Why does gland packing blowout?
Why does gland packing blowout?
(OP)
Ok, 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??
Thanks in advance.
Rob
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??
Thanks in advance.
Rob
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RE: Why does gland packing blowout?
RE: Why does gland packing blowout?
Best Regards
Qalander(Chem)
RE: Why does gland packing blowout?
RE: Why does gland packing blowout?
Water hammer is worth thinking about. Thanks for that suggestion 786392.
JLSeagull given that this was a steam service and steam quality is good, I'm not sure explosive decompression was involved in this case - or most of the examples in my industrial experience. Might be interesting to pursue for interests sake though, so how does opening a gate valve result in explosive decompression?
Jim, I had never thought about galvanic corrosion before. The stuffing box would need to be wet though - which it would be if steam was passing through the packing... that's really interesting. However, in my OP scenario, we had a virtual total evacuation of the stuffing box - not just a bit of particulate ejection and plus the stuffing box was dry - so I don't think GC can explain the situation.
I'm thinking that long term unpressurised exposure at highish temperatures is a hellish environment for packings and they just degrade over time. Any other takes to this notion?
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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."
RE: Why does gland packing blowout?
Although I am not 100% sure about prevalent conditions in the case under discussion;but
I've come across abnormally destructive forces produced due to Water/Steam Hammer once in a while.
Only as a result of not following/sticking to gradual warming up instructions of Steam systems by the operating staff(sometimes in a hurry)
Best Regards
Qalander(Chem)
RE: Why does gland packing blowout?
Yes. Graphite will oxidize over time, and faster at higher temperatures. Gasket manufacturers won't rate graphite over 800F in air for that reason. Steam will degrade graphite too (via water gas reaction), though it's not clear if this packing saw steam pressure (don't know why it wouldn't).
RE: Why does gland packing blowout?
It's sort of like a log jam in a river breaking loose.
RE: Why does gland packing blowout?
JAC
RE: Why does gland packing blowout?
Embellishing just a bit: once the leak path/fracture line is created thru the packing, it's over. Sonic velocity flow of steam will scour out every little black speck of packing in short order. (see: Grand Canyon)
RE: Why does gland packing blowout?
At the time of the incident, we recovered what we beleived was some of the extruded stuffing material. Our gasket supplier couldn't identify the type of packing that it was, but pointed out that it was not an example of good stuffing box practice. I'll see if I can include a pic.
Basically, it appears that the box wasn't "stuffed" with concentric rings, but had a spiral packing, which goes some way to explaining why the stuffing box evactuated the way it did. Once the packing started unwinding, it was all over.
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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."
RE: Why does gland packing blowout?
this adds not only to overall learning,but clarifies
some more pertinent issues which must be looked into whenever reliability is to be ensured or 'is in question'
Best Regards
Qalander(Chem)
RE: Why does gland packing blowout?
As the valve had been closed for several years, entrapped air or line compressible gas below the packing becomes an elastic extrusion mean for the packing material. That can happen mostly with a non lubricated, hardened and adherent gland packing.
When the operator opening the pressure underneath de packing that can really break the static friction and extrude in an explosive manner.
A good valve design should have a fully open position back seat to enable the gland repacking with the valve in Service. Hope you not dealing with hazard fluid conditions.
Good Luck.
Manuel
RE: Why does gland packing blowout?
This was a gate valve on the bypass around a high pressure desuperheater station and the valve was closed. So it had pressure on both sides of the gate. If the gate was sealing properly the bonnet and stuffing box shouldn't have been pressurised.
Does that change your picture about trapped gas?
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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."