Quick Question,
If a vessel has vacuum would that be the same as external pressure. Would a vessel need an ASME stamp if it ran @ -7 psig?
Mike

Not so quick answer: that depends on.

Talking about a pressure vessel, not generating steam, not classified as Nuclear Item, and operating in the atmosphere, your -7psi partial vacuum means that there is 7psi external pressure from the atmosphere on the vessel shell.
It is not in the scope of Section VIII Div.1, because the pressure is less than 15 psi. However, the user may order it with Code Stamp, then ist shall be built in accordance with the Code.

Clear?
DK

Mike, letter of the law is one thing, safety is another one, sometimes it's not the same pair of shoes. And vacuum vessels is a good example. Most pressure vessel codes treat them too indulgently. You as an engineer should ask yourselves a question: should this vessel be made according to a good PV code, even if it would mean more restrictive/costly requirements to be met? And the codes don't have good answers for such questios.
Ask as much "what if" questions as you can imagine, usually this helps in good hazard assesment.

Regards

_________________
Konrad Anikiel

For what it's worth, here is an interesting video of a railway tank car imploding under vacuum. I don't understand the German(?) sound track (my high school German is a bit rusty), but this looks like a set-up for demonstration.

See http://gizmodo.com/383045/how-to-implod ... r-a-second

Is this statment true?

ASME VIII applies to vessels under an internal pressure of 15 psig minimum and any external pressure.
Hogan, minus 15 psig doesn't exist because minus 14.7 psig (equal to zero psia) is absolute vacuum, and it can not exist a pressure lower than absolute vacuum.
Regarding ASME stamp, Bill, it is up to the buyer (or customer) to require it or not. If your customer does require (and pays for) it, you have to satisfy his request. Of course, an ASME stamped vessel is more expensive than a not stamped one.

So the external psi can only increase up to 14.7, but a vessel can collapse if there is too much internal vacuum???
Im new to ASME and need some basics on Internal External, and vacuum pressures and how they relate to the code.

@ mike

Not included in the scope of VIII-1 are:


Regarding Full Vacuum please look into Appendix 3 definitions:

The emphasis is placed on "definitions".

Michael