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Transcript of _ _ U~~~Ut-fl - DTIC

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AD—AQ ’e’ i $58 ILLINOIS UNIV AT URBANA—CHAMPAIGN DEPT Off CIVIL ENGIN ETC FIG 13/5EFFECTS OF LACI&OPPCtIETRATION AND LACK—0ff fUSION ON THE FAT IGU— ETC(U)JUl. 76 a a BUM. F V LAWRENCE NOOO2k 75 C~~45Ob

UNCLASSIFIED NL

1: I04 48~ B

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Oo 2’ F INAL RE F~~T..S.—, )

Submi tted to

~~~ Naval Sea Sys tems Coman dU. S. Navy

©on the

/ _EFFECTS OF LACK-OF-2ENETRATION AND LACK-OF-FUSION ON THE

FATIGUE PROPERTrES OF 5083 ALUMINUM ALLOY WELDS _/

- - -

by ..~

J. D.. Burk ‘. .

F V Lawrence , Jr1

/

I 3~~~u_i ~‘ Department of Civil Engineering‘. ~~ Univers ity of Illinois at Urbana-Champaign

~~~ L~_.. Urbana , I l l i n o i s

/ ; f, / ) Ju1R ~~76

.~i_’:i— ’ / .) .,,

~~~~~~~~ / .

L .~~~~~

.

_ _

LIST OF SYMBOLS

a Mater ial constant

b Fatigue strength exponent

Angle of inc l ina t ion for LOF defect

c Fati gue ductility exponent; also , crack len gth

c Ini tial crack length0

cf Final crack len gth

2c LOP defec t width0

dc/dN Incrementa l crack growth ra te

C Crack propagation material constant

E E las t i c modulus

e,L~e Nominal s tra in , range

True s t ra in , ran ge

Ce~~Ce True elas tic s t ra in , range

cf Fatigue duc t i l i t y coef f ic ien t

True plastic strain , ran ge

AK th Threshol d stress intensity factor

t i

Stress intensity factor range it

K ’ Cyc l ic stren gth coef f ic ien t

Kf Fatigue notch factor

Kt Elastic stress concentration factor

9. Len gth of LOF defec t

Projected width of LOF defect

---4

n Crack propagation material constant

n ’ Cycl ic s train hardenin g ex ponent

2N f Number of reversals to failure (2 reversals = 1 cycle)

N 1 Fati gue crack ini tia t ion l i f e

Fa ti gue crack propagation l i f e

NT To tal fat igue l i f e

2Nt Transi tion fatigue life

r Notch radius

R Stress ra tio

S,~S Nominal stress , range

5 Minimum distance of LOF defect from sure

• a,Acr True stress , ran ge

Fa tigue stren gth coef f ic ient

t Pla te thickness

w Width of the weld at reinforcemen t position

ACKNOWLEDGEMENTS

This study was sponsored by the U.S. Navy Naval Sea Systems

Command under Contract NOOO24-75-C-45O4~ The authors woul d like to thank

the sponsor; Mr. Tom West, the techn i cal moni tor ; and the Wel d ing Research

Counc il Aluminum Alloys Comittee*, Subcommittee on Weld Defects** for their

su pport and i nteres t throu ghout the durat ion of the inves ti ga t ion .

* i~lum inum Alloy s Committee : R. A. Kelsey , Chairman

** Subcommittee on Weld Defects: L. J. Christensen , Chairman; D . C . H i l l ;W . B. Jenk ins; W. J. Louis; R. 0. Merrick; G. R. Rothschild; W . Wong.

• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ •- ~~—. .

TABLE OF CONTENTS

Chapter Page

1 INTRODUCTION

1 .1 Back ground

2 SCOPE OF PROGRA M 2

3 EXPERIMENTAL PROCEDURES 3

3.1 Materials 33.2 Wel din g Procedures 33.3 Test Piece Pre parat ion 33.4 Non-Destructive Exami nation 43.5 Fatigue Test in g 43.6 Post-Test Examination 53 .7 Low Cycle Fa tig ue Spec i men

Pre para tion and Test in g 6

4 RESULTS 7

4.1 Description of LOP and LOF Flaws 74.2 Results of NDT Evaluation 84.3 Fa tig ue Test Results : Sound RI Test Pieces 84.4 Fatigue Test Results : LOP and LOF Test Pieces 94.5 Results for Strain Controlled Fatigue Testing 10

5 DISCUSSION 1 1

5.1 Inf l uence of Ful l Len gth LOP Defec ts 1 15.2 Infl uence of Intermittent LOF Defects 115.3 Predictions of Total Fatigue Life , N1 125.4 Effectiveness of NDT Evaluation 16

6 CONCLUSIONS 18

7 REFERENCES 19

TABLES 2 1

FIGURES 38

APPENDIX

A 61B 63

1. INTRODUCTION

1 .1 Back g roun d

The i nf luence of wel d defects on the mechan i cal p ropert ies of

construct i onal grade aluminum alloy wel dments has been the subjec t of con-

si dera b le recent interest . The in f luence of d i s t r ib ute d poros i t y on the

tensile and fatigue properties of 5083 (and 6061) alloy weldments has been

recen tl y invest i gate d by the authors 4.~-ç~). In the fatigue study 4.2~3,

defects other than the weld toe and/or distributed porosity (most notably

lack-of-fusion) were often found to result in substantially l ower fatigue

lives than would be expected from sound , as-wel ded test pieces. Consequently

i nternal , planar, weld-defects such as lack-of-fusion (LOF) or incomplete

joint penetration (lack-of-penetration - LOP) must be considered potentially

serious defects from the point of view of fatigue resistance .

Dinsdale and Young (3) studied the infl uence of “dou le o erator

defects ” i.e., lack-of-fusion and incomplete penetration in 1/2-in. (12.7—mm )

thick Al-Mg-Mn alloys (NP 5/6 and NP 8). The exact dimensions of the LOP in

their stu dy i s not c lear ly state d, but the defects apparently pers i sted for the

f u l l len g th of the weld and were between 1 4 to 25 percent of the th i ckness of

the jo ints , rather large defects by current U.S.N. standards (4,5) . The re-

sul t of Dins dal e and Young ’s work clearl y shows that LOP and LOF defects can

reduce the fatigue resistance of both reinforcement intact (RI) and reinforce-

men t removed (RR) test pieces below the norma l expectations for sound RI welds .

2

2. SCOPE OF PROGRAM

Zero to tension fati gue tests were performed on double-V butt welds

of 5083/5183 aluminum alloy which contained full-length LOP defects and

