The Vector Duoseal™ is an API qualified metal-to-metal seal that prevents both internal and external leakage of fluids and gases. The joints may be Optima® subsea connectors, special or compact flanges, Techlok® clamp connectors, valve bonnets or any other joint where two seals are preferred.
The bore seal capability has been PR2 qualified to 20,000 PSI. The hyperbaric seal acts to give a level of backup bore seal capability. The unique design of Vector Duoseal™ has independent internal and external seals with the capacity to carry out a reverse integrity (RIT) test on the seals.
The retention fingers on the Vector Duoseal™ are designed to locate in a special groove on the inside profile of the male Optima® hub. The profile of the fingers and the special groove give a positive location for the Vector Duoseal™ to prevent accidental release due to impact or shock loads, whilst allowing the Seal Removal Tool to be inserted and reliably remove the sealring when required. The number of fingers depends on the size of the sealring
Once the joint is pressurized, the Vector Duoseal™ becomes pressure energized. This of course could be due to either internal or external pressure. The pressure creates a seating force which further energizes either or both the inner and outer seals. In simple terms the radial sealing force for the inner and outer seals is as follows :
Therefore the greater the pressure the more sealing force exists. There is of course a maximum internal/external pressure that both the Duoseal™ and the joint can withstand; however this is much greater than normal operating pressures.
With the pressure differential between the internal and external values, the central rib will have a tendency to move towards the low pressure side. Finite Element Analysis and testing has shown that within the working limits of the Vector Duoseal™ the resulting deformations will not de-seat the outer pressure seal.
The void between the inner and outer seals is ideal for carrying out a Reverse Integrity Test (RIT). This test will prove that the joint has been correctly assembled and that the seals are intact. The selected pressure for the RIT test is independent of either internal or external pressures and purely tests the seals pressure integrity in-situ. The RIT pressure is attempting to lift the sealring off the seat. If the force on the sealring lips is “Frit” in simple terms the following is true:
Internal sealing force = Fm - Frit
External sealing force = Fm - Frit
This means as the RIT pressure increases it will get closer to the make-up force. At the point where Fm=Frit the seal would no longer be in contact with the seat. The test is therefore set to be conservative in nature.
The Vector Duoseal™ is proven in sizes from 2” to 36” in water depths up to 13,125ft (4,000m) at temperatures ranging from Duoseal™ cross section drawing A Section A-A INNER LIP SEAL OUTER LIP SEAL -50°C to 150°C, and at pressures up to 20,000psi, making it suitable for most known subsea applications, and as an alternative to RIT rings for Topside joint integrity.
The Vector Duoseal™ is shown as being separate from both joint faces. It is most likely that the sealring would be sitting or located in one of the seat pockets.
The Vector Duoseal™ can be manufactured from various materials, however most Duoseal™ sealrings installed subsea are made from Alloy 725 or similar. These materials are selected to utilize the higher strength and flexibility of the material. The seal face is inlaid with Alloy 625. Standard gaskets (such as API 6A BX gaskets) are crushed into place when the connection is made, requiring the seal faces to be harder than the sealrings. The Duoseal™ does not operate in this fashion. It is energized predominantly in the elastic range of the material, so there is no need to have the seal face harder than the sealring.
Duoseal - General FlyerEnglish V003-01-2014 available DOWNLOAD