Pietenpol-List: Galvanic Corrosion

[matronics]

Original Posted By:=0A=0A=0A=0A=0Aowner-pietenpol-list-server(at)matronics.com=0A[mailto:own
=0A=0A=0A =0A =0A=0A =0A=0A =0A=0A =0A=0A=0A=0A=0A=0A=0A=0A=0A=0AAll right, Dan.=C2- Now you=99ve=0Adone it and inspired my Geekiness to come to the surface.=C2- Let=99s=0Atalk a bit about Galvanic Corrosion.=C2- This occurs when you have dissimilar=0Ametals in intimate contact in an environment where they can get wet, such as at=0Athe ends of lift struts.=C2- Not all dissimilar metals cause problems =93=0Ait depends on how =9CAnodic=9D they are.=C2- There is a chart listing=0Athe Anodic Index of all common metals.=C2- To find the susceptibility to=0Acorrosion of any metal pair, find the difference in their anodic indices =93=0Athe corrosion will take place at the more anodic of the pair (this is why on=0Aoutboard motors that may be run in saltwater you will find =9Csacrificial=0Aanodes=9D of magnesium or zinc on the aluminum casings of the motor, so the=0Acorrosion takes place there rather than on the aluminum. =0A=0A =C2- =0A=0AThe rule of thumb to be safe from galvanic=0Acorrosion is to have a difference in anodic index of no more than about 0.15 - 0.20=0Afor an outdoor environment.=C2- Here is the chart: =0A=0A =C2- =0A=0AMetal Category=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- Anodic=0AIndex (volts) =0A=0A =C2- =0A=0AGold, solid and plated=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.00 =0A=0ARhodium plated on Silver-plated Copper=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.05 =0A=0ASilver, high Nickel-Copper alloys=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- =C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.15 =0A=0ANickel, Titanium, Monel=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.30 =0A=0ACopper, Silver Solder, high Copper-Nickel=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.35 =0A=0Aalloys, Nickel-Chromium alloys =0A=0ABrasses & Bronzes=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.40 =0A=0A18% Chromium Stainless Steel=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.50 =0A=0AChromium plating, Tin plating=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.60 =0A=0ATin-Lead solder=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.65 =0A=0ALead=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.70 =0A=0AAluminum, wrought, 2000 series=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.75 =0A=0AIron, plain carbon or low-alloy steel=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.85 =0A=0AAluminum, wrought alloys other than 2000=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.90 =0A=0Aseries (such as 7075) =0A=0ACast Aluminum alloys, Cadmium plating=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 0.95 =0A=0Aand Chromates =0A=0AHot-dip Zinc, galvanized steel=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 1.20 =0A=0AZinc=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 1.25 =0A=0AMagnesium=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 1.75 =0A=0ABeryllium=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- 1.85 =0A=0A =C2- =0A=0AOne of the important things to notice is=0Athat cad-plated steel (such as AN aircraft hardware) is not too bad when placed=0Aagainst 2024 series aluminum, and is even better against 7075 series.=C2-=0AWhat is surprising to most people is how bad stainless steel is against=0Aaluminum (difference of .40 to .50). =0A=0A =C2- =0A=0AHope this helps.=C2- By the way, I=0Achanged the subject to hopefully make this chart easier to locate in the=0Aarchives =0A=0A =C2- =0A=0AJack Phillips =0A=0ANX899JP =0A=0ASmith Mountain Lake, Virginia =0A=0A =C2- =0A=0A=0A=0A=0A=0A

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com
All right, Dan. Now you've done it and inspired my Geekiness to come to thesurface. Let's talk a bit about Galvanic Corrosion. This occurs when youhave dissimilar metals in intimate contact in an environment where they canget wet, such as at the ends of lift struts. Not all dissimilar metalscause problems - it depends on how "Anodic" they are. There is a chartlisting the Anodic Index of all common metals. To find the susceptibilityto corrosion of any metal pair, find the difference in their anodic indices- the corrosion will take place at the more anodic of the pair (this is whyon outboard motors that may be run in saltwater you will find "sacrificialanodes" of magnesium or zinc on the aluminum casings of the motor, so thecorrosion takes place there rather than on the aluminum.The rule of thumb to be safe from galvanic corrosion is to have a differencein anodic index of no more than about 0.15 - 0.20 for an outdoorenvironment. Here is the chart:Metal Category Anodic Index(volts)Gold, solid and plated 0.00Rhodium plated on Silver-plated Copper 0.05Silver, high Nickel-Copper alloys 0.15Nickel, Titanium, Monel 0.30Copper, Silver Solder, high Copper-Nickel 0.35alloys, Nickel-Chromium alloysBrasses & Bronzes 0.4018% Chromium Stainless Steel 0.50Chromium plating, Tin plating 0.60Tin-Lead solder 0.65Lead 0.70Aluminum, wrought, 2000 series 0.75Iron, plain carbon or low-alloy steel 0.85Aluminum, wrought alloys other than 2000 0.90series (such as 7075)Cast Aluminum alloys, Cadmium plating 0.95and ChromatesHot-dip Zinc, galvanized steel 1.20Zinc 1.25Magnesium 1.75Beryllium 1.85One of the important things to notice is that cad-plated steel (such as ANaircraft hardware) is not too bad when placed against 2024 series aluminum,and is even better against 7075 series. What is surprising to most peopleis how bad stainless steel is against aluminum (difference of .40 to .50).Hope this helps. By the way, I changed the subject to hopefully make thischart easier to locate in the archivesJack PhillipsNX899JPSmith Mountain Lake, Virginia _____

