The subject sounds like a noob question, but after 18 years in industry, I still haven't had a decent explanation regarding sudden and catastrophic failure of packing materials under pressure... I've seen the aftermath a few times though - thankfully never associated with an injury.

We just experienced a gland packing blowout on an 8" 600# gate valve in a 600psi steam service. The valve had been closed for several years. As the operator was opening it, the packing material extruded (in an explosive manner) out of the stuffing box, from between the gland follower and stem. The packing material appeared to be a graphite based sealing material of some kind, with a metal filament braid... hard to tell exactly since it was fairly disintegrated - suffice to say, it doesn't look like the expanded graphite flexible yarn that we would use today. They only have inconel wire strands on the outside.

I'm thinking that the older packings aren't as good as the current stuff, and that they "lose their nature" over time, due to temperature and age, especially if the gate valve is fully backseated so that there's no process pressure energising the stuffing box.

Any thoughts, comments, experiences, lessons, education to pass on??

Gate valves tend to be left in position for long periods of time.  Graphite packing can aggravate galvanic corrosion on the surface of the valve stem.  The stationary stem pits, the graphite conforms to the irregularities and sticks to the stem.  When somebody finally actuates the valve( monster cheater bars being likely tools), the packing shears and the small pieces can blow out.  Most name-brand packing is passivated with little zinc chips for the same reason that trash cans are galvanised-the zinc plates over preferentially and sacrificially to prevent corrosion of the base metal.  That only works as long as the zinc supply is not depleted.

MORE NEWS