“na tural ” , less- than-full -length LOF defects. The LOP and LOF defects were

incor porated in the wel ds us i ng “improper ” wel ding methods . The defects so

created were evaluated using normal incidence radiography and ultrasonic test

methods .

Fatigue tests were run on sound reinforcement intact (RI) and rein-

forcement removed (RR) welds and RI and RR welds containing full-length LOP

defects of various through thickness dimensions (2c). Fatigue tests were run

on RR wel ds con ta in in g var ious len gth “natural ” LOF defects in order to study

the behavior of less-than-full length , inclined defects .

The total fat i gue lives were predicted analytically. The effective-

ness of current U.S. Navy radiographic and ultrasonic test methods were examined

in the l ig ht of the experimental resu l ts .

_________________________ •

3

3. EXPERIMENTAL PROCEDURES

3.1 Mater i als

The test specimens were machined from welded panels 24-in. (61-cm)

by 36-in. (92-cm) which were donated by Chicago Bridge and Iron Co. The

panels were fa br i ca ted from 5083 alum i num base me tal us in g a 5183 w i re elec-

trode and were 3/8-in. (9.6-mm) and 1-in. (25.4-mm) in thickness. The base

meta l - f i l l e r metal com b ina ti on an d p late t hic knesses use d i n this work are

the same as those used in previous studies of welds and 5083/5183 welds con-

taining porosity (2,6). The nominal mechanical properties of the plate mate-

r ial an d 5183 weld metal are gi ven i n Ta b le 1 . The typ i cal chemical com pos i-

tion of 5083 base metal and 5183 weld metal are listed in Table 2. The

specimen nomenclature used in the study is outlined in Table 3.

3.2 Welding Procedures

All wel ded panels were fabricated in the flat position using a gas-

metal-arc process. Sound weld panels (level 1), were wel ded us i ng conven ti onal

proce dures . Three grou ps of panels were wel ded to in tent iona l l y p ro duce smal l ,

medium and large lack-of-penetration (LOP) defects and were designated by

sever i ty as leve ls 2, 3, and 4. Lack-of-fusion weld panels containing inter-

m i tterr t defects were a lso fa br i c a ted. Al l panels were furn i she d i n the as-

wel ded state without any post-weld terminal treatment.

3.3 Tes t P iece Pre parat ion

Fatigue test pieces were prepared by cutting 3 1/2-in. (89-mm) wide

s tr ip s from the wel ded panels . Radiogra phs of panels con ta i n i ng LOP defects

3:showe d a con tinuous defec t wh i le those of panels conta in in g LOF i ndi ca ted the

defects to be intermittent. Lack-of-penetration test pieces were therefore

continuously cut from one end of the supplied panels. Lack-of-fusion test

pieces were selectively cut from the panels with the aid of the panel radio-

graphs. A reduced cross—section having a gage length of 2-in. (51-mm ) and

wi dth of 2-in. (51-mm) for LOP test pieces or 2 1/2-in. (64-mm) for LOF test

p ieces was mach i ned in to the str ip s . The LOF tes t p i eces were w ide r to ins ure

the inclus ion of the defect in the test section . To avoid problems with test

equipment , LOP test pieces to be fatigued at higher stress ranges had their

width reduced to 1-in. (25.4-mm). All test pieces were either 3/8-in. (9.6-mm)

or 1-in. (25-mm) in thickness. The reinforcement was removed from the [OF test

piec r approximately half the LOP test pieces . The remainder of the test

pi b ested with the reinforcement intact. The geometry for a typical

cce is shown in Fig. 1.

3.4 Non-Destructive Examination

After machining, all test pieces were examined and rated using radio-

gra phi c an d ul t rason i c ins pec ti on me thods. Edge s hot ra di og ra phs were taken

of both the LOP and [OF test pieces. Each test piece was ultrasonically in-

spected prior to testing. Prior to each test, the ultrasonic equipment was

calibrated with a standard test block as described by the U.S. Navy inspection

standard (see Appendix A) (4).

3.5 Fati gue Tes tin g

The wel d test pi eces were tes ted to f a i l u re or app rox imatel y 1O~cycles wi th a 50 ,000 l b MTS closed-loop hydraulic test apparatus (shown in

5

Fi g. 2) at a frequency of 5 to 10 Hz under ambient laboratory conditions (20°C

and 50% relative humidity). A 600,000 MIS testing apparatus was used for the

1- in. (25.4-niii) LOF test pieces . Zero-to-tension (R = 0), s i nusoi dal , stress

cycles of 0 to 19 ksi (131.0 MPa) or 0 to 12 ksi (82.7 MPa) were employed .

These stress ran ges were selected on the bas is of the p rev i ous work of San ders

and the authors (2,6). The testing program is summarized below :

LOP Defe ct LevelThickness 1 2 3 4

Reinforcement in. (mm) (Sound)

RI 3/8 ( 9.5) 12 6 6 6

1 (25.4) 6 6 6 6

RR 3/8 (9.5) -- 6 6 6

1 (25.4) -- 6 6 6

In addition to the tests tabulated above , twe l ve 3/8-in. (9.6-mm ) and

ten 1-in. (25.4-mm) test pieces, containing intermittent LOF defects with rein-

forcement removed (RR) tested.

3.6 Post-Test Examination

After fatigue testing , the fracture surfaces were examined , and the

defect size was measured. The actual widths of the defects varied slightly on

the fracture surface , and the measurement of width was complicated by porosity

associated with the LOP. Lack-of-penetration width measurements were made at

the max imum w idth of the de fect on the frac ture surface or at the l oca ti on of

crack initiation (see Fig. 3). Lack-of-fusion defects were inclined to the

6

frac ture surface , and their wi dths were not read ily meas ure d. App rox i ma te

