4.
PIPE JOINTS.
a.
Welded Joints. Welded joints in chamber systems shall be
constructed in accordance with the requirements of Sections 127, 131, and
132 of the B 31.1 Code subject to the following additional restrictions:
Welded joints of 2-1/2" pipe size or smaller may be socket welded
or butt welded. Welded joints over 2-1/2" pipe size shall be butt
welded.
The finished interior surface of pipe joints shall be as smooth as
practically possible to reduce the amount of noise generated.
Backing rings when used in pressurization, depressurization or life
support loop lines shall either be removed or be of a consumable
type.
b. Brazed Pipe and Tube Joints.
(1) Brazed joints shall be made in accordance with the
requirements of NAVSEA 0900-LP-001-7000 (including changes) Fabrication and
Inspection of Brazed Piping Systems (Reference 12) or the AWS Brazing Manual
(Reference 13).
(2) Filler Metal. The filler metal used in brazing shall be a
nonferrous metal or alloy having a melting point above 800 deg. F (425 deg.
C) and below that of the metal being joined. The filler metal shall melt and
flow freely within the desired temperature range, and in conjunction with a
suitable flux or controlled atmosphere, shall wet and adhere to the surfaces
to be joined.
(3) Flux. Fluxes that are fluid and chemically active at the
brazing temperature shall be used when necessary to prevent oxidation of the
filler metal and the surfaces to be joined and to promote free flowing of the
filler metal.
(4) Corrosion Resistance. All brazed materials, components, and
fittings shall be of corrosion resistant metals (stainless steel, brass,
bronze, etc.). Combinations from NAVSEA 0900-LP-001-7000 (Reference 12),
Table 5-1, or from the AWS Brazing Manual (Reference 13) are recommended.
(5) Surface Preparation. The surface to be brazed shall be clean
and free from grease, oxides, paint, scale, and dirt of any kind. A suitable
chemical or mechanical cleaning method can be used to provide a clean
wettable surface for brazing.
(6) Joint Clearance. The clearance between surfaces to be joined
shall be no larger than is necessary to insure complete capillary
distribution of the filler metal. (See NAVSEA 0900-LP-001-7000, Table 5-2,
Reference 12.)
(7) Heating. The joint shall be brought to brazing temperature in
as short a time as possible to minimize oxidation.
(8) Brazing Qualification. The qualification of the brazing
procedure, and of the performance of brazers and brazing operators, shall be
in accordance with the requirements of Part QN, Section IX, of the ASME Code
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