research report 191 - health and safety executive · research report 191. references 1. gardner l,...

HSEHealth & Safety

Executive

Integrity of Repaired Welds (Phase 1)- Deliverable 5 Summary Report

Prepared by Serco Assurance for the Health and Safety Executive 2004

RESEARCH REPORT 191

REFERENCES

1. GARDNER L, MELVIN G T AND GOLDTHORPE M R

Integrity of Repaired Welds (Phase 1): Report on Tasks 2, 3, 4 and 5 (Deliverable D2),

Serco Assurance Report, Issued December 2001.

2. DIAZ GARRIDO F A, TOMLINSON R A AND YATES J R

Integrity of Repaired Welds (Phase 1): Report on Task 6 (Deliverable D3)

The University of Sheffield Report, Issued January 2002.

3. GOLDTHORPE M R

Integrity of Repaired Welds (Phase 1): Report on Tasks 7 and 8 (Deliverable D4)

M R Goldthorpe Associates, Issued January 2002.

4. BSI BS 7910:1999

Guide on Methods for Assessing the Acceptability of Flaws in Metallic Structures

British Standards Institution, London, 1999.

5. SHARPLES J K, CLAYTON A M, LACEY D J AND GREEN B L

Assessment of Fracture Mechanics Fatigue Predictions of T-Butt Welded Connections with

Complex Stress Fields

Department of Energy-Offshore Technology Information (OTI 88 536), London,

Her Majesty’s Stationary Office, 1988.

6. ROOKE D J AND CARTWRIGHT D J

Compendium of Stress Intensity Factors, Procurement Executive

Ministry of Defence (ISBN 0 11 771 336 8*), London Her Majesty’s Stationary Office, 1976.

7. R5: Assessment Procedure for the High Temperature Response of Structures

British Energy Generation Limited, Issue 2 Revision 2, 2001.

45

Tab

le 1

Dif

fere

nt

para

mete

rs t

o b

e c

on

sid

ere

d, w

ith

th

e c

od

e f

or

each

vari

an

t in

pare

nth

eses

Par

amet

er

Bas

e ca

se

Alt

ernat

ive

case

s

Pla

te T

hic

knes

s t=

40

mm

(P

T1

) t=

20

mm

(P

T2

)

Surf

ace

Unre

pai

red

def

ect

a=

13

mm

(S

U1

) a=

11

mm

(S

U2

) A

=9

mm

(S

U3

) a=

7m

m (

SU

4)

Em

bed

ded

Unre

pai

red

def

ect

(dep

end

ing o

n p

late

thic

knes

s)

2a=

13

mm

, p

=4

mm

(EU

1)

2a=

11

mm

, p

=6

mm

(EU

2)

2a=

9m

m,

p=

8m

m

(EU

3)

2a=

7m

m,

p=

10

mm

(EU

4)

2a=

11

mm

, p

=2

mm

(EU

5)

2a=

9m

m,

p=

4m

m

(EU

6)

2a=

7m

m,

p=

6m

m

(EU

7)

Evac

uat

ion W

idth

W

ide

exca

vat

ion

(VW

1)

Nar

row

exca

vat

ion

(VW

2)

Surf

ace

Rep

aire

d d

efec

t

a=9

mm

(S

R1

) a=

7m

m (

SR

2)

A=

5m

m (

SR

3)

a=3

mm

(S

R4

)

Em

bed

ded

Rep

aire

d d

efec

t

(dep

end

ing o

n p

late

thic

knes

s)

2a=

9m

m,

p=

4m

m

(ER

1)

2a=

7m

m,

p=

6m

m

(ER

2)

2a=

5m

m,

p=

8m

m

(ER

3)

2a=

3m

m,

p=

10

mm

(ER

4)

2a=

9m

m,

p=

2m

m

(ER

5)

2a=

7m

m,

p=

4m

m

(ER

6)

2

a=5

mm

, p

=6

mm

(ER

7)

2a=

3m

m,

p=

8m

m

(ER

8)

2a=

7m

m,

p=

2m

m

(ER

9)

2a=

5m

m,

p=

4m

m

(ER

10

)

2a=

3m

m,

p=

6m

m

(ER

11

)

2a=

5m

m,

p=

2m

m

(ER

12

)

2

a=3

mm

, p

=4

mm

(ER

13

)

2a=

9m

m,

p=

8m

m

(ER

14

)

2a=

7m

m,

p=

10

mm

(ER

15

)

2a=

5m

m,

p=

12

mm

(ER

16

)

2a=

3m

m,

p=

14

mm

(ER

17

)

Ten

sile

pro

per

ties

of

pla

te a

nd

Unre

pai

red

wel

d

As

mea

sure

d w

ith

over

-mat

ch

(TU

1)

Bo

th h

igher

yie

ld

(TU

2)

Bo

th l

ow

er y

ield

(TU

3)

Pla

te a

s m

easu

red

,

wel

d e

ven

-mat

ch

(TU

4)

Ten

sile

pro

per

ties

of

Rep

air

wel

d

met

al

As

mea

sure

d

(TR

1)

Even

-mat

ch (

TR

2)

Cycl

ic f

atig

ue

pro

per

ties

A

s m

easu

red

(C

Y1

)

Fra

cture

to

ughnes

s (K

)

pro

per

ties

of

Unre

pai

red

wel

d

As

mea

sure

d (

KU

1)

Lo

wer

than

bas

e

case

(K

U2

)

Lo

wer

than

KU

2

(KU

3)

Var

ious

oth

er c

ases

(KU

4 a

nd

so

on)

Fra

cture

to

ughnes

s (K

)

pro

per

ties

of

Rep

aire

d w

eld

As

mea

sure

d (

KR

1)

Sam

e as

KU

1 (

KR

2)

Lo

wer

than

bas

e

case

(K

R3

)

Var

ious

oth

er c

ases

(KR

4 a

nd

so

on)

46

Tab

le 1

(c

on

t’d

)

Dif

fere

nt

para

mete

rs t

o b

e c

on

sid

ere

d, w

ith

th

e c

od

e f

or

each

vari

an

t in

pare

nth

eses

Par

amet

er

Bas

e ca

se

Alt

ernat

ive

case

s

Res

idual

str

esse

s in

Unre

pai

red

wel

d

Full

y s

tres

s-re

liev

ed

wel

d (

RU

1)

Mea

sure

d

as-

wel

ded

(R

U2

)

Inte

rmed

iate

resi

dual

str

ess

case

(RU

3)

Res

idual

str

esse

s in

Rep

aire

d

wel

d

As

mea

sure

d (

RR

1)

Rep

air

wel

ded

und

er h

igh s

truct

ura

l

rest

rain

t (R

R2

)

Rep

air

wel

ded

und

er i

nte

rmed

iate

stru

ctura

l re

stra

int

(RR

3)

Par

tial

ly s

tres

s-

reli

eved

wel

d

rep

air

(RR

4)

Ser

vic

e S

tres

ses

Acc

ord

ing t

o B

S

55

00

w

ith 2

5%

over

load

(S

S1

)

Lo

wer

than

SS

1

(SS

2)

Hig

her

than

SS

1

(SS

3)

Var

ious

oth

er c

ases

(SS

4 a

nd

so

on)

47

Tab

le 2

Resu

lts o

f te

nsile t

ests

Sp

ec N

o

Tem

p

0.2

% P

S

Up

per

YS

L

ow

er

YS

UT

S

%

Elo

ng

ati

on

% R

edu

ctio

n

Ma

teri

al

°C

MP

a

MP

a

MP

a

MP

a

in a

rea

VE

8

19

5

13

6

28

3

1.5

7

9

Cen

tre

Wel

d,

As-

Wel

ded

VE

9

19

5

11

6

17

3

1

76

C

entr

e W

eld

, A

s-W

eld

ed

VE

11

1

9

35

5

41

1

35

1

53

0

43

7

3

Par

ent

VE

12

1

9

34

5

39

4

34

9

52

4

40

7

5

Par

ent

WI7

1

9

53

3

62

7

30

.7

78

R

epai

r w

eld

, n

ear

surf

ace

WI8

1

9

54

6

62

9

28

.9

76

R

epai

r w

eld

, n

ear

surf

ace

WI1

0

19

5

74

6

72

2

8.7

7

4

Rep

air

wel

d,

nea

r ro

ot

WI1

1

19

5

87

6

70

2

7.8

7

7

Rep

air

wel

d,

nea

r ro

ot

WI1

2

19

4

57

6

08

2

3.2

6

8.6

R

epai

r w

eld

, n

ear

roo

t

48

Tab

le 3

Ra

tio

of

cyc

les

to

lim

itin

g c

on

dit

ion

s (

Nre

pair

ed/N

un

rep

air

ed)

for

ed

ge

de

fec

ts i

n a

s-r

ep

air

ed

an

d u

nre

pa

ired

PW

HT

pla

te f

or

vari

ou

s d

ep

ths

an

d f

rac

ture

tou

gh

ne

ss

Nrep

air

ed/N

un

rep

air

ed

Fin

ite

Ele

men

t B

S 7

91

0

Init

ial

Cra

ck

Base

d o

n K

J

Ba

sed

on

K

Ori

gin

al

Ref

ined

K

JC (

MP

aÖ

m)

Dep

th (

mm

)

60

3

.33

0

.49

(0

.66

) 0

.64

(0

.66

) -

-

10

--

--

16.6

7

--

--

80

3

.33

0

.56

(0

.80

) 0

.80

(0

.80

) -

-

10

--

--

16.6

7

--

--

10

0

3.3

3

0.6

4

(0.8

9)

0.8

9

(0.8

9)

0.2

7

(0.2

7)

0.3

5

(0.3

4)

10

--

--

16.6

7

--

--

12

0

3.3

3

0.7

4

(0.9

7)

0.9

6

(0.9

7)

0.5

2

(0.5

1)

0.5

8

(0.5

7)

10

0

.84

(0

.62

) 0

.69

(0

.62

) -

-

16.6

7

--

--

14

0

3.3

3

0.7

7

(0.9

9)

0.9

9

(0.9

9)

0.6

6

(0.6

5)

0.7

1

(0.7

0)

10

1

.05

(0

.85

) 0

.90

(0

.85

) -

-

16.6

7

--

--

16

0

3.3

3

0.7

7

(1.0

0)

0.9

9

(1.0

0)

0.7

5

(0.7

4)

0.7

9

(0.7

9)

10

1

.13

(0

.84

) 0

.96

(0

.94

) -

-

16

.67

0

.26

(0

.21

) 0

.26

(0

.21

) -

-

No

te:

Val

ues

in

bra

cket

s o

bta

ined

fro

m E

qu

atio

n (

11

)

49

current practices

repairs and

literature review

engineering

engineering

Review of industrial

companies to assess

and problems

associated with weld

Scoping calculations

using simplified

methods to establish

likely matrix of cases

to consider

Weld/Specimen

Manufacture

Material

characterisation

(mechanical

properties plus

metallurgical

studies)

Residual stress

measurements

Validation

Development of

finite element models

Testing involving

photoelastic coating

and thermal

emission methods in

order to assess effect

of residual stresses

on crack growth

Validation

Application of

analytical models to

matrix cases

Structural tests to

evaluate influence of

weld repairs on

structural integrity

Assessment of

analytical models

and experiments by

procedure methods

General guidance on

weld repairs

General guidance on

procedure method

Figure 1 Flow diagram showing components of project

Figure 2 Test plate weld procedure

Figure 3 Test plate repair weld procedure

loadingloading

surface-breaking

defecta

B

repairside 2

side 1

loadingloading

embedded

defect2a

p

B

repair

side 1

side 2

side 1

a

B

loading loading

surface-breaking

defect

repair side 2

Figure 4 Surface defect at the weld root

2a

p

B

loading loading

embedded

defect

repair

side 1

side 2

Figure 5 Embedded defect near the weld root

2a

p

loading loading

original

surface-breaking

defect

wide

excavation

embedded defect

remaining

Figure 6 Wide excavation of surface defect, leaving embedded defect in repaired condition