measurements of the LOF widths were made from the edge shot radiographs as

shown in Fig. 4.

3.7 Low Cycle Fatigue Specimen Preparation and Testing

Smooth specimens for low Lycle fatigue (LCF) testing were cut from

a l-~n . (25.4-mm) thick sound 5083/5183 weld panel . Fatigue testing was con-

ducted with an MTS 20,000 lb. closed-loop hydraulic test apparatus (7) with

Wood’ s metal grips to ensure proper specimen alignment. Axial strains were

measured with a clip-on extensometer (see Fig. 5) for the 5083 base metal

specimens and calculated with an analog computer from measured load and dia-

metrical strains for the 5183 weld metal specimens. A completely reversed

(R — 1) sine wave was used to control specimen strain amplitude . Ei ght

specimens of both 5083 base metal and 5183 weld metal were fatigued to failure

under strain control to produce fatigue lives of 102 to 106 cycles. Monotonic

tension tests were performed on one specimen each of the weld and base metal

7

4. RESULTS

4.1 Descr ipti on of LOP an d LOF F laws

The fracture surfaces, norma l incidence radiographs , and edge shot

radiographs of typical lack-of-penetration defects are shown in Figs. 6 and 7

for both 3/8-in. (9.6-mm) and 1-in. (25.4-mm) thickness specimens. The frac-

ture surfaces in Figs. 6 and 7 show that larq2 amounts of porosity are asso-

ciated with the LOP. This porosity has been previously reported (3). There

was considerable variation in the distrib ution of the porosity along the LOP

defect as well as variation in the size of the porosity . The porosity shape

also var i ed from s pher i cal to el ongated , worm-hole porosity . an~L~uttion o~

the. 6 c ~twte vt t~ctcc ,~ ‘ea-e ~ed -tha~t ~a~tAigue ckac!z ~i1LtA ctt~cu ~~cwut~d y ’~c -

de~~~iatc t ~u ~iwm -the LOP de6ec~t avid wa.~ viot a oc..Late d a’LtIi t lic pe~~’~~~tt,’ .

Representative lack-of-fusion fracture surfaces and edge shot radio-

graphs are shown in Figs. 8 and 9. In contrast to the contin uous LOP defects ,

the LOF defects were crescent-shaped , intermittent defects and their length

was aligned with the axis of the weld: see Fi g. 4. Unlike the LOP defects ,

porosity was not associated with the [OF defects; but a dark oxide l ayer was

evident at the LOF defect internal surfaces.

The parameters used to characterize the LOP and [OF defects are

shown in Figs. 3 and 4. Dimensions of the LOP defects are listed in Tables 4

through 7. Tables 8 and 9 give the dimensions of the LOF defects. The [OF

defect width (2c0) ranged from 0.002 to 0.18-ir . ~0.5l to 4.6-mm) for 3/8-in.

(9.6-mm) thick test pieces and from 0.002 to 0.30-in. (0.51 to 7.6-mm) for

1-in. (25.4-mm) thick test pieces . The [OF defect projected width (9.~) did

• • •~~~~~~ •~~~~~~~~~~~~~~~• • ~~~~~~ •~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ • • • • •~~~~~~~~~~~~~ • .

not vary as much as the LOP defect length (2c 0) and ranged from 0.05 to

0.08-in. (1.27 to 2.03-mm) and 0.08 to 0.30-in. (2.03 to 7.62—mm) for 3/8-in.

(9.6-rn) and 1-in. (25.4-mm) test pieces , respectively.

4.2 Results of NDT Evaluation

All test pieces were rated ultrasonically using Navy code NAVSHIPS

0900-006-3010 (4); i.e., Class I, II, III, or rejection as outlined in Appendix

A . Each test piece rating is given in Tables 10-16. Almost all test pieces

containin g LOP defects were rated Class I: viovie weit e ‘tejected. The test pieces

containin g LOF were p re dom i na tely rate d as Class II or I I I . Severa l of the

3/8-in. (9.6—mm ) thick test pieces were rated as Class I. The [OF 1-in.

(25.4-mm ) test pieces was the onl y grou p wh i ch con ta ined tes t p ieces that were

rejec ted by ul t rason i c ins pec ti on.

Radiogra phs of the LOP test pieces and sound test pieces were rated

by U.S. Navy code NAVSHIPS 0900-003-9000 (5) as outlined in Appendix B. All

sound wel ds rece i ve d a Class I ra ti ng, an d aU LOP ~tei.~t p~eceo rve/Le ~rej cc- tcd .

The radiographs of LOP defects were similar to those shown in Figs . 6 and 7.

Test pieces containin g [OF defects were rated using the normal incidence panel

radiographs . A~U LOF ~te~t pi.~ece~ we’te ‘tej ec~ted.

4.3 Fatigue Test Results: Sound RI Test Pieces

The test results for the sound RI test pieces are given in Tab le 10

and plotted in Fig. 10. A least -squares line shown solid in the figure was

f itted to the open symbol test data for both the 3/8 and 1-in. (9.6 and 25.4-rn)

thick test pieces. The soli d symbols of the 3/8-in. (9.6-mm) test pieces

~

-- -

~

- . . -- --~~~~~~~~~~~~-..~~~~~~~~~~~~ - -.••~~~~~~~~~~~~~~-.- •-~~~

9

(numbers 1 though 6 in Table 10) were not considered in the least-squares

fit because these specimens had large joint distortions. Such distort ions

have been s hown to significantly reduce weld fatigue life (9). Results from

a prior study (2) are shown as dashed lines in Fig . 10.

Comparison of the best-fit lines in Fig. 10 shows that the 1-in.

(25.4—rn) welds in this study produced significantly better fatigue lives than

the 3/8-in. (9.6—mm ) welds . This result is opposite to that obtained in the

previous work and is attributed to the fact that the weld reinforcement of the

3/8—in. (9.6—mm) test pieces of this study were much larger than that of the

1-in. (25.4-mm ) test pieces . There is good agreement between the best-f i t

lines (solid and dashed ) for the 1-in. (25.4- mm test pieces for this study

and the prior work.

4.4 Fatigue Test Results: LOP and [OF Test Pieces

