Sealing Oilfield Valves and Down-Hole Oil Tools7008938
Sealing oilfield tools and valves is probably probably the most difficult jobs for any seal. High temperatures and pressures, corrosive chemicals, and abrasive particles get this to a nearly impossible part of most off-the-shelf seals. With careful engineering and modern materials, though, seals can be designed for this task that do the task they're asked of.
Let's first examine the oilfield environment. No longer are wells just drilled a couple of thousand feet to tap shallow oil fields. Those fields have been pretty much exploited within the last century and therefore are needs to dry out. Most are being mostly turn off because they don't produce as well as those 10,000+ feet down. When you get that far down, the temperatures are inside the 400 F (200 C) range with pressures of up to 40,000 PSI (275 MPa) Traditional rubber as well as PTFE seals have no potential for withstanding those environments.
Oil valves and tools should also withstand just about the most corrosive substances around, Hydrogen Disulfide gas. This eats through steel and stainless springs to render them useless quickly. If metal springs are used over these seals, they ought to be made of one of many nickel super-alloys, Inconel, Hastelloy or Elgilloy. These are the just that usually stays unaffected by experience of H2S without affecting their service life.
Seal jackets for that oil field environment must be made from polymer alloys to maintain their integrity underneath the high temperatures and pressures. Unfilled PTFE (Teflon) would squirt out of the gland like toothpaste from a tube if exposed 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 too.
The seal must be pliable enough to fill the micro-finish of the seal gland wall while being sturdy enough never to extrude through the clearances being sealed. It is a tall order and frequently can not be accomplished with a one-piece seal, so backup rings are often used to seal off, or at lease minimize the extrusion gap. These are definitely made from polymers having a higher modulus (stiffer) compared to seal rings, since they are not necessary to seal, only to close up the gap. Clever designs using multiple rings cammed against one another create the ideal sealing condition - an almost zero extrusion gap.
Designing seals for the severe environment of oilfield valves and down hole tools manufacturers is really a mix of proper mechanical design and of proper seal materials. Correct design could make for reliable, save equipment, even though the converse, improper design can lead to disaster.