Vessel Pressure

[amine errahal]

HELLO,
in order to do calculation basic on thickness calculation to separator. i do all the input in details (nozzles, manhole,saddle) i entered all the reinforcing of nozzles, the internal pression, temperature,allowable corrosion, diameter,thickness, the classes of flanges
but my problem is in the results (output):
i use a pressure of 6 bars but in calculation the pressure is defferent and with sign (-)
look here:
Required Thickness due to Internal Pressure [tr]:
= (P*Do*Kcor)/(2*S*E+2*P*(Kcor-0.1)) per Appendix 1-4 (c)
= (-16.801*1430.0000*0.994)/(2*-0.3E+07*1.00+2*-16.801*(0.994-0.1))
= -109.8021 + -84.0000 = -193.8021 mm

Max. Allowable Working Pressure at given Thickness, corroded [MAWP]:
= (2*S*E*t)/(Kcor*Do-2*t*(Kcor-0.1)) per Appendix 1-4 (c)
= (2*-0.3E+07*1.00*-224.0000)/(0.994*1430.0000-2*-224.0000*(0.99-0.1))
= -34.452 N/mm²

 

[XL83NL]

Are you using software like PVElite, or Excel? I asusme the first. This seems like an input or software error. Also, the value of pressure doesnt match; 6 vs 16.801. Are you using the right units (e.g. SI, fractional)?

 

[JStephen]

The static pressure due to liquid head is added to the design pressure. If it is possible to input a negative product weight or negative specific gravity or negative depth, they might produce such a result. I would think the software would catch the errant inputs, though.

 

[Steve-M]

Appendix 1-4(c) is for ellipsoidal heads under internal pressure. The internal design pressure should be a positive value (your formula shows a negative pressure value... -16.801). If it really is a negative pressure, that would be a vacuum or external pressure which is handled under UG-33 Formed Heads, Pressure on Convex Side.

Also, the numerator portion (P*Do*K) looks like it should work out to

16.801 * 1430.000 * 0.994 = 23881.3​

Then divided by whatever value you get in the denominator section ((2*S*E) + 2*P(K-0.1))
The final result is a simple division problem A/B = C thickness

If you are using Excel, you may need to insert some ( ) to force the software to do the math in the correct order.

Quote: "Sometimes, the biggest problems are caused by the smallest things. Pay Attention!" (Unknown)