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Unrestrained expansion and contraction |
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|  MIL-D-18641F(SH)
weight of the tube bundle plus that of the adjacent water box and that portion of the
shell between the expansion joint and the shell end flange adjacent to the support, in
the direction longitudinal of the heat exchanger.
3.14.l8.l Unrestrained expansion and contraction. Provision for unrestrained expansion and
contraction of the tubes of all shell and straight tube type heat exchanger components of the
distillation unit shall be made by use of an expansion joint in the shell, located between one
supporting foot and the shell end flange, or by use of floating head instruction- In the case of
heat exchangers with an odd number of passes, restraint of tube expansion and contraction shall
be avoided by providing an expansion joint in the piping connected to the water box adjacent to
the shell expansion joint or the floating head. If the piping is integral with the distillation unit, the
expansion joint shall be provided with the piping.
3.14.19 Component removal provisions. Adequate guides, slides, lifting lugs, and access
openings shall be provided to facilitate removal of the evaporator tube nests or baskets, mesh
vapor separators, stage condenser tube bundle and vapor feed heater tube nests from the shells
and for handling the water boxes of the distiller condenser, stage condensers, salt water feed heater
and the distillate cooler.
3.14.20 Jack screws. Jack screws shall be provided in all flanges of flanged joints that must
be disassembled for maintenance. Jack screws are not required for flanged joints which incorporate
O-ring face seals.
3.14-21 Bolts or stud bolts. The water box flange, tube sheet and shell flange joints of all
components shall be secured by through bolts or stud bolts. Studs shall not be used unless it is
impracticable to use through or stud bolts. If through bobs are used, alternate bolts shall be collar
bolts; if stud bolts are used they shall be driven into tapped holes in the tube sheets, so that the
joint between the tube sheet and shell flange will not be broken when the water boxes are
removed. Collar bobs shall be replaceable without removing the water boxes. Collar and stud bolts
shall be provided with one square end for use of a wrench to prevent turning when the nut at the
water box flange end is removed.
3.14022 Sight glass. Sight glass assemblies, if glass is used, shall be composed of a metal
flanged frame to be bolted to a boss or flange on the evaporator shell. The flame shall contain the
sight glass. The glass shall be secured with gaskets by means of a ring screwed into the flame so
as to obtain even pressure on the glass, and so that the pressure on the glass is not changed when
the sight glass frame assembly is removed from the evaporator shell. Jack screws shall be provided
in the flange of the frame. Glasses shall be in accordance with MIL-G-2860.
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3.14.22.1 Plastics acrylic sight glass assemblies. The use of plastic acrylic heat resistant sheet
shall be limited to applications having service temperatures below 150 "F. Sight glass assemblies,
if plastic acrylic heat resistant sheet is used in lieu of glass, shall be a single flange, bolted to the
face of a pad or flange on the evaporator shell, securing the plastic sheet thereto between resilient
gaskets. The flange shall be provided with jack screws. The plastic sheet shall be finish A in
accordance with MIL-P-5425 and shall be of suitable thickness for the intended service.
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