4.6 Weld & Fabrication: Reviewing PV Elite Datasheets

PV Elite is a pressure vessel and heat exchanger design software set to summarize ASME Section VIII and other international code rules into software making the design process convenient and easier to interpret as compared to reading sections after sections of the code book to skim for information often misinterpreting and confusing it with the involved parties. For using this, you will only see what you want to see based on what you want to produce without reading the 700 over pages of ASME Section VIII over and over again to confirm the confusing interpretations.

Some code sections which requires selection are also available as option for the designer to choose from based on client specification or following vendor standard design.

Analysis models can be generated for user check if nozzle or irregular shape designs exceed allowable stress and allows for further optimization of materials usage.

Design parameters and material properties are pre-loaded in the software such as tensile strength of materials at various temperatures, weld efficiency, etc.

* My job at the Company requires review of the output from this software from our Contractors, therefore I cannot give review and comments on how well functional this software is. But my personal opinion says that this is a good software to optimize work flow process and improve productivity through reducing the metal fabrication design lead time. Don't waste time on MS Excel spreadsheets, how much can you save from there as compared to:
i) Being awarded the entire pressure vessel contract for an EPC project because of the shorter design lead time?
ii) Submitting a no-nonsense and clear cut calculation output which is easy to interpret, reducing the design review time.


DESIGN CALCULATIONS
Below are typical of what design calculations will be generated by PV elite output for a typical ellipsoidal dish head pressure vessel.

Defined design pressure of the Pressure vessel internally and externally by the user.

Defined the MAWP (Maximum allowable working pressure) by the user

Defined the joints and radiography requirements. Followed by the material UNS number.

The pressure vessel is divided into nodes for analysis, mainly on the dish end, shell, followed by nozzles. Other stress calculations defined by the code will also be performed, calculations not defined by code can be or not be produced on the output datasheet.


1) Initially it will calculate for internally pressured requirements (DISH END)
a) The require thickness based on the specified design pressure will be calculated. [tr]
if the thickness is less than code UG-16 minimum of 0.0938", the code minimum thickness will be applied.

b) The maximum allowable working pressure (MAWP) based on the thickness after corrosion will be calculated. This is less the value of static head at the top of the vessel for hydro test purpose per UG99c.

We are safe at this moment, as long as this MAWP after corrosion is higher than user specified MAWP, which means that minimum thickness required can support user defined MAWP.

c) The Maximum allowable pressure (MAWP), based on New and cold thickness will be calculated.

d) The actual stress at given pressure and thickness after corrosion will be calculated. [Sact]

e) The head straight flange section require thickness will be calculated.

f) The head straight flange section MAWP will be calculated. Explanation is same as 1(b)

g) Factor K for corroded condition allowance will be calculated [Kcor]

h) Extreme Fiber Elongation to UCS-79 will be calculated.
If this is more than 5% after head forming, heat treatment will be required. Unless the 5 conditions exist which will allow fiber elongation to allowably go up to 40%.

i) MDMT calculation to UCS-66(w/o impact) and UCS-66(1) at dish knuckle portion

j) MDMT calculation to UCS-66(w/o impact) and UCS-66(1) at head straight flange section


2) Next it will calculate for internally pressured requirements (CYLINDRICAL SHELL)
a) The require thickness based on the specified design pressure will be calculated. [tr]
if the thickness is less than code UG-16 minimum of 0.0938", the code minimum thickness will be applied.

b) The maximum allowable working pressure (MAWP) based on the thickness after corrosion will be calculated. This is less the value of static head at the top of the vessel for hydro test purpose per UG99c.

We are safe at this moment, as long as this MAWP after corrosion is higher than user specified MAWP, which means that minimum thickness required can support user defined MAWP.

c) The Maximum allowable pressure (MAWP), based on New and cold will be calculated.

d) The actual stress at given pressure and thickness after corrosion will be calculated. [Sact]

e) MDMT calculation to UCS-66(w/o impact) and UCS-66(1)


3) Hydrostatic test pressure requirements 

This needs to be specified by the user:
Hydro test Pressure per UG99b = 1.3 x MAWP x St/Sd
Hydro test Pressure per UG99b[34] = 1.3 x Design Pressure x St/Sd
Hydro test Pressure per UG99c = 1.3 x MAWP x St/Sd - Static Head
Pneumatic test Pressure per UG100 = 1.1 x MAWP x St/Sd
Pressure per PED = 1.43 x MAWP


4) Externally pressured requirements (DISH HEAD)

Defined Elastic modulus based on material used.
Defined Material UNS number.

a) Calculation for Maximum Allowable External Pressure (MAEP) based on minimum thickness

b) Backward calculation for minimum thickness based on design pressure

c) Calculate required thickness due to internal pressure [tr]
being P = 1.67 * External design pressure per UG-33(a)(1)

d) The maximum allowable working pressure (MAWP) based on the thickness after corrosion will be calculated.

e) The final Maximum Allowable External Pressure (MAEP) will be the minimum of the calculated MAEP and MAWP.


5) Externally pressured requirements (CYLINDRICAL SHELL)

Defined Elastic modulus based on material used.
Defined Material UNS number.

a) Calculation for Maximum Allowable External Pressure (MAEP) based on minimum thickness

b) Backward calculation for minimum thickness based on design pressure

c) Calculate allowable pressure based on Maximum Stiffened Length (Slen)


6) Allowable stresses
Check allowable compressive and tensile stress for all elements based on strength of the material. This is what was done in college with Mohr's circle.


7) Longitudinal stress check
This checks for also the compressive and tensile stress based on live loading, weights and pressure


8) Nozzle check
Performs all the pressure, MAWP, allowable stress checks on the nozzle.


9) ANSI B16.5 Flange calculation
This is standard to check if flange meets requirement of pressure and temperature rating.


10) Vessel support check
Check that the legs, skirting, lugs and etc are adequate.


11) Rigging  check
Check that the vessel body and the lug locations are adequately designed for lifting and transfer.
The others below are straight forward and are part of college or technical school syllabus which assume that most reading this post should understand.


12) Vessel CG and weight data calculation
13) Vessel cross sectional area and moment of intertia
14) Natural Frequency
15) Vortex shredding 
16) Wind & Seismic loading



References:
PV Elite Design code and analysis capabilities
PV Elite Quick Start (pdf)