Hairline fractures on rivets

AX-O · #1 10-18-2006, 05:53 PM

I asked the question "when is a rivet too old" on this forum not long ago. A few people said that rivets from 2004 were not too old to use. So I used them. Here is my kitlog entry discussing what happened.

I started the day very anxious due to all those platenuts that needed to be installed on the main spar. The day started slow and I was in good spirit. First thing was to spot prime all the countersunk holes. After that I riveted all the platenuts for the #6 and #8 screw holes on the left wing. I used the left over rivets from my tail kit because they were newer and they looked to be in better shape than the ones that showed up with the wing kit. I used the same rivets on the left wing as well until I ran out. Once I ran out of the newer rivets, I started using the older ones (look at the picture below, the gold rivet are newer than the silver looking ones). Why am I making such a big deal about the rivets you ask? Well I bought the wing kit from a guy that no longer wanted it. The kit was delivered to him late 2004. He just inventoried the wing kit. No work was started. After I finished riveting all the platenuts on the right wing, I checked the work. I saw that over HALF of the rivets that I installed (old ones) had hairline fractures. I almost cried. I knew how much work was ahead of me. I had to drill out every one of those rivets. All the old rivets that I had were discarded and I ordered over $100 worth of new rivets. Not so happy but rivets hold the airplane together. Kind of need good rivets. After I went inside, ate a peanut butter and jelly sandwich (my girlfriend made it because she saw had mad I was) and calmed down, I fabricated W-731 and riveted the K1000-4 platenuts to the spar (with rivets from the tail kit). Do yourself a favor, don't use old rivets.

az_gila · #2 10-18-2006, 06:45 PM

AX-O (huh?)

Can you please describe the nature of the cracks and how the rivets were installed?

I've been using 10+ year old rivets with no problems .... and yes, I do inspect them carefully.

Could it be somewhat related to your installation technique?
Could you describe some of the cracked ones as over-driven?
Did you use multiple hits (a long rivet gun burst) to install?
Did any squeezed ones crack?

Any others care to comment?

gil in Tucson

Mel · #3 10-18-2006, 06:53 PM

I'm afraid I have to agree with Gil. You may have gotten a bad "batch" of rivets. I have used rivets over 15 years old and never had a problem. And, yes, as an A&P, I do inspect them thoroughly.

az_gila · #4 10-18-2006, 07:05 PM

Out of interest, I just checked the generic spec. for rivets...

NASM5764
RIVETS, STRUCTURAL, ALUMINUM ALLOY, TITANIUM COLUMBIUM ALLOY, GENERAL SPECIFICATION FOR

No mention of storage or age requirements for the "AD" rivets we use.

As Mel said, I think you got a bad batch.....

gil in Tucson

Bob Axsom · #5 10-18-2006, 07:10 PM

I would purge the "old" stock because they are bad not because they are old. It happens even in shipments of parts from approved suppliers with material certs. The application also can cause problems and the center portion of platenuts especially dimpled ones and floating ones require more care than regular structural riveting.

Bob Axsom

AX-O · #6 10-18-2006, 07:24 PM

Quote:

Originally Posted by az_gila

Could it be somewhat related to your installation technique?
I don't think so. I used the same technique with all the rivets (old and new). I only saw the fractures on the old ones. I have been doing the same thing over and over with all the rivets.

Could you describe some of the cracked ones as over-driven?
All the rivets were squeeze with a pneumatic rivet squeezer and checked with the rivet gauge.

Did you use multiple hits (a long rivet gun burst) to install?
Only one squeeze

Did any squeezed ones crack?
All the old ones

May be, it was just a bad batch.

AX-O · #7 10-18-2006, 07:29 PM

Another question, why do rivets show up with a date on the bag if the date is not important?

jcoloccia · #8 10-18-2006, 08:02 PM

Probably so you can track them. I'd send an e-mail to Vans about it. If it really is a bad batch, they might send out a notice to prevent people from using rivets from the same batch.

szicree · #9 10-18-2006, 08:15 PM

Rivets have a date on em? I've bought rivets from spruce plenty of times, and they just stick em in a little bag. I've never noticed any dating.

Bob Axsom · #10 10-18-2006, 08:23 PM

All you can say about a dated bag of rivets is they were all made before the date on the bag (assuming the date is not in error, a computer printed "1936" for example). There is absolutely nothing to preclude suppliers that are not the manufacturers from mixing many maufacturers parts from many production runs and non standard parts. They are treated as bulk stock by suppliers and they buy where they can get the best deal.

This kind of thing is a problem for aircraft manufacturers. In the early days of the F-15 we were having control knobs in the ICNIC (Intrgrated Communication/Navigation/Identification Control) panels breaking in the field. The specs were good and there was no good reason for the failures. A chemical analysis revealed that the supplier was substituting a cheap look-a-like material that did not have the physical properties of the specified material that were necessary for the application. We turned it over to the authorities for processing but RV builders are on their own.

Material and process control are very expensive they are applied with a certain amount of record keeping and trust in the aircraft world and they are carried to the extreme in the space flight hardware applications. In the RV world I am impressed with the quality and consistency of hardware we receive with no controls at all.

There are exceptions like the fact the if you order O-rings for the puck on Cleveland brakes from Aircraft Spruce they will substitute a different part with the same dash number that has different physical dimensions and will leak. I have talked to Aircraft Spruce about this and tech support engineers at Cleveland. They are both strong in their opposing positions Aircraft Spruce is convinced that it is a good substitute and Cleveland says it is absolutely not authorized and has never been tested. I have tested it in the field and the substitute parts leak! Meanwhile, Van's sells the correct O-ring.

"Let the buyer beware" is what we live by but we have no systematic control over what we are supplied. As I said at the beginning the date on the bag is no more than a date on a bag. The next later dated bag may have much older rivets in it.

Bob Axsom