6.1. ERMUSR 11-17-2009 - Laserfiche WebLink

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I~ ,, Daniel 1. Zienty is eviih Short Elliott Hendrickson (www.sehinc.com). St. Paul. Minn. Z 0 a study incorporated variations to the stud- welding and bolting fastening sequence and tested five sample bracket attachment methods in a controlled environment that simulated typical exterior exposure: ® Panel 1, stud-welding a painted bracket to the tank ~~ith a neoprene gasket between components ® Panel 2, stud-welding a painted bracket to the tank with silicone caulk around the edges ® Panel 3, bolting a painted bracket to the tank with a neoprene gasket between components ® Panel 4, bolting a painted bracket to the tank with. silicone caulk around the edges v Panel 5, seal-welding a painted bracket to the tanl: The study used five steel plates, mea- suring 12 in. by 20 in. by '/ in., to simulate the tanl: surface and five steel attach- ment plates, measuring 6 in. by 8 in. by '/ in., to simulate the attachment bralc- ets. Panel plates were prepared. in a shop em~ironment following standard specifica- tions for AWW'A Standard D102-06 Coat- ing Steel Water-Storage Tanlcs. Two coats of atwo-component epoxy were applied, followed by one coat of atwo-component aliphatic polytu•ethane. In addition, shop and field surface- coating specifications were incorporated, inluding surface preparation of the bare metal according to Society for Protective Coatings (SSPC) painting manual specifi- cations for cleanliness (2-3 mil profile), followed by application of prune and intermediate coats of epoxy (4-6 mils dit) and a finish coat of polyurethane (2-3 mils dit) based on compatibility with the tank's existing coating system. Inspections were conducted by a National Association of Corrosion Engineers-certified. inspec- tor during each phase of the process. Panels 1 and 2, Stud-Weld Attachment. For assembly, the 12-in. by 20-in. by 'L;-in. plates were marked. for stud location, and spot areas were ground down to expose bare metal. Studs were shot in two loca- tions, and bare areas were touched up with aspray-on cold galvanizing product. Attachment plates were fastened using nylon washers, followed by stainless steel and. lock washers and stainless nuts (Grade F593C). Panel 1 was assembled by placing a neoprene gasket between the two plates prior to fastening. For Panel 2, the two plates were in direct contact with a bead of silicone caulking placed around the edges to provide a seal. Panels 3 and 4, Bolt Attachment. Assembly of Panels 3 and 4 required drilling holes in the base of each metal plate in two locations each. Each hole was mechanically cleaned to remove any burrs or sharp edges. The bare meta} was then sprayed with a cold galvanizing product. Panel 3 was assembled by plac- ing aneoprene gasket between the two plates prior to fastening. For Panel 4, the two plates were in direct contact with a bead of silicone caulking around the edges to provide a seal. Grade A325 bolts and washers were used for fastening in the same sequence as used for Panels 1 and 2. Panel 5, Seal••Weld Attachment. For Panel 5, the edges of the attachment plate were masked to simulate field con- ditions (weld-area preparation). Follow- ing shielded metal arc welding, areas damaged in the heat-affected zone (both plates and plate tank/backsides) were mechanically cleaned according to SSPC power-tool leaning specifications to establish a minimum profile and feather- ing of the intact coating. After prepara- tion, the exposed areas were covered. with tvvo coats of epoxy and polyurethane. Final inspection of each assembly was conducted Uefore preparing the panels for shipment to the test facility. LABORATORY TESTS Laboratory testing compared exterior exposure performance of the bracket assembly coating repairs using capacitor- studs, bolted assemblies, and seal-welded assemblies. Lab personnel applied vinyl tape around the edges and backs of the panels to protect the surfaces from the elements. The panels were then subjected to six cycles of corrosion weath- ering, according to American Society for Testing and Materials standards. The large panels were fitted horizon- tally into a qualitative ultraviolet (QW) accelerated weathering tester without panel racks. In some cases, the panels were made slightly wider by bending an aluminum panel around the edge to form a "V." This allowed the panels to lie on the edge of the QLTV cabinet opening. Open areas in the cabinet were masked with bare aluminum panels. The panels were then photographed and rated at cycles 3 and 6. ti~~~ w.ac~~'a.or;;/opFlo~e October 2009 Opflo~r 21