The LOP test results for 3/8-in. (9.6-rn ) test pieces are listed in

Tables 5 and 6 and plotted in the S-N diagram of Fig. 11 . The data show a

large amount of scatter which results from differences in LOP width (2c0).

Those test p ieces having the larger LOP wid ths pro duce d shorter f a tigue l i ves

than those with smaller LOP defects . All but a few specimens failed at LOP

defects. A comparison of the best-fit lines for sound welds to the welds con-

tam ing LOP shows that the LOP te4-t pLece4 aLWay~6 pkodaeed ti~ve~s ~hon~t~ t than

40w’ld weJLcLs.

Results for the 1-in. (25.4-rn) LOP test pieces are l isted in Tables

7 and 8 and plotted in the S-N diagram of Fig. 12. As wi th the 3/8-in. (9.6-mm )

LOP welds , a large amount of scatter in the data resulted from the variation in

_ _ _ _ _

10

defect width (2c0). The fati gue lives of almost all the LOP test pieces were

shorter than those of sound welds: see Fig. 12.

The RR LOF test results for both the 3/8 and 1-in. (9.6 and 25.4-rn)

test pieces are given in Tables 9 and 10 and plotted in Figs. 11 and 12.

Figures 11 and 12 indicate that the LOF defects produce fatigue l ives which

are about the same or slightly less than sound RR welds . The RR [OF test

pieces gave greater fatigue l ives than most LOP specimens. This result is

not surprising since the projected widths of the [OF defects are generall y

smaller than of the width of most of the LOP containing test pieces.

4.5 Result •s for Strain Controlled Fatigue Testing

Resul t s of the comp le tel y reverse d s tra in con tro l l e d f a tigue tes ts

of 5083 base metal and 5183 weld metal are presented in Figs. 13 and 14 and

Table 17. The cyclic stress-strain parameters were determined for the 5183

wel d metal using the methods of Raske and Morrow (10) these data are also listed

in Ta b le 1 7. A compar i son of the fa ti gue resistance at lives greater than 1O 3

reversals shows that the 5183 weld metal can sustain a greater amount of

reversed strain than the 5083 -0 base metal ; however , t h i s d i f f e r e n c e i s not

large .

~~—- -~~~~~~~~~~~~~ -•

11

5. DISCUSSIO N

5.1 Influence of Full Length LOP Defects

As s hown in Figs. 11 and 12 , full length LOP defects have a profound

ef f e c t on f a ti gue life . Defects of large width are substantially more serious

than smal ler widt h def ec ts . Th i s ten dency i s i l l u s t r a ted i n F i gs. 17-20 in

wh ich the relationship between defect width (2c0 or 9.~) and fatigue life is

shown for each thickness and stress range . The solid lines in these figures

are predictions which wi l l be discussed in a subsequent section . Both the

reinforcement intact (RI) and reinforcement removed (RR) test pieces qave

substantially the same l ives. Naturally, the difference between sound RR test

pieces and LOP containing RR test pieces is substantially greater than the

d i ff erence between sound RI welds and these with LOP.

I f one uses soun d RI welds as a norm , the best fit curves (solid

lines of Fig. 12) would indicate that only the very smallest LOP defects tested

(— 0.05—in.) would give lives equal to or greater than the average expectancy

for sound RI welds . If one considers that sound RI welds can give lives as

sma l l as 3 x lO~ cycles at 19 ksi and 2 x 10~ cycles at 12 ksi , then from Figs .

18-21 , it would seem that LOP defects as large as 0.07 to 0.10-in, in width

coul d be permitted if one could accurately measure their width using conven-

tional NDT techniques. As will be subsequently discussed , this is probably not

possible.

5.2 Influence of Intermi ttent LOF defects

Althouth the shape , i ncl i nat i on and length of the “natural” LOP de-

fects was radically different from the full length LOP defects (see Fi gs. 6-9),

12

i t was f oun d that the resul t s f o r these LOF defects were s imi lar to the LOP

resul ts when considered on the basis of width projected onto a plane normal

to the tens i le stress (~~): see Fig. 4. As seen in Figs. 18-21 , an [OF of

given projected width (.Q0) gives approximately the same result as a similar

width LOP.

Thi3 fin ding leads to the following conclusions: the effect of an

[OF defect of projected width (9.~) is essentially similar to the effect of a

full len gth LOP of similar width . Furthermore , the finite lengths of the [OF

def ec ts had no ap prec i a b le i nf l u ence on the i r behav ior .

5.3 Predictions of Total Fatigue Life , NT

The total fatigue life of a weld may be considered to be composed of

a crack initiation period (N~ and a crack propagation period (Ne). Strain-

controlle d , smooth—specimen fatigue data such as that shown in Figs. 13 and 14

and Table 17 can be used to calculate the fatigu€ crack initiation period using

t he metho d of Topper , Morrow , Mart i n , and Mattos (11, 12 ,13,14). This method

considers fatigue crack initiati on to have occurred when a hypothetical fi l ament

of metal situated at the tip of the notch ([OP in the present circumstance)

fails by the accumulation of fatigue damage . This calculation is carried out

usin g a computer si mula ti on of the hysteres i s loop of the ma ter i al a t the notch

tip, (weld metal in this case). The scheme of the computation is diagrammed in

Fig. 15 and the use of the model requires :

1 . Determ i na tion of the e las t i c stress concentrat i on

fac tor of the notch For an e l i pt i cal flaw i n

a finite plate Kt is (15):

Kt = 1 + 2 sec ~ ] ~ (1)

