wet install rivets ? 2

[rb1957]

i've read that epoxy primer is preferred to sealant when wet installing rivets.

anyone (Will ?) have the back story ? i suspect it's something like the epoxy is better at repealing/resisting water ingress, and so better at resisting corrosion. i suspect there are reports of rivets installed with sealant being corrosion sites ?

it'd be nice to see the progession from dry rivets to sealant installed to epoxy installed.

another day in paradise, or is paradise one day closer ?

 

[berkshire]

rb1957.

I have lifted this quote right out of will Taylor's reply to the comment about driving DD rivets it also applies here: "Reason: sealant must be squeezed-out from under the heads and along the shank BEFORE bucking to prevent 'hydraulic-lock' action of the thick sealant from interfering with the mechanical settling/swelling of the rivet for a high mechanical tight fit. This usually requires the head of the rivet to be held tightly in-place for a few seconds before actual bucking begins [etc]. Also, sealant [which was intended to improve sealing and exclude moisture or pressure/fluid [fuel, etc] leakage] really gums-up everything it touches [what a mess]; and a tight rivet install [W/WO epoxy primer] tends to be a remarkably leak-proof joint."
I can also relate to pushing hard on rivets to bed them before driving , and being covered with " Purple passion" at the end of the day.
Also when driving AD rivets it was common practice when using sealant to come back and re-hit the rivets a few minutes later to ensure they were bedded. Wet epoxy being much thinner eliminates a lot of that.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

Thanks Berkshire!

Have I ever discussed in any detail, the evolution of fastened joint corrosion protection and sealing for fluid/pressurization?

The last 70-years evolution [from WWII] of structural design, manufacturing/assembly practices, structural materials [metallic/non-metallic], fasteners, finishes, sealants, adhesives, DADTA, EPA/OSHA rules and cost-controls have-taken/are-taking the industry down many/tortured pathways.

Dang this sounds like something for a writer's guild article/article-series.

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"

 

[tbuelna]

My own experience with wet installation of aircraft hardware is more related to components permanently installed in mechanical systems (threaded inserts, studs, pins, bushings, etc) rather than airframe rivets. The purpose here is to prevent moisture intrusion at the interface between between dissimilar metals and inhibit galvanic corrosion. As I recall one common sealant used were single-part alkyd base primers such as TT-P-645 or TT-P-1757. Single-part primers were used for wet installation of the components noted because they do not require mixing, cure very slowly, and are easy to clean up. This is an important consideration when the installation process for the components can be lengthy.

Here is an interesting NASA process spec covering wet installation of fasteners. However, the spec lists two-part Super Koropon primer as the preferred sealant for most applications. While Super Koropon primer is very high-performance, it is also incredibly expensive.

 

[rb1957]

imagine "incredibly expensive" and "NASA" in the same sentence ... sales rep "oh, you want the NASA spec ?"

pressurised fuselages wet install for the same reason (inhibit corrosion).

i've learned (yes, even old dogs ...) that instead of dipping the rivets in sealant we rely on the fay surface sealent that oozes out on final install of the dblr ... dblr is first cleco'd on, rivets piloted, rivet holes opened up, dblr removed for deburr, fay sealed, dlbr reinstalled with clecos, rivets installed. Not exactly our engineering spec but that's how we've done it for a looong time and it seems the corrosion is kept at bay. Now that we've asked and been told, the cat's out of the bag and we're looking for someone to flog !? (not me i hope) ... we'll probably just write up the procedure as an acceptable alternative ... sigh

another day in paradise, or is paradise one day closer ?

 

[tbuelna]

I hear what your sayin' about NASA hardware and costs rb1957. But you should also consider the cost of many materials/processes used on modern production commercial aircraft. In comparison to paying $40/lb for carbon tape or $50/lb for titanium alloys, paying $400/gal for Super Koropon primer does not seem quite so outrageous.

 

[rb1957]

that's why we use good ole 2024 !

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

USAF perspective.

Install rivets wet with MIL-PRF-23377 ty I Class C1, C2 or N [solvent borne epoxy primer].

WARNING.
NEVER install rivets with MIL-PRF-85582 [water-borne epoxy primer]: water trapped in a joint is generally “bad” for every imaginable reason. HOWEVER, IF allowed to dry before installation assy, then this primer is generally OK... but then this defeats purpose for "wet installation", where flowing epoxy primer fills microscopic holes/gaps for that specific fastener installation..

NOTE.
Over the years I have also specified that screws/bolts be installed into nutplates, thread inserts, etc "wet" with MIL-PRF-23377 part "A" [Part A = uncatalyzed base, part "B" ~=catalyst]. This provides corrosion protection to the holes/threads; yet does not cure, thereby easing disassembly. Reason: Cured epoxy primer can act like an adhesive, similar to anaerobic thread locking compound... whereas uncured primer generally has no shear or bond strength.


Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant û "Orion"