2a

p

loading loading

original

surface-breaking

defect

narrow

excavation

embedded defect

remaining

Figure 7 Narrow excavation of surface defect, leaving an embedded defect in repaired condition

surface

loading loading

original

defect

excavation

surface defect

remaining

Figure 8 Excavation of surface defect, leaving a surface defect in repaired condition

loading loading

original

embedded

defect

excavation

embedded defect

remaining

Figure 9 Excavation of embedded defect, leaving an embedded defect in repaired condition

t=40mm SU1 ER1 ER2 ER3 ER4 t=40mm SU2 ER5 ER6 ER7 ER8

a=13

2a=9

p=4

2a=7

p=6

2a=5

p=8

2a=3

p=10

a=11

2a=9

p=2

2a=7

p=4

2a=5

p=6

2a=3

p=8

t=40mm SU3 ER9 ER10 ER11 t=40mm SU4 ER12 ER13

a=9

2a=7

p=2

2a=5

p=4

2a=3

p=6

a=7

2a=5

p=2

2a=3

p=4

Figure 10 Proposed defect configurations to be studied in the 40 mm thick plate – surface defect in unrepaired condition (solid line) and embedded in repaired condition

(dashed line)

t=40mm SU1 SR1 SR2 SR3 SR4 t=40mm SU2 SR1 SR2 SR3 SR4

a=13

a=5 a=7

a=3

a=9

a=11

a=5 a=7

a=3

a=9

t=40mm SU3 SR1 SR2 SR3 SR4 t=40mm SU4 SR2 SR3 SR4

a=9

a=5 a=7

a=3

a=9 a=7

a=5 a=7

a=3

Figure 11 Proposed defect configurations to be studied in the 40 mm thick plate – surface defect in both unrepaired (solid line) and repaired (dashed line) conditions

EU1 ER14 ER15 ER16 ER17 EU2 ER14 ER15 ER16 ER17

t=40mm t=40mm

2a=13 2a=9

p=8

2a=7

p=10

2a=5

p=12

2a=3

p=14

p=4

2a=11 2a=9

p=8

2a=7

p=10

2a=5

p=12

2a=3

p=14

p=6

EU3 ER14 ER15 ER16 ER17 EU4 ER15 ER16 ER17

t=40mm t=40mm

2a=9 2a=9

p=8

2a=7

p=10

2a=5

p=12

2a=3

p=14

p=8

2a=7 2a=7

p=10

2a=5

p=12

2a=3

p=14

p=10

Figure 12 Proposed defect configurations to be studied in the 40 mm thick plate -embedded in both unrepaired (solid line) and repaired (dashed line) conditions

ER3 ER4ER2ER1 SU2 ER8ER6ER5

2a=7

a=13

SU1

2a=5 t=20mm 2a=3

2a=9

p=4

p=6

p=8 p=10

a=11

t=20mm

ER7

2a=9

p=2

2a=7

p=4

2a=5

p=6

2a=3

p=8

SU3 ER9 ER10 ER11 SU4 ER12 ER13

a=9 t=20mm t=20mm a=7

2a=5

p=2

2a=3

p=4

2a=3 2a=5 2a=7

p=6 p=4

p=2

Figure 13 Proposed defect configurations to be studied in the 20 mm thick plate – surface defect in unrepaired condition (solid line) and embedded in repaired condition

(dashed line)

SU2 SR3SR1SU1 SR3 SR4SR2SR1

a=7

a=11

a=5

t=20mm

SR4

a=3

SR2

a=9 a=7

a=13

a=5

t=20mm

a=3

a=9

SU4 SR2 SR3 SR4SU3 SR1 SR2 SR3 SR4

t=20mm a=9 a=9 t=20mm a=7 a=7 a=7

a=5

a=3

a=5

a=3

Figure 14 Proposed defect configurations to be studied in the 20 mm thick plate – surface defect in both unrepaired (solid line) and repaired (dashed line) conditions

2a=7 2a=11

2a=5 t=20mm 2a=3 2a=9

p=2 p=4

p=6 p=8

p=10

EU5 ER1 ER2 ER3 ER4

EU6 ER3 ER4ER2 EU7 ER3 ER4ER2

2a=7 2a=9

2a=5 t=20mm 2a=3 2a=9

ER1

p=4 p=4

p=6 p=8

p=10 2a=7

2a=7

2a=5 t=20mm 2a=3

p=6 p=6 p=8

p=10

Figure 15 Proposed defect configurations to be studied in the 20 mm thick plate -embedded defect in both unrepaired (solid line) and repaired (dashed line) conditions

Fig

ure

16

T

es

t p

late

us

ed

fo

r a

ll e

xp

eri

me

nta

l w

ork

0

50

100

150

200

250

2

D

J-2

J-2

J, kJm-

VE

1 S

ing

le s

pec

imen

dat

a

End p

oin

t V

E1

VE

2 S

ing

le s

pec

imen

dat

a

End p

oin

t V

E2

Curv

e fi

t

J=234.6

1a^

0.5

0062

0.2

BL=

115.5

kJm

0.2

=104.7

kJm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

ST

AB

LE

CR

AC

K E

XT

EN

SIO

N,

mm

Fig

ure

17

J

-R c

urv

e o

bta

ine

d f

rom

fra

ctu

re t

es

ts o

n a

s-w

eld

ed

sp

ec

ime

ns

0

50

100

150

200

250

300

J, kJm-2

D

J-2

J-2

WI2

End

poin

t of

WI2

Curv

e fi

t to

WI2

Curv

e fi

t to

VE

1/V

E2, as

-wel

ded

mat

eria

l

J=263.3

5a^

0.5

9206

0.2

BL

=119.0

kJm

0.2

=101.6

kJm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

ST

AB

LE

CR

AC

K E

XT

EN

SIO

N, m

m

Fig

ure

18

J

-R c

urv

es

ob

tain

ed

fro

m f

rac

ture

te

st

on

re

pa

ir-w

eld

ed

sp

ec

ime

n

da

/dN

(m

/cy

cle

)

1.00E-05

1.00E-06

1.00E-07

1.00E-08

VE5 da/ dN = 1.360* 10-11 DK2.786

Validity Limit

WI6 da/ dN = 1.153* 1-11 D0 K2.762

VE5 Pre weld repai r

WI6 Post weld repair

10 100

DELTA-K(MPam0.5)

Figure 19 Fatigue crack growth test results

Depth (m m ) 40

35

30

25

20

15

Gauges 1

& 5

Gauges 2

& 6

Hole

-drilli

ng v

alu

e,

Sid

e 1

Hole

-drilli

ng v

alu

e,

Sid

e 2

10 5 0 -4

00

-200

0

200

400

600

800

Str

ess (

MP

a)

Fig

ure

20

A

s-w

eld

ed

re

sid

ua

l s

tre

ss

- Y

dir

ec

tio

n -

pe

rpe

nd

icu

lar

to w

eld

Depth (m m )

40

35

30

25

20

Gauges 3

& 7

Gauges 4

& 8

Hole

-drilli

ng v

alu

e,

Sid

e 1

Hole

-drilli

ng v

alu

e,

Sid

e 2

15

10 5 0

0

100

200

300

400

500

600

700

800

Str

ess (

MP

a)

Fig

ure

21

A

s-w

eld

ed

re

sid

ua

l s

tre

ss

- X

dir

ec

tio

n -

pa

rall

el

to w

eld

Depth (m m )

40

35

30

25

20

Gauges 1

& 5

Gauges 2

& 6

Hole

-drilli

ng v

alu

e, S

ide 1

Hole

-drilli

ng v

alu

e, S

ide 2

15

10 5 0 -4

00

-200

0

200

400

600

800

Str

ess (

MP

a)

Fig

ure

22

R

ep

air

-we

lde

d r

es

idu

al

str

es

s -

Y d

ire

cti

on

- p

erp

en

dic

ula

r to

we

ld

Depth (mm)

40

35

30

25

20

15

10 5 0 -1

00

0

100

200

300

400

500

600

700

800

Str

ess (

MP

a)

Fig

ure

23

R

ep

air

-we

lde

d r

es

idu

al

str

es

s -

X d

ire

cti

on

- p

ara

lle

l to

we

ld

Gau

ge

s 3

& 7

Gau

ge

s 4

& 8

Hole

-drilli

ng v

alu

e, S

ide 1

Hole

-drilli

ng v

alu

e, S

ide 2

Figure 24 Specimen dimensions, in mm

-5

0

5

10

15

20

25

30

Öm

Str

ess In

ten

sity F

acto

r R

an

ge

, M

Pa

Mode I by RAT

Mode I by FGD

Mode II by RAT

Mode II by FGD

KI Theory

AEA3, R=0.13

4 6 8 10 12 14 16 18

Crack length, mm

Figure 25 DKI against crack length. Included is a comparison of the results of processing by

different operators

da/d

N, m

m/c

0.000001

0.00001

0.0001

0.001

AEA1, R=0.13

AEA2, R=0.1

AEA_F3, R=0.58

AEA1, R=0.13, Deltatherm data

AEA2, R=0.1, Deltatherm data

AEA_F3, R=0.58, Deltatherm data

AEAT growth equation

1 10 100

DK

Figure 26 Original weld crack propagation results, using stress intensity factors calculated from

published calibration equations and measured directly using Deltatherm

35

30

25

20

15

10

5

0

0 5

Original weld, R=0.13 Original weld, R=0.1 Repair weld, R=0.13 Repair weld, R=0.1 Repair weld, R=0.28 Original weld, R=0.58 Repair weld, R=0.58

10 15 20

Clo

sure

K,

MP

aÖ

m

25

-5

Crack length, mm

Figure 27 Estimates of crack closure

1

2

3

4

56

7

8

9

Original Weld Side 1Side 2

1

2

3

4

Repair WeldSide 2 Side 1

1

2

3

4

56

7

8

9


1

2

3

4

56

7

8

9

1

2

3

4


1

2

3

4

Plane of symmetry

1

2

3

4

5 6

7

8

9


1

2

3

4


Plane of symmetry

Figure 28 Front face of finite element model of the plate in the region of the weld

axisymm

mesh of

repair weld

axis of

rotation

original weld

etric

sphere

repair weld

axis of

rotation

original weld

axisymmetric

mesh of sphere

Figure 29 Axisymmetric finite element mesh of equatorially welded sphere

Tru

e st

ress

, M

Pa

700

600

500

400

300

200

Specimen VE8, weld material

100 Specimen VE9, weld material

Specimen VE11, parent plate

Specimen VE12, parent plate 0

0.00 0.01 0.02 0.03 0.04 True strain

oFigure 30 Measured true stress versus true strain results at 20 C

(a)

0

100

200

300

400

500

600

700

0.00 0.01 0.02 0.03 0.04True strain

Tru

e st

ress

, M

Pa





Extrapolated parent with Luders strain removed

Smoothed weld data

Modified weld data incorporating 12% plastic strain

(b)

