Oxygen Service is a layout function or production procedure that is offered on some measurement devices that make it possible to measure pure oxygen or use in environments containing dangerous or risky concentrations of oxygen.
How dangerous is Oxygen?
An oxidizing agent like oxygen is one among the 3 things required for fire, the other two are a fuel (something to burn) and a supply of heat or ignition. Once an uninhibited chain reaction is added to an environment with a powerful oxidizing agent, the result are often explosive.
As there is always a risk of fire, choosing highly compatible materials for valves is necessary. Not only this, it is essential to utilize the best practices from design to manufacture, to the point of operating the product.
Valves for oxygen service application
When ball valve is partially open, thin edges of the ball are exposed to the flow stream. Ball valves are inherently fast opening that results in concerns regarding adiabatic compression and temperature rise, particularly for any elastomers downstream within the piping system. Ball valves could also be equipped with gear operators to make sure slow gap.
In addition, ball valves shall be designed with internal pressure relieving features to avoid pressure build up from liquid or cold gaseous oxygen trapped within the ball cavity.
When open, butterfly valves operate with the valve disk within the flow stream. In case of reverse flow, the seat groove will become a thin part within the flow stream area and wishes to follow the represented burn resistance methodology. The shaft to bonnet or shaft to body bearing/bushing ought to be a metallic design and shall be designed to fulfill the mechanical needs at maximum pressure differential across the valve disc.
Globe valves are usually utilized in cold oxygen on-off (open-closed) or throttling applications and can be manual or automatic. The trim design varies with specific valve manufacturers however it will have a relatively thin section fitted with non-metallic inserts to reduce leakage. Sometimes, for high differential pressures, cage trims are used, that are sometimes of thin section and provide sites for debris to be trapped and make friction. During this case, the trim of the globe valve shall be designed for a higher burn resistance.
Pressure relief valves
Pressure relief valves in cold oxygen service can experience warm gaseous relief throughout initial opening and high velocities across the trim. there’ll be impingement on the exhaust a part of the housing and outlet piping though these areas are commonly at or close to atmospheric pressure. The size of the trim and also the valve inlet determines the gas velocity at the valve inlet.
If particles are present there’ll be impingement on the exhaust a part of the housing and outlet piping. When performing an oxygen hazard analysis and risk assessment on pressure relief valves the potential for contamination or plugging of the exhaust vent shall be considered. just in case of the latter, the pressure within the exhaust pipe will exceed 100 pc of the set pressure.
For pilot operated pressure relief valves, the pilot valve are going to be exposed to oxygen and shall be designed accordingly.