Structural Integrity

1. INDIAN STRUCTURAL INTEGRITY SOCIETY
WORKSHOP
Structural Integrity Assessment of Nuclear Energy Assets
9th – 10th May 2018
AERB Auditorium,Niyamak Bhavan-B Mumbai .

2. SIMULATED DESIGNED DELIVERED

3. INTRODUCTION
Pressure vessels is defined as the
container with pressure differential
between inside and outside, it can
carry and store the fluids.( The inside
pressure is usually higher than
outside).
Pressure vessels usually handle high
temperature, hazardous(chemically
active) and radioactive(flammable)
fluids which are very dangerous, so
proper designing has to be done
considering all the safety measures to
ensure the safety of plant, workers
and investments.

4. APPLICATIONS
Pressure vessels are used in various industries like:-
 The power generation
 Nuclear power plants
 Petrochemical
 Chemical handling plants
 Food & Beverage
The failure of pressure vessel lead to
loss of human lives, Investments..etc.
So to ensure the safety of plant, workers & Investments, ASME has developed standard stringent codes which shall
be followed by the Designer, Analyst, Fabricator & Inspector depending upon the class of safety requirements.

5. TYPES OF PRESSURE VESSELS
 Horizontal Pressure Vessels (Saddle
support)
 Vertical Pressure Vessels (Column type)
 Spherical Pressure vessels

6. Seismic Qualification of Pressure Vessels
/ Strainers as per ASME Code

7. Typical Workflow for Seismic Qualification
1. Safety Class of component
2. Seismic category of component
3. Individual load cases
4. Create the 3D cad model
5. Create the FE model
6. Modal Analysis
7. Check the first natural frequency
8. FRS Analysis / Equivalent static Analysis
9. Load combination
10. Comparison of obtained Stresses Vs Allowable as per
ASME codes.
11. Report

8. 3D Cad models of Pressure vessels
Cad modeling is done by using various
cad modeling tools like, CATIA,
NX,INVENTOR, PROE,
SOLIDWORKS…etc
 Cad modeling

9. 3D Cad models of Strainers
Y-type of Strainer
Basket type of Strainer
T-type of strainer

10. CAD & FE Model
BAFFLE, BALLAST TUBE & PIPING
•Shell elements used to model the tank
structure, baffles & tubes
•1-D elements (pipe31 & elbow31)
are used for piping One leg fixed,
other leg sliding
Typical Pressure vessels qualified as per ASME

11. Typical Pressure vessels / Strainers qualified as per ASME
Suspended Tank
Duplex Fuel Filter

12. Typical Pressure vessels / Strainers qualified as per ASME
Basket Type
T - Type Y - Type

13. PNAE Vs. ASME code comparison for seismic
qualification of equipment's

14. WHY CODE COMPARISON?
 To check & understand the technical similarities and differences between
ASME Code & PNAE code in seismic qualification of the equipment.
 To understand the service conditions & their corresponding allowable
limits.
 To understand & compare the safety categorization of the equipments as
per ASME & PNAE.
 To understand how the allowable stress intensities are arrived form both
the codes.

15. ASME PNAE Remarks
Safety class 1: The structures, systems,
equipment and components whose
malfunction or failure could lead to undue
radiological consequences.
Group A: The failure of
components leads to accidental
situations.
Group B: These components are
used to activate the reactor core
cooling systems, failure of which
leads to non-recoverable leakage
of coolant.
Group C: Failure of these
components leads to leakage of
coolant & High or intermediate
level radioactive release to
environment.
There is not necessarily a
like correspondence
between PNAE G-7-008-
89 Safety Groups A, B,
and C and ASME Class
1, 2 and 3.
All groups of PNAE are
more closely aligned
towards ASME Class 1.
Safety class 2: The structures, systems and
components which prevent Anticipated
Operational
Occurrences from leading to Accident
Conditions;
Safety class 3: The features which are
provided to mitigate the consequences of
malfunction
or failure of structures, systems or
components.
Construction and operation rules depends on the safety groups according to PNAE G-7-008-89
SAFETY CLASS COMPARISON

