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|  MIL-D-18641F(SH)
3.14.28.1.1.1 Tube sheet tube holes. For submarines, in heat exchangers subjected to
submergence pressure, the tube sheet shall be drilled as specified in 3.14.14 or 3.18.12, except that
the holes for 3/8 inch, 5/8 inch or 3/4 inch od tubes in the outer tube sheets shall have three
grooves 1/8 inch wide and 0.012 inch deep, located 1/8 inch apart, and the holes for 3/8 inch,
5/8 inch or 3/4 inch od tubes in the inner tube sheets shall have two grooves 1/8 inch wide and
0.012 inch deep, located 1/8 inch apart. In heat exchangers not subjected to submergence pressure
in submarines and in those for saturated steam propelled surface ships, the tube sheets shall be
drilled as specified in 3.14.14 or 3.18.1.2 except that the inner tube sheet holes shall have one
groove 1/8 inch wide and 0.012 inch deep.
3.14.28.1.1.2 Tube expansion. Tubes shall be expanded into both inner and outer tube sheets
at each end specified in 3.14.13.1.1. Minimum depth of expansion in the inner tube sheet shall be
1/2 inch for 3/8 inch od tubes, 5/8 inch for 5/8 inch cd tubes and 3/4 inch for 3/4 inch od tubes,
The expander shall be set such that a wall reduction of approximately 10 percent is attained. After
expansion of the tube ends, the specified water side hydrostatic test pressure shall be applied to
the spaces between the double tube sheets (see 4.3.1.1).
3.14.28.1.1.3 Water box flanges. The water boxes shall have either internal or external flanges.
Internal water box flanges shall be studded, with nuts on the shell side of the inner tube sheet, and
guide pins longer than the studs and inserted in holes having smaller diametrical clearance than the
holes for the studs shall be provided to prevent damage to the threads on the studs when the
water boxes are installed. Through bolts shall be used with external water box flanges.
3.14.28 .1.1.4 Parts subjected to submergence pressure Parts subjected `to submergence
pressure including structure composed of outer and inner tube sheets together with short sections
of tubes between paired inner and outer tube sheets, shall be constructed in accordance with the
requirements of the ASME Boiler and Pressure Vessel Code, Section III, Nuclear Power Plant
Components, class 1 components, as a minimum, except welding shall be in accordance with
MIL-STD-278. Reinforcement of openings shall be integral with the water box shell or nozzle (or
both). Separate pads or saddle type reinforcements shall not be used. Welds shall be ground
smooth and the comers and fillets shall be well rounded as necessary to minimize notch effect.
In the design of heat exchangers, the forces exerted by the circulating water inlet and discharge
piping on the respective water box nozzles shall be as follows:
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