0

200

400

600

800

1000

1200

1400

0.00 0.10 0.20 0.30 0.40True strain

Tru

e st

ress

, M

Pa





Extrapolated parent with Luders strain removed

Smoothed weld data

Modified weld data incorporating 12% plastic strain

Figure 31 True stress versus true strain at 20oC as used in the analyses: (a) for small

strain, (b) for larger strains, solid blue and red curves show the properties used in the

analyses

(a)

Plate measurements and analyses: Transverse stress perpendicular to weld (S22)

0

10

20

30

40

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm

Original Plate Weld - Gauges 1 & 5


FEA - Original Plate Weld, no PWHT

Plate Repair Weld - Gauges 1 & 5


FEA - Original Plate Weld (no PWHT), then Repair

(b)

Plate measurements and analyses: Longitudinal stress parallel to weld (S33)

0

10

20

30

40

-200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm







Figure 32 Variation of measured and predicted residual stress through the middle of the

plate weld: (a) transverse, (b) longitudinal

(a)

Plate analyses: Transverse stress perpendicular to weld (S22)

0

10

20

30

40

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm



FEA - Plate Weld with PWHT

FEA - Plate Weld with PWHT, then Repair

(b)

Plate analyses: Longitudinal stress parallel to weld (S33)

0

10

20

30

40

-200 -100 0 100 200 300 400 500 600 700 800Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm





Figure 33 PWHT and repaired weld predictions of residual stress in the plate: (a)

transverse, (b) longitudinal

(a)

Sphere analyses: Transverse stress perpendicular to weld (S22)

0

10

20

30

40

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm

FEA - Sphere Weld, no PWHT

FEA - Sphere Weld (no PWHT), then Repair

FEA - Sphere Weld with PWHT

FEA - Sphere Weld with PWHT, then Repair

(b)

Sphere analyses: Longitudinal stress parallel to weld (S33)

0

10

20

30

40

-200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm

FEA - Sphere Weld, no PWHT

FEA - Sphere Weld (no PWHT), then Repair



Figure 34 PWHT and repaired weld predictions of residual stress in the sphere: (a)


(a)

Comparison of Plate and Sphere residual stress analyses: Transverse stress perpendicular to weld (S22)

0

10

20

30

40

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

from

Sid

e 1

, m

m





(b)

Comparison of Plate and Sphere residual stress analyses: Longitudinal stress parallel to weld (S33)

0

10

20

30

40

-200 -100 0 100 200 300 400 500 600 700 800

Stress, MPa

Dep

th m

easu

red

fro

m S

ide

1,

mm





Figure 35 Comparison of residual stress predictions for the plate and the sphere: (a)


(a)

40 Comparison of Analyses of Deep and Shallow Repairs in Sphere: Transverse stress perpendicular to weld (S22)

Dep

th m

easu

red

fro

m S

ide

1,

mm

Dep

th m

easu

red

fro

m S

ide

1,

mm 30

20

10

0

-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800Stress, MPa



FEA - Sphere Weld with PWHT, then Shallow Repair

(b)

40 Comparison of Analyses of Deep and Shallow Repairs in Sphere: Longitudinal stress parallel to weld (S33)

30

20

10

0



FEA - Sphere Weld with PWHT, then Shallow Repair

-200 -100 0 100 200 300 400 500 600 700 800Stress, MPa

Figure 36 Residual stress predictions for deep and shallow weld repairs in the sphere:

(a) transverse, (b) longitudinal

(a)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

K,

MP

a m

1/2

Plate PWHT weld, Edge crack, 220 MPa











(b)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

K,

MP

a m

1/2

Plate Repaired weld, Edge crack, 220 MPa











Figure 37 K for various nominal primary stresses versus edge crack depth in plate: (a)

unrepaired PWHT, (b) as-repaired

(a)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

KJ,

MP

a m

1/2












(b)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

KJ,

MP

a m

1/2












Figure 38 KJ for various levels of primary stress versus edge crack depth in plate: (a)


(a)

0

2

4

6

8

10

12

14

16

18

20

0 10000 20000 30000 40000 50000 60000 70000 80000

number of cycles, N

cra

ck d

epth

, a

, m

m

Plate PWHT weld, Edge crack, Op=180MPa, Max=225MPa, (deltaKJ), ao=16.67mm









(b)

0

2

4

6

8

10

12

14

16

18

20

0 10000 20000 30000 40000 50000 60000 70000 80000

number of cycles, N

cra

ck d

epth

, a

, m

m

Plate Repaired weld, Edge crack, Op=180MPa, Max=225MPa, (deltaKJ), ao=16.67mm









Figure 39 Crack depth versus number of cycles for different initial edge crack depths in

plate subjected to 180 MPa cyclic primary stress: (a) unrepaired PWHT, (b) as-repaired

(a)

160

140

1/2

100

120

Jc

, Edg , Op , , ( ),

fra

ctu

re t

ou

gh

nes

s, K

. M

Pa

m









Plate PWHT weld e crack =180MPa Max=225MPa deltaKJ ao=3.33mm

80

60

40

20

0

0 10000 20000 30000 40000 50000 60000 70000 80000number of cycles to limiting condition, Nf

160

140

100

120

Jc

p , Edg , Op , , ( ),

fra

ctu

re t

ou

gh

nes

s, K

. M

Pa

m









Plate Re aired weld e crack =180MPa Max=225MPa deltaKJ ao=3.33mm

1/2

80

60

40

20

0


(b)

Figure 40 Fracture toughness versus cycles to the limiting condition for different initial

edge crack depths in plate subjected to 180 MPa cyclic primary stress and occasional

225 MPa overload: (a) unrepaired PWHT, (b) as-repaired

160

140

1/2

fr

act

ure

to

ug

hn

ess,

KJ

c. M

Pa

m

120

100

80

60

40

Plate Repaired weld, Edge crack, Op=180MPa, Max=225MPa

Plate PWHT weld, Edge crack, Op=180MPa, Max=225MPa

4 6 8 10 12 14 16 18 20 critical crack depth ac, mm

Figure 41 Fracture toughness versus critical crack depth to give limiting condition for

edge defects in unrepaired PWHT and as-repaired plate subjected to 225 MPa overload

stress

0.0

0.5

1.0

1.5

Nf

f

, KJc=50

(rep

air

ed)/

N(u

nre

pa

ired

)

deltaKJ, KJc=160

deltaKJ, KJc=150

deltaKJ, KJc=140

deltaKJ, KJc=130

deltaKJ, KJc=120

deltaKJ, KJc=110

deltaKJ, KJc=100

deltaKJ, KJc=90

deltaKJ, KJc=80

deltaKJ, KJc=70

deltaKJ, KJc=60

deltaKJ

0 2 4 6 8 10 12 14 16 18 20

initial crack depth, mm

Figure 42 Ratio of cycles to limiting condition for edge defects in as-repaired and

unrepaired PWHT plate for various initial depths and fracture toughness

(a)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90

% reduction of repaired toughness from original PWHT value

Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)

KJc(orig)=160, ao_unr=5.00, ao_rep=5.00














KJc(orig)=80, ao unr=5.00, ao rep=3.33

(b)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 43 Ratio of cycles to limiting condition for different size edge defects in as-

repaired and unrepaired PWHT plate as a function PWHT fracture toughness and

percentage toughness reduction in repaired state, for depth before repair

of (a) 5 mm, (b) 6.7 mm

(c)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















(d)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 43 (cont’d) Ratio of cycles to limiting condition for different size edge defects in

as-repaired and unrepaired PWHT plate as a function PWHT fracture toughness and


of (c) 9.2 mm, (d) 10.8 mm

(e)

2.0 N

f(re

pa

ired

)/N

f(u

nre

pa

ired

) 1.5

1.0

0.5

0.0

( g) , ao , ao p















KJc ori =80 unr=13.33 re =5.00

0 10 20 30 40 50 60 70 80 90



as-repaired and unrepaired PWHT plate as a function PWHT fracture toughness and


of (e) 13.3 mm

(a)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

KJ,

MP

a m

1/2

Sphere PWHT weld, surface crack, 220 MPa











(b)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack depth a, mm

KJ,

MP

a m

1/2

Sphere Repaired weld, surface crack, 220 MPa











Figure 44 KJ for various levels of primary stress versus edge crack depth in sphere: (a)


(a)

0

2

4

6

8

10

12

14

16

18

20

0 10000 20000 30000 40000 50000 60000 70000 80000

number of cycles, N

cra

ck d

epth

, a

, m

m

Sphere PWHT weld, surface crack, Op=180MPa, Max=225MPa, (deltaKJ), ao=16.67mm









(b)

0

2

4

6

8

10

12

14

16

18

20

0 10000 20000 30000 40000 50000 60000 70000 80000

number of cycles, N

cra

ck d

epth

, a

, m

m

Sphere Repaired weld, surface crack, Op=180MPa, Max=225MPa, (deltaKJ), ao=16.67mm









Figure 45 Crack depth versus number of cycles for different initial edge crack depths in

sphere subjected to 180 MPa cyclic primary stress: (a) unrepaired PWHT, (b) as-repaired

(a)

160

140

1/2

1

/2

fra

ctu

re t

ou

gh

nes

s, K

Jc.

MP

a m

120

100

Sphere PWHT weld, surface crack, Op=180MPa, Max=225MPa, (deltaKJ),

ao=16.67mm Sphere PWHT weld, surface crack, Op=180MPa, Max=225MPa, (deltaKJ),




ao=10.00mm Sphere PWHT weld, surface crack, Op=180MPa, Max=225MPa, (deltaKJ), ao=8.33mm

80

60

40

20

0


(b)

160

140

100

120

Jc

Sp p , , Op , , ( ),

fra

ctu

re t

ou

gh

nes

s, K

. M

Pa

m









here Re aired weld surface crack =180MPa Max=225MPa deltaKJ ao=3.33mm

80

60

40

20

0


Figure 46 Fracture toughness versus cycles to limiting condition for different initial edge crack depths in sphere subjected to 180 MPa cyclic primary stress and occasional 225

MPa overload: (a) unrepaired PWHT, (b) as-repaired

160

140

1/2

fr

act

ure

to

ug

hn

ess,

KJ

c. M

Pa

m

120

100

80

60

40

Sphere Repaired weld, surface crack, Op=180MPa, Max=225MPa

Sphere PWHT weld, surface crack, Op=180MPa, Max=225MPa

4 6 8 10 12 14 16 18 20 critical crack depth ac, mm

Figure 47 Fracture toughness versus critical crack depth to give limiting condition for

edge defects in unrepaired PWHT and as-repaired sphere subjected to 225 MPa overload

stress

0.0

0.5

1.0

1.5

Nf

f

, KJc=55

(rep

air

ed)/

N(u

nre

pa

ired

)

deltaKJ, KJc=110

deltaKJ, KJc=105

deltaKJ, KJc=100

deltaKJ, KJc=95

deltaKJ, KJc=90

deltaKJ, KJc=85

deltaKJ, KJc=80

deltaKJ, KJc=75

deltaKJ, KJc=70

deltaKJ, KJc=65

deltaKJ, KJc=60

deltaKJ

0 2 4 6 8 10 12 14 16 18 20

initial crack depth, mm

Figure 48 Ratio of cycles to limiting condition for edge defects in as-repaired and

unrepaired PWHT sphere for various initial depths and fracture toughness

(a)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















(b)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 49 Ratio of cycles to limiting condition for different size edge defects in as-

repaired and unrepaired PWHT sphere as a function PWHT fracture toughness and

percentage toughness reduction in repaired state, for depth before repairof (a) 5 mm, (b) 6.7 mm

(c)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















(d)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)

















as-repaired and unrepaired PWHT sphere as a function PWHT fracture toughness and


of (c) 9.2 mm, (d) 10.8 mm

(e)

2.0 N

f(re

pa

ired

)/N

f(u

nre

pa

ired

) 1.5

1.0

0.5

0.0

( g) , ao , ao p















KJc ori =70 unr=13.33 re =5.00

0 10 20 30 40 50 60 70 80 90



as-repaired and unrepaired PWHT sphere as a function PWHT fracture toughness and

percentage toughness reduction in repaired state, for depth before repair of (e) 13.3 mm

(a)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack height 2a, mm

KJ,

MP

a m

1/2

Plate PWHT weld, Embedded crack, 220 MPa











(b)

-40

-20

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14 16 18 20

crack height 2a, mm

KJ,

MP

a m

1/2

Plate Repaired weld, Embedded crack, 220 MPa











Figure 50 KJ for various levels of primary stress versus height of plate embedded

defects (p+2a=16.7 mm): (a) unrepaired PWHT, (b) as-repaired

(a)

160

140

1/2

1

/2

fra

ctu

re t

ou

gh

nes

s, K

Jc.

