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SP0178-2007
<br /> 3.2.2 Rivets shall not be used. 3.4.2 If appurtenances inside the tank or vessel,
<br /> including nuts and bolts, cannot be lined, they shall be
<br /> 3.2.3 The use of internal bolted connections should made of corrosion-resistant materials. (CAUTION: See
<br /> be avoided to the fullest extent possible. Paragraph 3.3.2.1.)
<br /> 3.2.4 Continuous lap-welded joints may be used but 3.4.3 If bolted connections are necessary and cannot
<br /> are not preferred. For sheet lining material,this type of be made of corrosion-resistant materials, the mating
<br /> construction may not be acceptable. surfaces shall be lined before assembly. Gaskets shall
<br /> be used on mating surfaces and the sealing surfaces of
<br /> 3.3 Connections nuts and bolts to protect the lining.
<br /> 3.3.1 All connections to the tank or vessel shall be 3.4.4 Dissimilar metals shall be electrically isolated
<br /> flanged. from the steel tank or vessel surface whenever
<br /> possible. Where dissimilar metals are used, selection
<br /> 3.3.2 Threaded connections should not be used in shall be such that the galvanic effect is minimized.
<br /> tanks and vessels operating in corrosive environments Other corrosion mitigation methods may be required
<br /> (see Figure A4, Appendix A). However, if threaded (see Figure A8,Appendix A).
<br /> connections cannot be avoided in corrosive
<br /> environments, these parts shall be fabricated of 3.4.5 Heating elements shall be offset from the tank
<br /> corrosion-resistant materials, or constructed as shown or vessel surface to provide access for surface
<br /> in Figure Al 0,Appendix A. preparation, application, inspection, and cleaning.
<br /> Elements shall be positioned so as not to damage the
<br /> 3.3.2.1 CAUTION: Dissimilar metal (galvanic) lining system.
<br /> corrosion occurs when, for example, an alloy is
<br /> used to replace the steel bottom of a tank, or in a 3.5 Structural Reinforcement Members
<br /> similar circumstance when alloy appurtenances
<br /> must be part of the construction of a vessel. If a 3.5.1 Structural support members should be installed
<br /> lining is then applied to the steel and part of the on the exterior of the tank or vessel. However, if such
<br /> alloy (usually 150 to 610 mm [5.9 to 24 in.]), any members are installed internally, they shall be
<br /> discontinuity in the lining exposes a small anode fabricated of simple shapes such as smooth, round
<br /> surface. Once corrosion starts, it progresses bars or pipe for ease of applying the lining material.
<br /> rapidly because of the large exposed alloy
<br /> cathodic area to the much smaller anodic area. 3.5.2 The use of internal flanged connections,
<br /> Without the lining, galvanic corrosion causes the stiffening rings, reinforcement pads, angles, channels,
<br /> steel to corrode at the weld area, but at a much I-beams, and other complex shapes should be
<br /> slower rate. The recommended practice is to avoided. If they must be installed internally, these
<br /> apply the lining to all of the alloy as well as the members shall be fully welded and welds and sharp
<br /> steel, thereby eliminating the possible occurrence edges ground to a radius of at least 3.2 mm (0.13 in.)
<br /> of a large-cathode-to-small-anode surface. or as agreed between the tank or vessel fabricator,
<br /> tank or vessel owner, and lining applicator(see Figures
<br /> 3.3.3 Nozzle connections to be lined shall be as short Al and A6,Appendix A).
<br /> as possible and be a minimum of 50 mm (2 in.) in
<br /> diameter (see Figure A4, Appendix A). Connections 3.6 Heat Sinks
<br /> less than 50 mm (2 in.) in diameter shall be suitably
<br /> attached through a reducing flange (see Figure A10, 3,6.1 Heated, forced curing of lining systems is often
<br /> Appendix A). When trowel-applied thick-film linings are preferred if not specifically required. During tank or
<br /> required, additional nozzle inside diameter shall be vessel design and fabrication, especially with field-
<br /> allowed for lining thickness. erected units, consideration must be given to avoiding
<br /> or minimizing heat sink areas. Such areas might
<br /> 3.4 Appurtenances Inside the Tank or Vessel include opposite saddles or support lugs, flat bottoms
<br /> on foundations,and stiffening rings.
<br /> 3.4.1 The standard practices in Sections 3, 4, and 5
<br /> shall apply to any item to be installed inside a tank or 3.6.2 These situations may be addressed either by
<br /> vessel that is to be lined. Such appurtenances include, tank or vessel design or by construction or insulation of
<br /> but are not limited to, agitators, anti-swirl baffles, outlet the foundation or supports. Another possible solution
<br /> connections, gauging devices, vortex breakers, and is the use of temporary constructions, such as false
<br /> internal piping. floors or temporary shelters,to achieve uniform heating
<br /> and curing.
<br /> 2 NACE International
<br /> 185
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