Sealing Oilfield Valves and Down-Hole Oil Tools4196049
Sealing oilfield tools and valves is probably just about the most difficult jobs for almost any seal. High temperatures and pressures, corrosive chemicals, and abrasive particles make this a nearly impossible part of most off-the-shelf seals. With careful engineering and modern materials, though, seals could be developed for this which 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 pretty much exploited over the past century and are beginning to dry up. Many are being mostly shut down because they don't produce in addition to those 10,000+ feet down. When you are getting that far down, usually the climate is in the 400 F (200 C) range with pressures as high as 40,000 PSI (275 MPa) Traditional rubber or even PTFE seals don't have any potential for withstanding those environments.
Oil valves and tools should also withstand probably the most corrosive substances available, Hydrogen Disulfide gas. This eats through steel and stainless-steel springs to render them useless in short order. If metal springs are used in these seals, they ought to be made from one of the nickel super-alloys, Inconel, Hastelloy or Elgilloy. These are the basic only that usually stays unaffected by exposure to H2S without having affected their service life.
Seal jackets for your oil field environment should be made of polymer alloys to keep up their integrity beneath the high temperatures and pressures. Unfilled PTFE (Teflon) would squirt from the gland like toothpaste from the tube if exposed to these pressures. Combinations of inert fillers like chopped glass or carbon fibers, minerals and graphite are essential along with mixtures of polymers, like PFTE (Teflon) and PPS (Ryton.) Other polymers have proven themselves useful also.
The seal must be pliable enough to fill the micro-finish of the seal gland wall while being sturdy enough to not extrude through the clearances being sealed. This is a tall order and often cannot be accomplished having a one-piece seal, so backup rings are often used to close off, or at lease minimize the extrusion gap. These are definitely manufactured from polymers with a higher modulus (stiffer) compared to the seal rings, because they are not essential to seal, only to close off the gap. Clever designs using multiple rings cammed against the other person make the ideal sealing condition - an almost zero extrusion gap.
Designing seals for your severe environment of oilfield valves and down hole tools manufacturers is really a combination of proper mechanical design and of proper seal materials. Correct design can make for reliable, save equipment, as the converse, improper design can lead to disaster.