MP

a m

80

60

40

20

0

0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000number of cycles to limiting condition, Nf

100

120 , , Op , , ( ),

Plate PWHT weld, Embedded crack, Op=180MPa, Max=225MPa, (deltaKJ), 2ao=13.33mm






Plate PWHT weld Embedded crack =180MPa Max=225MPa deltaKJ 2ao=3.33mm

(b)

160

140

100

120

Jc

p , , Op , , ( ),

fra

ctu

re t

ou

gh

nes

s, K

. M

Pa

m

Plate Repaired weld, Embedded crack, Op=180MPa, Max=225MPa, (deltaKJ), 2ao=13.33mm






Plate Re aired weld Embedded crack =180MPa Max=225MPa deltaKJ 2ao=3.33mm

80

60

40

20

0

0 20000 40000 60000 80000 100000 120000 140000 160000 180000 200000number of cycles to limiting condition, Nf

Figure 51 Fracture toughness versus cycles to limiting condition for different initial plate

embedded crack heights (with p+2a=16.7 mm) subjected to 180 MPa cyclic primary

stress and occasional 225 MPa overload: (a) unrepaired PWHT, (b) as-repaired

160

140

1/2

fr

act

ure

to

ug

hn

ess,

KJ

c. M

Pa

m

120

100

80

60

40

20

Plate Repaired weld, Embedded crack, Op=180MPa,

Max=225MPa Plate PWHT weld, Embedded crack, Op=180MPa, Max=225MPa

4 6 8 10 12 14 16 critical crack height 2ac, mm

Figure 52 Fracture toughness versus critical crack height to give limiting condition for

embedded defects (with p+2a=16.7 mm) in unrepaired PWHT and as-repaired plate

subjected to 225 MPa overload stress

160

Jc

fra

ctu

re t

ou

gh

nes

s, K

. M

Pa

m

Plate Repaired weld, Embedded crack, Op=180MPa,

Max=225MPa Plate PWHT weld, Embedded crack, Op=180MPa, Max=225MPa

140

120

100

80

60

40

20

4 5 6 7 8 9 critical crack height 2ac, mm

1/2

Figure 53 Fracture toughness versus critical crack height to give limiting condition for embedded defects (with p+2a=10.8 mm) in unrepaired PWHT and as-repaired plate

subjected to 225 MPa overload stress

0.0

0.5

1.0

1.5

Nf

f(r

epa

ired

)/N

(un

rep

air

ed)

deltaKJ, KJc=110

deltaKJ, KJc=100

deltaKJ, KJc=90

deltaKJ, KJc=80

deltaKJ, KJc=70

deltaKJ, KJc=60

deltaKJ, KJc=50

deltaKJ, KJc=40

deltaKJ, KJc=30

0 2 4 6 8 10 12 14 16 initial crack height 2a0, mm

Figure 54 Ratio of cycles to limiting condition for embedded defects in as-repaired and

unrepaired PWHT plate for various initial heights of embedded crack (with p+2a=16.7

mm) and fracture toughness

0.0

0.5

1.0

1.5

Nf

f(r

epa

ired

)/N

(un

rep

air

ed)

deltaKJ, KJc=60

deltaKJ, KJc=55

deltaKJ, KJc=50

deltaKJ, KJc=45

deltaKJ, KJc=40

deltaKJ, KJc=35

deltaKJ, KJc=30

0 1 2 3 4 5 6 7 8

initial crack height 2a0, mm

Figure 55 Ratio of cycles to limiting condition for embedded defects in as-repaired and

unrepaired PWHT plate for various initial heights of embedded crack (with p+2a=10.8

mm) and fracture toughness

(a)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)

KJc(orig)=110, 2ao_unr=5.00, 2ao_rep=5.00














KJc(orig)=70, 2ao unr=5.00, 2ao rep=3.33

(b)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 56 Ratio of cycles to limiting condition for different height embedded defects (with

p+2a=16.7 mm) in as-repaired and unrepaired PWHT plate as a function PWHT

fracture toughness and percentage toughness reduction in repaired state,

for height before repair of (a) 5 mm, (b) 6.7 mm

(c)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















(d)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 56 (cont’d) Ratio of cycles to limiting condition for different height embedded defects

(with p+2a=16.7 mm) in as-repaired and unrepaired PWHT plate as a function PWHT

fracture toughness and percentage toughness reduction in repaired state,

for height before repair of (c) 9.2 mm, (d) 10.8 mm

(a)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















(b)

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50 60 70 80 90


Nf(

rep

air

ed)/

Nf(

un

rep

air

ed)
















Figure 57 Ratio of cycles to limiting condition for different height embedded defects (with

p+2a=10.8 mm) in as-repaired and unrepaired PWHT plate as a function PWHT

fracture toughness and percentage toughness reduction in repaired state:

for height before repair of (a) 5 mm, (b) 6.7 mm

Fig

ure

58

Cra

ck d

ep

th v

ers

us n

um

ber

of

cycle

s f

or

cra

ck d

ep

ths o

f 3.3

3 m

m,

10 m

m a

nd

16.6

7 m

m i

n p

late

su

bje

cte

d t

o 1

80 M

Pa

cycli

c p

rim

ary

str

ess –

un

rep

air

ed

PW

HT

– B

S 7

910 c

alc

ula

ted

co

mp

are

d w

ith

th

ose o

f F

E (

Fig

ure

39(a

))

02468

10

12

14

16

18

20

010000

20000

30000

40000

50000

60000

70000

Nu

mb

er

of

Cycle

s,

N

Crack Depth (mm)

FE

, P

WH

T,

DK

, a0-3

.33m

m

FE

, P

WH

T,

DK

, a0=

10.0

0m

m

FE

, P

WH

T,

DK

, a0=

16.6

7m

m

FE

, P

WH

T,

DK

J,

a0=

3.3

3m

m

FE

, P

WH

T,

DK

J,

a0=

10.0

0m

m

FE

, P

WH

T,

DK

J,

a0=

16.6

7m

m

BS

7910,

PW

HT

, a0=

3.3

3m

m

BS

79810,

PW

HT

, a0=

10.0

0m

m

BS

7910,

PW

HT

, a0=

16.6

7m

m

Fig

ure

59 C

rack d

ep

th v

ers

us n

um

ber

of

cycle

s f

or

cra

ck d

ep

ths o

f 3.3

3 m

m,

10 m

m a

nd

16.6

7 m

m i

n p

late

su

bje

cte

d t

o 1

80 M

Pa

cycli

c p

rim

ary

str

ess –

rep

air

ed

co

nd

itio

n –

BS

7910 c

alc

ula

ted

co

mp

are

d w

ith

th

ose o

f F

E (

Fig

ure

39(b

))

02468

10

12

14

16

18

20

010000

20000

30000

40000

50000

60000

Nu

mb

er

of

cycle

s,

N

Crack Depth (mm)

FE

, R

epair

ed,

DK

, a0=

3.3

3m

m

FE

, R

epair

ed,

DK

, a0=

10.0

0m

m

FE

, R

epair

ed,

DK

, a0=

16.6

7

FE

, R

epair

ed,

DK

J,

a0=

3.3

3m

m

FE

, R

epair

ed,

DK

J,

a0=

10.0

0m

m

FE

, R

epair

ed,

DK

J,

a0=

16.6

7m

m

BS

7910,

Repair

ed,

a0=

3.3

3m

m

BS

7910,

Repair

ed,

a0=

10.0

0m

m

BS

7910,

Repair

ed,

a0=

16.6

7m

m

0

20

40

60

80

100

120

140

160

180

IC (MPam) Fracture Toughness, K 1/ 2

BS

7910,

As-W

eld

ed

BS

7910,

PW

HT

BS

7910,

Repair

ed

0

2

4

6

810

12

14

Cri

tical

Cra

ck D

ep

th (

mm

)

Fig

ure

60

Fra

ctu

re t

ou

gh

ness v

ers

us c

riti

cal

cra

ck d

ep

th f

or

ed

ge d

efe

cts

su

bje

cte

d t

o 2

25 M

Pa o

verl

oad

str

ess –

BS

7910 r

esu

lts

fo

r th

ree d

iffe

ren

t w

eld

co

nd

itio

ns

0

20

40

60

80

100

120

140

160

180


FE

, P

WH

T

BS

7910,

PW

HT

BS

7910 R

efined,

PW

HT

0 2

4 6

8 10

12

14

16

18

Cri

tical

Cra

ck D

ep

th (

mm

)

Fig

ure

61

Fra

ctu

re t

ou

gh

ness v

ers

us c

riti

cal

cra

ck d

ep

ths f

or

ed

ge d

efe

cts

su

bje

cte

d t

o 2

25 M

Pa o

verl

oad

str

ess –

un

rep

air

ed

PW

HT

– B

S 7

910 r

esu

lts c

om

pare

d t

o t

ho

se o

f F

E (

Fig

ure

41)

20

0

20

40

60

80

100

120

140

160

180


FE

, R

epair

ed

BS

7910,

Repair

ed

BS

7910 R

efined,

Repair

ed

0

2

4

6

8

10

12

14

16

18

Cri

tical

Cra

ck D

ep

th (

mm

)

Fig

ure

62

Fra

ctu

re t

ou

gh

ness v

ers

us c

riti

cal

cra

ck d

ep

ths f

or

ed

ge d

efe

cts

su

bje

cte

d t

o 2

25 M

Pa o

verl

oad

str

ess –

rep

air

ed

co

nd

itio

n –

BS

7910 r

esu

lts c

om

pare

d t

o t

ho

se o

f F

E (

Fig

ure

41)

40

0

30

0

20

0

10

0 0

-10

0

-20

0

-30

0

-40

0

-50

0

-60

00.0

00

0

5.0

00

0

10

.00

00

1

5.0

00

0

20

.00

00

2

5.0

00

0

Str ess Per p en d icular to Weld (MPa)

As-W

eld

ed

As-W

eld

ed

-Re

pa

ir

As-W

eld

ed

-PW

HT

As-W

eld

ed

-PW

HT

-Re

pa

ir

Dis

tan

ce

fro

m S

ide

of

Pla

te (

mm

)

Fig

ure

63

Mo

dif

ied

resid

ual

str

ess d

istr

ibu

tio

ns

0

20

40

60

80

100

120

K1 (MPa m^ 0.5)

