CoatingsPro Magazine

MAR 2018

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 18 of 84

18 MARCH 2018 COATINGSPROMAG.COM trapped by the por tion of sea l that hasn't fai led, and no sea l wou ld have caused less damage. A nother negative can be that a f unctioning sea l may delay detection of a tank-bottom lea k. First, it may depend on what is inside and what the sea l mater ia l is. A n aspha lt sea l for a d iesel or kerosene tank is likely to sof ten the aspha lt and show sig ns of seepage. T hat polysu lf ide may ta ke a bit more time. Graded ag g regate trenches set over per forated tubing and a lea k detec- tion system can avoid the detection concer n, but the old reg u lar wa l ks around the tank per imeter may not. Add a minor focus on perimeter leaks (the leaks that a walk around might detect), which are often the most likely because the soil at the perimeter of the tank tends to have a higher level of aeration. As such, the perimeter is more prone to corrode than soil further to the center. Exceptions are tank pads that are not properly graded to prevent rainwater migration and tanks that frequently run at reduced levels. At low levels, the war ped and buck led f loor plate pops up, and that, too, draws fresh air under the tank. Covering that chime w ith a polysulfide and a bond breaker/ expansion joint also ensures that the chime cannot be inspected w ithout removing the seal material. Here I' ll repeat that the chime is an important structural part of the tank design, as well as an indicator that tank bottom corrosion may be occurring and should not be overlooked at each external tank inspection. One might conclude that I'm not a big fan of polysulfide, but it is a great material and has its place. Just choose w ith caution, like any other material. A: If many other important variables aren't addressed, a chime seal may be of no benefit, or worse, a detriment. I have seen the mastic seal work where similar equip- ment failed in about 10 years. A painted bottom ring might have served the same purpose, but building the tank without damaging that coating is another story. Vessel Inspections Q: I have to inspect a pressure vessel, and now I need to know the procedures and how to start the inspection. I also need to know which information we should collect. T he [client] requests [ISO standard 8501-1] Sa 2½ for ver y thorough Re ad e r In qui r y at co ati n g sp ro m a m /i n q0318

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