Expansion damage caused by corrosion product forming in a tight joint. Rust takes up several times the volume of the steel it replaces, so pack rust building between back-to-back angles, lap plates or under bolt heads exerts enough force to bow plates, crack welds and snap rivets or bolts. Bridge inspectors and coating crews treat it as structural damage, not cosmetic, and seal joints with caulk or penetrating sealer to keep water out.
Rust jacking has the gusset bowed a quarter inch off the chord, write it up as structural, not paint.
Also heard as
- pack rust
- rust packing
Related terms
Crevice corrosion
Localized attack inside tight gaps under gaskets, deposits or lap joints where the solution stagnates.
Stripe coat
Extra coat brushed onto edges, welds, bolts and corners to build thickness where spray runs thin.
Uniform corrosion
Corrosion spread evenly over a whole surface, thinning the metal at a fairly predictable rate.