0
Research Papers: Design and Analysis

Stress Mitigation Design of a Tubesheet by Considering the Thermal Stress Inducement Mechanism

[+] Author and Article Information
Masanori Ando

Japan Atomic Energy Agency,
4002 Narita, Oarai,
Higashi-ibaraki,
Ibaraki 311-1393, Japan
e-mail: ando.masanori@jaea.go.jp

Hideki Takasho

ASCEND Co., Ltd.,
4002 Narita, Oarai,
Higashi-ibaraki,
Ibaraki 311-1393, Japan
e-mail: takasho.hideki@jaea.go.jp

Nobuchika Kawasaki

Japan Atomic Energy Agency,
4002 Narita, Oarai,
Higashi-ibaraki,
Ibaraki 311-1393, Japan
e-mail: Kawasaki.nobuchika@jaea.go.jp

Naoto Kasahara

The University of Tokyo/Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan
e-mail: kasahara@n.t.u-tokyo.ac.jp

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received October 23, 2012; final manuscript received May 20, 2013; published online October 7, 2013. Assoc. Editor: Somnath Chattopadhyay.

J. Pressure Vessel Technol 135(6), 061207 (Oct 07, 2013) (10 pages) Paper No: PVT-12-1162; doi: 10.1115/1.4024618 History: Received October 23, 2012; Revised May 20, 2013

Adoption of double-wall straight-tube steam generators (SGs) made of Mod.9Cr-1Mo steel is planned for next-generation fast breeder reactors (FBRs) in Japan. One of the major concerns with the SG is the structural integrity of the tubesheet. During a transient event, a maximum thermal stress may be induced by the temperature distribution in the tubesheet, and the magnitude of the stress depends on the configuration of the tubesheet. Therefore, the stress generation mechanism of a tubesheet was studied through finite element (FE) analysis. Semispherical tubesheet models were investigated for the first survey of the thermal stress mechanism. The calculated results of the semispherical tubesheet model indicated an extensive peak stress around the outermost hole. The recognized thermal stress mechanism of a semispherical tubesheet is as follows: (1) The dominant thermal stress is hoop stress caused by the temperature difference between the perforated and surrounding regions. (2) The thermal stress is insensitive to the size of the specific portion, although it is dominated by an interaction mechanism between the perforated and surrounding regions. (3) The stress concentration around the edge of the holes generates a peak stress. (4) The amplitude of the peak stress depends on the tubesheet penetration angle, and the stress concentration becomes greatest near the outermost hole. Based on the above stress generation mechanism, we proposed a stress-mitigated tubesheet, a center-flattened spherical tubesheet (CFST), as an improved configuration. The calculated peak stress of the CFST was smaller than that of the semispherical tubesheet. Further investigation revealed the detailed stress generation mechanism of the CFST during a thermal transient. There were, in fact, two different comparable thermal peak stress mechanisms observed for the CFST. Both the location and magnitude of the maximum peak stress depended on the steam temperature histories during the thermal transient. The radial stress caused by structural discontinuity, which was located at the outermost hole, depended on the rate (dT/dt) of the steam temperature change. The hoop stress caused by the interaction between the perforated and surrounding regions, which occurred at the first inner layer hole (with respect to the outermost layer holes) depended on the range (ΔT) of the steam temperature change.

Copyright © 2013 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Tubesheet structure for double-wall-tube steam generators in FBRs

Grahic Jump Location
Fig. 2

Steam temperature in the SG for a thermal transient based on the manual trip of the reactor

Grahic Jump Location
Fig. 3

Axisymmetric models for investigating the interaction mechanism between the perforated and surrounding regions

Grahic Jump Location
Fig. 4

Stress distribution along the inner surface of the tubesheet

Grahic Jump Location
Fig. 5

Partially perforated model for investigating the local stress concentration mechanism around the tube holes

Grahic Jump Location
Fig. 6

Local stress distribution around the holes at 368 s after initiation of the thermal transient: (a) distribution around the holes and (b) distribution along the holes

Grahic Jump Location
Fig. 7

Relationship between the stress intensity along the inner surface and the penetration angle

Grahic Jump Location
Fig. 8

Geometries of the CFST

Grahic Jump Location
Fig. 9

Optimization of the tubesheet design for (A) pressure conditions and (B) thermal transient conditions

Grahic Jump Location
Fig. 10

Partially perforated model for investigating the local stress concentration mechanism in the CFST

Grahic Jump Location
Fig. 11

Local stress distribution around the holes at 400 s after initiation of the manual trip

Grahic Jump Location
Fig. 12

Comparison of the local stress distribution around the holes at 400 s to 916 s, where the hole IDs are defined in Fig. 9. (a) The outermost hole (13-1). (b) A hole in the second outermost layer of holes (19-2).

Grahic Jump Location
Fig. 13

Relationship between the steam temperature and stress intensity of hole edges for holes 13-1 and 19-2

Grahic Jump Location
Fig. 14

Thermal transient conditions for the steam temperature in the SG assumed to investigate the relationship between the change in the temperature and the thermal stress inducement mechanism

Grahic Jump Location
Fig. 15

Local stress distributions around the holes at 1280 s and 1920 s: (a) distribution around the outermost hole 13-1 and (b) distribution around the second outer layer hole 19-2

Grahic Jump Location
Fig. 16

Relationships between the stress intensity and thermal transient parameters (a) Stress intensity versus ΔT, (b) stress intensity versus dT/dt. (Note that dT/dt is average rate of temperature change from ti to tj, where ti and tj are the times of the thermal transient history: 500 °C, (t = 0) → 520 °C → 500 °C, (ti) →minimum temperature (tj))

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In