Need:
The customer is focused on customized expansion bellow according to
functionality requirements. Finite Element Analysis has been adopted for the
expansion bellows due to the limitations in traditional design methods. In this
work the expansion bellow was analyzed for different loading conditions as per
TEMA standards using Finite Element Analysis.
Scope:
The objective of this work is to determine the spring rate, and compute
membrane & bending stress along Stress Classification Lines(SCL) using
Stress linearization.
Methodology:
·
Load cases
are considered as follows;
·
Differential
Expansion Only
·
Shell side
Pressure Only
·
Tube side
Pressure Only
·
Shell side
Pressure + Tube side Pressure
·
Shell side
Pressure Only + Differential Expansion
·
Tube side
Pressure Only + Differential Expansion
·
Shell side
Pressure + Tube side Pressure + Differential Expansion
The modeling of the bellow is done as per the guidelines given in
RCB-8.42. Mesh is refined at the critical sections to capture stress
accurately. At first, the CAD model (2D Axisymmetric geometry of FSE) is meshed
considering eight node quadratic axisymmetric elements and the boundary
conditions shown in figure RCB-8.42. The axial translation of the FSE is
restrained at the FSE axial plane, pressure of shell side is applied in the
inner face of FSE and an axial displacement is applied for stress
determination.
In order to evaluate the stress, minimum number of stress classification
lines (SCL) are established to compute linearized both membrane and membrane +
bending stress intensities at each SCL in order to compare these stress values
with the allowable stress limits defined in the design Code.
Main Challenges:
As specifications vary from application-to-application, designers have
to carefully craft each expansion bellow keeping unique environmental
challenges in mind.
Due to the complex shape, there is also a possibility of overestimated
stresses at the knuckle to annular plate discontinuity. As a result of such
complexities to avoid the risk factor designers tend to use oversize models
which in increases the material cost and affect overall performance.
Results Outcome:
FEA results are used to address ASME code rules as per ASME Section VIII
Div 2 Part 5. optimum thickness has been decided based on FEA analysis. The
induced stresses in the optimized expansion joint have been found to be within
the allowable limits. Hence the modeled geometry of the expansion joint is
adequate for analyzed conditions. Thus, Stress limits of ASME Sec VIII Div.2
are met
