and non-destructive testing
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.1 Welding should be carried out in accordance with
6.3.
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.2 Post-weld heat treatment should be required for
all butt welds of pipes made with carbon, carbon-manganese and low alloy steels.
The Administration may waive the requirement for thermal stress relieving of pipes
having wall thickness less than 10 mm in relation to the design temperature and
pressure of the piping system concerned.
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.3 In addition to normal controls before and during
the welding and to the visual inspection of the finished welds, as necessary for
proving that the welding has been carried out correctly and according to the
requirements of this paragraph, the following tests should be required:
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.3.1 100% radiographic inspection of butt welded
joints for piping systems with design temperatures lower than -10°C and with
inside diameters of more than 75 mm or wall thicknesses greater than 10 mm. When
such butt welded joints of piping sections are made by automatic welding
procedures in the pipe fabrication shop, upon special approval by the
Administration, the extent of radiographic inspection may be progressively reduced
but in no case to less than 10% of each joint. If defects are revealed the extent
of examination should be increased to 100% and should include inspection of
previously accepted welds. This special approval can only be granted if
well-documented quality assurance procedures and records are available to enable
the Administration to assess the ability of the manufacturer to produce
satisfactory welds consistently.
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.3.2 For other butt welded joints of pipes not
covered by 5.4.6.3.1, spot radiographic tests or other
non-destructive tests should be carried out at the discretion of the
Administration depending upon service, position and materials. In general, at
least 10% of butt welded joints of pipes should be radiographed.