Steam rings for hydrogen service

[swtmoon]

It is known that steam rings are used for fire suppression caused by hydrogen leak among the hydrogen piping joint part around the Hydrocracker.

But I can't decide where steam rings to be installed.
Should I install every piping joint part? or is there some guidelines for steam ring installation?

I expect to hear from lots of experienced engineers.

 

[25362]

Visit thread378-55061 and thread483-21387.

 

[Homayun]

On our project we had them on the vessel flanges and where the pressure / temperature combination was high enough to cause an auto ignition upon H2 elease.
Maybe this helpful to you

 

[swtmoon]

Dear Homayun,

Thanks for information.

On reference, AIT(Auto ignition temp.) of H2 is shown as above 520 degree C.
But I guess pressure may contribute lower the AIT.
Could you please advise more detail values of pressure and temperature?

 

[swtmoon]

Homayun,

I can find related topic regarding H2 self-ignition.
Visit <a href="

http://www.eng-tips.com/viewthread.cfm?qid=51712">thread

135-51712</a> Tons of informations for H2

 

[25362]

Beside the "secondary" preventive line of action aimed to eliminate ignition sources, "primary" safety efforts and design procedures are aimed to exclude the causative risk, i.e., leakages, as detailed in the above-mentioned threads.

Although the AIT for a self-sustained combustion of a stoichiometric mixture of hydrogen in air is around 600[sup]o[/sup]C, kindly consider that hydrogen-air mixtures' ignition energy is quite low, [&asymp;]0.02 mJ, and their flammability limits are indeed affected by temperature, becoming ~1% to ~95% at 400[sup]o[/sup]C.

 

[Homayun]

SWTMOON,
IT's been a while since I worked on this particular project. It was a Shell project where a UOP Penex Isomerization unit was to be built. The steam rings came where hot hydrogen was intoduced, mostly around the reactor rings. I don't recall the exact pressure/temperautre conditions. But I think you can have a look at the typical UOP Penex unit and see around what pressure/temperature this unit performs. That should be an indication.
Regards

 

[swtmoon]

Thank you 25362 and Homayun.

From the other plant data, I can find that steam rings are installed pressure at 5~7 bar, temperature 220~280 deg C.
This pressure/temperature region is just below the hydrogen embrittlement region of carbon steel.

If hydrogen self-ignition is only pressure dependent (See thread 135-51727), I can figure out that steam rings are installed at potential weak point from hydrogen attack.