Exi vs Exd transmitters in oil/gas industry

[pan_x000]

Hi

I have following question. Why do we often use Exi pressure, level or temperature transmitter in II zone (methane) with appropriate Intrinsic Safety isolators whereas total cost of combination Exi transmitter with Intrinsic Safety isolators mounted in control cabinet is more expensive than Exd transmitter mounted in the field alone?

Thanks in advance for answers!

 

[roydm]

Good Question, why would you use Intrinsic Safe, I work in related industry but we seldom do any more. It's not just the hardware but to do it right special cable, dedicated trays, segregated panels.

Occasionally you strike a situation where Intrinsic Safe is the only approval you can get for a particular instrument. I'm looking at a guided wave radar in a tank with Hydrogen gas. I dare say the barriers will be somewhere close by.

I don't see Exi in the Methods of Protection list Ex ia, EX ib, Ex ic
There are so many variations in hazardous location designation, can you share the location of the project, complete hazardous zone designation?

 

[scenes]

One point to pay attention is the whole cost of the implementation.

You can't only consider the prices of the equipment; you need to analyze the whole project. Usually, you need considerable structure, and you spend more time to implement an Ex d than an Ex i project.

The cost per hour of people involved in the installation and project + the cost of devices should be the right analyze before say that Ex i is more expensive than Ex d in all projects.

One example is the Wireless projects, where the cost of devices are higher than standard devices but you save money in time and installation cost.

I'd like to read an opinion from colleagues with more experience with this type of projects.

Thanks

 

[ScottyUK]

Ex'd' hardware is expensive but the supporting infrastructure is simple and conventional. No special earths, no exotic overload relays, no awkward design, no limitation to low-powered instrument circuits. I'd contend that an Ex'd' installation may work out cheaper in some instances. Equally in Zone 0 then Ex'ia' is the only option open to you, so there isn't even a choice to be made.

It depends on the overall installation. There is no single answer which is universally accurate. The design engineer should be looking for the lowest cost solution which meets the technical requirements of the specification.

 

[kekessalman]

As mentioned above, some applications come only in Ex-i due to the medium.
Ex-d installations will end up more expensive than Ex-i if Junction Boxes and local control stations are also bought Ex-d. And the hassle of maintenance to Ex-d boxes..
A good designer would use Ex-d instruments but place the JB's outside hazardous Zone 1, use Ex-e JB's for an optimum solution. But this is not so obvious to EPCM companies these days..

 

[Texagere]

Hi All

It is in fact a project philosophy: as said previously, supporting infrastructure is simple and conventional for Ex d.
It is to fast and simple to said that the cost of Ex i[*] is lower or higher than Ex d (which is not sure for all instruments and equipment): it depends where! onshore and offshore installation are very different for this approach due to the cost of the infrastructure or the weight also, etc.
on offshore, for example, Ex d is often considered because the cost of the m2 of technical room is huge, the size is limited, and sometimes for some project, the weight (technical room) is limited and we try to limit the size of technical room (marshaling cabinet or remote i/o cabinet).
on onshore, the cost of the square meter m2 is different and it is easy to design a technical room with enough space to install cabinet and barriers Ex i in quantity without impacting dramatically the total coast of the control room versus the Ex d solution.