Effect of Weld Discontinuities on Fatigue of Aluminum Butt Joints

A 40% to 75% reduction in fatigue life was observed in weld repaired specimens that did not have their weld

reinforcement properly ground or peened

BY G. E. NORDMARK, W. C. HERBEIN, P. B. DICKERSON AND T. W. MONTEMARANO

ABSTRACT. Transverse and longitudinal CMA welded butt joints in VA-\T\. (6.35-mm) thick aluminum alloy 5456-H116 plate were subjected to tensile and fatigue tests to study the advisability of repairing weld discontinuities. Gross porosity and incomplete penetration were produced in a localized length of weld in test specimens designed to retain high levels of residual stresses compara­ble to those present in welded structures. The effects of preheating and postheat­ing the weld repairs and the use of multiple repairs were studied for both weld bead reinforcement intact and weld reinforcement removed specimens. Sev­eral crack arrest procedures were stud­ied, namely: drilled stop holes, expanded stop holes, interference bolts, repair welding and welded or bonded doubler patches.

For joints having their weld reinforce­ment intact, the levels of incomplete penetration —0.07 in. (1.8 m m ) - a n d gross porosity present in these specimens did not lower the fatigue strength. How­ever, the discontinuities served as crack initiation sites for some specimens having their weld reinforcement removed. Weld repair of the discontinuities of reinforce­ment intact specimens reduced fatigue life by 40% to 75%, unless the weld rein­forcement of the repair was treated by grinding or by brush peening. Postheating repair welds appeared to prolong the life a small amount. On the other hand, pre­heating weldments before a repair appears to have been detrimental.

Drilling stop holes at the end of short fatigue cracks delays propagation some-

C. E. NORDMARK, W. C. HERBEIN and P. B. DICKERSON are with Aluminum Co. of Ameri­ca, Alcoa Technical Center, Alcoa Center, Pa. T. W. MONTEMARANO is with David W. Taylor Naval Ship R&D Center, Bethesda, Md.

Paper presented at the 67th Annual AWS Meeting, held April 13-18, 1986, in Atlanta, Ca.

what, but a 4% expansion of the holes did not increase the delay. However, insertion of interference bolts in such holes completely arrested propagation of cracks for both longitudinal and trans­verse joints. Bonded or fillet welded dou­bler patches also greatly increased the crack arrest produced by stop holes. Repair welding can fully negate the effect of the crack if the weld bead reinforce­ment is ground so that the repair does not provide a stress concentration more severe than that of the original weld.

Introduction

When discontinuities are discovered in aluminum welds, the question of whether or not to repair weld must be addressed. Will the discontinuity shorten life under repeated service loadings? Since it is usually more difficult to make a sound, local repair weld, it is possible that the repair might lower the fatigue perfor­mance. Slater (Ref. 1) noted this possibili­ty in a survey of published literature on repair welding in the structural steel industry.

Current specifications greatly limit the amount and size of discontinuities that are acceptable in a weld, and welds not meeting the applicable standard must be repaired. For example, NAVSHIPS Specifi-

KEY WORDS

Aluminum Butt Joints Weld Discontinuities Effect of Fatigue Transverse CMA Welds Longitudinal CMA Welds 5456-H116 Aluminum Discontinuity Repair Crack Arrest Methods Stop Holes Interference Bolts

cation 0900-003-9000 (Ref. 2) requires that "welds containing any type of crack shall be rejected" (Section 3.1.2) and repair welded. The specification also lim­its size, distribution and concentration of gas porosity voids. As fracture mechanics concepts become better understood and accepted and nondestructive evaluation (NDE) methods are improved, codes may be rewritten to allow for a greater level of discontinuities. In the meantime, how­ever, welds found to contain discontinui­ties exceeding the present limits must be repaired.

Repair welding is costly and time-consuming. Because it can increase dis­tortion and residual stresses, as well as introduce stress concentrations, repair welding may produce a weld having lower fatigue resistance than that of an unrepaired weld containing discontinui­ties. Fatigue performance can be a critical consideration in many structures. There­fore, it is important to determine the effect of repair welding on fatigue per­formance and to determine what steps could be taken to improve the fatigue life of repair welds.

Published data (Refs. 1, 3-5) are not conclusive regarding the effect of repair welding on mechanical properties. With the exception of work by Hersh (Ref. 4), showing that repair welding significantly reduced the fatigue strength of welds in alloy 2219 sheet, there apparently had been little work done to evaluate the fatigue performance of repaired alumi­num welds. Therefore, the U. S. Navy funded an investigation at Alcoa Labora­tories to provide information on repaired butt joints in VA -in. (6.35-mm) thick alumi­num alloy 5456 plate.

Scope of Investigation

To address the issues of the effect of discontinuities and the effectiveness of weld repair or crack arrest procedures, transverse and longitudinal welded butt joints in '/4-in. (6.35-mm) thick aluminum

162-s | JUNE 1987

56 in. (142.2 cm)

30 in. (76.2 cm)

Rolling direction 5456-H116 plate 1/4 in. (0.6 cm) thick

Side struts are cut here for low residual stress specimens

12 in (30.5 cm)

8 in. 1 in. (20.3 cm)_(2.5 cm)

8 in. ,(20.3 cm)

• • • • . . • • • . • • . . • • • • • • • i . . n i

0.5 in. R (1.3 cm)

r

Fig. 1 — H-Plate fatigue specimen with transversely loaded weld

alloy 5456-H116 plate were subjected to tensile and fatigue tests. Baseline fatigue results for sound, unrepaired butt joint welds were obtained to determine the effects of residual stress level, weld rein­forcement, and weld orientation.

