Too late to make you r modifications and paint the whole thing red before calling for inspection? Doubt any of us are providing a blast finish onsite. Letter from Allied on XL and black?
George L. Church, Jr., CET Rowe Sprinkler Systems, Inc. PO Box 407, Middleburg, PA 17842 877-324-ROWE 570-837-6335 fax g...@rowesprinkler.com -----Original Message----- From: sprinklerforum-boun...@firesprinkler.org [mailto:sprinklerforum-boun...@firesprinkler.org] On Behalf Of å... .... Sent: Friday, September 28, 2012 4:58 PM To: SprinklerFORUM@firesprinkler.org Subject: galvanized to steel connections If zinc reacted with steel wouldn't it occur on galvanized pipe itself as well. Zinc does react with steel, and that is the precise method by which it is used to protect the steel. The zinc is the 'white knight' that falls on its sword to save the steel. However, if the steel is hermetically sealed in a film of zinc, then there is no physical motivation for the sacrifice, because the complete circuit has not been 'set up.' When there is a complete film of zinc, there is no electrolyte (usually water) to act as one of the 'wires ' that carry current in a completed circuit. In the real world, pipe is not always unloaded from the truck, let alone shipped to the distributor from the foundry, with actions taken with consideration that the zinc needs to treated with kid gloves to maintain its hermetically sealed status. While the steel doesn't have to be * hermetically* sealed, the fewer imperfections, the less the zinc has to work at sacrificing. When the breaks in the zinc film are small (~ < 2 mm) and there is water over/in/on the break, the zinc does what the zinc is supposed to do -- react by corroding away into the water as the cation in a newly dissolved salt. But as the breaks in the zinc become bigger it gets more and more difficult for the zinc on the perimeter-of-the-break to effectively protect the steel pipe furthest from this zinc. In the case of the questioner, there obviously is a 'substantial break' in the zinc film occuring at the zinc-steel pipe union. Zinc will corrode on that interface, if there is water present. This is where a well cleaned and painted steel surface comes in (my bad for not mentioning earlier that sandblasting a zinc coating is probably not the best design that has been offered up). A painted steel surface prevents (ideally) the water from acting as the necessary-and-previously-missing-wire that completes the galvanic cell circuitry. Now, new evidence has been introduced. We now know the steel-zinc interface occurs indoors. While an indoor steel-zinc interface may appear to be better than an outdoor steel-zinc interface, unfortunately, nuances and devilish details enter here that keep corrosion engineers busier than fitters. Steel-zinc interfaces outdoors in Yellowknife, NWT are usually quite dry, because water freezes out of the air up there. Corrosion in Yellowknife, is relatively slow. Outdoors at Dead Horse Point, UT is not very corrosive either, not because it is cold, but because it again, is so dry. Depending upon where your 'indoors' is located with respect to outdoors, you could have very ripe conditions for accelerated corrosion. Consider air conditioning in a St. Louey, MO office in late August (I think they used to offer tropical pay to foreign consulars there). As the A/C drops the air temperature down to its dew point, that water vapor is going to last as long as cross at a KKK convention if a sprinkler pipe is around to absorb heat from its condensation. If you want examples of steel-zinc corrosion happening indoors, I can refer you to the man who can provide you that photo forum. While it does not make for inspiring, charismatic or a reassuring FOX news interview , the answers to corrosion remains: " 'Not if, but when'. And if 'when', then that depends." scot deal excelsior fire -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://fireball.firesprinkler.org/mailman/private/sprinklerforum/attachments/20120928/17335134/attachment.html> _______________________________________________ Sprinklerforum mailing list Sprinklerforum@firesprinkler.org http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list Sprinklerforum@firesprinkler.org http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum
