6.1. ERMUSR 11-17-2009 - Laserfiche WebLink

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T~~ atta~hm~aat rn~th®d gtorage 'I"ank Integrity ~~®u~d b~ based ®~ ®veras~ c®st-b~nefet t® the tenant and tank ®vvnea~, Corrosion Wea#hering R®sults Stud-weld attachmerits'for sample panels 1 and 2 showed exteristve~rust-hleedsfrom the stud,ifself: Fix the problem by placing Flexible • .. pfasfic caps; over the,'studs. ~ ' ' -Panel 1 Panel 2 . _ Panei ~3 Panel ~ Paneh$: ; 4' ~', m. m' ~ -. d' I• a RESULTS All penetrations (holes) were inspected following plate separation to check for signs of early rusting, undercutting, or other modes of coating system failure around the edges. i`Io failures were iden- tified on any of the test panel plates. Panels 1 and 2, Stud-Weld Attachment. Sample Panels 1 and 3 showed extensive rusting at cycles 3 and 6. However, the observed rusting was attributed to rust- bleed coming from the stud itself. When the plates were separated, Panels 1 and 2 showed no rusting on either plate sur- face. In addition, no rusting was observed from contact with the neoprene gasket or direct contact with the edges sealed with silicone. Panels 3 and 4, Bolt Attachment. Similar results were observed on the outer face of test Panels 3 and 4, where oxidation appeared limited to the fastener materials. It's possible that the bolts themselves pro- vided some sacrificial protection. When the panels were taken apart, results sim- ilar to those observed in test Panels 1 and 2 wet•e shown; there was no rust- ing of plate surfaces in contact with the neoprene gasket. Minor pinholing was observed in Panel 4 where the edges were sealed with silicone caulk. Panel 5, Seai-Weld Attachment. Minor rusting from pinholing was observed on the front and back of the panel in the heat-affected zone, which appeared to be the result of weld spatter not fully removed. THE BOTTOM LINE Because of its structural properties, seal- we(ding has been the preferred method for attaching support brackets for tele- communications equipment. However, the damage caused to [he coating sys- tem, adjacent areas, and reverse-side immersed surfaces can be severe. The damage can result in additional time and costs related to tank draining, steriliza- tion, and spot repairs. In addition, recon- ditioning damaged areas may require equipment remobilization and temporary sector shutdowns. In simulated testing of exterior con- ditions, results confirmed that properly painted and fastened stud-welding and bolt-attachment methods can perform as well as seal-welded attachments. Bolt attachments should always be installed opposite a dry tank interior, and both methods must include strict adherence to specifications regarding shop surface preparation, painting, and inspection. In i~i~ f it , pN .1 4 :.. ; s iM~~ F~ ~ '~ j addition, placing a i/.i6-in. neoprene gas- ket between the painted tank and bracket plate surfaces may provide better protec- tion against corrosion than applying sili- cone caulk. Although extensive rust-bleed was observed on plate surfaces from rust- ing copper studs, the problem can be remedied by placing flexible plastic caps over the studs. The type and sequencing of the nylon washer fasteners played an important role in preventing corrosion, especially around drill holes. The attachment method should be based on overall cost-benefit to the tenant and tank owner. For the tenant, following the prescribed attachment fas- tening variations promotes on-time site operation. Also, variations reduce proj- ect costs and the potential for weather- related punch-list items. For the owner, using the proper attachment and repair methods ensures tank and protective coating integrity. ,, Author's Note: Thanks to the follow- ing for their assistance: AFB Welding & Constrtcction, Ham Lake, !Minn.; lndtts- trial Painting Specialists, Hugo, !Minn.; Vinco, Forest Lake, Nlinn.; and Shertvin- Willianas, Bttrnso~ille, rYlinn., ctnd War- rensville Heights, Ohio. 22 OpFlow October 2009 www.awwa.orn/opFlow