c.
Flanged Joints/Bolted Flanges.
(1) All bolted flanged joints shall be fitted up so that the
gasket contact faces bear uniformly on the gasket, and then shall be made up
with relatively uniform bolt stress.
(2) In bolting gasketed flanged joints, the gasket shall be
properly compressed in accordance with the design principles applicable to
the type of gasket used.
(3) All bolts shall be engaged so that there is visible evidence
of complete threading through the nut or threaded attachment.
(4) Where bolted flange joints are used in breathing gas systems,
the fabricator shall provide making and unmaking instructions with the
system. The instructions shall include as a minimum: required bolt and nut
materials, required gasket material, maximum and minimum allowable nut
torques, and torquing sequence.
(5) The pressure design of bolted flanges and blanks shall be in
accordance with para. 104.5 of the B 31.1 Code (Reference 2) with the
following additional restrictions:
Flanges shall be joined to the pipe by butt welding, socket
welding threading or other proved mechanical joining techniques.
Slip-on flanges shall not be used.
(6) Flat face O-ring unions and other mechanical joint designs
employing self-energizing seals where effective sealing is not dependent on
bolt pre-loading are recommended over bolted flanges.
d.
Threaded Joints.
(1) Threaded connections shall be made with fittings. Fittings
shall have a working pressure rating equal to or greater than the maximum
allowable working pressure (MAWP) of the system in which they are used.
(2) Straight thread O-ring sealed fittings may be used up to the
manufacturer's rated MAWP with no limitation on size. For helium service, it
is recommended that pipe threads be avoided wherever possible, especially in
the larger sizes, at higher pressures or where stainless on stainless joints
are required. Straight thread O-ring sealed fittings are recommended over
pipe thread fittings for helium service, However, for marine systems
consideration must also be given to the availability of replacement fittings.
Straight thread O-ring sealed fittings are not nearly as readily available as
are pipe thread fittings.
(3) Any compound or lubricant used in threaded joints shall be
suitable for the service conditions and shall not react unfavorably with
either the service fluid or the piping materials. Chapter 12 contains a
listing of thread compounds and lubricants that are known to be acceptable
for oxygen and breathing gas service.
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