9 replies to this topic

[EvdB]

In our facility I have several reactors with a jacket. The insulation is not according to the requirements in API 521, so I can not take credits for this.

But can I take any credits for the jacket, since it is also a pressure vessel (DP jacket = 5 barg) in a external fire case?

And what about a half-coil, that will reduce also the heat input in case of a fire?

Can I calculate the environmental factor for the jacket with the maximum thermal conductivity of the fluid in the jacket and with the thickness of the gap between the jacket and the reactor?

[fallah]

EvdB,

 

A jacket same as one you described, should be itself protected against overpressure same as any pressure vessel; i.e. by applying a fire case PSV for code compliance...then one can't take any credit on jacket based on supposing it can play the role of fire insulation...

Edited by fallah, 26 August 2015 - 06:40 AM.

[latexman]

Once the jacket boils dry, the half-coil (half-pipe?) can act like heat transfer fins on the RXs.  No credit.

[EvdB]

Thanks for the quick replies.

The reactors with jackets and the reactors are individually protected with a TRV. 

When the jacket or the half-coil boiled dry, the vapor in the jacket will limit the heat transfer to the reactor in case of a fire and the jacket jacket can resist the water pressures and fire temperatures and can withstand temperture of 904°C for 2 hours.

[fallah]

EvdB,

 

The jacket with pressurized steam water inside will fail soon when engulfged in a pool fire and the reactor itself will be subject to fire at the time well before 2 hours from fire getting started...

[latexman]

Half-coil = half-pipe?  We use 3" half-pipe on a 4.5" pitch.  The half-pipe walls welded to RX act like a heat transfer fin to the RX.  The heat from the fire will be conducted through these fins into RX quite efficiently.  No credit.

 

Dimple jacket - no credit.

Conventional jacket with spiral baffle - no credit.

Conventional jacket with no baffles - yes credit.

[EvdB]

Sorry for the confusion but I mean a half-pipe. On our site we have several types of jackets, including half-pipe and dimple jackets, but also conventional jacket with no baffles.

How much credit can I take for this type of jacket?

Edited by EvdB, 01 September 2015 - 10:07 AM.

[latexman]

I don't know what credit your company will allow.  It's a risk based decision that your Engineering and Safety management should agree on.

 

My company would allow a 30% reduction of the wetted area under the jacket.  Effective area = wetted area not under jacket + 0.7 * wetted area under jacket.  If qualified, other credits could be taken too, like insulation.

[EvdB]

Currently my company does not have any standards on what they allow for credit for a jacket.

@latexman. Do you llow a 30% reduction of the wetted area under the jacket for all types of jackets? How did you calculate this 30% is a safe and acceptable value?

[latexman]

EvdB,

 

See Post # 6, only on a conventional jacket with no baffling.  The high thermal conductivity members used for structural or baffling reasons that connect the outside jacket area to the inside of the reactor will act like a heat transfer fin.  The heat will flow from high temperature source (fire) to low temperature source (reactor).