Cross porosity and incomplete pene­tration were produced in a localized length of weld in test specimens designed to retain high levels of residual stresses, comparable to those present in welded structures. The performances of the welds with gross porosity and incomplete penetration were compared to the per­formances of welds with single or multi­ple repairs with weld reinforcement

removed (RR) or intact (Rl). The effective­ness of preheating and postheating weld repairs was also evaluated.

The investigation also included an eval­uation of methods for arresting the growth of existing fatigue cracks. The arrest methods studied were: drilled stop holes, expanded stop holes, interference bolts, repair welding and welded or bonded doubler patches.

Test Program

Preliminary Tests

Preliminary fatigue tests were made on sound welds to study the effects of 1)

8 in.

"

2 2

(20.3 cm)

/ = /

\

in. (55.9 cm)

48 (121.

in. 3 cm)

: 7.25 (18.4

n. R

r

1 l

] )

f

cm)/ f

// 4 in.

• v

I

1

I

: 1

(10.2 cm) |

Weld dressed in gr

y

ip section

-^ Low residual stress specimen

V

Fig. 2 — Longitudinal joint fatigue specimen showing longitudinally loaded weld

direction of loading, 2) level of residual stresses and 3) presence of weld rein­forcement (Ref. 6). Because of the large number of variables that were included in the overall investigation, the test pro­grams were planned to obtain the most significance from duplicate tests for each condition. For example, the test program for the preliminary fatigue tests consisted of eight combinations of test variables in a 23 factorial experimental design.

The H-Plate specimen (Fig. 1), devel­oped by Alcoa Laboratories (Refs. 7, 8), was used to evaluate the fatigue perfor­mance of transversely loaded butt joints. The unique feature of this specimen is that it contains residual stresses trans­verse to the weld, simulating those found in actual structures. (As the weld in the center strut cools, tensile residual stresses are developed transverse to the weld as a result of the restraint against shrinkage provided by the side struts.) Toyouka used the same principle for smaller spec­imens in carbon steel (Ref. 9). Low resid­ual stress specimens are obtained by simply cutting through the side struts of H-Plates-Fig. 1.

The specimens shown in Fig. 2 were used to evaluate the fatigue performance of longitudinally loaded butt joints. High residual stresses are obtained by machin­ing the test section to final dimensions before welding. Low residual stresses are obtained by machining the specimen out of a larger weldment.

Weld Procedures

The H-Plate specimens were solvent cleaned, stainless steel wire brushed and held flat during welding. Figure 3 shows the transverse joint preparation, weld sequence and the weld variables. Small

WELDING RESEARCH SUPPLEMENT 1163-s

(

Back-chip

U 1

6.35 mm

1.6 mm 1.6 mm

Fig. 3—Weld joint preparation and welding variables for H-Plate specimens. Circled numbers indicate the welding sequence for the CMA weld. The welding variables are: '/te-in. (1.6-mm) diameter alloy 5556 electrode: 225 A, 30 V; 60 cfh of 40He/20Ar gas flow; root of first pass was back gouged; and the interpass temperature was 150"F maximum

ll

$ in. 9 mm

1

, >

* 22 in.

(559 mm)

I

r *

4 in. (102 mm)

J [

l l

r

\

1/4 in. (102 mm)

\

I i 1/8 in. 1/4 in.

(3.2 mm) (6.4 mm)

Fig. 4 - Longitudinal weld with incomplete penetration fatigue specimen

run-off weld tabs were positioned in the specimen slots for proper initiation and termination of the flat position welds. After weld completion, the tabs were removed and the slot openings, which were initially VA -in. (6-mm) undersize, were machined to their final dimension.

Because the longitudinal joints utilized automatic CMA welding, the root open­ing was eliminated, the abutting land increased to Va in. (3.2 mm) and a slightly higher heat input of 250 A and 28 V utilized. Again, run-off weld tabs were positioned at the beginning and end of the weld.

Discontinuities

Gross porosity was produced by add­ing 3 cfh of hydrogen to the shielding gas

during welding of each pass in the center 4 in. (102 mm) of the weld. Incomplete penetration was introduced by eliminat­ing the groove from the center 4 in. (Fig. 4) and increasing the rate of travel; i.e., for the longitudinal welds, the rate was increased locally from 28 to 44 ipm (0.71 to 1.12 m/min). Furthermore, neither the first nor the second weld pass was back gouged in this region of the weld. The procedures produced continuous incom­plete penetration.

The geometry of the weld reinforce­ment has been shown to significantly affect the fatigue strength - particularly for transverse loadings (Ref. 10). The effect of internal discontinuities would be expected to be greater for RR welds than for Rl welds (Refs. 11, 12). Accordingly, one half of the specimens containing

discontinuities were tested with the weld reinforcement removed by a portable milling cutter, followed by grinding in the direction of loading.