As-W

eld

ed

As-W

eld

ed -

Repair

As-W

eld

ed -

PW

HT

As-W

eld

ed -

PW

HT

- R

epair

5

10

15

20

25

Cra

ck

De

pth

(m

m)

Fig

ure

64

Str

ess i

nte

nsit

y f

acto

rs f

or

as-w

eld

ed

, as-w

eld

ed

-rep

air

, as-w

eld

ed

-PW

HT

an

d a

s-w

eld

ed

-PW

HT

-rep

air

cases

0

0

10

20

30

40

50

60

70

80

Bendin

g

K1 (MPa m^ 0.5)

As-W

eld

ed -

PW

HT

Cosim

e D

istr

ibution

Mem

bra

ne

0

5

10

15

20

25

Cra

ck

De

pth

(m

m)

Fig

ure

65

Str

ess i

nte

nsit

y f

acto

rs f

or

as-w

eld

ed

-PW

HT

, sin

uso

idal,

ben

din

g a

nd

mem

bra

ne c

ases

0

50

100

150

200

250

Bendin

g

K1 (MPa m^ 0.5)

As-w

eld

ed-P

WH

T-R

epair

Cosin

e

Mem

bra

ne

5

10

15

20

25

Cra

ck D

ap

th (

a)

Fig

ure

66

Str

ess i

nte

nsit

y f

acto

rs f

or

as-w

eld

ed

-PW

HT

-rep

air

, sin

uso

idal,

ben

din

g a

nd

mem

bra

ne c

ases

0

0

20

40

60

80

10

0

12

0

14

0

16

0

18

0

I) Stress I nt ensi t y Fact or, K (MPam1/2

BS

7910 S

olu

tion

FE

Solu

tion

Sharp

les e

t al S

olu

tion

Rooke &

Cart

wri

ght

Solu

tion,

Restr

ain

ed B

endin

g

Rooke &

Cart

wri

ght

Solu

tion,

Un-R

estr

ain

ed B

endin

g

0

5

10

15

20

25

Cra

ck

De

pth

, a

(m

m)

Fig

ure

67

Co

mp

ari

so

n o

f K

I so

luti

on

s f

or

mem

bra

ne s

tress o

f 220 M

Pa –

ed

ge c

rack

0

10

20

30

40

50

60

I Stress Intensity Factor, K (MPam1/2)

BS

7910 S

olu

tion

FE

Solu

tion

Sharp

les e

t al S

olu

tion

Rooke &

Cart

wri

ght

Solu

tion,

Restr

ain

ed B

endin

g

Rooke &

Cart

wri

ght

Solu

tion,

Un-R

estr

ain

d B

endin

g

0

5

10

15

20

25

Cra

ck D

ep

th,

a (

mm

)

Fig

ure

68

Co

mp

ari

so

n o

f as-w

eld

ed

-PW

HT

resid

ual

str

ess K

I valu

es –

ed

ge c

rack

(No

te:

BS

7910 a

nd

Ro

oke a

nd

Cart

wri

gh

t valu

es a

re f

or

a m

em

bra

ne s

tress o

f 69 M

Pa)

0

50

10

0

15

0

20

0

25

0

30

0

Stress Intensity Factor, KI (MPAm1/2)

BS

79

10

So

lutio

n

FE

So

lutio

n

Sh

arp

les e

t a

l S

olu

tio

n

Ro

oke

& C

art

wri

gh

t, R

estr

ain

ed

Be

nd

ing

Ro

oke

& C

art

wri

gh

t, U

n-R

estr

ain

ed

Be

nd

ing

0

5

10

15

20

25

Cra

ck

De

pth

, a

(m

m)

Fig

ure

69

Co

mp

ari

so

n o

f as-w

eld

ed

-PW

HT

-rep

air

ed

resid

ual

str

ess K

I valu

es –

ed

ge c

rack

(No

te:

BS

7910 a

nd

Ro

oke a

nd

Cart

wri

gh

t valu

es a

re f

or

a m

em

bra

ne s

tress o

f 345 M

Pa)

0

10

20

30

40

50

60

Stress Intensity Factor, KI (MPam1/2

)

BS

7910 S

olu

tion K

FE

Solu

tion K

Rooke &

Cart

wright

0 2

4 6

8 10

12

14

16

Cra

ck D

ep

th, 2a (

mm

)

Fig

ure

70

Co

mp

ari

so

n o

f K

I so

luti

on

s f

or

mem

bra

ne p

rim

ary

str

ess o

f 220 M

Pa –

em

bed

ded

cra

ck

-6-4-202468

10

12

14

0

2

4

6

8

10

12

14

16

I (MPam1/2

) Stress Intensity Factor, K

BS

7910 S

olu

tion

FE

Solu

tion K

FE

Solu

tion K

J

Cra

ck D

ep

th,

2a (

mm

)

Fig

ure

71

Co

mp

ari

so

n o

f as-w

eld

ed

-PW

HT

resid

ual

str

ess K

I valu

es –

em

bed

ded

cra

ck

(No

te:

BS

7910

valu

es a

re f

or

a m

em

bra

ne s

tress o

f 69 M

Pa)

0

10

20

30

40

50

60

0

2

4

6

8

Stress Intensity Factor, KI (MPam)

-20

-10

10

12

14

16

1/ 2

BS

7910 S

olu

tion

FE

Solu

tion K

FE

Solu

tion K

J

Cra

ck D

ep

th,

2a (

mm

)

Fig

ure

72

Co

mp

ari

so

n o

f as-w

eld

ed

-PW

HT

-rep

air

ed

resid

ual

str

ess K

I valu

es –

em

bed

ded

cra

ck

(No

te:

BS

7910 v

alu

es a

re f

or

a m

em

bra

ne s

tress o

f 345 M

Pa)

APPENDIX 1

LITERATURE REVIEW

A1.i

A1.1 INTRODUCTION

Repair welds may be necessary where flaws or defects have been found in weldments during the

fabrication of vessels or in-service. However, in some cases this process may have a deleterious

effect on the residual lifetime of the component. This can be due to defective repair welds,

inadequate removal of original defects or inappropriate repair weld properties. High residual stresses

may be present in welds that haven’t received sufficient stress-relief. A combination of these factors

can lead to re-cracking of the weld and further losses in productive time or more seriously,

catastrophic failure of the vessel.

For defects found during fabrication, standards such as BS5500 (Reference A1.1) require repair welds

to be carried out to an approved procedure and that they are subjected to the same acceptance criteria

as the original work. For defects found in-service there are no specific standards available that

provide guidance on the necessity to repair.

This Appendix is a review of current industrial practices and previous problems contained in the open

literature.

A1.2 LITERATURE SURVEY

A literature search for papers related to repair welds initially identified over 100 abstracts for

references dated from 1976. Following a review of these abstracts, twenty-five papers were identified

as of possible interest. A list of all these papers is given in Annex 1 of this Appendix.

The papers reviewed can be categorised by the following:

- Numerical analysis: These relate to the prediction of residual stresses in weldments.

- Case Studies: These papers discuss the metallurgical examination of repair welds and the

evaluation of found defects.

- Weld Repair Procedures and Techniques: These papers present weld repair techniques

- Performance of Repair Welds: An assessment of how various weld repairs have performed in

service.

The papers are briefly described in this next section with the aim of seeking information on current

practices dealing with weldment flaws, which will be useful for later stages in the project.

A1.2.1 Numerical Analysis

Eight references were identified relating to the prediction of residual stresses using numerical

techniques. The papers are briefly described in chronological order to illustrate the increase in

complexity of the numerical analysis that is now used to predict residual stresses in repair welds.

Rybicki and Stonesifer (References Annex1.1 - Annex1.3) describe the analysis of weld repairs of

heavy section steels. The vessel analysed was one of the intermediate pressure vessels used as part of

the Heavy Section Steel Technology (HSST) program at Oak Ridge National Laboratory (ORNL)

(Reference Annex1.4). This program looked at repair weld residual stresses in thick –walled steel

pressure vessels. The repair welds were performed in accordance with Section XI of the American

Society of Mechanical Engineers (ASME) boiler and pressure vessel code. The repair procedure

employed, known as the half-bead or temper-bead technique, was devised for repair welds that for

A1.1

practical considerations could not undergo routine high temperature thermal post weld heat treatment

(PWHT).

These papers may now be considered ‘dated’ considering the progress that has been made in the use

of finite element techniques to predict residual stresses. Nevertheless, they did illustrate the feasibility

of developing an efficient residual stress model to understand the complexity of residual stresses due

to weld repairs.

Further numerical techniques are described from simple approximations of residual stress patterns

(Reference Annex1.5) to three dimensional analysis (Reference Annex1.6) which examine the effects

of residual stresses and mechanical characteristics of repair welds. A further complexity of predicting

residual stresses is described by Oddy et al (Reference Annex1.7), which is the effect of

transformation plasticity on the magnitude of residual stresses in welds which undergo phase

transformation during cooling of the weld.

Leggatt describes a one-dimensional computer model (Reference Annex1.8) used to evaluate

transverse residual stresses in repair welds. However, the finite element analysis of residual stresses

in repair welds (Reference Annex1.9) describe the importance of using three dimensional models in

order to obtain valid residual stress information at the weld end regions where crack initiation is often

observed.

A1.2.2 Case Studies

Only two references were identified which describe the analysis carried out for components with weld

repairs. Each of the references has been briefly described highlighting the analysis used in assessing

the components structural integrity.

Chowdhury et al (Reference Annex1.10) describes the analysis of a failure in a weld repaired turbine

casing. The turbine casing operates at a temperature of 600oC and a pressure of 10-18 MPa. After 25

years of service, a crack was detected and repaired by welding. However, after 5 years of service,

since the repair, a crack was again detected in the weld. The casing was weld repaired by a high Cr-

Ni weld metal (24Cr-32Ni-4Mn-Fe). The base metal is low alloy ferritic steel (1Cr -0.5Mo steel).

The paper describes the analysis carried out to examine the cause of cracking and the metallography

of the base metal used to assess whether the turbine could be re-employed again after repairing the

new crack.

An experimental procedure is described whereby a sample, cut from the weld repair region, was

subject to visual examination, chemical analysis, microstructure and fractography analysis using a

scanning electron microscope and hardness testing. This analysis was used to consider whether the

base and weld metal was still in good metallurgical condition and if the choice of filler metal in the

weld repair was the correct choice. This analysis showed that holes and cavities were present in the

weld, which were responsible for initiating the cracks. The choice of filler metal was incorrect which

led to higher stresses due to the large difference in the thermal expansion coefficient of the weld and

base metal.

The paper highlights the consequences of using improper filler metal in weld repairs and that

appropriate advice should be sought when making a weld repair. The value of good metallographic

analysis is well described, however the basis for the initial weld repair is not given.

Corbit et al (Reference Annex1.11) describes the justification for continued service of a HP turbine

steam chest subject to a weld repair. The operating temperature is 538oC (1000

oF) and pressure is

1450 psig. Numerous cracks were found in the steam chest weld HAZ of the turbine shell during a

A1.2

scheduled outage. Replication was used to determine crack propagation along the surface and a boat

sample was removed to observe the crack path into the steam chest as well as checking the chemistry

of the weld metal.

Cracks were sized using ultrasonic inspection to determine the extent of the grinding and weld repair

necessary. Excavations were made to a maximum depth set by the turbine manufacturer. This left

cracks below the surface of the excavation. The cause of cracking was determined to be creep or

creep-fatigue related. An analysis was then performed to determine whether a repair weld was

required. Since cracks were left below the excavation, a remaining life assessment was carried out to

demonstrate the continued operation of the steam chest. A leak-before-break evaluation was also

carried out to demonstrate that leaking would develop before a catastrophic rupture.

