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Freeing up a corroded stainless/aluminum joint

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Old 01-11-2008, 08:24 AM
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ps - Freon around an open flame or red hot metal turns into all kinds of nasty acids & poison gas
Ya it does. But it works.
Dry Ice (CO2) or Liquid Nitrogen if you can get your hands on it would be the best choice as they're pretty much inert, but whatever you have on hand will work as well.

MBam's on the right track here. The coefficient of thermal expansion of aluminum is about 24 and stainless is 16. That's 1.5 to 1. So even if you heat them at the same rate, the aluminum would still expand 1.5X as much as the steel part and could free them. But heating the aluminum part and cooling the steel part would work the best.
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Old 01-11-2008, 10:03 AM
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ages old trick I learned ages ago. To free up aluminum fittings threaded onto steel fittings in a/c systems, soak the joint with iodine repeatedly. It doesn't happen fast but over a short period of time, the solid aluminum oxide disolves. I don't know the chemistry behind it but I can say after doing it for years, it has saved my but on several occasions when the 50 dollar part needed to be removed from the 500 dollar part without damage.
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Old 01-11-2008, 12:12 PM
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For the "chill" go buy a can of dust off and put the straw on it and turn it upside down and spray....comes out f uc kin cold.
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Old 01-11-2008, 06:55 PM
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For the "chill" go buy a can of dust off and put the straw on it and turn it upside down and spray....comes out f uc kin cold.
Another idea for the "Chill" is to buy Compound W Freeze off. It is a home wart removal kit. Not sure exactly what is the icold stuff it sparays but it is a very good way to get pin point application of the cold.
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Old 01-11-2008, 08:48 PM
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When you are cooling it down spray the PB Blast on it. It will suck it into the joint like the way solder flows into a pipe fitting.
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Old 02-19-2008, 10:30 AM
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Update:

After 2 weeks of soaking, the PB Blaster didn't make it happen, so I cut along both side of the aluminum part and split it with a chisel. The stainless part was fine, so I re-assembled everything with Tef-Gel Corrosion Inhibitor. It looks and acts like teflon pipe thread sealant, but apparently is not the same. It must be the good stuff if Cigarette, Hatteras, Latham Marine, Rybovich, TNT Custom Marine, and the US Navy use it: Tef-Gel Information

Interesting: I was unaware that a joint between stainless steel and aluminum is big-time bad news for galvanic corrosion. Although each material has good corrosion resistance on its own, they are at the far ends of the Galvanic scale. Watch out, all you salt-water boaters!
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Old 02-19-2008, 10:42 AM
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Good observation. Anytime dis-similar metals are assembled in intimate contact without any isolators, barriers or inhibitors there will be a galvanic reaction leading to corrosion.

For harsh environments, such as outdoors, high humidity, and salt environments, there should be not more than 0.15 V difference in the Anodic Index. For example; gold – silver would have a difference of 0.15V being acceptable.

For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the Anodic Index

For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.

Tef-Gel is good stuff. It's a highly effective barrier coating with lubricating properties, so caution should be exercised when using on non-locking bolts as they could work their way loose. Even better is a PRC-Desoto product called CA-1000.
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Old 02-19-2008, 11:08 AM
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The shifter handle on my 6hp kicker engine froze, and my mechanic couldn't free it. I drilled a 1/8" hole on the "up" side of the housing just to the SS shaft, and filled it with PB Blaster every few days. Worked like a charm.
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Old 02-19-2008, 12:31 PM
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Interesting: I was unaware that a joint between stainless steel and aluminum is big-time bad news for galvanic corrosion.
I used to laugh when customers whould install GPS Antenna's, spot lights, radars etc. on top of aluminum radar arches with stainless steel screws without any protection! Not only did the screws become permanently installed it also bubbled up the powdercoat, effectively ruining the arch!
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Old 02-19-2008, 12:33 PM
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Ya it does. But it works.
Dry Ice (CO2) or Liquid Nitrogen if you can get your hands on it would be the best choice as they're pretty much inert, but whatever you have on hand will work as well.

MBam's on the right track here. The coefficient of thermal expansion of aluminum is about 24 and stainless is 16. That's 1.5 to 1. So even if you heat them at the same rate, the aluminum would still expand 1.5X as much as the steel part and could free them. But heating the aluminum part and cooling the steel part would work the best.
Gee Nick are you a Chemistry/Physics professor by trade? Cool explanation. Do you go boating down to AMI? I'll be down next month and will be taking the little Cig out. Maybe we can meet up for lunch at the Rod And Reel pier or something. Barry
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