Inspections

All weldments were radiographically inspected with a 140-kV General Electric Model OX-140 x-ray machine with vari­able milliamperage control, using Eastman Kodak Type AA film. The welds were rated according to the ASME Boiler and Pressure Vessel Code (Ref. 13) and NAV­SHIPS 0900-003-9000 (Ref. 2) acceptance standards for radiographically deter­mined rounded indications in welds.

The welds were also subjected to contact ultrasonic pulse echo inspection. The plates were scanned near each weld reinforcement edge with a 5-MHZ-1/ 2+1-GAMMA G03953, 70°(s) 65°AL search unit. As might be expected, the porosity was obvious in all four scans. However, significant linear incomplete penetration discontinuities were missed by some of the scans. Apparently, the surfaces of the incomplete penetration were forced together tightly enough by the weld solidification shrinkage that they did not always interrupt the echoes.

Repair Welding Procedures

Repair welds were made with manual GMA welding in the flat position using run-out tabs for the start and stop of the welds. Repair welding was restricted to that required to repair the discontinuities. The discontinuities were removed by chipping with a pneumatic chisel from one side to mid-thickness of the plate and rewelded manually with three stringer bead passes using the welding variables employed on the original weld, and then the same procedure was repeated on the other side, lust before their weld repairs, some of the H-PIates were preheated to 450°F (232°C), using an oxyacetylene torch with a rosebud nozzle. The tem­peratures were measured with a contact pyrometer. Since localized repair welds are more likely to contain discontinuities than the original welds, multiple repairs are common. This was evidenced in this investigation by the fact that short-life failures of two H-Plate specimens initiated at unintentional, internal oxide inclusions near an end of their repairs. To study the effect of multiple repairs, some of the H-PIates and longitudinal butt joints were repaired three times.

Even careful repair welding produces stress concentrations at the ends of the repair. These stress concentrations may be more detrimental than the original discontinuity. Accordingly, to obtain the best possible repair, the weld reinforce­ment of most repaired H-PIates was removed in the area of the repair and a transition blended into the unrepaired

164-s | JUNE 1987

weld reinforcement. On the other hand, the reinforcement of the longitudinally loaded joints was left intact except that the ends were chipped to reduce the stress concentration —Fig. 5. Incomplete penetration was not expected to be par­ticularly detrimental in longitudinal joints, so it seemed more important to study the effect of a more conventional repair procedure.

Postweld Treatments

The effectiveness of two postweld treatments of repair welds was studied. Rl and RR H-Plate specimens were locally heated with a torch for 30 min to a temperature of 525°F (274°C). Weld removal for the RR specimens was more thorough than usual. The reinforcement remaining after use of the weld shaver was filed and sanded flush with the base material. For comparison with sound RR welds, the entire weld reinforcement, including the unrepaired ends, was removed.

The second method of postweld treat­ment was brush shot peening —Fig. 6. Both Rl and RR H-Plate specimens were peened, but only Rl longitudinal joints were peened. Since this was basically a study of what is required to restore the fatigue strength of a repaired weld to the level of a sound weld, only the area of the weld repair was peened. Further, for the RR H-PIates, the weld dressing with the weld shaver was limited to the area of the weld repair, and the weld rein­forcement edge filing was minimized. The repair welds of the H-Plate speci­mens were peened with 1- X 9/16-in. (25.4- X 14.3-mm) tungsten carbide shot brushes rotating at a speed of 6000 rpm, which produced an equivalent Almen rating of 9A. Increasing the rotational speed to 7000 rpm for the longitudinal joints produced a higher intensity of 10A to 11 A. These intensities are lower than the 13A shot peening reported (Ref. 14) to improve the fatigue strength of alumi­num longitudinal joints, but higher than brush peening intensities which Monte­marano (Ref. 15) showed to be beneficial for transverse joints.

Residual Stress Measurements

Two methods of determining welding residual stresses were utilized. Mechani­cal Berry gage readings were taken on many specimens before and after they were welded. The distribution of the residual stresses for an as-welded H-Plate specimen and the stress distribution under the applied load are shown in Fig. 7. Readings taken after the specimen was cycled five times indicated that there was no appreciable stress relief because of the initial loadings.

In the second method, coupon remov­al, the stresses were determined from

Fig. 5 — Weld repair of longitudinally welded butt joint

readings of electrical strain gages mounted close to the weld when cou­pons containing the gages were sawed out of the specimen. The distribution of longitudinal stresses measured for longi­tudinal joints by the coupon removal method is shown in Fig. 8. As would be expected, the additional heat and weld shrinkage of the three weld repairs and the widening of the weld increased the width of the zone of tensile residual stress, the tensile stress levels, and the magnitude of the compressive stresses at the edges. The repaired specimen had higher bending stresses than the unre­paired specimen.

Fig. 6 — Brush peening of repair weld

30

03

01

55

Stress distribution with applied

-r test load

Residual stress distribution

Fig. 7 — Distribution of residual stresses and superimposed applied test stress for H-Plate specimen calculated from Berry gage strain readings

Fatigue Crack Stoppage Specimens

The study of crack stoppage included some methods which might be consid­ered temporary and others which would be expected to be permanent. A limited test section width mandated that the repair procedures be tried on relatively short cracks. Centrally located, 1- or 2-in. (25- or 51-mm) long fatigue cracks were developed in specimens from '/2-in. (12.7-mm) long electrical discharge machined (E.D.M.) crack starters. For the H-PIates, the notch was machined at an edge of the weld reinforcement, since this is the normal location for crack initia­tion for a transversely loaded weld. For the longitudinal joints, the transverse crack starter was centered in the weld. The crack was propagated at a load which would produce a net stress of 17

WELDING RESEARCH SUPPLEMENT 1165-s

30

10 (A

(fi <D

• * *

(/)

a 3

•o w - 1 0 Hi oc

20

- 3 0

I

•

A / • s A A

I

I

•

/ A

* —D

I

/

I I * I A

A

- Weld containing • Front surface • Back surface

LOP repaired 3 A Front surface A Back surface

I i I

I

A

_•_ V. "5" X LOP \

times

I

I

\ A

A

I

• -6

A

A

0.00 1.01 2.03 3.04 4.05 5.06 6.08 7.03 8.10 Distance across panel, inches

Fig. 8 - Residual stresses in longitudinally welded but joints (incomplete penetration)

ksi (117 MPa) on the final uncracked area, and the same load was usually used for the subsequent crack arrest test.

Crack Arrest Methods

The first crack arrest method studied was repair welding. The cracks of two H-Plate and two longitudinal specimens were gouged out and repaired using procedures similar to those used for repair of the welds containing gross porosity. The results for these specimens were used to evaluate the effectiveness of some of the other procedures.

<sH@

Hole drilling, a common method of blunting cracks to retard crack growth (Ref. 16), was another standard by which the effectiveness of other procedures was evaluated for the H-Plate specimen. Stop holes of 0.28-in. (7.11-mm) diameter were drilled at each end of the 2-in. (51-mm) long crack. Similar holes were used for all of the other arrest proce­dures, except weld repair.

The stop holes of two H-Plate speci­mens were expanded by pulling a man­drel through an accurately sized 0.252-in. (6.40-mm) hole; a split sleeve is used to prevent scoring of the hole. The manu­facturer reports that an uncracked hole is expanded about 4%. This produces favorable residual stresses around the hole and has been reported to improve fatigue strength of precracked fastener holes (Ref. 17). Installation of interference

Fig. 9 — Failure of specimen ha ving interference bolt crack stoppers

Fig. 10 —Location of strongbacks

bolts in the stop holes also produces favorable residual stresses and props the holes open, thus reducing the cyclic stress range. Tapered bolts were inserted in the 0.28-in. holes of two H-PIates and two longitudinal joints after the holes were reamed with a specialized, tapered reamer. The lubricated nuts (Fig. 9) were torqued to 190 in.-lb (21.5 Nm), which the manufacturer reports will produce an interference of about 0.003 in. (0.076 mm).

Application of doubler patches is another method of possible weld repair (Ref. 18). Doubler patches such as can be seen in Fig. 10 were fillet welded to both surfaces of two H-Plate specimens after the stop holes were drilled. The doublers were the same alloy and VA -in. (6.35-mm) thickness as the specimen, and extended 1 in. (25 mm) beyond each end of the crack. As noted, the weld reinforcement had been dressed flush in the area of the patch, and the weld ends were blended into the original weld reinforcement. Sim­ilar patches were adhesive bonded to one surface of two specimens. Again, the weid reinforcement was dressed flush in the area of the patch. The patches and mating areas of the specimen were cleaned with HCI and bonded with a room-temperature curing epoxy adhe­sive, Hysol 9320 A/B.

Tensile Tests

Four tensile specimens were obtained from panels having transverse and longi­tudinal butt joints with each of the fol­lowing weld conditions: sound weld, gross porosity, gross porosity — 3 repairs, incomplete penetration, and incomplete penetration — 3 repairs. The same proce­dures were utilized for preparation of the panel as for the comparable fatigue spec­imens. For the longitudinal joints, at least one-third of the 1 '/2-in. (38-mm) test specimen width was weld metal; there­fore, only weld and heat-affected zone (HAZ) material was tested. The weld reinforcement was removed from half of the specimens by milling or shaving fol­lowed by grinding. Yield strength and elongation values for the longitudinal joints were determined using a 10-in. (254-mm) gage length centered on the weld. Elongation values were also deter­mined for a central 2-in. (50.8-mm) gage length.

The severity of incomplete penetration present in the transverse tensile coupons did not affect the tensile properties of Rl specimens —Fig. 11. The failures oc­curred on shear planes at an edge of a weld reinforcement. However, the porosity in Rl transverse joints was severe enough to cause the failures to occur in the welds at reduced tensile strengths and elongations. Three of four Rl repaired joints had similar tensile proper-

166-slJUNE 1987

5 0

4 0

* 3 0 tn

I 20 09

10

0

Weld reinforcement

Number of repairs

Sound welds

•

Incomplete penetration

Tensile strength Yield strength Elongation Mean tensile strength

Gross porosity

r~n

Min. Tens. Str. Alloy 5456

Rl RR Rl

SO

• : :

3 0

2 :

- 10 i

0

Fig. 11 — Effect of discontinuities and their repair on the static strength < transversely welded butt joints (0.25-in./6.35-mm 5456-H116 plate)

6 0

5 0

; 4 0

j 3 0 ) i 20

10

Weld reinforcement

Number of repairs

Sound welds Incomplete penetration & I Tensile strength o I Yield strength O ' Elongation