16. MATERIAL DETAILS
ASME PNAE G-7
ASME SEC II Part D & NB-2000 PNAE G-7-002-86 (3).
Mechanical material properties used in strength analysis are given in PNAE G-7-002-
86 (Appendix A)
Methods for determination of mechanical properties are defined in PNAE G-7-002-
86 (Appendix 2).
List of materials accepted for use as per ASME & PNAE G-7 codes
ASME SEC II Part D PNAE G-7-002-86 (Appendix 9)
Material list defined is based on ASTM
specifications
The PNAE G-7-002-86 list is based on
*USSR standardization documents
*USSR:- Union of Soviet Socialist Republics

17. SERVICE LEVELS
ASME PNAE
Design Condition: The auxiliaries or their supports
must satisfy these sets of limits in the performance of
their specified service function.
Design pressure at design temperature
Normal (Service level A): Operation of NPP with
specified operational limits and conditions including
shutdown, Power operation, starting up, maintenance,
testing and refueling.
Normal operating conditions (NOC) – service
conditions at operation provided by NPP’s operations’
schedule (steady-state conditions, start up, safety control
system operation, changing power, shutdown)
Upset(Service level B): All Operation processes
deviating from normal operation which is expected to
occur once or several times during the operating life
of NPP and which, In view of appropriate design
provisions do not cause any significant damage to
items important to safety or lead to accident condition.
Violation of normal operating conditions (VNOC) –
any deviation from NOC (of pressure, temperature, loads,
etc.), that requires reactor shutdown to eliminate this
deviation but not putting systems of emergency cooling of
active zone into operation.

18. SERVICE LEVELS
ASME PNAE
Emergency (Service level C): The occurrence of stress
up to these limits may necessitate the removal of
auxiliary from service for inspection or repair of
damage.
Emergency situation (ES) – any deviation from NOC and
VNOC whose consequences can lead to such malfunction
of active zone cooling that requires putting systems of
emergency cooling of active zone into operation
Faulted (Service level D): These limits permit gross
general deformations with loss of dimensional stability
and damage requiring repair, which may require
removal of the auxiliary from service.
 From the comparison of service loadings we can say that “The service loadings of ASME and
PNAE are similar to each other”.

19. SERVICE LEVELS COMPARISON
PNAE G-7 ASME Code
NOC Level A limits
VNOC Level B limits
ES
Level C limits
Level D limits
Beyond design basis accident Level D limits
Additionally, cases of simultaneous service and seismic loads are considered in PNAE G-7.
Two types of earthquake are defined:
• Maximum design earthquake (MDE) is an earthquake with average recurrence of 10,000
years.
• Project earthquake is an earthquake with average recurrence of 100 years.

20. ALLOWABLE STRESS CALCULATION
PNAE-code ASME-code
Design Stress Intensity is calculated as
Where,
ST = Specified Min Ultimate strength @ room temp
RT = Ratio of Average temperature dependent trend curve
value of tensile strength to the room temperature tensile
strength
SY = Specified Min Yield strength @ room temp
RY = Ratio of Average temperature dependent trend curve
value of yield strength to the room temperature yield strength
From the comparison,
Safety margin for UTS
PNAE =2.6
ASME = 3
Safety margin for Yield strength
PNAE & ASME =1.5
Nominal allowable stress for equipment is
calculated as
Where,
RmT = Min Ultimate strength
Rp0.2T = Yeild strength