[matronics]

Original Posted By: pietflyr(at)bellsouth.net
Now that's what we were looking for. However=2C I will say that we put all stainless bolts on our float fittings (non structural) and had zero corrosion after 10yrs. Go figure.Doug DeverIn beautiful Stow Ohio

[matronics]

Original Posted By: "Jack Phillips"
Does anyone have experience with this galvanic corrosion preventative product onaircraft, or have a thought as to why it would or would not be a good productfor aircraft? A friend says it is very well thought of in the boating industry,where electrolysis is a much bigger problem. Wondering if it would work ondissimilar aircraft metals, except where lubrication is not recommended, suchas locking nuts etc.Stevehttp://www.tefgel.com/contain.php?param=tefgel ... et.comRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Don't know anything about it. In general, I don't think galvanic corrosionis a huge problem on aircraft as long as you are careful with disimilarmetals as much as possible. Maybe if your plane stayed outdoors near abeach where the salt in the air could cause corrosion it would be a problem.I know when I lived on the gulf coast of Texas, everything in my shop wouldrust if I didn't keep oil on it.When I was working at General Dynamics on the F-16 program, corrosion was ahuge concern. There, the standard practice was to dip every rivet in wetepoxy primer before driving it, and every part was painted with epoxyprimer. Of course, that was in 1975 and those airplanes are still flying 37years later so maybe the concern was justified.Jack PhillipsNX899JPSmith Mountain Lake, Virginia-----Original Message-----

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com [mailto:owner-pietenpol-lis
All right=2C Dan. Now you=92ve done it and inspired my Geekiness to come to the surface. Let=92s talk a bit about Galvanic Corrosion. This occurs when you have dissimilar metals in intimate contact in an environment where they can get wet=2C such as at the ends of lift struts. Not all dissimilar metals cause problems ' it depends on how =93Anodic=94 they are. There is a chart listing the Anodic Index of all common metals. To find the susceptibility to corrosion of any metal pair=2C find the difference in their anodic indices ' the corrosion will take place at the more anodic of the pair (this is why on outboard motors that may be run in saltwater you will find =93sacrificial anodes=94 of magnesium or zinc on the aluminum casings of the motor=2C so the corrosion takes place there rather than on the aluminum.The rule of thumb to be safe from galvanic corrosion is to have a difference in anodic index of no more than about 0.15 - 0.20 for an outdoor environment. Here is the chart:Metal Category Anodic Index (volts)Gold=2C solid and plated 0.00Rhodium plated on Silver-plated Copper 0.05Silver=2C high Nickel-Copper alloys 0.15Nickel=2C Titanium=2C Monel 0.30Copper=2C Silver Solder=2C high Copper-Nickel 0.35alloys=2C Nickel-Chromium alloysBrasses & Bronzes 0.4018% Chromium Stainless Steel 0.50Chromium plating=2C Tin plating 0.60Tin-Lead solder 0.65Lead 0.70Aluminum=2C wrought=2C 2000 series 0.75Iron=2C plain carbon or low-alloy steel 0.85Aluminum=2C wrought alloys other than 2000 0.90series (such as 7075)Cast Aluminum alloys=2C Cadmium plating 0.95and ChromatesHot-dip Zinc=2C galvanized steel 1.20Zinc 1.25Magnesium 1.75Beryllium 1.85One of the important things to notice is that cad-plated steel (such as AN aircraft hardware) is not too bad when placed against 2024 series aluminum=2C and is even better against 7075 series. What is surprising to most people is how bad stainless steel is against aluminum (difference of .40 to .50).Hope this helps. By the way=2C I changed the subject to hopefully make this chart easier to locate in the archivesJack PhillipsNX899JPSmith Mountain Lake=2C Virginia