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Maximum hydrogen content before using a toroidal ring on a vent stack

Maximum hydrogen content before using a toroidal ring on a vent stack

Maximum hydrogen content before using a toroidal ring on a vent stack

(OP)
Hello fellow engineers;

I am currently reviewing a relief systems internal standard for a client of ours. In reference to vent stacks, there is a clause saying that any vent stack relieving a gas mixture with over 20 mol% H2 should be fitted with a toroidal ring. I have done considerable web searching on this and haven't been able to find a reference to back up this declaration. I am fully aware of the NASA work done which initially recommended the use of toroidal rings with H2 releases to prevent electric static spark or corona discharge, but nowhere was able to find mention of mixtures, let alone a definitive hydrogen content to begin considering a ring.

Have any of you fine folk had some experience with this?

Thanks in advance

Yearn fer it, Learn it, confirm it, earn from it!

RE: Maximum hydrogen content before using a toroidal ring on a vent stack

for info

Quote (ExxonMobil's std. GP 03-02-04)

4.3.4.3. Discharge risers for PR devices in hydrogen service at greater than 50 mole % hydrogen shall be equipped with toroidal rings ...

Quote (Shell's std. DEP 80.45.10.10)

3.4.2. ... A toroidal ring shall be installed where hydrogen content of the vapour exceeds 20 % (mol) to minimise the risk of ignition by static electricity ...

Quote (API 521-2020)

5.8.4.2.3 Release of Hydrogen-rich Streams
This conclusion pertains to hydrocarbon vapor releases. Experience indicates that streams with a high hydrogen content are susceptible to ignition by static electricity as a result of the described mechanism because of electrostatic discharges at the sharp edge of the vent outlet. NASA investigated this phenomenon [123] and found that such electrostatic discharges can be prevented by installing a toroidal ring on the vent stack outlet. This ring inhibits the static discharge at the vent stack exit by removing the sharp-edged geometry of the vent outlet, which is conducive to spark formation.
...
[123] NASA 11, Toroidal Ring Prevents Gas Ignition at Vent Stack Outlet, Technical Brief 67-10098, 1967

RE: Maximum hydrogen content before using a toroidal ring on a vent stack

(OP)
Thank you shvet. Looking at that second reference, its the second time in reviewing this spec that that operator has come up matching something in the spec. I have a distinct feeling that whomever wrote up the client spec I am reviewing, definitely had some dealings with said operator. Much appreciated!

Yearn fer it, Learn it, confirm it, earn from it!

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