I I ! Mean tensile strength

Gross porosity

Min. Tens. Str. Alloy 5456 6 0

5 0 £

6 4 0 .£

3 0 * c o

2 0 n ut c O

1 0 uj

Fig. 12 — Effect of discontinuities and their repair on the static strength of longitudinally welded butt joints (0.25-in./6.35-mm 5456-H116 plate)

ties and failed in the HAZ. Removing the weld reinforcement

from the transverse joints allowed failure to occur in the weld at a reduced strength compared to the corresponding Rl specimen. Both types of discontinuities lowered the strength of the RR welds; others (Refs. 11, 19) have reported similar effects for RR welds. The incomplete penetration in the tensile specimens was intermittent and had maximum depths of 0.05 in. (1.3 mm). The repaired RR welds had strengths close to those of sound RR welds.

The tensile strengths for sound welds in longitudinal joints (Fig. 12) are a little higher than the respective average values reported for Rl and RR transverse joints-Fig. 11. Since the entire length of the longitudinal specimens is weld or heat-affected zone, and they do not have the transverse physical or metallur­gical notches of the transverse joint, the elongations of the longitudinal joints are about two-thirds greater. The weld bead reinforcement constitutes an appreciable, although unmeasured, percent of the cross-section of the longitudinal joints. Accordingly, the measured strengths are lowered when the reinforcement is removed. However, the removal did not affect the elongation.

The percent elongation of the longitu­dinal joints measured over a 10-in. gage length was generally lower than that measured over a 2-in. gage length. This difference probably is a result of the restraint on stretch provided by the grip ends — the ends of the 10-in. gage lengths are only V2 in. (12.7 mm) from the start of the radius for the grip ends. The influence of the local strain concentration is evidenced by the fact that most failures occurred at the start of the radius. Natu­rally, the measured elongation would be greater if it included the fracture; thus, the difference between longitudinal and transverse elongations would have been even greater if the failures had occurred within the gage lengths of the longitudinal specimens.

The severity of incomplete penetration present in the longitudinal tensile cou­pons did not affect the tensile strength — Fig. 12. Only one of four incomplete penetration specimens failed in the cen­tral 4-in. (102-mm) section containing the discontinuity. Incomplete penetration did reduce the elongation — possibly because the reduced heat input of the weld pro­duced less softening. The specimens con­taining gross porosity all failed in the porous section at strengths 10% lower than those for sound welds. The porosity also reduced the elongation.

The repaired longitudinal tensile speci­mens had strengths equivalent to those of sound welds. However, the failures of the reinforcement intact specimens gen­erally occurred at an end of the enlarged weld reinforcement at a reduced value of elongation. Removal of the strain con­centrations of the weld reinforcement restored the elongation to the levels of sound welds.

Fatigue Test Procedures

Most specimens were tested in a 250-kip (56.2-kN) MTS closed loop servo-hydraulic machine —Fig. 13. The small longitudinal joints were tested in a 5-kip Krouse direct stress fatigue machine. Restraining strongbacks (Fig. 10) were clamped to the side struts of the H-PIates to keep the specimens flat during testing; the strongbacks were separated from the specimen by Teflon pads. The ends of the slots in the H-Plate specimens were rotary shot peened to prevent failure at these stress concentrations.

Most tests were conducted at the same maximum applied stress level so that a direct comparison of the lives could be made. The criterion for choos­ing the test stress level was to test at as low a stress level as possible without encountering lives beyond 2,000,000 cycles. A maximum applied stress level of 17 ksi (117 MPa) was chosen from previ­ous welded joint data (Refs. 20, 21) to meet this criterion.

Fatigue Test Results

The fatigue results for the joints having sound welds are presented in a bar chart of the login mean lives of the eight duplicated test conditions — Fig. 14. The low residual stress longitudinal joints with the reinforcement removed have the longest fatigue lives, while the high resid­ual stress, transverse joints with the rein­forcement intact have the shortest fatigue lives.

In each case, the transverse joints have shorter lives than the comparable longitu­dinal joints. Regardless of residual stress level, the failures of the Rl transverse joints initiated at an edge of the weld reinforcement. The presence of this transverse stress concentration is the major cause of the shorter lives of Rl transverse joints.

The lives of the low residual stress, Rl H-Plate specimens are in agreement with earlier tests (Ref. 20) of conventional 4-in. (102-mm) wide transverse joints in %- in . (9.5-mm) 5456-H321 plate. However, the earlier tests showed a larger advantage

Fatigue test setup for H-Plate speci-

WELDING RESEARCH SUPPLEMENT 1167-s

Maximum stress = 17 ksi (117 MPa), R = 0.1

a io' re o "5. 3

•D 10' o

_3

o 10 5 _

tf) .22 o >. o c (0 (D

5

10'

Transverse joint I Longitudinal joint

High Low High

1 V 1 Rl RR

_J l _

1 !

i v\

1 2

P3

z

i r Rl RR

_l l _

I 4

m

2

I Rl RR

_ | L_

Low

1

vx

I fa

Rl RR _|

tf) tf) 0

tf)

"ra 3

'tf) (V

OC

E V o o

« % a -

c '3

ka

5

Fig. 14 -Fatigue test results for sound welds

for removing the weld reinforcement. The lives of the Rl longitudinal joints are similar to those reported (Ref. 21) for similar 5-in. (127-mm) wide joints in %- in . 5456-H321 plate.

