slots or bolts for boxing up pressure vessel

[amasvikeni]

i am working on a case in which a pressure vessel with ammonia and air recently exploded. The bolts attaching the head to the vessel (slotted) just fell off and were not damaged and i am therefore assuming that for some reason the vessel opened up releasing the mixture (6 bar, 900 degrees celsius) culminating in the explosion.
Now my question is why is the design of the vessel such that the bolts are placed in slots rather holes where there is no chance of them falling off as happened?

 

[corus]

Slots allow thermal expansion

corus

 

[arto]

Or swing bolts for quick opening - [usually a "Tee" or Eye though]

 

[pennpoint]

amasvikeni
I am very interested in this, can you post pictures to a web site?
How do you mean "just fell off".
Hope no one was injured.

Thanks

pennpoint

 

[TomBarsh]

Slotted holes are frequently used for "quick opening" needs as mentioned.

However, bolts under even a modest pressure load shouldn't just "fall off". And if the nuts are at least hand-tight then the bolts shouldn't fall off under no load.

Were the nuts still attached to the bolts? What Code was this vessel designed to?

 

[solidworkswell]

dont know much about this topic. but where the bolts were pre-loaded. slots are put for thermal expansion, but if your vessel is circular where the two vessels are comming together, i wonder y u need slots, as metal expands along its circumfrence, so theroetically the bolt circle shoud move along with the circumfrence keeping its original mate.

i hope i make sense.

 

[diamondjim]

I think an oversize hole rather than a slot
would be a better design.

 

[waskillywabbit]

Slots are used for swing bolts to make it faster to open...I don't think there is anything else to that...

Bolts just don't "fall" off...somebody forgot to tighten them or put them back on period...



Brian

 

[Rich2001]

A couple of ideas:

1. The bolts coming out of the slots is an results of the lose of pressure (explosion) not the cause, or a lose of pressure via the safety relief valve for example might allow the bolts to slip out of the slots.

2. The bolt material is has a higher coefficient of thermal expansion then the pressure vessel flange material.


What is the relevant Pressure Vessel code or is there any regulations on the design, manufacture, inspection and operation of pressure vessels in your area of the world?

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