~~~~~~~~-•-~~~~~~~~~~~ -- • -

13

2. Estimation of the fatigue notch factor (Kf)

f rom Kt throu gh the use of Peterson ’s equa tion (16):

K - iK = 1 + (2)f

r

3. Knowl edge of the cyclic stress -strain properties of

the mater ial at the notch root: n ’ , K’ , etc.

4. Knowledge of the strain-life properties at the notch

root: Gf~ Cf~ b, c, etc.

The nom inal stresses (S) are related to the notch root stresses and

s tra i ns th rou gh the use of Neu ber ’s Rule whi ch governs the max imum value of

the product (a e) dttained in a given reversal:

(K f S ~ 2

E (3)

Dama ge is calc u la ted on a reversal by reversal bas i s by the computer s imulat i on

from the rela tionship:

* =

~*)e or (

~-‘) +

~~ (4)

where: (~—~\ is the dama ge per reversal resul ti ng from the\ ~Ie elas ti c s t ra in amp l i tu de

(~~‘—‘

~ is the damage per reversal resu lting from a

%, f J~~~ plastic strain amplitude

~~~~ is the additional damage resulting from the

\ f/0 presence of a mean stress.

14

For the present ca l cu la t ions , the level of p las tic stra i ns were so

low that essen ti a l l y no mean s tress relaxa ti on occurre d , an d the mean s tress

was therefore cons idered to be cons tant. The computer prog ram s imula ted the

cyc l ic har den i ng an d sof ten i ng of the ma ter i a l . Fa i l u re of the hypothe ti calf i l amen t was consi dered to occur when :

~~~~~~~~~. ~c (2N.) = 1 (b)

Values of Kf were determined using Eqs. 1 and 2. It can be shown that

achieves a max imum value (Kf max~ for a critical value of (r) which is of

the order of (a) in Peterson ’s E qua ti on . Values of K f max were used in this

calculation since it is believed to be physically realistic that a radius equal

to that giving Kf max should exist somewhere along the length of the [OP defect.

In addition , this assumption gives the most pessimistic estimates of N 1 . Values

of K f max are plotted as a function of plate width and LOP width in Fig. 16.

The results of these calculat ion s are summarized in Fig. 17 in which

the relationship between a given severity of LOP ( i .e., Kf max~ and cylces to

crack initiation (N 1) is given. Actual predictions of N1 are plotted in

Figs. 18-21.

The fatigue crack propagation portion of life (N e ) was estimated using

the power law model for fatigue crack growth (17):

= C(~ K) ’~ (6)

which can be numer i c a l l y integra ted to gi ve :

Cf

N~ ~

( A K) ~~ dc (7)

_ _ _

15

where AK for the LOP defect in a finite width plate is taken as (18):

AK = tS [~ic sec (8)

where : N~ = fatigue crack propagation life

AK = ran ge in s tress intensi ty

= fatigue crack growth rate

C,n = material properties

C0

= initial defect width

Cf

= final defect width

The calculated values of N~ are very sensitive to the initial value

of defect length (c0) and to the material properties C and n. The initial

defect length (c0) w taken as the half-width of the LOP at its widest point

or at the point where crack propagation ori gi na ted . I n those cases where the

measur ed val ue of c0 gave AK values less than reported values of AKth(8 ksi ~‘ThT), then the c0 defined by AK th for the stress range in question was

used. The f i nal value of crac k length (C f ) was taken as one-half the plate

thickness. The material properties, C and n used inthe calculations are listed

in Ta b le 17 and are measure d values for 5083 base metal under R = 0 cond iti ons

(19). The limited information available on the C and n values for weld metal

woul d in d icate that wel d metal is s imi lar to or sl ig htl y more res is tan t to

fatigue crack growth than base metal (20).

Values of N~ ca lcu la te d us in g the a bove metho d are p lo tte d i n F ig s .

18-21. The total fatigue life (NT) was calcula ted as the sum of N1 an d N~ and

i s a l so p lo tted in these f i gures .

16

The calculated and measured total l ives s hown in Figs. 18-21 are

in good general agreement. A surprisingly large fraction of life is devoted

to crack init i ation . The in i t i a tion an d pro pa ga ti on l i ves become equal i n

the l i f e re gi on of ~~ and l0~ cycles. At greater lives , crack init iation

appears to dominate . At the l ower stress level (12 ksi) and particularly for

the 3/8-in, specimens, crack initiation appears to play a predominan t role.

At the higher stress levels and particularly for the 1-in , specimens , propaga-

tion dominates.

5 .4 Ef f e c ti veness of NDT Eva lua t ion

As argued in Sections 5.1 and 5.2, all but the smallest width [OP

and [OF defects must be considered rejectable. As seen in Tables 11-16 , al l

[OP and [OF specimens were rejected by the current U.S. Navy radiographic

standards which are reproduced in Appendix B. Although these standards are

based on the length rather than the through-thickness width of the defect which

la tter dimensi on was shown to control , the effec t of these current s tan dar ds

was to disallow any of the LOP and [OF defects , albe it, for the wrong reason .

In contrast to the radiographic standards, the ul trasonic ins pection

standards , reproduced in Appendix A, are based both upon def ec t len gth and widt h

by reason of the f a c t that def ec t s g i vin g in d icat ions below a d isre gar d level

are to be ignored regardless of their apparent length.

Each specimen was examined using the current Navy ultrasonic test

code (4) and calibration block. As seen in Figs. 22 and 23, very few of the

LOP and LOF specimens were rejectable, and there is no apparent pattern to those

which fall into the Class II and III categories. In the light of the above

17

observations , it must be conclu ded that the current USM ultrasonic test

standards are rather unconservati ve as regards the defects studied here .

In summary, neither normal incidence radiography or conventional

ultrason ic test methods can reliably measure the controlling through-the-

thickness dimension of the [OP type defect wi th the precision necessary to

discriminate between serious and ignorable defects . Since [OP and [OF defects

larger than about 0.1-in , in width were shown to drastically reduce the fatigue

life by amounts generally larger than a factor of ten , it would seem that any

[OP or [OF in dication should be rejected to insure fatigue lives no less than

tha t of soun d RI wel d s . The current ul trason i c code woul d seem to be qu ite

unconserva tive . The current radiographic code, although based upon a dimension

havin g l itt le i nf luence , has the effect of rejecting serious LOP and [OF defects

and woul d theref ore seem just i f i ed.

-

18

6. CONCLUSIONS

1. Lack of penetration (LOP) defects can seriously reduce the fatigue life

of both reinf orcement intact an d re i nf orcemen t removed wel ds . The

magnitude of this reduction is determined by the through-thickness

di mens i on of the LOP . The poros i ty assoc i a ted wi th these def e c t s seeme d

to exert no influence .

2. Less than fu l l l engt h , incl ined lack—of-fusion ([OF) defects were generally

less serious than [OP defects but if compared with LOP defects on the basis

of width projected normal to the tensile stress, they were found to follow

the same trends as equivalen t width LOP . The length of the [OF along the

ax i s of the wel d seemed to have no i nfl uence on the i r eff ec t.

3. Predictions of total fatigue life (NT) based upon separate , conservative

estimates of the crack initiation period (N1 ) an ” crack propagation life

(N e) agreed well with the experimental data. A surprisingly large reaction

of life was attributable to crack initiation.

