PSI - Issue 14

Ramesh Kumar et al. / Procedia Structural Integrity 14 (2019) 577–583 R. Kumar/ Structural Integrity Procedia 00 (2018) 000–000

580

4

3 +

σ σ

σ

=

h

a

hyd

1

(

)

1

+

p σ ν

σ

=

hyd

2

3

where σ p is peak stress at flaw tip location σ h and σ a are nominal hoop stress and nominal axial stress in pressure tube.

2.2. Elastic peak flaw-tip stress calculation for a bearing pad fretting flaw

The peak principal flaw-tip stress at a bearing pad fretting flaw was calculated for elastic material behavior using elastic stress concentration factor, kt. The peak principal flaw-tip stress at a bearing pad fretting flaw was calculated using

t n p k σ σ =

2.3. Acceptance criteria for bearing pad fretting flaw for service level A loading

For flaw-tip hydride ratcheting conditions, prevention of DHC initiation was demonstrated by satisfying the following inequality for each Service Level A loading of concern:

σ σ <

p

th

σ p = peak principal flaw-tip stress based on linear elastic material behaviour σ th = threshold peak flaw-tip stress for onset of DHC initiation under flaw-tip hydride ratcheting conditions

3. Bounding envelop of bearing pad fretting flaw sizes for DHC initiation

Bounding envelop of bearing pad fretting flaw was developed for threshold bulk H eq and volumetric flaw depth for DHC initiation at sustained hot condition. Several flaw root radius (r) were assumed to arrive at bounding flaw sizes and threshold bulk H eq in the PT. Peak stress evaluation was performed assuming hydride ratcheting condition at flaw tip at sustained hot condition. Four locations, rolled joint inlet/ outlet and PT main body inlet/outlet were selected to assess DHC initiation for volumetric flaws.

3.1. DHC initiation condition away from rolled joint region

The assessment was performed for pressure tube inlet and outlet region away from rolled joint. Bounding flaws for DHC initiation were assumed to have axial flaw length (2c) equal to 30mm. Only internal pressure loading of primary heat transport system was applying during sustained hot condition. The result of threshold bulk H eq and respective bounding flaw sizes for DHC initiation are plotted in Fig. 3-4.