Owing to the need for more reliable and safer subsea valves or isolating systems, the development of the W K or easily maintainable ball valve was begun. By studying the state of the art for valves and by looking into the complicated systems that are used for isolating a subsea pipeline (Fig. 1) it was felt that a new approach should be considered.
Usually six valves are built into the system for shutting off a subsea line A double system consisting of a main valve with actuator and two isolating valves must be installed to protect the line against flooding during maintenance and repair of the valve. A similar bypass system is installed to prevent loss of production during repair and maintenance.
Six valves are installed at the same time, at the same date The disadvantage of this is that the deterioration of the valves due to the media/product and the environment will occur over the same period for all the valves. Any damage to (Fig. 1 is available in full paper)the valves from these causes will therefore occur at the same elapsed time for all the valves.
Based on experience, demands and the hope of development the following basic specifications for a future valve were established.
The valve must have a longer operational life than current valves.
Internal leakage in service is to be avoided or minimized.
It must be able to stand alone in a subsea pipeline without cover and allow repair and maintenace without flooding of the line.
The valve is to be maintained and repaired easily without reducing or stopping production.
The subsea version of the valve must allow:
retraction of actuator to surface,
change of seals,
grinding of seats for seals under the same;
conditions as in (3) but all operations to be done diverless
No valves presently on the market satisfy these requirements. The main problem areas are main seal and sealing system, stem, with sealing system, actuator. The most frequent problems are associated with the seat and jamming of the ball. The same jam occurs for the stem and its seal system. The consequence is a blocked valve.
The W K is a hydraulically operated top entry ball valve, primarily intended as a shut-off valve in subsea oil and gas pipelines. However, the area of application also includes process systems in offshore as well as land-based installations. The main components are (see Fig. 2):
valve body,
bonnet with clamps and locking ring,
upper ball unit with main seals;
lower ball unit;
sleeves;
actuator,
hydraulic channels.
The valve is shown in open/operating position and the sleeves in the forward position. It is seen that all media pass through the valve flow in a ‘pipeline’ through body and sleeves. This constellation of sleeves protects the main seal and seats from the media flowing through the valve.
If the valve is mounted in a process or subsea pipeline and seldom used, the cavity may be filled with a protecting oil to ensure good performance for the seal and seat.