4. The curren t ul t rasonic NOT s tan dar ds did no t di scr imi na te between acce p-

table and unacceptable [OP or [OF defects, and this standard seems quite

unconservat i ve . The curren t ra di ogra phi c stan dar d seems s tr i ngent enou gh

in that all [OP and [OF defects were rejected , and this rejection would

seem warran ted by the test res ul t s . Ne ith er NDT s tan dar d i s ra ti onal i n

the sense that it is not based upon the controlling defect dimension , the

through th ickness wid th .

-.

19

7. REFERENCES

1. Lawrence, F. V. Jr. and Munse, W. H., “Effects of Porosity on the TensileProperties of 5083 and 6061 Al uminum Alloy Weldments ,” WRC Bull. 181 ,New York , 1973.

2. Lawrence , F. V. Jr., Munse, W. H. and Burk , J . D., “Effects of Porosityon the Fatigue Properties of 5083 Al uminum Alloy Weldments ,” WRC Bull. 206,New York , 1975.

3. Di nsdale , W. 0. and Young, J. G., “Si gnificance of Defects in AluminumAllo y Fusion Welds ,” Weld. Res., 9, 8, 1 962.

4. UL a..~on..Lc In4pee.t~on P-’wcedt .t ’te and Accep ance S.tandvLd.~ son. KaLe St-’we.tw~.eP-’wdac..t~ion and Repctvt. We1~d~, NAVSHIPS 0900-006-3010, Naval Sea SystemsC ommand , January 1 966.

5. Rad~o~’z.aph~c Standa..’td4 ~~ Piwduc.t.~on and RepaL’t. UPe.Cd4, NAVSH IP S0900 -003 -9000 , Naval Sea Systems Command , March 1967.

6. Sanders , W . W . and Gannon , S. M., “Fatigue Behavior of Aluminum Al loy 5083Butt Welds ,” W RC Bull. 199 , New York , 1974.

7. Feitner, C. E. and Mitchell , £4. R., “Bas ic Resea rc h on the Cycl ic Deforma-tion and Fracture Behavior of Materials ,” Manual on Low Cycle FatigueTesting, ASTM STP 465 , 27, 1969.

8. Martin , J. F., “Cyclic Stress-Strain Behavior and Fatigue Resistance ofTwo Structural Steels ,” Univers ity of Illinois FCP Report No. 9, 1973.

9. Burk, J. 0. and Lawrence , F. V. Jr., “Influence of Bending Stresses onthe Fatigue Crack Propagation Life in Butt Welds ,” Submitted to WeldingJournal for publication , March 1976.

10. Raske , 0. T. and Morrow , JoDean , “Mechanics of Materials in Low CycleFatigue Testing, ” Manual of [ow Cycle Fatigue Testing, ASTM STP 465, 1 969.

11. Topper, T. H. and Morrow , JoDean , “Simulation of the Fatigue Behav i or atthe Notch Root in Spectrum Loaded Notched Members,” Un i vers i ty of Ill i no i sTAM Report No. 333 , 1970.

12. Morrow , JoDean , “Fa tigue Properties of Metals , Fat igue Des ign Handbook ,SAE , 4 , 3.2 , 1968 .

13. Martin , J. F., “Fatigue Damage Anal ysi s for Irregular Shaped StructuresSubjected to Representative Loads, ” University of Illinois FCP ReportNo. 10, 1973.

14. Mattos , R. J., “Est imation of the Fatigue Crack Initiation Life in WeldsUsing [ow Cycle Fatigue Concepts ,” University of Illinois, Ph.D. Thesis ,1975.

20

15. Peterson , R. E., Stress Concen tration Factors, Wi l ey & Sons , New York ,1 974.

16. Peterson , R. E ., Metal Fatigue , Chapter 13 , Sines and Wa i sman (ed.),McGraw-H i 11 , 1959.

1 7. Par i s, P. C. and Erdogan , F., “A Criti cal Analysis of Crack PropagationLaws ,” J. Bas ic Eng. ASME Trans. Series 0, 85 , 528 , 1 963.

18. Tada, H., Par is, P. 0. and Irwin , G. R., The Stress Anal ysi s of CracksHandbook , Del Researc h Corp., Hellertown , PA., 1973.

19. Nordmark , G. E., Private Communi cation , Alcoa Techn ical Center,Alcoa Center, PA ., 1976.

20. Kau fman , J. G. and Kelsey , R. A., “Fracture Toughness and Fatigue Propertiesof 5083-0 Plate and 5183 Welds for [iquified Natural Gas Applications ,”ASTM STP 579,138, 1975.

21

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33

C.0. 0, 0. C. C. 0. C) 0.CD CD C) C) C) C) Si C)Si Si Si Si Si Si Si

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0 4) 0 4-’ 0. 0 C 4) 04 ) 0- 0 0 4” 0. 0. 0. 0. 0. 0 0 0.0 ‘a’ .0 -a- 4-( .~~~~-a’ .0 ‘a- 5- .0 -a’ C) 5- 5- 5-

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0. 0) 0 0 U 0 U U U 0 0 0 0 0 0 0 0 0 0 0a- ‘0 U) C) C) C) 0 ) 0 ) C) Ci C) C) 0 ) 0 ) 0 ) ~~~~~0) C) (3) 51) (3)

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34

C.0. 0)

0, 0, C. C. CD C. 0. C. 0. C’., C. 0. 0, 0. CX, SiC) C) C) C) .4 0 C) 0 Cl C) C) C) 0) C) 0Si Si Si Si Si Si Si Si Si Si Si Si Si Si .0

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0 0 0 0 U) a - C ) 0 - 0 0 0 0 0 0 0 0 0 00, 0. 0~ 0- 0 ‘a- 4) 0. 0. 0- 0. 0. 0, 0. 0. 0- 0. ‘V5- ( C C 0 C0 ) 0 ) 0 ) a- 0 ‘4- -a’ ~~ a - a - a - a - a -a - a - a -a - - a - I CC” C) C )a - 0. ‘a’ a - a - a - a - a ” a - a - a - a - a -S.. S.. 5 - ( C U. ‘V CC ‘0 ‘ 0 ( 0 (0 ‘0 ‘ 0 ( 0 (0 (C L’.,‘ 0 ( 0 1 0 C) 0 0 Ci E C) C) C) C) C) C) E C) C ) C ).4 .4 Si U) ~~ Si 3 LI) U’. U) LI) L/) U) U) CI) (I) Cl) Si

