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|  MIL-D-18641F(SH)
3.14.28 .1.1.4.1
Force loading. In the design of heat exchanger salt water sides, full
consideration shall be given to the cyclic nature of the pressure and external force loading. The
design shall be based on the number of total depth changing cycles specified in NAVSEA
T9070-AA-DDT-010/(C) SUBS, with associated temperature variation in conjunction with that
piping reaction load (see 3. 14.28.l.l.4) that produces the highest stress, 8,000 cycles of start up and
shut down, 200 cycles each of the specified hydrostatic test pressure when applied in the water box
or between the double tube sheets and 300 cycles of loss of seawater (see 6.3 and appendix C).
The analysis shall be in accordance with the methods and criteria of ASME Boiler and Pressure
Vessel Code, section III, division 1, class 1 components. Design fatigue curves for materials
commonly used in distillation units and design stress intensity values for materials not covered in
section III (class 1 components) of ASME code shall be obtained from NAVSEA or the purchaser.
Method of analysis of flat perforated plates shall be in accordance with Article A-8000, of Section
III of ASME Code, division 1, appendices. Cumulative usage factor for all cyclic transients shall
not exceed 0.8.
3.14.28.1.1.4.2 Submergence pressure Heat exchangers subjected to submergence pressure shall
have an even number of salt water passes, so that the inlet and outlet salt water nozzles will be
on the same water box. Thus the stiffness of the piping will not affect expansion or contraction
of the heat exchanger tubes.
3.14.28.l.l.5 Bolts and studs composition Bolts and studs subjected to submergence pressure
shall be nickel-copper alloy in accordance with QQ-N-281, class A, hot finished; or nickel-copper
alloy in accordance with MIL-N-24106, cold drawn, and stress relieved or hot finished; or nickel-
copper-aluminum alloy in accordance with QQ-N-286, class A, hot finished, annealed and age
hardened or cold drawn, annealed and age hardened. Nuts for these bolts and studs shall be nickel-
copper alloy in accordance with QQ-N-281, class A or B, hot finished condition; or nickel copper
alloy in accordance with MIL-N-24106, cold drawn and stress relieved or hot finished; or nickel-
copper alloy in accordance with ASTM B 164, hot finished. Nickel-copper-aluminim alloy bolts and
studs shall also conform to MS 18116.
,
a. Calculated bolt stress due to design pressure shall be limited to one-third of the yield
strength of the material at the design temperature.
b. Maximum value of service stress average across bolt cross-section and neglecting stress
concentration factor shall be limited to two-thirds of the yield strength of the material
at the design temperature.
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