Hydrogen & pressure transmitter

[betruth]

There is a decay tank with a local pressure indicator.
The tank includes hydrogen gas with other gases. So, The tank keeps a positive pressure to prevent explosion from air inleakage.

Question : Could I replace a local pressure indicator to a pressure transmitter despite the risk of explosion derived from a electrical device ?

 

[quark]

You can either use intrinsically safe transmitters or you can keep the sensor in the tank and keep the transmitter in a safe location. Tail pipes with silicon oil are used to transmitt the pressure signal from the sensor to the transmitter.

 

[RPG]

The best option is to replace the local pressure gauge with a pressure transmitter that comes with a local readout. Most industrial units are rated for Class 1 Division 2 areas where you do not expect to have a flammable atmosphere but the unit will contain any ignition. You can spend more and buy a Class 1 Division 1 instrument that is designed for flammable atmospheres. The one that I am most familair with is the Rosemount 3051S, see the link

http://www.rosemount.com/products/pressure/compare_gage.html

 

[jsummerfield]

RPG is correct - and you need more detail. Electronic instrumentation is normally used in many hydrogen applications. You need to assure that those responsible for the installation are familiar with the National Electrical Code Article 500 requirements.

You should determine what electrical classification is assigned to the area. I would expect the area to be classified Class I, Division 2, Group B. The group rating depends upon the concentration of hydrogen and other components. Hydrogen requires group B, acetylene requires group A. The Rosemount transmitter should be available compliant with the Class I, Division 1 and 2, Group B rating as a standard. I am certain that the transmitter is available Class I, Division 1, Group B; likely the same cost for Division 1 as Division 2. Others can better explain the differences that require Division 1 over Division 2. Generally, Division 1 assumes that the combustible gas is normally present and Division 2 anticipates the potential for the combustible gas in the event of an upset release or an equipment failure. For your application, this can affect the conduit and cable seals and termination details. Consult an electrical engineer familiar with the installation practices for your application.

I assume that you are using an instrumentation system that powers the transmitter via 24 VDC for display on a computer based system or analog instruments. Typically we do not use intrinsically safe (IS) installation methods domestically onshore in the USA. Some plants do, most don't. Avoid specifying the IS version and certification if IS is not a plant standard. Intrinsically safe installations utilize an intrinsic safety barrier that limits the available energy level even with two failures. This requires segregated wiring from non-IS circuits. The IS installation may require special grounding to assure less than one ohm resistance to ground and certification of the loop devices.

I too like the idea of a HART based smart Rosemount transmitter with integral meter that displays the engineering units. You can select the units. You need to select absolute pressure or gauge pressure. The models also vary based upon the maximum pressure. Assure that the body is specified to exceed the relief valve setting. You did not mention high pressure. However, check this if your pressure is in the 2000 psig neighborhood. Buy Blue enclosure model.

Yes there is still more to know but this should help to keep you out of trouble.

John