API 650 Pressure Coverage

[Baby-Engg]

Gentlemen,
This is clearly stated that API 650 can be used up 2.5 PSI

then 1.1.1 confusing me stating

because ATM pressure is 14.5 PSI!
what is mean by: approximating atmospheric pressure ( internal pressure not exceeding weight of the roof plates.)?

 

[Geoff13]

This was just asked a few days ago.

Please read thread794-517507

 

[LittleInch]

Baby-Engg,

NO. Atmospheric pressure is 0 psi.

Atmospheric pressure at sea level is approx 14.5 psia, but unless otherwise stated all normal standards and specifications use guage pressure, relative to local atmospheric pressure. Local atmospheric pressure changes with altitude.

What is says is that the internal guage pressure is basically 0 psi / 4 inches water column or I think 1kPa has been used before now or the equivalent pressure that is the weight of the roof divided by its square area.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Baby-Engg]

@LittleInch

Oh! now it make sense!

Thank your dear for the simplest explanation.

 

[Baby-Engg]

@Geoff13

Thank you for the ref. psot