In article <12ho4iuevokq...@corp.supernews.com>,
Pat Flannery  <flan...@daktel.com> wrote:

Vacuum welding, aka cold welding, is basically a myth.  There are *no*
documented cases of it actually occurring in orbit, except in experiments
deliberately designed to provoke it (with susceptible materials, great
care to avoid contamination, and deliberate mechanical removal of oxide
layers etc.).

A number of early problems were ascribed to cold welding, but those are
now thought to have been mostly cases of galling -- surface damage due to
metal-to-metal rubbing -- with lubrication absent, inadequate, improper,
or migrated.  A few others were simple design botches.  No spacecraft
anomalies have been attributed to cold welding since 1966, around the time
when people started having doubts about its reality.

No cold welding was found anywhere in LDEF's mechanical systems.  All
apparent cases of it were eventually shown to be galling damage during
installation, or improper removal techniques leading to galling then.
(Stainless-steel fasteners, in particular, gall very easily.)
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