The ball valve should be located on the riser foot and it should be operable with hydraulic actuators.
The design of the ball valve should be in accordance with API SPEC 6D.
Body and Pressure Seal
The body and the pressure seal should be designed for a fatigue life of 30 years, taking into account the following:
- External loading resulting from axial tension
- Base shear force and bending moment
The body construction of the ball valve should meet the following requirements:
- The valve should be of top entry construction.
- The valve should be of full bore and suitable for pigging.
- The ball should be trunnion mounted; seating should be capable of blocking and bleeding.
- The stem seals should be designed to withstand the ingress of seawater, assuming atmospheric pressure in the body of the valve.
- Both the stem and the body seals should be capable of being sealed by a secondary sealant injection system.
- The different parts of the valve should be subjected to inspection and non-destructive testing using ultrasonics, radiography, magnetic particle inspection, and liquid penetration inspection, as appropriate.
- Remedial action, consistent with industry practice, should be taken for any defects located in the valve.
- The valve actuator should be single-acting with spring return, which makes the ball valve fail-safe open. The return spring should be capable of opening the valve at maximum line pressure.
- The break torque of the actuator should exceed the torque required by the valve by 25 percent when operating against a differential pressure of 290 psi (2000 kPa).
- A valve position indicator should be incorporated into the design. A mechanical indicator, showing open or closed positions, should be clearly visible to a diver.