Laserfiche WebLink
SP0178-2007 <br /> f._Roof <br /> Weld Inside=Eliminate Crevice Inaccessible for Grinding or <br /> „�-.-�„ Proper Lining Application <br /> Inside of Tank or <br /> Vessel Inside of Tank or <br /> Vessel <br /> Shell <br /> DO DON'T <br /> FIGURE A7 <br /> Roof-to-Shell Joint. Eliminate crevice and lap weld at roof-to-shell joint in a tank or nonpressure vessel. <br /> I <br /> .__ Pit(Anode) Pit(Anode) <br /> Steel I Steel <br /> 1Y(C1ode) L::cathode) <br /> rotective Protective <br /> DO DON'T <br /> FIGURE A8 <br /> Dissimilar metal (galvanic) corrosion occurs when, for example, an alloy is used to replace the steel bottom of a tank, or, in a <br /> similar circumstance,when alloy appurtenances must be a part of the construction of a vessel. If a lining is then applied to the <br /> steel and part of the alloy(usually 150 to 610 mm [5.9 to 24 in.]), any discontinuity in the lining exposes a small anode surface. <br /> Once corrosion starts, it progresses rapidly because of the large exposed alloy cathodic area to the much smaller anodic area. <br /> Without the lining,galvanic corrosion causes the steel to corrode at the weld area,but at a much slower rate. The recommended <br /> practice is to apply lining to all of the alloy as well as the steel,thereby eliminating the possible occurrence of a large-cathode-to <br /> small-anode surface. <br /> NACE International 9 <br /> 192 <br />