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QJ Q) a, CI) 4) U. U.‘C- U U U

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38

U’In4)CSU

‘C— I— ..—

(ww6’88)’u!~/~

U,

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E a)

i

-

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(~~i

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~~~~~~~~

-

_ _ _ _ _ _

~

39

-

~~~~~~~~~~~~~~~~~~~~~~~~~

, ‘ . ,

i~

a.~~~~

i” ~~~~

“. ‘ ‘

~~~~~

~~~~~~~~

Fi g. 2 Fatigue testing apparatus

a- -‘~~~~.-.-‘-~~~~~~

- -------

~~~~~~~

40

w4

L 2CH

1—

Fig, 3 Width (w), plate thickness (t), and defect width (2c0)describing LOP test p iece defec ts

—4

. - - a-— - - --- - .-- -.. ——- - ---

41

LOF Defect

w

Fig. 4 Width (w), length (2), projected width (~~~

), angle ofincl ination (s) , and surface distance (s) describing LOFtest pi~ ..e d~fects J

- - -~~~~~~~~~~~~ - -

42

.•~‘.‘

~~-.‘ ~~~~~~~~~~~~~~~~~~~~

-

_ _

Fig. 5 Strain -control 5083 base metal fatigue specimen w i th at tache dextensometer in testing apparatus

- 43

P1-2-2-5 AS = 12 ksi (82.7 MPa ) N f = 413,920(small ) 2c = 0.06-in. (1 ,52 mm)

I _ _ _ _I “

-

P1— 3 —1 -2 AS = 19 ksi ( 131,0 MPa) N = 14,050(medi um) 2c = 0,08-in, (2.03 mm)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-‘ -2P1-4 -3 — 6 AS = 12 ksi (82 ,7 MPa) Nf = 133 ,880(large ) 2c 0

= 0,08-in. (2.03 mm)

Fig, 6 Test piece fracture surface wi th edge and norma l incidenceradiographs for typica l small , medium and large LOP defectsin 3/ 8—in , (9.6-mm) thick 5083/5183 Aluminum welds

44

I

-

~~~~

P1-2-2-5 ‘S = 12 ks i (82 .7 MPa) N = 292 ,610(smal l) 2c = 0,17-in , (4.32 mm)

P1-3 -1-4 .\S = 19 ksi (131,0 MPa) Nf = 3 ,830(medium) 2c 0 = 0.24-in. (6.10 mm )

ii

P2-4-3-6 AS = 12 ksi (82.7 MPa) Nf = 40,850

(large) 2c0 = 0.30-in, (7.62 mm)

Fig. 7 Test piece fracture surface with edge and normal incidenceradiographs for typical small , medium, and large LOP defectsin 1-in. (25-rn) thick 5083/5183 Al uminum welds

--~- - ------— -‘---a-- - .

45

P3—1— i AS = 19 ksi (131.0 MPa) Nf = 46,070

= 0.08—in. (2.03 mm)

LIP3—1—2 AS = 19 ksi (131.0 MPa) Nf

= 34,970= 0.07—in. (1.78 rn)

P3-2-10 AS = 12 ksi (32.7 MPa) Nf = 1,040 ,590

Fig. 8 Test piece fracture surface and edqe shot radiograph of typicalintermittent LOF defects in 3/8-in. (9.6-rn) th ick 5083/5183Aluminum welds .

_ _ _

- . - - . ‘

~~~~-- . - -~~~~~--~~ ~~--- - - ~~~~~.a -~~~~~~ - - - --- -. - ----a-

~~~~~

. .- -,

46

P3-3-6 AS = 12 ksi (82.7 MPa) N 1 ,222,010= 0.30-in. (7.62 mm)

P3—3-7 ,~S = 12 ksi (82,7 MPa) N = 222 ,830= 0.12-in. (3.05 mm)

- ~

-_ _

P3—3—8 ~S = 12 ksi (82.7 MPa) N f = 407 ,180

= 0.10-in. (2.54 mm)

Fi g. 9 Test piece fracture surface and edge shot radiograph of typicalinterm i ttent LOF defects in 1-in. (25-mm) thick 5083/5183Al uminum welds

~~~~~~~ -

-- -; . a-a-_

- -

47P.O

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50

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0_ I —

c’JI—

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4)‘0

a.E

0.001 —

0 0001 —_____10 102 o4 o5 10

1

Reversals To Failure , 2N f

Fi g. 13 Strain-life plot for 5083-0 Aluminum base metal for smoothspecimens tested under completely reversed (R = - 1) straincontrol . (Note that 2 reversals = 1 cycle.)

- a- - -

- - —

51

1.0 I I I I I

-0.890 -0.107A4/2 0.58# (2N f) + 0.00897 (2Nf )

0.1 —

c~J5,•~,

,~~~ 0.0I — 0

a.E4

0C.~~

C/)

0.001 —

I I I I IQ000, 2 3 4 5 6 7 8I 10 10 10 0 10 10 tO 10

Reversals To Failure, 2N f

Fi g. 14 Strain-life plot for 5183 Alumin um weld meta l for smooth C

specimens tested under completely reversed (R = - 1) straincontrol .

L . -—-- .--~~~~~~~~~~~~- - . ~~~~~~~~~~~- - -

- — a -

52

I I

9 — 1 /w S in. (25.4 mm)

8 — -

— w : /2 in. (P7.7mm)

-

8

06 — w 3/8 in. (9.6 mm) -

‘CUaz -

4)

04

4 — -

EEo 3 — -

2

I I I0 0.05 0.10 0.15

C0, Half Crock Length , ift

Fig. 15 The relationship between the max imum fatigue notch factor (Kf max~and the half-length (c 0) of the LOP defect for various platethicknesses. The material constant (a) in Peterson ’ s equation wastaken as 0.003-in. (0.076-mm )

-- - — - -- - a - - — - - -. - - - - -. - - -- - - -a- -- a----- . . ---- -- -~~~~~~~~~~

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54

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58

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59

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‘a’

60

________________________________________________ 0— I II I I —

_

t- — (C

- I 0.