Effect of Discontinuities

Failures of the two Rl H-PIates contain­ing incomplete penetration discontinuities initiated at the stress concentration at the edge of their weld reinforcements. This indication that the internal penetration discontinuities did not affect the fatigue

life is confirmed by the fact that the lives bracket those of the sound RI welds — Fig. 15. As can be seen in weld cross-sections (Fig. 16), the width of the incomplete penetration in these specimens was about 0.07 in. (1.8 mm). Naturally, if the penetration discontinuities were severe enough, they would have caused failure at reduced lives. Burk and Lawrence (Ref. 14) reported that incomplete penetration having a depth greater than 0.10 in. (2.54 mm) caused significant reduction of life for RI welds in %- in . (9.5-mm) 5083-0 plate. With the reinforcement removed,

.y%

•%^r

Fig. 76 — Cross-sections showing incomplete penetration in H-Plate fatigue specimens. Plate thickness: 0.25 in. (6.3 mm)

failure initiated at the incomplete pene­tration, greatly reducing lives. Pense and Stout (Ref. 11) and Burk and Lawrence (Ref. 14) also reported the increased effect of penetration discontinuities for RR welds. Thus, although weld reinforce­ment is usually considered to be detri­mental to the fatigue strength, it can negate the effect of some incomplete penetration.

The incomplete penetration in the lon­gitudinal joints did not affect their fatigue strength —Fig. 17. The Rl specimens had lives equivalent to those of sound speci­mens. Further, none of the failures of the longitudinal joints occurred in the sec­tions containing incomplete penetration. Removal of the weld reinforcement

10"

<D

ro

2 1 0 5

tf) 0)

U >> O

Sound welds

T Rl RR

No No

Incomplete penetrat ion

A X

Rl RR RR*RR* RR*RR* Rl RR RR*RR* RR*RR*

1

1 0 4

Weld re inforcement

Number of repairs

Preheat tempera ture (°F)

Fig. 15 — Effect of discontinuities and their repair on the fatigue strength of transversely welded butt joints (0.25-in./6.35-mm 5456 H-PIates). Maximum stress: 17 ksi (117 MPa); R: 4-0.1

No No No No 4 5 0 4 5 0

Gross porosity

Legend I I - L o g 1 0 mean life

A - Test result * - Repair areas only

r&-

No No No No 4 5 0 4 5 0

168-s | JUNE 1987

resulted in a very long life without failure for one specimen, but a short life for the other. The failure of the latter specimen initiated at a subsurface pore. The depth of incomplete penetration for these joints was similar to that in the H-PIates. The incomplete penetration would be ex­pected to have less effect on the longitu­dinal joints since it is aligned in the direc­tion of loading; presumably it would be only the transverse notches at the ends of the incomplete penetration or abrupt changes in depth which would be likely to initiate a fatigue crack.

As was true for incomplete penetra­tion, the presence of gross porosity did not affect the failure origins nor the lives to failure of Rl H-PIates - Fig. 15. With the reinforcement removed, the failures did initiate at porosity and one of the two specimens had a life only half that of Rl specimens. The presence of gross poros­ity did not affect the fatigue lives of either Rl or RR longitudinal joint specimens — Fig. 17. In both cases, the lives were equivalent to those of sound welds. Fur­thermore, most failure origins were out­side the region of gross porosity. It can­not, however, be said that porosity did not affect the results since many of the failures initiated at surface or subsurface pores. Thus, porosity limits the advantage which might be attained by removing the weld reinforcement.

As evidenced by tests of welds con­taining gross porosity or incomplete pen­etration, weld quality is more important for RR joints than for Rl joints. Discontinu­ities which would not have affected the fatigue performance of Rl welds may negate the improvement expected for removal of the reinforcement or even substantially reduce life.

Weld Repair

In the majority of cases, the weld repaired H-Plates had lives equivalent to those of specimens with sound Rl welds —Fig. 15. This is evidenced by the fact that they had primary failures initiat­ing at edges of unrepaired welds. How­ever, others had primary or secondary failures at surface pores or unintentional internal incomplete fusion. Statistical anal­ysis showed no difference in the results for welds repaired one or three times.

For the longitudinal joints, however, the weld repairs were detrimental. The lives of the repaired welds were on the order of half those of specimens contain­ing the discontinuities —Fig. 17. The enlarged weld reinforcement of the repair serves as a stress concentration; furthermore, the quality of the repair weld is not as good. For example, the repaired weld surface is not as smooth and contains more surface porosity. Thus, the failures initiated in the repairs at reduced lives. Three repairs did not

1 0 ' =

i 106

o • a—

•

£ i o 5

O

10" Weld reinforcement

Number of repairs

-I-&-,

Sound welds

Rl RR

Incomplete penetration Gross porosity

r&-i

I Rl RR Rl Rl

A Test result I I Log mean life

* Did not fail

r^-i

I T T Rl RR Rl Rl

Fig. 17 —Effect of discontunuities and their repair on the fatigue strength of longitudinally welded butt joints (0.25-in./6.35-mm 5456-H116 plate. Maximum stress: 17 ksi (117 MPa); R: 4-0.1

60

OJ 50 u >• u c 40

u> U) 0) at 3 0 to

<

3

E 2 "io 2

i i i mill

_

-

—

i i I

i i I I I I I I I i i Mini i i uuul i i i "HI i i mini i > mm

o Sound welds • Repaired welds _

R = 0.1 \

\ -. Low residual stress specimens _ \^y from 3/8 in. (9.5 mm) 5456-H321

v welded panels

\ \

\ \

<• CD \

\ V .

