Evaluate stresses from Ansys®, CAESAR II® or any other program for fatigue, high temperature or fitness-for-service.
This article discusses how to convert CAESAR II® or general purpose FEA results into
values that can be used in MatPRO to perform fatigue, high temperature or fitness
for service (FFS) calculations. Use MatPRO effectively in pressure vessel and piping
analysis.
Using CAESAR Results
|
Item |
Load Case |
Conversion |
Result |
Summary |
|
SL |
Sustained stress |
SL |
PL |
PL = SL |
|
S |
Operating stress |
(2/1.35)(S) |
PL+PB+Q |
PL+PB+Q = (2/1.35)(S) |
Using Ansys (or other FEA Program Results)
|
Load Case |
Operation |
Result |
|
Primary Loads - Typically Weight + Presure |
Integrate stresses through thickness at critical section |
PL |
|
Operating Loads - Including Weights and Pressure |
Linearize Sx, Sy, Sz, Txy, Tyz, Tzx through thickness at critical section and compute
stress intensity from result |
PL+Pb+Q |
The above values for PL and PL+PB+Q can be used in MatPRO to evaluate any
given stress state.
The MatPRO PL and PL+PB+Q text cells are
shown below.
MatPRO supports a B31.3 and ASME Section II Part D data base along with
“condition calculators” that evaluate calculated stress states in welds,
base metal, or flawed pipes and vessels.
The MatPRO “condition calculator” determines:
- How close you are to failure,
- If creep-fatigue interaction is a concern, and
- Whether a crack, corroded, or eroded area satisfies API 579 Fitness for Service Rules.
MatPRO is a program no pressure vessel or piping engineer should be without!
The more you know about MatPRO – the more you learn.
The “condition calculator” is invoked by specifying the material, e.g. SA 106 Grade B,
the temperature, and the stress state. The stress state is retrieved automatically
from NozzlePRO or FE/Pipe, and can be easily entered with results from Ansys or
CAESAR II.
The major “condition” buttons are shown below.
To perform a fatigue analysis using a computed stress from FE/Pipe, NozzlePRO,
CAESAR or Ansys, the MatPRO you would click on the “Fatigue Calculations”
button shown in the figure below.
The Fatigue input screen is shown below.
Fatigue Evaluation MatPRO Input Screen
Note that time, temperature and thickness may all influence creep life.
Output includes detailed text reports and plots of fatigue curves using
allowable limits prescribed by Markl, API579, BS 5500, the MasterCurve,
ASME and EN13445.
MatPRO Fatigue Curve Comparisons
MatPRO also produces material property plots for all combinations of yield,
tensile, allowable stress, creep rupture properties, etc.
The plot below shows the allowable stress, tensile strength and yield stress
for an SB-409 plate material at 300,000 hours. Note how the drop in tensile
strength at about 1100F affects the allowable stress, while the yield strength
remains high!
MatPRO – The more you use it – the more you learn. No engineering desktop
should be without it.