On 2017-10-06, Christopher Tidy wrote:
Am Freitag, 6. Oktober 2017 02:00:24 UTC+2 schrieb David Billington:

Items that are hot dip galvanised have to be vented in order to prevent
dangerous pressure build-up, I've had many items dipped and it is a good
process* but the* sections need to be vented to relieve the pressure
build up.

Makes sense. Not what I guessed, though. I was guessing it was to
prevent stagnant water from building up inside the tubes and causing
corrosion.

Even if it were not galvanized, there is another reason to do
it. When I was welding up some tubing to make a support for a corner
notcher I started with a top rectangular frame with three sides milled
off each end of two of the four sides, leaving a flap which covered the
open end of the other two tubes. I drilled holes in each of the
un-flapped tubes to vent into the flapped ones, plus holes to vent into
the following upright legs. The reason for this was I expected
expansion of the air trapped in the tubes, and when welding that could
blow the fill material (Tig welding, FWIW) out of some of the joints.
Give it vents, and you won't have expanding air pushing out the melted
metal and weakening the joints.

Later tubes joining the legs part way down were also drilled on
the underside to avoid similar air induced holes.

Enjoy,
DoN.

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