Discussions on NACE TM0177 and API 5CT DCB Tests

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15 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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1

Discussions on NACE TM0177 and
API 5CT DCB Tests




Xin

Long

Pete Moore


U. S. Steel Tubular Products


Westminster, CO

06/12/2012

2

Acknowledgments


Dr. Karol
Szklarz


Dr. David
Sponseller

3

Outline


Introduction


Effects of Slot/Crack Tip Location on K
ISSC

&
K
Iapplied


Effects of Fatigue
Precrack

on K
ISSC


Summary

4

Introduction


DCB Test (Dynamic Process) Includes:


Mechanical Driving Force: Cracking


Electro
-
Chemical Driving Force: Cracking
Resistance


Interaction between Mechanical and Electro
-
Chemical Driving Forces

5

Effects of Crack / Slot Tip Locations on
K
Iapplied

Precrack

(0.04
-
0.12")
with Chevron

slot

a
i
=1.58"

EDM slot (0.125“)

slot

a
i
=1.63"

In Proposed Revision of NACE TM0177
-
2005











length
crack
inital
a
nt
displaceme
arm
where
h
a
h
a
h
a
h
B
B
a
h
Ea
K
i
i
i
i
n
i
i
Iapplied










:
/
054
.
12
/
447
.
20
/
71
.
105
5168
.
9
/
/
38
.
2
3
2
3
2
2
/
3
3
/
1
h

B

Chevron crack
starter

slot

a
i
=1.50"

B
n

Example:

C110 in 100% H
2
S



= 0.02 inch

K
Iapplied

(Chevron starter)
= 31.3
ksi

in
0.5

K
Iapplied

(
precrack
)
= 29.3
ksi

in
0.5

K
Iapplied

(EDM slot 1)
= 28.1
ksi

in
0.5

K
Iapplied

(EDM slot 2)
= 25.5
ksi

in
0.5

Both can affect
K
Iapplied

EDM slot (0.25“)

slot

a
i
=1.75"

(highest
K
Iapplied
)

(medium
K
Iapplied
)

(medium
K
Iapplied
)

(lowest
K
Iapplied
)

6

Effects of Crack / Slot Tip Locations on K
ISSC
&

K
LIMIT

In NACE TM0177
-
2005











length
crack
a
load
off
lift
P
where
Bh
B
B
a
h
Pa
K
n
ISSC





:
/
/
38
.
2
3
2
2
/
3
3
/
1
It may also affect K
LIMIT

K
Iapplied

(EMD slot 2)

K
Iapplied

(Chevron with
Precrack
)

K
Iapplied

(Chevron crack starter)

[1]

[1] K
LIMIT

figure from David
Sponseller

‘s presentation at API
summer meeting in 2011, San Francisco, CA

K
ISSC

variation caused by different arm
displacement, it should also apply to
K
ISSC

variation caused by crack length

7

Rationale

a
p

a
p

expected

a
p

actual





length
crack
a
load
off
lift
P
where
Bh
B
B
a
h
Pa
K
n
ISSC





:
/
/
38
.
2
3
2
2
/
3
3
/
1
Decreased electro
-
chemical driving
force with the time increasing results
in to a higher K
ISCC

for lager
K
Iapplied

Higher electro
-
chemical driving
force results in to a lower K
ISCC

for
smaller
K
Iapplied

Larger
K
iapplied

(larger arm displacement)

Standard
K
Iapplied

Arm Displacement Effect

a
p

a
p

expected

a
p

actual

Smaller
K
iapplied

(lower initial load)

Standard
K
Iapplied

Crack Length Effect

8

Crack / Slot Locations: Recommendation

Chevron crack
starter

(highest
K
Iapplied
)


Precrack

(0.04
-
0.12")
with Chevron

(medium
K
Iapplied
)

EDM slot (0.25" / 0.125")

(lowest
K
Iapplied
)

slot

slot

slot

a
i

a
i

a
i

B
n

B

EDM slot to line up
with Chevron base

slot

a
i

For mild sour environment:


Need to study if the EDM affect the crack initiation.

0.25”

9

Crack / Slot Tip Locations: Compliance

Chevron

EDM slot

(0.125” /0.25”)

slot

slot

a
i

a
i

B
n

B

Slightly compliance change for EDM slot
due to more material removed, and results
in
K
Iapplied

4
-
5%

lower than Chevron slot.

[commented by Dr. Karol
Szklarz
]

EDM line up

slot

a
i

Initial calculation:



0.25” EDM slot and 0.125” EDM slot has
0.013 in
3

and 0.008 in
3

less material than
Chevron specimen, respectively.



EDM slot line up has 0.001 in
3

less
material than Chevron sample

expecting similar compliance to Chevron
specimen.



Austrian student has lined EDM slot up middle
of the Chevron and got same results as Chevron
slot. [commented by Dr. David
Sponseller
]. It
was found it has 0.005 in
3

more material.


Need more detail compliance study [commented
by Dr. Karol
Szklarz
]

slot

EDM line up
2

10

Crack / Slot Locations: Compliance FEA

CEB

a/h

11

Effects of Fatigue
Precracking

on K
ISSC


Fatigue Loading for
Precrack


NACE TM0177


Max. K
I

for
precrack

loading is the
lesser

of 70% of
expected
K
Iapplied

and 27
ksi

in
0.5


Crack should be sharpened at
2/3

of the max loading
at final stage.


API 5CT


Max. K
I

for fatigue loading <
18.6

ksi

in
0.5

Feasible ???

Material

Environment

Arm Disp.
(in)

a
i

(in)

0.7*
K
iapplied

(
ksi

in
0.5
)

Max.
Fatigue
Load (lb)

Final
Fatigue
Load (lb)

C110

100% H2S

0.020

1.50

21.9

340

227

C110

7% H2S

0.035

1.50

38.4 ‒›

27

420

280





2
/
3
3
/
1
/
/
38
.
2
3
2
Bh
B
B
a
h
Pa
K
n
I


12

Effects of Fatigue
Precracking

on K
ISSC

Szklarz
, K.E. and Perez, T.E., “Observation on the Use of the Double
Cantilever Beam Specimen for Sulfide Stress Corrosion Tests”, NACE
CORROSION 1995, paper No.95048. (Houston, TX, 1995)

Scatter


What Happens if Fatigue
Precrack

Loading Is too High?

13

Fatigue
Precracking
: Recommendation


Fatigue Loading for
Precrack


Max. K
I

for
precrack

loading is less than
90%

expected
K
Iapplied

Material

Environment

Arm Disp.
(in)

a
i

(in)

0.9*
K
iapplied

(
ksi

in
0.5
)

Max.
Fatigue
Load (lb)

C110

100% H2S

0.020

1.50

28.2

436

C110

7% H2S

0.035

1.50

49.3

762

Suggested by Dr.
Karol
Szklarz

14

Summary


Initial crack length should cause attention.


EDM slot line up with Chevron base.


Possible work group for compliance
development.


Max. K
I

for fatigue
precrack

to be less than
90% of expected
K
iapplied
.

15



Questions?




Thank you!