Typically, that the fastener is installed with a sealer and/or adhesive either in the hole or on the adjacent mating surfaces. Sealers/coatings are used to reduce corrosion, esp. when there is a possibility of galvanic corrosion between the fastener and substrate. Adhesives are used for thread locking and/or for improving the overall joint strength.
or primer in airplanes, particularly for the rivets in the fuel tanks and the pressurised cabin ... to make a fluid tight seal, to keep water out, to minimise corrosion
On several aircaft I have repaired over the years the structural repair manual (SRM) called out for the rivets to be dipped in epoxy primmer and installed (wet). Other manuals call out installing fuel cell rivets dipped in 8802 sealant. And on other repairs an engineering change order (ECO) would call out either using primer or sealant depending on the location.
Wet = liquid coated. As noted above, either the fastener or hole is physically coated with primer paint or other sealer before the assembly.
For sealing, especially important if dissimilar metals or metal + composite is involved.
For more information, see MIL-STD-7179, FINISHES, COATINGS, AND SEALANTS, FOR THE PROTECTION OF AEROSPACE WEAPONS SYSTEMS.
Also, MIL-STD-889 Dissimilar Metals.
These, and all the Federal & MIL documents referenced within, can be downloaded from ASSIST. Just enter the bare number without the prefixes or any suffixes, in the Document Number box. This will also give the QPL (Qualified Products List when finding materials specifications. E.g., 23377 gives both the specification MIL-PRF-23377J(1) PRIMER COATINGS: EPOXY, HIGH-SOLIDS & QPL-23377-19.
Hi All,
As a DER if I ever have to replace a standard solid AD rivet with a CherryMax I always insist on "wet" installation with a two-part structural epoxy ie Hysol/Loctite EA 9309 or equiv. Even more important is that the components are squeeky clean or the epoxy is just along for the ride.
The epoxy does two things, helps protect from dissimilar metal problems but more importantly since these mechanically pulled rivets do not expand in their diameter like the AD does, it locks them in place and you have less "smoking" rivets later and they do not spin if and when the next guy has to remove them.
JQC
