Oxygen Service valves require careful consideration in selection. Due to Oxygens volatility each valve application should reviewed to ensure correct body material, the seals and style of operation. Decide if Ball, globe or needle style is best suited for the particular service.
Oxygen is a member of the chalcogen group in the periodic table, a highly reactive nonmetal. It is an oxidizing agent that readily forms oxides with most elements as well as with other compounds.
Generally speaking applications for Oxygen are Commercial and Medical. It can be in 2 states Gaseous (GOX) and Liquid (LOX). GOX is relative to this industry valving while LOX is under the Cryogenic industry requiring more specialized valving. LOX temperatures are below -183 Deg C (297F).
Valve and Flow Control Specialists supply valves approved for GOX and LOX service. DK-Lok manufacture Instrument valves such as regulators, needle, manifold and ball valves. It is important to specify at time of order that valves are for Oxygen service. It is best practice that valves come from the manufacturer prepared for Oxygen service. DK-Lok Ultra pure and Oxygen prepared valves and fittings ensure passivation is done in accordance with ASTM A380. Ultra-sonic cleaning in a class 100 clean room environment is standard. Implemented with resistivity over 18M D.I water after finishing the passivation for precision cleaning. After controlled drying has occurred each component undergoes individual visual inspection under ultraviolet lighting and before assembly / testing. The product then receives double packaging in a clean room environment using anti-static polyethylene bags and high purity nitrogen inclusion. We term this as cleaned, degreased and bagged for Oxygen service to the most stringent standards.
Fitting and Valve Standards
ASTM and CGA have relevant standards and recommendations on Oxygen service valving. Many of the major Gas companies will have their own specifications or compliance requirements for Oxygen service. On occasions local Standard Authorities such as AGA may list valving submitted for local testing particularly on products not covered by the more stringent international ASTM standards.
Oxygen Plant engineers reference the fire triangle. Oxygen fires occur when three elements come together: a fuel, an oxidizer, and an ignition source. Simply put, contaminants are fuels that ignite easily in oxygen and burn vigorously. Common contaminants include hydrocarbon-based oils and greases (use no oil in gauges) as well as metal particulates and other debris. The biggest problem with these contaminants is that once they ignite, they can kindle ignition to other less flammable materials. If you have ever started a campfire, you know that you must first ignite paper and small twigs in order to spread the flame to the larger logs. We call this a kindling chain, and often contaminants can initiate kindling chains in an oxygen systems because they are so easy to ignite
Valve selection
So what style of valves do we use on Oxygen service (GOX)? Instrumentation valves can be ball or needle types. Some schools of thought prefer not to use ball valves as the quick action 1/4 turn operation is considered a risk however in low pressure medical gas small bore ball valves seem popular. The risk factor seems to be more relevant to the larger bore non instrumentation valves where globe valves are more prevalent as the globe design is a lot slower in operation.
Consider this when you select a style of valve: The low ignition point materials like oil, rubber in the valve will ignite at a local high temperature. The metal reacts in oxygen, and this oxidation reaction is significantly intensified by increasing the purity and pressure of oxygen. For example, in front of the valve is 15MPa, the temperature is 20℃, the pressure behind the valve is 0.1MPa, if the valve is opened quickly, the oxygen temperature after the valve can reach 553℃ according to the calculation of adiabatic compression formula, which has reached or exceeded the ignition point of some valve or pipe materials.
Materials
But what materials should we use? Body materials can include 316 stainless steel, monel, bronze and brass. On non instrumentation valves ie larger bore valve bodies consider the use of stainless steel under 3MPa; Inconel 625 or Monel 400 alloy steel above 3MPa.
Oxygen service valves irrespective of service in Commercial or medical applications due to the nature of potential hazards either by leakage to atmosphere or reverse ingress of contamination need to be of the highest quality design and testing.
Valve and Flow Control Specialists are glad to assist in small and large bore valves of the various styles and materials in both manual and actuated versions.
