Sealing Oilfield Valves and Down-Hole Oil Tools5994219
Sealing oilfield tools and valves could very well be one of the most difficult jobs for any seal. High temperatures and pressures, corrosive chemicals, and abrasive particles make this a virtually impossible job for most off-the-shelf seals. With careful engineering and modern materials, though, seals can be built for it might be that do the job they're asked of.
Let's first check out the oilfield environment. No longer are wells just drilled several thousand feet to tap shallow oil fields. Those fields have already been just about exploited over the past century and so are starting to dry up. The majority are being mostly shut down as they do not produce as well as those 10,000+ feet down. When you are getting that far down, usually the temperatures are within the 400 F (200 C) range with pressures as high as 40,000 PSI (275 MPa) Traditional rubber or perhaps PTFE seals have no potential for withstanding those environments.
Oil valves and tools should also withstand just about the most corrosive substances available, Hydrogen Disulfide gas. This eats through steel and stainless springs to render them useless quickly. If metal springs are utilized during these seals, they ought to be made of one of the nickel super-alloys, Inconel, Hastelloy or Elgilloy. These are the basic only that usually stay unaffected by experience of H2S without affecting their service life.
Seal jackets for that oil field environment has to be manufactured from polymer alloys to keep their integrity beneath the high temperatures and pressures. Unfilled PTFE (Teflon) would squirt out from the gland like toothpaste from a tube if subjected to these pressures. Mixtures of inert fillers like chopped glass or carbon fibers, minerals and graphite are needed along with combinations of polymers, like PFTE (Teflon) and PPS (Ryton.) Other polymers have proven themselves useful also.
The seal should be pliable enough to fill the micro-finish from the seal gland wall while being sturdy enough not to extrude through the clearances being sealed. This is a tall order and often cannot be accomplished with a one-piece seal, so backup rings can be used to close up, or at lease minimize the extrusion gap. These are typically manufactured from polymers with a higher modulus (stiffer) compared to the seal rings, since they are not essential to seal, simply to close off the visible difference. Clever designs using multiple rings cammed against each other make the ideal sealing condition - an almost zero extrusion gap.
Designing seals for that severe environment of oilfield valves and down hole tools manufacturers is really a combination of proper mechanical design as well as proper seal materials. Correct design could make for reliable, save equipment, while the converse, improper design can lead to disaster.