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Zac Weidner
09-25-2009, 11:03 PM
We had new drain fittings welded on our fuel tanks and read in AC 43 that the tanks are supposed to be "immersed in either a 5 percent nitric or 5 percent sulfuric acid solution...then test the efficiency of the cleaning by applying some acidified 5 percent silver nitrate solution to small quantity of the rinse water used last to wash the tank..."
Is all of this really necessary? Seems like a pain but we would just like to know more about the process and how important is really is.

Also, what do you use to regulate 3.5 pounds of air for the pressure test? I have heard about using the balloon, the welder said to use a rubber glove, and something else on the forum about a garden hose with water as a regulator, but what is really the best?

Thanks any tips or advice.

JohnW
09-26-2009, 08:03 AM
Zac, Zac, Zac... AC 43.13 is titled "Acceptable Methods, Techniques and Practices". You can (and should) interpret that to mean that these are the MINIMUM things you should do when you perform these maintenance actions on an aircraft. The thought of doing "less than the minimum practices" should present to you a self-evident answer. Why do you suppose "they" took the time to write down a procedure like this??? Good welding practice ALWAYS prevents future corrosion (which leads to failure, in the long term). Good welders clean the area they work before AND after welding.

When ya run into a situation like this, where you don't fully understand WHY something is "necessary"...it behooves you to sit back, take your baseball cap off, wipe your forelocks back over your head and smile...think that "I will NEVER know EVERYTHING there is to know, and somewhere there is somebody that REALLY KNOWS about 'this stuff', and the Powers that be believe this is a MINIMUM Acceptable Practice." Why ask "why?" Do ya honestly think YOU can "write the book" on acceptable methods, techniques and practices??? Never think you are smarter than the guy that wrote the book. Take the time to research and find out if the guy was right, IF you are so inclined. But admit to yourself when your questioning indicates you really don't know "all there is to consider", and follow the advice of the person leading you by the hand. It'll make you a better person AND A MUCH SAFER AIRPLANE MECHANIC (know matter HOW MUCH you actually do know).

There are any number of ways to accomplish a tank pressure test (probably as many as the number of people "performing them"). I use a "homebuilt" manometer of my own construction because if you "go over redline" with the pressure FOR ANY REASON, it is "self relieving"...blowing the water "out the top" and venting the pressure. I have used several methods of pressurizing...hand pumps, bicycle pumps, my "tiny" O/A tanks and my jeweler's torch. I PREFER to use nitrogen (since it sucks up and disappears any water that may be in the tank AND if you find a leak, you have just commited 90% of the purge required to weld it again...). "Accomplishment" is not the problem, you can "use whut ya brung", if you get my meaning. Just provide "overpressure relief", and understand that the ugliest thing you can see is a ruptured airplane fuel tank (if you can FIND IT AGAIN after it "departs the work area"!).

So, yeah. You should follow the recommendation is AC43.13. As a minimum.

[edit] I should add..."Keep up the good work."

Steve Pierce
09-26-2009, 08:26 AM
Zac, I use a rubber glove and a pressure gauge screwed into the outlet fitting along with a spray bottle full kids bubble solution. I have used aluminum etch to clean the aluminum prior to welding when we had corrosion in the welded seam. It worked very well. I haven't ever cleaned after welding so now I am learning something already this morning. What do you use John?

redbarron55
09-26-2009, 08:47 AM
What was the method of welding? Wasflux used? If the tank was welded using TIG process and the metal was cleaned mechanically what was the flux. Argon gas is a shield and inert, leaving no residue of flux to clean.
If the fitting etc. were gas welded then there was a flux used and it must be removed since it is very corrosive to clean the joint for good joining of the metals.
Pressure testing is still a very good idea.

JohnW
09-26-2009, 10:14 AM
For pre-cleaning aluminum parts prior to GTAW welding, I use good, clean stainless steel brushes AND nice, fresh acetone within one hour of welding. After welding, I use SS wire brushing and acetone again (danger..., parts must be "cold" -cooled ALL THE WAY DOWN- after welding. Acetone has a very low flash point).

I have "recently" found a good "Commercial welder" that lays down "pretty beads" in circles around me...he uses "state of the art" commercially sold pre- and post- welding cleaning solutions (as well as the SS wire brushing) iaw all the latest tech specs. He's a "Detail Freak" and eats, sleeps and dreams "melting metal together". I believe if challenged to, he could TIG a two-by-four to a concrete floor! This guy practices "Eutectics", not "welding". Everything except 4130 thin wall tubing repairs that I am getting involved in is going to HIM from about eight months ago, forward (and some of it will be "him coming to me"). He's much more "picky" about "stuff" than even me! ...and I don't say that about just anybody. He likes gettin' airplane rides, and will pretty much "drop what he's doing" to weld an airplane fuel tank, and he charges "accordingly". My kinda guy. :D

pmanton
09-26-2009, 10:31 AM
Just provide "overpressure relief", and understand that the ugliest thing you can see is a ruptured airplane fuel tank (if you can FIND IT AGAIN after it "departs the work area"!).

Many, and I mean many years ago, I decided to pressurize a motorcycle gas tank. I added just a teeny bit too much air and splat ! I no longer had a gas tank it had turned into a steel turtle. :o

Cheers:

Paul
N1431A
2AZ1

Zac Weidner
09-26-2009, 11:51 AM
Thanks for all of the replies guys. We did find out that the welder we used used a TIG with no flux, so this cleaning process is not necessary after all. We will do the pressure test with soap and a bicycle tire pump seems like the way to go.

Hillbilly
09-26-2009, 01:49 PM
I'd like to add to Johns SS wire brush practice, I use one brush for aluminum and another for stainless, and one for steel,never interchanging. If a brush gets polluted it goes into the "use on any(grimy,rusty,nasty)thing box".

Lownslow
09-29-2009, 12:44 PM
This is good stuff guys. There is always something that we venture into that we can eventually feel confident in doing if we have the forum to ask the silly question of someone that will share their vast knowledge and experience. I once knew a lot about a few things, but I've since forgot half it and can't remember the rest.

Lou S.

Steve Pierce
09-29-2009, 02:46 PM
Now it is all here for eternity and we can refer back to it. Sometimes I can't remember stuff that I posted here and have to look it up so I can use it. :lol: :shock: