| Applies To | |
| Product(s): | AutoPIPE Vessel |
| Version(s): | ALL |
| Area: | General |
| Date Logged & Current Version |
Nov 2023 44.00.00.111 |
Problem:
Why values of modulus of elasticity considered in external pressure calculation is not correct?
For example: Modulus of Elasticity for material SA516 Gr70 as per code and table given in software at design temperature 3500C is 179000MPa, But in calculation it has taken 172091MPa.
Also value of factor B is not correct.
Solution:
Reviewing the applicable code will help with understanding how these values are calculated. The following values were calculated based on Design code = ASME VIII July 2021 and referencing the output report sub section "Element(s) of geometry under external pressure". For each of the components and load conditions, the report will mentioned a code section from which information was taken (ex. ASME VIII Div.1 2021 UG-33).
For Modulus of Elasticity (E):
Under ASME VIII Div.1 2021 UG-33, one can find a information for Modulus of Elasticity (see UG-28)
Under UG-28, locate a definition for Modulus of Elasticity ( E ): "For external pressure calculation shall be taken from the applicable materials chart in Section II, Part D, Subpart 3...".
This indicates that the Modulus of Elasticity is not taken from Table TM of the code but will need to be referenced from the correct Figure / Table located in Section II, Part D, Subpart 3.
Per the output report, material SA516 Gr70 falls under vacuum curve CS2 (Yield strength higher than 207Mpa), See image below from ASME Section II Part D, Subsection 3.
From above figure, for temperature 2600C Modulus of Elasticity (E) is 186000MPa. Similarly for temperature 3700C Modulus of Elasticity (E) is 169000MP.
So, if we interpolate it for temperature 3500C then we will get the Modulus of Elasticity values as 172091MPa.
For calculation of factor B:
Recall:
1. From Above, section UG-33 references section UG-28 for values of A, B, E, and P.
2. From output report, B(Subpart 3 Section II Part D or AE/2 (note, this equation is derived from UG-28, (c) Cylindrical Shells and Tubes, Step 6 & 7).
The formula of factor B = AE/2 is only applicable if factor A falls left to the material curve line.
In particular below case factor A = 0.000616, See Figure CS-2 attached above, factor A falls to the right of the curve.
In this case factor B does not calculated by formula but taken from the graph by interpolating the values given.
Hence, value of factor B is not matching with the value calculated by formula (B=AE/2).
See Also