A detailed repair procedure was then developed to address the creep damage found in the HAZ of the

weld. The repair process utilised a half-bead temper technique in order to minimise the need for a full

PWHT. The weld repair was carried out using the shielded metal arc welding (SMAW) process. A

controlled pre-heat was used before welding commenced and magnetic particle (MT) inspection was

performed to verify that no additional cracking or growth of the remaining cracks had not occurred.

MT inspections were carried out after each weld pass to confirm that cracking had not occurred in the

weld metal.

This paper provides a good illustration on the decisions that need to be carried out when carrying out

the successful repair of defects found in situ.

A1.2.3 Weld Repair Procedures and Techniques

An overview of weld repair techniques was described by Jones (Reference Annex1.12) in 1994.

General principles are defined which consider the questions that need to be asked before carrying out

a repair. They provide practical considerations that need to be considered when evaluating the need

to repair and are repeated below:

· Is welding the best method of repair?

· What is the composition and weldability of the base material?

· Is the repair location accessible?

· Can preheat be tolerated?

· Which welding procedure should be applied?

· Is PWHT necessary?

· Will the repair be fit for purpose?

· Can the repair be inspected and tested?

Several weld repair techniques are available, the choice of which rests on the consideration of a

number of factors. These are:

· Conventional buttering

· Half-bead

· Two-Layer

· Six-Layer

Factors influencing the choice of method are summarised in Table A1.1. The paper reflects that each

weld repair is usually unique, and whilst definitive rules are not possible, similar criteria need to be

considered when assessing the feasibility of a weld repair and deriving an appropriate weld procedure.

This can be achieved by guidelines that consider the general principles highlighted above.

A1.3

The half-bead weld or temper bead repair technique as outlined in ASME XI, was employed in the

HSST program (References Annex1.4, Annex1.13, and Annex1.14) examining repair weld residual

stresses. The procedure was developed for repair welds that for practical reasons could not undergo

routine PWHT. Whilst the adequacy of the technique was demonstrated by the results of destructive

and non-destructive testing the main concern were the high values of residual stresses associated with

very deep repairs.

The six-layer GTAW repair procedure is described by Alberry and Feldstein (Reference Annex1.15)

as an alternative to the ASME XI half-bead repair procedure. The need was for an in-service repair

capability, for use on light water reactor pressure components, which avoided the major disadvantage

of the half-bead technique. This was the heavy reliance on manual activities, notably the need to

remove, by grinding, the half of the first layer thickness deposited by welding.

The six-layer methodology uses the principle of controlling individual layer thicknesses of weld metal

to promote high levels of refinement and tempering in the underlying HAZ. The method has been

validated experimentally for a wide range of welding parameters for SA508 Class 2 steels. In

particular, it has been shown to accommodate variations in wire speed of up to ±30%, which makes

the technique suitable for all positional welding.

An as-welded repair procedure for C-0.5Mo coke drums is described by Moore (Reference

Annex1.16). The procedure was developed to allow through wall repairs of coke drums of up to 1-

inch thickness without PWHT. A preheat is applied before the first pass. Unlike the half-bead

procedure the grinding of the first pass is not required. Instead the electrode size is increased to

temper and refine the HAZ of the first pass, but precise heat input control and bead placement typical

of controlled deposition repairs are not used. On completion of welding, the preheat temperature is

increased, and the welds are post heated for 2 hours to allow hydrogen to diffuse.

In order to improve productivity by reducing time due to the manual labour required for grinding and

SMAW repairs, an automatic arc gouging and GMAW was developed. No experience of re-cracking

had been observed in service for either of the two procedures. The main benefits of the two

procedures compared with repairs with PWHT were lower repair costs and decreased repair time.

A1.2.4 Performance of Repair Welds

The effect of repair welds on various aspects of service performance is considered in several of the

references. Slater (Reference Annex1.17) describes a literature search relating to repair welding in

the structural steel industry in 1985. Problems associated with poor weld repairs were listed:

· Incomplete removal of defect being repaired

· Introduction of further defects

· Microstructure, material or toughness degradation

· Increased residual stresses and distortion

· Unfavourable environmental conditions

It was recognised that a fracture mechanics approach was required to assess the initial need to repair

and that guidance was needed on how to repair when necessary.

Booth, Threadgill and Wylde (References Annex1.18 and Annex1.19) observed a significant number

of service failures in welded structures involving weld repairs. These failures fell into three

categories:

· Defective repair welds

A1.4

· Inadequate removal of original defects

· Inappropriate repair weld properties

The importance of evaluating whether a repair is necessary was again recognised. It was estimated

that 'over 90 per cent of weld repairs carried out in some industries was unnecessary' because

‘workmanship’ acceptance criteria were used instead of a quantitative fitness-for-purpose concept.

Lai and Fong (Reference Annex A1.20) examined the fatigue performance of repaired pipeline steel

welds. Evaluating three welding processes, SMAW, GMAW and inner-shield welding (IW), only the

GMAW repairs exhibited a reduction in the fatigue life whereas the other repairs appeared to give

better fatigue resistance. This fatigue resistance of the repair weld was clearly dependent up on the

quality of the repair.

Evans et al (Reference Annex1.21) examined the performance of structural steel after multiple weld

repairs. It was shown that satisfactory multiple repairs are possible as long as the process is carefully

controlled. However, a review of weld repair by Prosser and Boothby (Reference A1.2) concluded

that through thickness and part wall repairs should be limited to one or two attempts respectively.

The application of the temperbead technique weld repair has been demonstrated by Viswanathan et al

for ferritic steel piping girth welds (References A1.3, A1.4, Annex1.22) and ferritic header welds

(Reference A1.5). In 1994, the US National Board Inspection Code (NBIC) reconsidered the

requirement of PWHT of weld repairs on 1.25Cr-0.5Mo and 2.25Cr-1Mo steels. It recognised that the

requirement to PWHT in accordance with the original code of construction may be inadvisable or

impractical, and thus allowed for alternative repair methods to be used. To address this a

comprehensive R&D study, co-ordinated by EPRI was performed to address these issues. A repair

guideline document was prepared based on the current state-of-the-art (This is not available in the

open literature). Secondly, a detailed survey was carried out to document industry experience and

practices with respect to weld repair. This is discussed further in the next section. Lastly a major

experimental program was conducted on repair welds to aged CrMo piping.

The tests have compared Shielded metal arc weld (SMAW) repairs with PWHT, Gas Tungsten arc

weld (GTAW) with PWHT and SMAW using the temperbead technique. The welds have been

evaluated prior to and after repair to study the effects of degradation on repairability, the effectiveness

of temperbead repairs and the remaining life achieved by the weld repair. The overall results of the

study indicated that service aged piping systems can be successfully repaired with or without PWHT

and that life extension by several decades may be achieved under design conditions.

Brett and Jones (Reference A1.6) reviewed the development of repair procedures without PWHT in

the power plant industry. Commercial pressures are now dictating that repairs without PWHT are

carried out as long as appropriate safety criteria are met. This includes an appraisal of the nature of

the repair that is required, consideration of the consequences of repair welding without PWHT, close

supervision of the repair welding and monitoring of the subsequent service performance of the

repaired plant.

A1.2.5 EPRI Survey

EPRI has carried out an industrial survey (Reference A1.7) on the weld repair technologies currently

used by utilities and repair organisations to extend the life of high temperature, high pressure

components. The responses that may be pertinent to the UK industry are related to here. The

components of most concern were steam turbine casing, piping and headers.

A1.5

Most of the utilities indicated that a cost-benefit analysis played a major role in their repair decision

process. The utilities usually rely on the original equipment manufacturer and/or specialist consultant

for repair methodologies. Interestingly, only 50% of the utilities that responded indicated that they

used some form of life assessment program or methodology to determine if and when repairs should

be performed. Most repair decisions were made on a case-by-case basis with no specific methodology

employed.

Most repairs are carried out in-situ, which is the preferred situation, again to reduce costs.

Recurrence of cracking was particularly observed where dissimilar weld metal was used. In headers

and piping, half of the reported cracking observed re-cracking within one year.

Over 70% of the utilities stated that repairs had been conducted without implementing PWHT, i.e.

temperbead techniques were employed. Grinding, machining or gouging were used for defect

removal. The SMAW welding process is the most common for weld repair.

A1.3 DISCUSSION

Defects in welded structures can occur during the fabrication process due to ‘workmanship’ or in-

service due to working conditions. During fabrication, BS5500 states that ‘unacceptable

imperfections shall be either repaired or deemed not to comply with this standard’. Repair welds have

to be carried out to an approved procedure and subjected to the same acceptance criteria as the

original weld. Thus all welds have to satisfy the requirements of the design specification before

acceptance by the purchaser or inspecting authority.

For defects found in-service there are no standard guidelines available for utilities to use to make a

decision on the need to carry out a weld repair. The industrial survey carried out by EPRI for utilities

in the United States has shown that utilities will rely on the original manufacturer or outside vendors

to assist on this decision. However, it is not clear that the assessment procedures used are consistent

or are indeed reliable. In the UK, the repair of welds appears to rely on in-house experience in the

absence of guidelines to follow. However, this review shows that re-cracking of repair welds still

occurs due to lack of understanding on why original defects have occurred and how they should be

repaired.

Whilst the decision to repair a defect may be aided using an assessment procedure the practical

considerations identified by Jones [A1.12] should also be considered. These show that repair welds

should be considered on a case-by-case behaviour, therefore a definitive set of ‘rules’ can not be

given. Instead, the guidelines need to be produced which provide good practice in assessing defects

in welds and the requirements for carrying out a ‘safe’ repair.

A number of references have been found illustrating the capabilities of performing a repair weld

without the need for PWHT. This was introduced by the half-bead technique defined in ASME XI

primarily for the nuclear industry. This has been superseded by other temperbead techniques, which

are all aimed at improving the properties within the weld HAZ, whilst saving time and costs by

precluding the time for PWHT. There is evidence that this method is employed by other industries in

the USA, but it is unclear on the use of this practice in the UK.

In the references associated with case studies and the performance of weld repairs, only a few

references have related to residual stresses. These papers have indicated that the magnitude of

residual stresses in repair welds can be of yield magnitude. The most recent advances in welding

simulation were presented at the IMechE conference (Reference A1.8) in November 1999. The

conference demonstrated the developments that had been made, mainly in the use of FE, to predict

A1.6

residual stresses. Sufficient confidence in numerical analysis needs to be demonstrated by

comparison with measurement methods.

When developing guidelines for the assessment of defects in repair welds sufficient advice needs to

be given to the user as to when residual stresses need to be considered in the assessment. Advice also

needs to be provided on when the user should use simple approximations of the residual stress pattern,

e.g. R6 residual stress compendium (Reference A1.9), or to use finite element analysis techniques to

predict the complex behaviour of the material during welding.

A1.4 RECOMMENDATIONS

The literature review has re-affirmed that an assessment procedure is required to enable users to

evaluate if a defect needs to be repaired. This needs to consider the magnitude of residual stresses,

not only in the as-welded condition but also after temperbead welding or PWHT.

Practical guidelines are also required which give guidance on how the weld repair should be carried

out and the necessary requirements that it needs to meet.

Further information needs to be sought from appropriate industrial companies in the UK in order to

ascertain their current practices dealing with weldment flaws.

A1.5 REFERENCES

A1.1 British Standard BS 55000:1994, ‘Specification for unfired fusion welded pressure vessels’.

