PSI - Issue 60

7

Rahul Mittal et al. / Procedia Structural Integrity 60 (2024) 604–613 Rahul Mittal/ Structural Integrity Procedia 00 (2019) 000 – 000

610

Table 2 . Comparison of Linearized results for Mesh sensitivity Stress Category Path 1 (Fine Mesh)

Path 2 (Present Mesh)

Difference (percentage)

P L

151.45 265.18

151.49

0.02% 0.007%

P L + P b

265.2

6. Loadings & constraints: Thermal Transient analysis: Each temperature transient is divided into load steps and sub steps depending upon the nature of the cycle. Bulk mean temperature with respect to time applied on inner surface of the Shell to find temperature distribution across the thickness. Corresponding heat transfer coefficient with respect to temperature is applied. Adiabatic condition with reference outside temperature of 40°C is assumed on the outer surface shell and nozzle. Adiabatic condition is considered at the outer face of shell and nozzle as they are insulated. Structural Static Analysis: Temperature mapping with respect to time used (extracted from Thermal Transient analysis) as input to perform stress analysis for Level A and Level B service conditions. Tangential and axial structural constraints at appropriate locations of the assembly are applied. Also, pressure, End thrust pressure, Gravity, and other external loads (nozzle load/piping reaction on nozzle) are applied to account primary stress contribution. The minimum and maximum stress intensities evaluated for the selected sections for various time steps.

Table 3. Loadings Thermal (secondary) & Mechanical (Primary) Conditions Description of conditions Gravity Nozzle Loads

Seismic (OBE/SSE)

Thermal Transients/Temperatures Material properties at Design Temperature Level-A Process Transient Level-B Process Transient and OBE (50 Cycles) Material properties at Design Temperature

Pressure

Design

Design

Y

Y

Y

-

Level A

Operating

Y

Y

-

Y (±OBE) Y (±SSE)

Level B

Operating ± OBE

Y

Y

Y

Level D

Operating ± SSE

Y

Y

Y

Hydro

Test

Y

Y

At Hydro Test temperature

Typical operating transients of hot shutdown to cold shutdown temperature transients vary from 40 0 C to 120 0 C @ of 5 0 C per minute for 1000 cycles. Whereas on secondary side of SG is still at 256 0 C. In case of crash cool down transients the temperature drastically falls from 180 0 C (full power condition) to 40 0 C whereas, in the secondary side of the pressure boundary is still at 256 0 C.

Table 4.Allowable Stress Limit for Pressure Boundary Components as per ASME Section III, Sub-section NB[1] Service condition Code Clause ASME Section III, Sub-section NB Allowable stress limit Design Condition NB-3221 Pm < Sm PL < 1.5 Sm Pm or PL + Pb < 1.5 Sm Level-A NB-3222 PL+ Pb +Q < 3 Sm PL+ Pb +Q+F → Sa, CUF <1 for Fatigue *