Issue 52

S. Budhe et alii, Frattura ed Integrità Strutturale, 52 (2020) 137-147; DOI: 10.3221/IGF-ESIS.52.12

t

th max





(4)

P

flow



r  

i

Sr. No Criteria

Damage factor/remaining strength

Defect Shape

Bulging/Folias factor

Flow stress



IfA

4,

f



  

2 2 1 3        d t A d t f

2 1 3  





1





 

ASME B31G [6]

L

 

 







1.1

Parabolic

1

0.893  

A

flow

y

 

f

D t

t







IfA

4 ,

t d  

f

2

 

 

 

  

2

2

L

L

1             d t M

RSTREN G (Modified ASME B31G) [9]

 

0.00375    

M

1 0.275

1 0.85 

Effective area/length mixed

t

0.85

D t 

D t 

  



69

t

2



 

flow

y

d t       

1 0.85

2





L

3.3 0.032   

M

   

t

D t



  

1            d t Q

1

2 1 0.31 L 



   



  Rectan.



 



  

Q

3

DNV [8]

   

flow

ult

d t         

D t

1



d t          

  

1

1

Ritchie and Last criterion [11]

M

t

1

 







2







0.9

L

Rectan.

4

d t       

flow

ult

1 0.8   

M

   

1

t

D t



1

   

    



  

   

   

PRC Battelle [11]

d

L

 



1 1       exp



5

Elliptical

0.157

flow

ult



 R t d



t

 

 

Table 1: Damage factor (remaining strength) and flow stress equation of different criteria/model

There are many existing semi-empirical models available in the literature and the most widely used are listed in Tab.1 da Mattos et al. [11] found that the remaining strength factor value differs almost 50-80% with respect to different semi- empirical models for the same defect size on metallic pipelines. This is a large variation in the remaining strength factor value found for the same defect geometry and hence proper selection of the model is necessary, as per the area of application. Similarly, the flow stress value also differs with respect to the selection of the model (Tab. 1). However the flow stress value should be less than the ultimate strength of the pipe material ( ≤ ) for safe design. On the contrary, the flow stress exceeds the ultimate strength as per RSTRENG 0.85 criterion due to the high strength pipe metal having a very small difference in yield and ultimate strength [19]. Therefore, for a high strength metal pipe, it would be better to take the ultimate stress as the flow stress. In summary, the remaining strength factor and flow stress factor play an important role for predicting the burst pressure.

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