A1.2 K Prosser and P J Boothby, ‘Weld repair of pressurised equipment’, Conference

Proceedings, Developments in Materials Usage for Pressure Systems, IMechE, November

1999.

A1.3 R Viswanathan and D W Gandy, ‘Performance of repair welds on aged Cr-Mo piping girth

welds’, Conference Proceedings, International Conference on Integrity of High Temperature

Welds, 3-4 November 1998, IOM Communications, ISBN 1 86058 149 8.

A1.4 R Viswanathan, D W Gandy and S Findlan, ‘Weld repair of 1-¼Cr-½Mo steel piping girth

welds’, PVP-Volume 388, Fracture, Design Analysis of Pressure Vessels, Heat Exchangers,

Piping Components, and Fitness for Service –1999, ASME 1999 p 373-382.

A1.5 R Viswanathan, D W Gandy and S Findlan, ‘Weld repair of 2-¼Cr-1Mo service-aged header

welds’, Journal of Pressure Vessel Technology, Volume 121, November 1999 p345-352.

A1.6 S J Brett, D J Abson and R L Jones, ‘The repair welding of power plant without post-weld

heat treatment’, Conference Proceedings, International Conference on Integrity of High

Temperature Welds, Professional Engineering Publications, ISBN 1 86058 149 8, 1998.

A1.7 D W Gandy, S J Findlan and R Viswanathan, ‘Weld repair of steam turbine casings and

piping – An industry survey’, PVP-Volume 388, Fracture, Design Analysis of Pressure

Vessels, Heat Exchangers, Piping Components, and Fitness for Service –1999, ASME 1999

p 355-359.

A1.8 Recent Advances in Welding Simulation, Proceedings of the Conference organised by the

Materials and Mechanics of Solids Group of the IMECHE, IMECHE headquarters, 26

November 1999.

A1.7

A1.9 S K Bate, ‘Compendium of residual stress profiles for R6’, AEAT/NJCB/000006/00, March

2000.

A1.8

Tab

le A

1.1

A

pp

licati

on

Ch

ara

cte

risti

cs o

f A

s-W

eld

ed

Rep

air

Tech

niq

ues [

A1.1

2]

C

on

ven

tio

nal

Bu

tter

ing

H

alf-

Bea

d

Tw

o-L

ayer

S

ix-L

ayer

Mo

de

of

app

lica

tio

n

SM

A

SM

A

Mai

nly

SM

A b

ut

mec

han

ised

GM

A p

oss

ible

Mec

han

ised

GT

A o

nly

Deg

ree

of

HA

Z

mic

rost

ruct

ura

l co

ntr

ol

Hig

h r

efin

emen

t p

oss

ible

(80

% m

ax)

lim

ited

tem

per

ing.

Hig

h r

efin

emen

t p

oss

ible

(9

5%

max

) li

mit

ed t

emp

erin

g

Fu

ll r

efin

emen

t p

oss

ible

, li

mit

ed

tem

per

ing u

sin

g t

wo

-lay

ers.

Mo

re e

ffec

tive

tem

per

ing p

oss

ible

usi

ng t

hre

e la

yer

s.

Fu

ll r

efin

emen

t an

d

tem

per

ing p

oss

ible

.

Pro

ced

ure

Co

ntr

ol

Lo

w t

ole

ran

ce

Hig

h w

eld

bea

d o

ver

lap

(60

%)

must

be

ob

tain

ed

Mo

der

ate

tole

ran

ce

Gri

nd

ing t

ole

ran

ces:

- 0.6

mm

+ 1

.1 m

m

Go

od

to

lera

nce

to

wel

d b

ead

over

lap

an

d w

eld

ing p

aram

eter

s

(typ

ical

ly ±

15

%)

Hig

hly

to

lera

nt

to

var

iati

on

s in

wel

din

g

par

amet

ers

eg.

±3

0%

on

wir

e fe

ed s

pee

d

Pro

du

ctio

n F

acto

rs

Rel

ativ

ely e

asil

y a

nd

rap

idly

app

lied

Co

ntr

ol

of

gri

nd

ing i

s d

iffi

cult

N

eed

fo

r la

rge

rep

air

pre

par

atio

ns.

D

etai

led

wel

din

g

tria

ls a

nd

wel

der

tra

inin

g m

ay b

e

nee

ded

Slo

w a

nd

co

stly

.

Su

itab

le f

or

rem

ote

op

erat

ion

. S

imp

le r

epai

r

wel

d g

eom

etri

es o

nly

e.g

.

pip

ewo

rk

A1.9

ANNEX 1 OF APPENDIX 1

LIST OF REFERENCES FROM LITERATURE REVIEW

Annex 1.1 Rybicki E F and Stonesifer R B, ‘Residual stresses at weld repairs in pressure vessels’,

Report NUREG-CR-0078 (PB-281853 / 25L)9, Publ. Washington DC, Nuclear

Regulatory Commission, Division Of Reactor Safety Research, April 1978.

Annex 1.2 Rybicki E F and Stonesifer R B, ‘Development of a computational model for residual

stresses due to weld repairs in pressure vessels’, Repair Aspects and Procedures.

Proceedings, International Working Group on Reliability of Reactor Pressure

Components Technical Committee Meeting, Riso, Denmark, 13-15 Sept.1978. Report

IWG-RRPC-79 / 1. Publ. Vienna, Austria, International Atomic Energy Agency

(IAEA), July 1979, pp221-231.

Annex 1.3 Rybicki E F and Stonesifer R B, ‘An analysis procedure for predicting weld repair

residual stresses in thick walled vessels’, Transactions of the ASME, Journal of

Pressure Vessel Technology, Vol.102, No.3. Aug.1980, pp.323-331.

Annex 1.4 Smith G C and Holz P P, ‘Repair induced residual stresses in thick walled steel

pressure vessels’, ORNL / NUREG / TN-153 (NUREG / CR-0093). Publ. Oak Ridge,

Tenn. 37830; Oak Ridge National Laboratory, June 1978, 130pp.

Annex 1.5 Bloom J M, ‘An analytical assessment of the effects of residual stresses and fracture

properties on service performance of various weld repair processes’, Transactions of

the ASME, Journal of Pressure Vessel Technology, Vol.103, No.4. Nov.1981, pp373-

379.

Annex 1.6 Ueda Y, Kim Y C, Garatani K, Yamakita T and Bang H S, ‘Mechanical characteristics

of repair welds in thick plate. Report 1: Distributions of three-dimensional welding

residual stresses and plastic strains and their production mechanisms’, Transactions of

JWRI, Vol.15, No.2. Dec.1986, pp359-368.

Annex 1.7 Oddy A S, Goldak J A and Mcdill J M J, ‘Transformation plasticity and residual

stresses in single-pass repair welds’, Weld Residual Stresses and Plastic Deformation.

Symposium during 1989 Pressure Vessels and Piping Conference and Exhibition,

Honolulu, HI, 23-27 July 1989.

Annex 1.8 Leggatt R H, ‘Computer modelling of transverse residual stresses in repair welds’,

Welding Journal, Vol.70, No.11. Nov.1991, pp299s-310s.

Annex 1.9 Feng Z, Wang X L, Spooner S, Goodwin G M, Maziasz P J, Hubbard C R and Zacharia

T, ‘A finite element model for residual stress in repair welds’, Residual Stresses in

Design Fabrication, Assessment and Repair, ASME 1996 Pressure Vessels and Piping

Conference, Montreal, Canada, 21-26 July 1996. Ed: R W Warke. PVP Vol.327. Publ.

New York, NY 10017, USA; American Society of Mechanical Engineers (ASME),

1996. ISBN 0-7918-1774-1, pp119-125.

A1.10

Annex 1.10 Chowdhury S G, Mukhopadhyay N K, Das G, Das S K and Bhattacharya D K, ‘Failure

analysis of a weld repaired steam turbine casing’ Engineering Failure Analysis, Vol. 5,

No. 3, 1998, pp205-218.

Annex 1.11 Corbit R B and French S M, ‘ Weld repair adds life to power plant turbine’, Welding

Journal, Vol.76, No.1. Jan.1997, pp51-55.

Annex 1.12 Jones R L, ‘Overview of weld repair techniques’, Inspection, Assessment and Repair of

Welded Structures and Components. Proceedings, 10th Annual North American

Welding Research Conference, Columbus, OH, USA, 3-5 Oct.1994. Publ: Abington,

Cambridge CB1 6AH, UK; Abington Publishing, (1994). Session 6. 15pp

Annex 1.13 Goins W and Merrick E, ‘Weld repair of Heavy Section Steel Technology Program

vessel V-7’, DVS Berichte, No.52. 1978. Proceedings, Conference, Welding in

Nuclear Engineering, Hamburg, 28-29 Nov.1978. Publ. Dusseldorf, W.Germany;

Deutscher Verband fur Schweisstechnik, 1978. ISBN 3-87155-353-0, pp164-167.

Annex 1.14 Canonico D A and Whitman G D, ‘Evaluations of half-bead weld repair procedures

with thick-wall pressure vessels’ Jnl. Criteria for Preventing Service Failures in Welded

Structures. Papers presented at JWS 3rd

International Symposium, Tokyo, 26-28 Sept.

1978. Publ. Tokyo, Japan Welding Society, 1978. Paper 3 JWS-24, pp197-202.

Annex 1.15 Alberry P J and Feldstein J G, ‘Weld repair of light water reactor pressure boundary

components’, Welding Journal, Vol.66, No.12. Dec.1987, pp33-42.

Annex 1.16 Moore D E, ‘Weld repair of carbon-moly (molybdenum) coke drums without postweld

heat treatment’, WRC Bulletin 412, 1996, pp70-76.

Annex 1.17 Slater G, ‘The effect of repair welds on service performance’, Welding Journal, Vol.64,

No.3. Mar.1985, pp22-29.

Annex 1.18 Booth G S, Threadgill P L and Wylde J G, ‘Significance of repair welds in service

failures’, ISTFA '87: Advanced Materials. Proceedings, International Symposium,

Testing and Failure Analysis, Los Angeles, CA, 9-13 Nov.1987. Publ. Metals Park,

OH 44073, USA, ASM International, 1987. ISBN 0-87170-312-2, pp.305-308.

Annex 1.19 Wylde J G, Threadgill P L and Booth G S, ‘Service failures associated with weld

repairs’, Weld Failures. Proceedings, International Conference, London, 21-24

Nov.1988. ed: J. D. Harrison. publ: Abington, Cambridge, UK; The Welding Institute;

1989.ISBN 0-85300234-7. Paper 27, pp11-17.

Annex 1.20 Lai M O and Fong H S, ‘Fatigue performance of repaired pipeline steel welds’, Journal

of Materials Science Letters, Vol.7, No.12. Dec.1988, pp1353-1354.

Annex 1.21 Evans C, Apps R L and Fenn R, ‘The performance of structural steel after multiple

weld repair’, International Journal for the Joining of Materials, Vol.10, No.3-4.

Dec.1998, pp63-68.

Annex 1.22 Viswanathan R, Gandy D and Findlan S, ‘Performance of repair welds on service-aged

2.25%Cr-1%Mo girth weldments’, Transactions of the ASME, Journal of Pressure

vessel Technology, Vol. 119, November 1997, pp414-422.

A1.11

Annex 1.23 Minnick W H, ‘Weld repair’, Gas Tungsten Arc Welding Handbook. Publ. South

Holland, IL 60473, USA, Goodheart-Willcox Co., Inc. 1996, ISBN 1-56637-206-2.