• •

i i mini i i mini i i mini i i I i i mini i i mill

10 1 0 2 1 0 3 1 0 4 1 0 5 1 0 6 1 0 7 1 0 l

Cycles Fig. 18-Effect of weld repair on the fatigue strength of 0.25-in. (6.35-mm) H-Plate specimens

shorten the fatigue lives any more than one repair. Removing the weld bead reinforcement in the area of the repair, as was done for repairs to the transverse welds, might have eliminated the reduc­tions in life if the repairs were sound.

Repair welded, Rl H-PIates were tested at maximum stresses of 10 and 17 ksi (69 and 117 MPa) to obtain some information on the relationship between stress and life for specimens having the reinforce­ment beads of the weld repairs intact. The S-N data (Fig. 18) include the H-Plates having sound welds and an average curve for low residual stress specimens (Ref. 20). The detrimental effect of the repair weld is obvious. The weld rein­forcement of the repair weld is higher

and has a steeper approach angle than that of the unrepaired weld (Fig. 5), and this produces a more severe stress con­centration. The limited S-N data for Rl repair welds lies 10 ksi below the average curve for low residual stress specimens and 7 ksi (48 MPa) below the results for sound H-Plates. Furthermore, at 17 ksi the lives of the repaired Rl specimens are only one-quarter those of specimens whose reinforcements were removed in the repaired section.

Preheating and Post Repair Treatments

Preheating the weld area of some H-Plates just before the repair weld seems to be undesirable. First, it was

WELDING RESEARCH SUPPLEMENT 1169-s

10 6 -

_3

"<5 •taa

- m 5 -</) 0) o >a

o

10° =

Sound welds Repair welds (3 repairs)

A - Test result ~J - Log mean life

Z + - Weld reinforcement ~ Z Rl - Intact

:

-

E

-

r-A-

A

A

I RR - Removed * - Rer>air areas onlv

|

A

-&-

A A

A A

A

A

l-A-l

i i | i i I I I I

Rl RR Rl RR* Rl RR Rl RR

_

-

None ! None 1/2 hr. at 525°F Brush peened

1 0 *

Weld reinforcement"1"

Post repair treatment

Fig. 19 —Effect of postweld repair treatments on transverse groove welds (0.25-in. /6.35-mm 5456 H-Plates). Maximum stress: 17 ksi (117 MPa); R: 0.1

1 0 6

_3

S 1 0 5

w 9 o >> o

1 0 4

Post repair treatment Number of repairs

Sound welds

-

l — A —

Gross porosity

A

w

- Test result - Log mean life

eld reinforcement intact A

A

A

A

-

I None None

0 0

None Brush peened 3 3

Fig. 21 —Effect of postweld repair peening on longitudinally welded butt joints (0.25-in./6.35-mm, 5456-H116 plate). Maximum stress: 17 ksi (117 MPa); R: 4-0.1

1 0 f

2 10 4 -u> o

u > o

-_ —

-

—

-

A - Test result

| 1 i I - Long mean life I 1

A

2

3

n a 9 oc

ui

o .c a o CO

A

C o (A

c a. X

0 o I

— B —

o a a o c 9 i ••— a_

»

A A

(A

.c u

+ a

o o £ T3

o 3 </) CM

A

O

+ w (fl a

<D T3

O S

Q. O O J3 tf) T-

--

-

—

-

10' Fig. 22 —Effect of crack arrest procedures on transverse groove welds (0.25-in./6.35-mm 5456 H-Plates). Maximum stress: 17 ksi (117 MPa); R: 0.1

Fig. 20 —Failure of peened, repaired longitudi­nal weld

difficult to preheat sheet this thin to a precise temperature. Second, the pre­heated specimens tended to have shorter lives (Fig. 15) , particularly for the speci­mens repaired because of gross porosi­ty.

Post repair heating of H-Plate speci­mens at 525°F (274°C) appeared to be of some benefit for the Rl specimens. Lives of two heated specimens were about 50% and 100% longer (Fig. 19) than spec­imens receiving no post repair heating. However, their lives are only about half those of specimens having sound welds or welds having their reinforcement removed in the repair area. All weld reinforcement, repaired and unrepaired areas, was removed from the two RR H-Plate specimens which were to be post repair heated. This allowed comparison with RR sound specimens. One heated specimen failed at a life equal to 80% of the shorter lived sound specimen. The other resisted as many cycles as the shorter lived sound specimen before suf­fering a failure away from the weld. Apparently, the heating was not a major benefit. Accordingly, post repair heating was not investigated for longitudinal joints.

