« BACK TO Subsea Systems

HPHT Seal Design Options

High Pressure, High Temperature


When using elastomers and thermoplastics in critical service applications,
there are a number of options in terms of seal configuration and material
choice that effectively seal and provide maximum product reliability. These
combinations vary based on the sealing conditions faced. Greene, Tweed
design engineers pick the best matched material characteristics for optimum
seal performance. The table below focuses on designs of multiple redundant
seal stack combinations for both uni- and bi-directional HPHT (High Pressure
High Temperature) and LPLT (Low Pressure Low Temperature) applications.



Vee stacks were introduced from a redundancy perspective but used the
same compound across the stack. Greene, Tweed introduced the composite
stack that combines different elastomers, thermoplastics and metals to cover
all service conditions. The following design geometries incorporate materials
developed specifically for downhole environment.


This design incorporates end adapters, center adapters and combinations of
steel, elastomeric, Ryton (PPS) and filled PTFE (Avalon®) Vee Rings. In this
specific example Arlon® 1000, Fluoraz® 799 and Avalon 16 are used.
The combination of elastomer, steel and thermoplastic will seal at both HPHT
and LPLT.

Bi-directional—Nonelastomeric MSE®
This design incorporates end adapters, center adapters and combinations of
thermoplastic and filled PTFE (Avalon) Vee rings. In this specific example
Arlon 1000, Fluoraz 799 and Avalon 16 are used. The combination of
elastomer and thermoplastic will seal at both HPHT and LPLT. The multiple
redundancy concept ensures reliable sealing.


MSE® with Back-up Ring MSE Stack Assemblies
Unidirectional MSE assembly on a choke valve featuring an MSE with
aproprietary Avalon® jacket with a Elgiloy double-coil spring and Arlon® 1000
back-up ring. The Avalon jacket was chosen to pass a 200 psi (1.38 Mpa)
nitrogen gas test at ambient temperaure. In addition, it also had to hold
15,000 psi (103.42 Mpa) at a higher temperature (350°F, 177°C). It has a
cam-activated Arlon 1000 back-up ring to prevent creep and extrusion of the
jacket. For static applications the cam-activated back-up ring is preferred
because it encourages the backup to close any extrusion gap.

MSE—Bi-directional with Hat Rings
Typically two separate grooves are used to handle bi-directional pressure.
Greene, Tweed looked at this and developed a single seal assembly capable
of handling pressure from both sides, reducing machining cost, simplifying
hardware design and installation. The hat ring stabilizes and supports the
stack while eliminating damage to the seal. This, in effect, is a modified end
adapter. The center adapter prevents twisting and ensures the seal stack
remains stable in the gland. This is an effective seal at 350°F (177°C) and
15,000 psi (103.42 Mpa).

MSE—Combination Stack Assembly
The next evolutionary step is the MSE stack assembly. This incorporates
primary and secondary sealing to ensure multiple redundancy. The MSE is the
primary seal, the inclusion of Vee-style seals allows the design to feature
combinations of thermoplastics capable of resisting various hostile conditions.
This seal is capable of holding 20,000 psi at 350°F (177°C) and passing ports
at shifting pressures of 1,500. Our proprietary Avalon material is a high-wear
material suited for erosive conditions.