Chapter 23, pp235-239.

Annex 1.24 Veron P, ‘Weld repair and life extension’, Engineering Design in Welded

Constructions. Proceedings, International Conference, Madrid, Spain, 7-8 Sept.1992.

Publ. Oxford OX3 0BW, UK; Pergamon Press for International Institute of Welding

(IIW); 1992. ISBN 0-08-041910-0, pp231-239.

Annex 1.25 Smith E, ‘The stresses associated with a crack in a repair weld’, International Journal

of Fracture, Vol.53, No.4. Feb.1992. ppR59-R62

A1.12

APPENDIX 2

MICROSTRUCTURAL EXAMINATION OF WELD SAMPLES UNDERTAKEN BY

SHEFFIELD UNIVERSITY METALS ADVISORY CENTRE (SUMAC)

A2. i

A2.1 SAMPLES PROVIDED

(a) One, approximately 10 mm thick, slice cut from a weld test piece of a double-V

preparation butt weld in 40 mm plate. Designated SISD/SK/1944/3

(b) One, approximately 14 mm thick, slice cut from a weld test piece of a double-V preparation butt weld in 40 mm plate, with a simulated weld repair. Designated SISD/SK/1944/8

A2.2 NOMENCLATURE

In this Appendix the welds will be treated as orientated in the macrographs of Figure

A2.1. The larger V-preparation is at the top and this is designated 'Weld 1'. The smaller

V- preparation is at the bottom and this is designated 'Weld 2' (in the case of sample

SISD/SK/1944/8 this is the weld repair). References to "left hand side' (LHS), 'right

hand side' (RHS), top and bottom are as viewed in Figure A2.1. The final weld runs, on

either side of the plate, which immediately abut the plate surfaces will be designated as

'toe' welds

A2.3 MACROSECTIONS AND BRITISH STANDARD HARDNESS TESTS

One surface of each slice was ground, polished and etched to reveal the weld profile, as

illustrated in Figure A2.1. The welds were clearly sound with no evidence of inter-run

lack of fusion or porosity.

Hardness measurements were made on each sample in accordance with BS EN 288-

3:1992/A1:1997, section 7.4.5 and using the "narrow HAZ" configuration shown in

figure 10 of the standard. The results of these tests are tabulated below.

SISD/SK/1944/3: Hardness (HV10) Tests according to BS EN 288-3

position matrix HAZ Weld HAZ Weld

Top 162, 165, 206,248*,266* 227,209, 254*, 237*, 165:151, 148

167 199, 213, 235, 187

229

Root 163, 195, 201,218,221*, 236, 232, 257*, 240*, 181, 184, 176

187 246*, 216* 231 222*, 248,

209

Bottom 165, 187,

219

228, 274* 281* 242, 253,

259

299*, 310*,

253, 195

179, 168, 154

A2. 1

SISD/SK/1944/8: Hardness (HV10) Tests according to BS EN 288-3

position matrix HAZ Weld HAZ Weld

Top 156, 154, 174 245, 265*, 234, 227, 270*, 261*, 176, 207, 159

247*, 251* 214, 237, 299 274*, 222

Root 161, 179, 177 191, 199, 229, 234, 230 211*, 200*, 177, 177, 163

231*, 222*, 230*, 198,

241* 211

Bottom 159, 162, 176 325*, 335*,

318*, 213

234, 216, 247 318*, 339*,

308*, 268

175, 166, 159

* hardness test within 0.5 mm of fusion line

This hardness survey is within the permitted limits as specified in Table 2 of BS EN 288-

3:1992A1:1997.

A2.4 MICROSTRUCTURE

The Heat Affected Zone (HAZ) microstructure follows the typical pattern of a multi-pass

weld with a zone of grain growth at the fusion line, backed by a band of recrystallization

followed by a spheroidized/tempered zone before the unaffected matrix. Each weld pass

imposes a further HAZ on the underlying weld (and it's HAZ) leading to a refined

microstructure at the overlap.

The grain growth and recrystallization zones have a microstructure of grain boundary

and Widmanstatten ferrite (the amount depending on the local austentising temperature

and subsequent cooling rate) in a transformed matrix. In carbon and low alloy steels of

this type, the matrix can be a mixture of the phases ferrite, pearlite bainite and

martensite.

With the exception of the 'toe' welds, the grain growth zones in all the weld passes, in

both samples, were similar, with significant amounts of pro-eutectoid ferrite in a

relatively coarse matrix. Figure A2.2 illustrates a typical example of the microstructure,

which is believed to be bainitic in origin.

In sample SISD/SK/1944/8, Weld 2 both the LHS and RHS 'toe' welds were similar as

illustrated in Figure A2.3. There was less pro-eutectiod ferrite and a much coarser

matrix structure. It is believed that this could be a bainite/ martensite mixture. In Weld

1 of the same sample, more ferrite was in evidence and the matrix was a mixture of the

coarse and fine microstructures in Figures A2.2 and A2.3.

In sample SISD/SK/1944/3, all the 'toe' welds were similar, (for both Weld 1 and Weld

2) with pro-eutectoid ferrite and a mixed matrix structure as described in the above

paragraph. The essential difference between the two welds of this sample, was that less

ferrite was evident in the 'toe' welds of Weld 2.

A2. 2

A2.5 MICROHARDNESS SURVEYS

An informal and unrecorded survey was made of the HAZ regions in both samples in

order to assess the areas which may be significant in terms of high hardness. This survey

indicated that, with the exception of the 'toe' welds, all HAZs, in all zones, were well

below any limiting hardness value. The 'toe' welds on Weld 1 in both samples indicated

that, whilst hardness values may be a little higher in the grain growth zone, they would

still fall well within specification.

In sample SISD/SK/1944/8, the indications were that hardness values could be high in

the grain growth zone of the 'toe' welds of Weld 2. For sample SISD/SK/1944/3, it

appeared that hardness values in the grain growth zone of the 'toe' welds could be high,

but not attaining the levels in sample SISD/SK/1944/8.

The survey also showed that, whenever ferrite was visible in the area of microstructure

under test, the hardness value would be low. If ferrite were not visible in the

transformation structure (the centres of grains) then the hardness value would be higher,

but the optical appearance of the phase would be no guarantee that the hardness value

measured would be in a category which could be described as a 'hard spot'.

Recorded hardness measurements were taken and these are given in the attached Tables.

These measurements were mostly confined to the grain growth zones of the HAZs and

specifically sited to avoid visible ferrite. In Tables A2.1 and A2.2, where hardness is

falling rapidly the trace is entering the recrystallized zone. In general these traces

(Tables A2.1 and A2.2) follow the accepted pattern of high values close to the fusion line

which decay gradually into and beyond the recrystallized zone. In Tables A2.3 and

A2.4, the hardness trace follows closely with the fusion line and clearly demonstrates

that high hardness values ('hard spots') are associated with the HAZ of the toe welds on

the lower weld of both samples.

A2.6 MICROANALYSIS USING ENERGY DISPERSIVE X-RAYS

X-ray mapping to demonstrate segregation of the constituent elements of a steel by use

of the scanning electron microscope and energy dispersive x-ray analysis is a long

process with uncertain results. The different areas of the HAZ were assessed by area

scanning for compositional make-up. This process is an order of magnitude quicker,

although the results may be equally uncertain. The most important element, which will

affect hardness is carbon, and this cannot be quantitatively assessed by this technique.

Area scans (approximately 10 x 15 microns) were made in known hard and soft zones in

the grain growth area of the HAZ and an equivalent area, just outside the HAZ (in the

unaffected matrix). The results are given in Tables A2.6 and A2.7.

At this stage, the analytical errors were considered. For the minor elements - chromium,

nickel, copper and molybdenum - the analysis program gave 2sigma as approximately

0.15 wt%, indicating that the majority of the values given were unreliable. Our scanning

electron microscopist estimated that for manganese the error would be at least plus or

minus 0.1 and for silicon about plus or minus 0.05. In light of this, the prospect of

producing a contour map of element concentration, using a grid of analysis spots to cover

a selected area, seemed inappropriate. Furthermore, these errors assume a perfectly

A2. 3

polished surface. Some etching was required in order to identify the fusion zone and, in

analytical terms, this is regarded as undesirable. We are advised that electron probe

microanalysis, which could include carbon analysis, is the only possible route which

might give results of any value.

No more scanning microscopy was carried out.

A2.7 COMMENT

BS EN 288-3 prescribes the areas on which hardness measurements should be made.

These are precisely in the regions where the weld may encounter more rapid cooling

rates than elsewhere. The toe welds cannot be tempered by any further weld runs and the

same may apply in part to the root run. The only tempering that can occur is when

transformation temperatures, within the alloy, are high such that some auto-tempering

can occur after transformation whilst the weld cools to ambient.

With the two samples, the root run area is completely refined and tempered and contains

no 'hard spots'. The macro and micro-hardness testing indicate that the 'toe' welds in

weld 2 of both samples have higher hardness values than elsewhere. The microstructure,

whilst not exhibiting defined 'pools' of hard phase, do show structural refinement and

reductions in pro-eutectoid ferrite that could explain the increased hardness.

Microhardness measurements should be treated with caution. There is not yet a standard

which provides for absolute values when using small indentation loads. For this exercise

we tested calibrated 300 HV10 and 450 HV10 hardness blocks for the readings obtained

at HV300g. We found that the values obtained at the low load were at least 20 hardness

'points high. It would be wise therefore, to regard the microhardness data as comparative.

Both weld samples pass the hardness requirement (HV10) and some potentially high

hardness values obtained by microhardness should not detract from this, particularly as

they are in the areas where this might be expected and are not found elsewhere in the

weld.

A2. 4

Table A2.1 Microhardness traces (HV300g) within 2mm of the plate surface in the grain growth zone of the ‘toe’ welds and running parallel to the plate

surface (d is distance from the fusion line)

A2. 5

Table A2.2 Microhardness traces (HV300g) within 2mm of the plate surface in the grain growth zone of the ‘toe’ welds and

running parallel to the plate surface (d is distance from the fusion line)

A2. 6

Table A2.3 Microhardness traces (HV300g) along the HAZs of weld 2 and within 0.5mm of the fusion line Sample SISD/SK/1944/3

(d is distance from surface around the HAZs)

A2. 7

Table A2.4 Microhardness traces (HV300g) along the HAZs of weld 2 and within 0.5mm of the fusion line Sample SISD/SK/1944/8

(d is distance from surface around the HAZs)

A2. 8

Table A2.5 Microhardness measurements recorded but not illustrated graphically

A2. 9

Table A2.6 Microanalysis of HAZ (grain growth zone) and Matrix of weld runs in Weld 2 of Sample SISD/SK/1944/3

A2. 10

Table A2.7 Microanalysis of HAZ (grain growth zone) and Matrix of weld runs in Weld 2 of Sample SISD/SK/1944/8

A2. 11

Figure A2.1 Photomacrographs of the weld samples

A2. 12

Figure A2.2 Typical Microstructure in the grain growth zones of the weld pass HAZs

(excluding ‘toe’ welds)

Figure A2.3 Typical Microstructure in the grain growth zones of the ‘toe’ weld HAZ: SISD/SK/1944/8 – Weld 2

A2. 13

Printed and published by the Health and Safety ExecutiveC30 1/98

Printed and published by the Health and Safety ExecutiveC1.10 05/04

ISBN 0-7176-2800-0

RR 191

78071 7 628001£30.00 9

research report 191 - health and safety executive · research report 191. references 1. gardner l,...

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