.

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— C)- 0 4 - 4 - 0//2~th/ ~~~~~

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_ _ _ _ -- - — - - - - -~~~~~~~~~- -- -a-~~~~~~~~~

61

Appendix A

Code Con t r o l l i n g PermissibleLOP ar.d LOF Defects for

U l t r a n s o n i c F4DT

NAVSHIPS 0900 - 006 - 3010 (January 1966) Ultrasonic Inspection Procedureand Acceptance Standards for N u l l Struc ture Produc tion and Repa irWel ds

Section 6 Ultrasonic Inspection Procedure Requirements

6.3.4 Reference Calibration Standar ds

6.3.4,1 The calibration standards for the equipment sensitivitysha l l be capab le of p rovi d in g cons tant reference sensi ti vi tylevels for all angles of search an d inspection depth . Thestandar d reflecting surface shall be a 3/64-in, d i ame ter holedrille d through a 1-1/4 in. wide b lock . The tes t surface ofthe block shall be approximately 250 r.m .s . or com pared to sur-face f i n i s h standards.

6.3.5 Cal i brat i on

6.3.5,1 When a calibrated decibel control is used , the instrumen tgain shal l be adjuste d to peak al l si gnals fr om the referencec l ib ra t ion holes at 20°~ of fu l l screen hei ght . The corre-spon d in g depth an d locat ion of the peaked s igna ls from thereference c a l i b r a t i o n standard sha l l be worke d alon g the baseline of the viewing screen . The gain shall be increased 12decibels. At this gain se t t in g, the 20% l i ne on the viewin gscreen is the DRL (Disregard Level), and the ARL (AmplitudeRejecti on Level ) is 12 decibel s above this line. For evalua -t ion of indica tions above th i s DRL , the ca l i b rate d deci belcontrol is used.

Section 7 Acceptance - Rejection Criteria

7.3.1 Full Penetration Butt Welds and Corner Welds (Class I)

7.3.1.1 Any discontinuity whose reflection exceeds the ARL shallbe rejected.

7.3.1.2 Indications less than the DRL shall be disregarded.

7.3.1.3 Discontinuities whose relections equal the ORL , or aregreater , up to and including the ARL , shall be evaluate d asfollows :

--

62

a. If the discontinuit y length exceeds 1/2t (t=thick-ness of the thinner member ) it shall be rejected.In no case shall any sin gle discontinuity lengthexceed 1-1/2 inches.

b. Adjacent discontinuities separated by less than 2Lof sound metal (L=Length of longest discontinuity )shal l be cons id ered as a s i n g le d i scont i nu ity .The max imum di stance between the ou ter extrem iti esof any two such discontinuities or the sum of theirlen gths , wh i chever is grea ter , sh a l l no t excee dthe sum of their length specified in 7,3,1.3 (a).

c. If the total accumulative length of discontinuitiesin any 12 inches of weld length exceeds it , thatweld length shall ~e rejected ,

7,3.2 Full Penetration Butt Welds and Corner We ’ is (Class II)

7.3.3.1 An discontinuity whose reflection exceeds the ARL andhas a len gth w hi ch excee d s 1/2 11 shall be rejected , Adjacentdiscontinuitjes whose reflections exceed the ARL , separatedby less than 2L of sound metal L=length of longest discon-tinuity , shall be considered as a single discontinuity .

7.3.3.2 Indications less than the DRL shall be disregarded .for class I I I , the DRL shall be increased from 20% to 40%of f u l l screen hei ght.

7.3.3.3 Discontinuities whose reflections equal the DRL , orare greater , up to an d i nclu di ng the A RL , shall be rejectedif the di scontinu i ty len gth excee ds 1 11 or l t, whichever isgreater (t thickness of the thinner member).

7.3.3,4 Adjacent dis continuities separated by less than 2 L ofsound metal , (L length of longest discontinuity ) shall becons id ered as a sin gle di scont i nu i ty . The max imum di stancebetween the outer extremit ies of any two such adjacen t d is-continuities or the sum of their lengths , whichever isgreater , shal l not exceed the length specified in 7.3.3.1for discontinuities having refl ections above the ARL , or7.3 .3~3 for discontinuities having ref lect ions equal to theURL, up to and inc luding the ARL .

7.3.3.5 If the total accumulat ive length of discontinuit ies inany 12 inches of weld length exceeds 2t , that weld lengthshall be rejected ,

- . -- -- . --— -- -- - - -a-- - - - - a-- - - - - ---- -- -~~~~~~ a- -. -~~~~~~~~~~~~~~

63

APPENDIX B

Code Con tr o l l i n g Permiss ib leLOP and LOF Defectsfor Ra d io gra ph NDT

NAVSHIPS 0900 - 003 - 9000 (March 1967) Radiographic Standards for Pro-duc t ion an d Repair We ld s

3,2 Class I Acceptance Standard for Welds

3.2,2 Incomplete Fusion and Incomplete Penetration WeldsShal l be free of inc omp le te fusi on an d incom p le te pene-tration indications which exceed the limits of Figure B—l .Acceptable incomplete fusion and incomplete penetrationshall be treated as slag when determining the total accum-mulated length of slag.

3,3 Class II Acceptance Standards for Welds

3.3.2 Incomplete Fusion and Incomplete Penetration shall befree of incompl ete fusi on and incomple te pene tra tion ‘indi-cations which exceed the limits of Figure B-2 , Acceptableinc omp le te fusi on an d inc omple te pene tra t ion sha l l betreated as slag when determining the total accummulatedlen gth of s la g.

3,4 Class III Acceptance Standards for Welds

3,4.2 Incomplete Fusion and Incomplete Penetration Weldssha l l be free of incom p le te fu sion an d incomple te pene-tration indications which exceed the limits of Figure B-2Acceptable incom plete fusion and incomplete penetrationshall be treated as slag when determ ining the totalaccumulated len gth of s la g .

_ _ --~~~~~~~~~ -- a-- a- a- -- a- -~~~~~~~~~~~~~~~

_ -- — a - -

~~~~~

64

_ _ _ _ _ ______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

4.

oz_ _ _ _ _ _

c..J_ _ _ _ _ _ _ ~~~

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— c%j _—~~~~w

( f l Z Wd~~~~I— z

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