API 6D Two - Piece
Cast Trunnion
Mounted Ball Valve
Atlas Series
Document Number:
Revision:
Release Date:
EDC 506
0
01/03/2018
IOM: Installation, Operation and Maintenance Manual
9/17
4.4 BODY CAVITY RELIEVING SYSTEM
Trunnion mounted ball valves do have a body cavity where pressure can be trapped in a closed volume.
Under this circumstance, any increase of the contained fluid temperature or any degradation of the
contained fluid can result in an uncontrolled pressure increase of the trapped fluid potentially above the
design pressures of the valve.
To avoid the above scenario, all of the C&C trunnion mounted ball valves are provided with one of the
following body cavity relieving systems (depending on the design of the seats):
Self-Relieving Seats:
The design of a self-relieving seat is such that when the pressure in the body cavity exceeds the
rated pressure of the valve, not to exceed 1.33 times the maximum operating pressure (MOP) then
the seat will automatically disconnect from the ball and allow pressure equalization between the
body cavity and the pipeline.
When one or both of the seats are of the Self Relieving type, there is
no need for any other type of body cavity relieving systems.
Pressure Relief Valve:
When both of the seats are not of the self-relieving type (i.e. both of the seats are of the Double
Piston Effect Type), the body cavity must be protected from overpressure by means of a Pressure
Relieving Valve (PRV) set to relieve excess pressure.
The standard PRV connected to the body cavity has been pre-set and tested in the factory to
relieve at approximately of 1.33 times the maximum operating pressure (MOP) of the valve.
It is a mandatory requirement to keep body cavity pressure relieving system functioning correctly. Failure of
the body cavity pressure relieving system can lead to failure of the valve pressure containment capability
with consequent injures to personnel, damage to the environment and loss of production.
5 MAINTENANCE
Maintenance personnel performing this operation shall be fully trained to handle pressure-containing
equipment. Opening pressure containing equipment without having released all of the internal pressure
and having safely isolated the pipeline where the valve is assembled can lead to serious injury or even
death of the personnel involved. DO NOT PROCEED IF IN DOUBT. ALWAYS DOUBLE CHECK.
Some pipelines may contain fluids that are dangerous or lethal to human beings, animals and to the
environment. Always check with the HS&E manager before releasing any fluid to the atmosphere.
5.1 VALVE MAINTENANCE IN OPERATION
5.1.1 STEM LEAKAGE
The C&C Atlas series valve is provided with a stem sealant injector, stem leakages can be temporarily
stopped by injecting sealant into the stem fitting (38).
Before opening the bleed fitting, note orientation of the exhaust hole in the
bleed valve. Never open bleed fitting while valve is exposed to line pressure.
