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Which Fasteners Should You Specify for Harsh Environments?

Posted by Tom on 4/14/2013
It is always easy for us to recommend to customers 316 stainless steel fasteners in all harsh environment and when long serviceable life is needed. We try to inventory and sell the fasteners our customers would normally use in their strut channel related projects, which includes zinc plated and 316 Stainless Grade 5 bolts, strut nuts, flat, fender, and spring washers. Customers never ask for other options, probably because the fastener industry does not provide other easy to acquire options other than 304 and 316 stainless. At G-P LLC we are attempting to apply our auto industry experience to our construction products business by offering most fasteners and even smaller brackets with superior finishes that are lower cost then stainless and sometime better. When the auto industry, worldwide, decided in early 1990's to build cars and trucks that did not rust or fall apart after 2-3 years, they converted most of their undercarriage (under car) fasteners and brackets from E-Coat or hot dipped galvanized finishes to a zinc prime and finish paint process with most of the industry using the Dacromet or Geomet licensed process from Magna Group. Mufflers and undercarriage items stopped rusting and literally falling off the vehicles, like many of us experienced in our earlier days. 700 hours to 1,000 hours of salt spray resistance became the standard verse a fraction of that with typical finishes. In the past 20-years the Dacromet process has been replaced by a non-chromium product, later called Geomet and now is called Magni 565 that is accepted worldwide as environmentally safe. The auto industry forced the development of non-chromium finishes during the 1990's for fasteners and smaller brackets that has proven to be a great improvement for the transportation industry and our environment. Then, why is the construction industry still using finish specifications many dozens of years out of date? Hot dip galvanizing fasteners makes assembly quite a challenge because of uneven build-up on the threads and is a threat to our environment, not to mention the high risk of hydrogen embrittlement with delayed cracks in high strength fasteners, so to play it safe high strength fasteners are left raw and allowed to rust unless otherwise protected. American Bridge and Fluor Engineering are currently constructing the San Francisco-Oakland Bay Bridge. It is the largest construction project in the history of California. They decided to build the bridge with A490 high strength bolts with the Dacromet finish. In the past the A490 bolts would have raw finish to avoid threats of hydrogen embrittlement. They did their homework to assure the Dacromet would not cause adverse torque release problems and they probably accepted the data from 20 years with the auto industry's success. The A490 fasteners are made in the USA and finished with the Dacromet process and then shipped to Shanghai where the bridge is being constructed... Now, to me, America should be building their own bridge... What a shame! ! !

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1 Comments

TOM
Date: 4/17/2013
I was just told by experts that the company that owns and licenses the Dacromet, Geomet, and most widely used Magni 565 process have an even better finish that can offer 2,000 to 3,000 hours of salt spray protection. Perhaps, us construction material suppliers need some advice and a push in the right direction.

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