discontinuity material

1. Stress
Analysis
Weekly
Presentation
DISCONTINUITY STRESS
By M. Avicenna Diannegara

2.  The real big question…!!!
 1. What is the DISCONTINUITY STRESS..????
 2. Why we must learn about DISCONTINUITY STRESS..????
 3. What area can DISCONTINUITY be APPLIED??
DISCONTINUITY STRESS

3. Pressure vessels are
containers fabricated /
mechanical equipment
design to hold liquids or
gases under pressure.
It’s usually contain
regions where abrupt
changes in geometry,
material or loading
occure
PRESSURE VESSELS
- Pressure Vessel -

4. All Pressure Vessel contain discontinuities that can be
described as:
1. Abrupt deviation or changes in shell geometry, thickness, material
properties, loads or temperatures.
2. Openings or cutouts in the prressure vessel surface
3. Geometric irregularites resulting from variations in the
manufacture of structural parts.
DISCONTINUITIY STRESS
These Discontunities may couse high local stress, which in turn can
cause pressure vessel to FAIL!!

5.  The following standard analytical mehods are used to determining stresses
resulting from gemotric or material property descontinuities:
1. Numerical Integration
constitutes a broad family of algorithms for calculating the numerical
value of a definite integral, and by extension
2. Finite Element Modeling
is a numerical technique for finding approximate solutions to boundary value
problems for differential equations. It uses variational methods (the calculus of
variations) to minimize an error function and produce a stable solution.
3. Finite difference techniques
numerical methods for approximating the solutions to differential equations
using finite difference equations to approximate derivatives

6.  The Finite element method is based upon mathematically
modeling the pressure vessel structure as an assemblage of
finite elements connecting nodal location.
 It can be used to calculate deflection, stress, vibration,
buckling behavior and many other phenomena. It can be used
to analyze either small or large-scale deflection under loading
or applied displacement
FINITE ELEMENT ANALYSIS
- FEM MODEL-

7. FINITE ELEMENT ANALYSIS
The purpose of this structural analysis is to
evaluate the strength of HEATER ORF-1822-H-
3101-
A/B head plate and its pipe support.
Finite Element Analysis is carried out using
structural analysis
program FEMAP with NX Nastran in order to
determine the deformation and stress
condition in
case of operation condition.

8. FINITE ELEMENT ANALYSIS MODEL

9.  Unit system adopted in this analysis is: Length – mm; Force –
N. For all the structure, the steel is of Young’s modulus
2.05E5 MPa, density 7.85 T/m 3, Poisson’s ratio 0.3. All the
steel is mild steel and the yield strength is 240 MPa.
 As we are concern the connection between pipes and head
plate, the heater body shell is modeled partially with head
plate.
FEM PLOT FOR RESULTS

10. FEM PLOT FOR RESULTS
Max VM stress 68.87MPa < Yield Stress 240 MPa
Based on ASME Section II, Part D, the yiled stress has an aound 8% reduction at 100°C. That is,
the yield stress is 221MPa. Because the loads of extreme cases are used for the check, the allowable
stress is equal to the yield
stress.
The UC of max VM stress is 68.87/221=0.31< allowable value 1.0.
From the analysis results, it is concluded that the designed head plate and its pipe support of the
heater have sufficient structural strength to withstand the provided loads for operation condition.

11. FEM PLOT FOR RESULTS

12.  A piping system may involve more than one material, or may
connect to an equipment of different elastic or thermal
properties.
 When two pipes of different materials are joined toherter, the
joint produces additional discontunity due to the diffirences in
expansion rate, thicness, and modulus elasticity.
STRESS AT JUNCTION BETWEEN DISSIMILAR
MATERIALS
Junction Between Dissimilar Materials
Thermal Discontunity Stress

13.  Example:
Austenitic SS joined with carbon steel at 4270C.
αa = 18.18 x 10-6 mm/mm/0C,
αb = 11.4 x 10-6 mm/mm/0C ,
E = 172.72 ´ 10 3 MPa
SE,t....??
S E,t = 0.06 E (T2-T1) (αa-αb)
S E,t = 0.6 ´ 25.05 ´ 740 ´ (10.1 - 7.8)
= 25,581 psi (176.376 MPa)
A piping system that does not connect to any rotating equipment
can have an expansion stress plus sustained stress of about
30,000 psi for most of the common piping materials.
STRESS AT JUNCTION BETWEEN DISSIMILAR
MATERIALS

14.  In comparison to the uniform junction discussed above, a pipe
connected to a rigid section is an other extreme of application.
The maximum shell bending stress, which occurs at the junction,
is :
The pipe segment Mat-a in this case has to deflect in the radial
direction the full differential expansion. Therefore, the
circumferential membrane stress is:
A PIPE CONNECTED TO A RIGID SECTION

15. The consequences of discontinuity stress failures may range to :
 Leakage
 Bursting
 Detimental deformation
DISCONTINUITY STRESS FAILURES
Failure Cases:
 A steel motor case failed as a result of high stresses at a nozzle
junction casused by a mismatch of the two components.
 A fuel tank test ended in failure at less than half of the design
pressure because of a discontinuity in the surface conture in the
form of a flat spot which caused excessive local stress.

17. THIS IS THE END OF THE
PRESENTATION