21. ACCEPTABLE LIMITS FOR SERVICE LEVELS
SL
No
Service levels
Allowable Stress Intensity in
MPa As per ASME Code
Allowable Stress Intensity in MPa
As per PNAE Code
Stress
Intensity
(Membrane,
Sm)
Stress Intensity
(Membrane +
Bending)
Stress
Intensity
(Membrane,
σ1 )
Stress Intensity
(Membrane +
Bending, σ2)
1
Design Condition /
Design Sm 1.5Sm σ 1.3σ
2
Service level A /
NOC 3Sm 3Sm σ 1.3σ
3
Service level B /
VNOC 1.1Sm 3Sm 1.2σ 1.6σ
4
Service level C & D /
ES 1.2Sm 1.8Sm 1.4σ 1.8σ

22. CASE STUDY

23. CASE STUDY
Description: The tank is class 1 equipment. The tank has been analysed and qualified for different load
cases, Load combinations (Service levels) as per ASME Sec III sub section NB & PNAE code. The results
are provided in the below slides.

24. CAD & FE MODEL
Cad Model
FE Model
The tank has been analysed for individual load cases like DW, DP,NL,OT, OBE & SSE cases and also for
load combinations.
Material:- SA240 gr 304L
UTS (Su)= 485MPa
Yield strength (Sy) = 170MPa
Modulus of Elasticity (E) = 1.74E5
Poisson's ratio = 0.3
Design stress intensity
@ Design Temp = 95.7Mpa
The material properties are taken from Table -2A of ASME SEC II Part D & the same are shown above

25. SL No
Service Levels
ASME PNAE G7-002-86
1
Design Condition / Design
(DW+DP+NL)
Design
(DW+DP+NL)
2
Service level A / Normal
(DW+OP+OT+NL)
NOC
(DW+OP+OT+NL)
3
Service level B / Upset
(DW+OP+OT+NL±OBE)
VNOC
(DW+OP+OT+NL±DE)
4 Service level C & D / Emergency / Faulted
(DW+OP+NL±SSE)
ES
(DW+OP+NL±MDE)
LOAD CASES & LOAD COMBINATIONS

26. RESULTS FOR DESIGN CONDITION
Pm + Pb / σ2 Pm / σ1
Top Middle

27. RESULTS FOR DESIGN CONDITION
Pm + Pb / σ2
Bottom

28. Pm + Pb / σ2 Pm / σ1
Top Middle
RESULTS FOR SERVICE LEVEL - A

29. RESULTS FOR SERVICE LEVEL - A
Pm + Pb / σ2
Bottom

30. RESULTS FOR SERVICE LEVEL - B
Pm + Pb / σ2
Pm / σ1
Top Middle

31. RESULTS FOR SERVICE LEVEL - B
Pm + Pb / σ2
Bottom

32. RESULTS FOR SERVICE LEVEL - C
Pm + Pb / σ2
Pm / σ1
Top Middle

33. RESULTS FOR SERVICE LEVEL - C
Pm + Pb / σ2
Bottom

34. RESULTS COMPARISON
SL No Service levels
PNAE ASME Obtained stress
Allowable stress Allowable stress
Membrane
Membrane
+ BendingMembrane (σ1)
Membrane +
Bending (σ2)
Membrane,
Pm
Membrane +
Bending
(Pm + Pb)
1 Design Condition
(Design)
95.7 124.41 95.7 143.55 9.43 40.94
2 Service level A
(NOC)
95.7 124.41 287.1 287.1
19.32 49.55
3 VNOC (Service level
B / NOC+DE)
114.84 153.12 105.27 287.1 42.92 64.10
4 EC (Service level
C/D, NOC+MDE)
133.98 172.26 114.84 172.26 13.68 41.14
Stress intensity @ Design Temp = 95.7Mpa

35.  From the results table it is clear that the PNAE code has higher safety margin
compared to ASME in Normal operating condition (1.15) and violation to normal
operating condition (1.85).
 The strength analysis rules for all safety groups are the same within PNAE code and
are generally consistent with Class 1 as defined ASME Section III Div 1 Subsection
NB.
 The acceptable criteria's changes in ASME code as the safety class of the equipment
changes. In PNAE code the acceptable criteria remains the same irrespective of the
class of the component.
SUMMARY

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