Download Pipelines Defects Assements - Will Defect Fails ? PDF

TitlePipelines Defects Assements - Will Defect Fails ?
Tags Mechanical Engineering Yield (Engineering)
File Size296.8 KB
Total Pages22
Table of Contents
                            HOW A PART WALL DEFECT IN A PIPELINE FAILS
BACKGROUND TO METHODS FOR ASSESSING METAL LOSS DEFECTS
DEFECT DIMENSIONS (THROUGH WALL DEFECT)
THROUGH WALL DEFECTS
‘FOLIAS’ OR ‘BULGING’ FACTOR
FOLIAS FACTOR
THE FLOW STRESS
SUMMARY - FAILURE OF THROUGH WALL DEFECTS
DEFECT DIMENSIONS (PART WALL DEFECT)
PART WALL DEFECTS
FAILURE OF PART WALL DEFECTS - FAILURE
FAILURE OF PART WALL DEFECTS - LEAK RUPTURE
SUMMARY - ASSESSING AN AXIAL METAL LOSS DEFECT
SAFETY FACTORS ON PIPELINE DESIGN PRESSURE
ESTIMATED REPAIR FACTOR
                        
Document Text Contents
Page 1

1

Page 2

2

Gas Operations manager
By: Khaled Al Awadi

Page 11

THE FLOW STRESS

11

The flow stress is not a precisely defined term, it lies
somewhere between the yield strength and the ultimate
tensile strength of the material.
A number of different definitions of the flow stress have
been proposed (often depending on what form gives the
best fit to the experimental data).

The following have been quoted in the published literature:

y + 10 ksi
1.1 y
1.15 y
( y + u)/2
0.9 u

Page 12

12

SUMMARY - FAILURE OF THROUGH WALL
DEFECTS

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6 7 8

2c/(Rt)^0.5

Fa
ilu

re
S

tr
es

s/
Yi

el
d

S
tr

en
gt

h

RUPTURE

LEAK

This boundary is not sensitive to pressurising medium

2c or l

t

Page 21

ESTIMATED REPAIR FACTOR

21

An intelligent pig inspection report will often refer to the ERF (estimated
repair factor) of a defect.
The ERF calculation is another way of expressing an ASME B31G
assessment.
If the ERF is less than one the defect is acceptable to ASME B31G.
If the ERF is greater than one the defect is not acceptable to ASME
B31G.
P’ =failure pressure

'P
MAOP

ERF

4.0Bfor11.1

04for

13
2

1

3
2

1
1.1

'
2

t
d

P

.B

At
d
t
d

P
P

Dt
L

A m893.0

P is the design pressure

1
167.01.1

2

td
td

B

Page 22

22

PIPELINE DEFECT ASSESSMENT - USING THE
HYDROTEST LEVEL AS A SAFETY MARGIN

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

2c/(Rt)^0.5 (normalised defect length)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

d/
t (

no
rm

al
is

ed
d

ef
ec

t d
ep

th
)

DESIGN PRESSURE (72 percent SMYS)

HYDROTEST PRESSURE (100 percent SMYS)

Safety Margin

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