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11 NACE INTERNATIONAL: VOL. 56, NO. 8 MATERIALS PERFORMANCE AUGUST 2017 THE BLOG Continued on page 13 The following are excerpts f rom the NACE International Corrosion Net work (NCN) and NACE Coatings Net work . These are email-based discussion g roups for corrosion professionals , with more than 3 ,000 participants . The excerpts are selected for their potential interest to a large number of NACE members . They are edited for clarit y and leng th . Authors are kept anony mous for publication . Please be advised that the items are not peer-reviewed , and opinions and sug gestions are entirely those of the inquirers and respondents . NACE does not g uarantee the accuracy of the techni- cal solutions discussed . M P welcomes additional responses to these items . They may be edited for clarit y. For information on how to subscribe to these f ree list ser vers , click on the "Corrosion Central " link and then "Online Corrosion Communit y List Ser vers" on the NACE web site: www.nace .org. Peak at the "On" Potential Q: I am recording pipe-to-soil potentials during an "on"/"off " interruption cycle. We have installed several recorders in three pipelines, but in two recorders' potential the transition between the "off " and "on" potential starts with a high peak. This peak is not present all the time and varies in inten- sity. I have not seen this kind of peak in the transition "off " to "on" potential. Does someone have any explanation for this phenomenon? A: We all are aware of an "anodic spike" when rectifiers are turned off. So, a "cathodic spike" when rectifiers are turned on is also a possibility for the same reasons (i.e., inductance/capaci- tance of the system for the pipeline, recti- fiers, and groundbeds). I have seen it in the waveprints we collect during close- interval surveys but not always. Use of Brass Clad Tube Sheet Q: For economic reasons, we are trying to use clad instead of solid metallic material. In our case, the licensor of the plant has specif ied solid naval brass as tube sheet material of heat exchangers with cooling water service in the tube side. The service of the tube side is fresh water from a cooling tower and the material of the water box is carbon steel (CS). Is it possible to use a CS tube sheet with brass clad on one side only? A: If the leak path in the rolled joint from the water box to the CS is very short (<15 mm), the water will weep to the CS and the resulting rust will destroy the tube-to-tube sheet integrity. When clad tube sheets are used, the joint is almost always seal welded. One other solution is to coat the tube sheet after tube installation with a high-solids epoxy.