3.3) PLASTIC INJECTION:

This kind of seal systems are widely used in secondary seals pack-off devices and they work thanks to the injection of a plastic compound ( Teflon plus plastificants materials) inside a plastic injection port in the bottom flange of a casing spool, or tubing head, and in some designs is also used as primarily seal in tubing bonnets; when plastic being injected reaches the seal element, which can be a rubber strip, chevron packing stacks, the objective is to push the elastomer to the surface to seal by an appropriate hydraulic and portable gun machine, and the seal is ready to be tested at the working pressure of the flange where is installed. This operation is accomplished by the service man's company on field, locations, by using a portable pressure gun like an: "Enerpack style" or some of other approved manufacturers devices.Notice that when seal is energized it has to be tested (on field generally) and the same portable pressure machine has to be used for that purpose, the test of the seal is at working pressure of the flange where it is installed .

POINT OF ADVICE . WARNING !!!!!!!!!

TESTS UNDER PRESSURE REQUIRE EXPERIMENTED AND TRAINED CREW, SO TAKE A MOMENT TO THINK ABOUT THE TESTING COMPANY'S PROCEDURE, AND PLAN CAREFULLY YOUR ACTIONS. ALWAYS CHECK YOUR EQUIPMENT, AS WELL AS SITE WORKING CONDITIONS.

Next drawing one of my many standards , developed by me ,and where in a generic way you can appreciate what is all about.

plasticstdcolor.jpg (30474 bytes)

 

Take a look at what is the 1/2" L.P. injection port , and observe that there is also, an opposite one 180 deg. apart, the reason is create a full circulation of the plastic injected material, where by displacing air out to the groove ,the seal can work much better, and have the control of the pressure. Note the elastomeric seal element in not shown in this explanation.Ahead a pack-off secondary seal plastic injected where in the current view the assembly and its parts are shown.

plasticenergizedHPcolor.jpg (25948 bytes)

Next drawing a magnification of the groove area:

plastenerggroovedetcolor.jpg (26164 bytes)

 

 

One more time please consider this are not manufacture drawings but only informative ones.Plastic injected seals are reliable, and has an advantage in comparison with the O-Ring style seals , that is: they can be reenergize, by filling extra plastic material, so if they lost the seal, that can be solved reenergising them, by adding extra material into the plastic injection port. The pressure that this kind of seals need to work generally is low, and a low torsion by hand with an Allen screw system in some of self-energized designs, is enough, others may need up to 1,200 psi but it will depend on the flange working pressure.

Next drawing a simulation on what is a plastic energized seal.

plasticassycolor.jpg (27202 bytes)

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