Surprisingly, brush peening the weld repairs was not consistently beneficial. One peened Rl H-Plate specimen had a life within the scatter of those of as-welded specimens, whereas the other had a life almost twice as long. To match the lives of the sound Rl specimens, it was necessary to remove the reinforcement

170-s | JUNE 1987

in the repair area before peening. On the other hand, brush peening weld repairs of the longitudinal joints overcame the detrimental effect of the repair. The fail­ures occurred outside the repaired area (Fig. 20) at lives comparable to those obtained for sound welds —Fig. 21. The peening intensity was somewhat higher for the longitudinal joints. However, Montemarano had reported an improve­ment in the fatigue strength of sound welds from brush peening to a lesser intensity (Ref. 15). Polmear showed that brush peening was not as effective as needle peening for 5083 fillet welds (Ref. 22).

Crack Arrest Tests

The results for specimens tested to study various methods of crack arrest are presented in Figs. 22 and 23. The loading of these specimens was intended to rep­resent loading on a wide panel where the crack was not long enough to significant­ly change the gross stress. Thus, loads were calculated for a net section stress of 17 ksi (117 MPa) on the uncracked width. Since the effectiveness of the patches was unknown, their test loads were based on cracked area, i.e., the area of the patches was ignored. The repair welds of the H-Plates differ somewhat from those reported previously. Because the crack was at a weld edge (Fig. 24A), an enlarged weld is created —Fig. 24B. However, this did not appear to affect the fatigue life. Apparently, the weld reinforcement angle was still the critical factor.

Conversely, the transverse Rl weld repairs did not provide a particularly good crack stopper for the longitudinal joints. Fatigue failures initiated at an edge of the weld bead reinforcement (Fig. 25) and failure occurred at lives less than 10% of those of sound longitudinal welds. However, those lives were somewhat longer than those of similarly repaired transverse welds. Based on the crack propagation rates to develop the 2-in. (51-mm) crack, it appears that '..nrepaired specimens would have failed within 3000

| 10

o

o > O

6

5

4

A

: I

—

—

- Test result

" I " - 1

.ong mean l i fe

7 ksi (117 MPa) net stress with 1.28 in. (32.5 mm) notch

A

•o 5 3

•a c 3 o tf)

A

(a) *C

tx 3

A A

ar

(fl

"5 a a a c a S

«*• ka fl)

-

—

—

~ 10° -

1 0 Fig. 23 — Effect of crack arrest procedures on longitudinally welded butt joints (0.25-in./6.35-mm 5456-H116 plate) with weld reinforcement intact. Maximum stress: 17 ksi (117 MPa); R: 4-0.1

cycles. Thus, the weld repairs did length­en the specimen lives by a factor of about 10. Longer lives could undoubtedly have been attained if the weld reinforce­ment had been removed.

The effect of drilling stop holes at the ends of the 2-in. (51-mm) crack in an H-Plate can be discerned from the a/N (crack length-cycles) plot of Fig. 26. The jog in the a/N plot indicates that blunting the crack tips with holes arrested the propagation briefly. However, the holes had no effect on the rate of fatigue crack propagation after crack reinitiation. Reini­tiation of cracking was noted after about 2400 cycles. The weld reinforcement may have affected the crack propaga­tion. It provides a stress concentration in front of the advancing crack. In several tests it was noted that the crack appeared to spurt ahead because of initiation at the weld reinforcement ahead of the crack front. Further, some of the reinitiation sites were at the edge of the weld reinforcement, Vs to VA in. (3 to 7 mm) beyond the stoppage hole. This suggests that the cracks might have been initiated before the hole was drilled.

Expanding the stop holes in H-Plates did not prolong crack arrest. The lives to test section failure were equivalent to those of the non-worked holes. Refer­ence 23 reported that stretching stop holes of low-alloy steel sheet 10% to 15% in the direction of loading produced sig­nificant improvement and that the gain was much larger if the enlargement was 20%. A similar method was successful for aluminum alloy sheet (Ref. 24). The nom­inal amount of circumferential stretch was much less in this investigation — only 4%. The cracks may have been too long for this degree of cold working to be effective. For instance, Ref. 25 reported that hole working using similar equipment was beneficial for open hole specimens having precracks of a VA in. or less. Mann (Ref. 26) reported a benefit only for short cracks.

Installation of interference bolts pro­duced significant increases in life to failure for both H-Plate specimens and longitudi­nal joints. The bolt props the hole open and the interference produces favorable residual stresses. The failures of both longitudinal and one H-Plate specimen

B

TOP F.&P pfT

Fig. 24-A -Repair of a 4-in. length of porous weld; B — Repair of a 2-in. long fatigue crack at the edge of the weld

WELDING RESEARCH SUPPLEMENT 1171-s

Fig. 25 — Failure of a longitudinal weld speci­men which had a transverse weld repair

initiated at edges of weld reinforcement remote from the original crack. Thus, the bolts essentially negated the presence of the short cracks.

Patches

The patches fillet welded over H-Plate cracks terminated by stop holes provided a satisfactory repair. Failure initiated at an edge of a fillet weld, and radiographic examination showed that no cracks grew out of the stop holes. Although fillet welded joints usually have lower fatigue strengths than butt welded joints, the lives of the patched specimens were similar to those of repair welded speci­mens—Fig. 22. A patch on one side only might have been sufficient.

The lives of the H-Plate specimens using stop holes and bonded patches exceeded those of repair welds. Since a bonded patch should provide less of a stress concentration than the welded patches, only one side was patched. Cracks in the adhesive at an end of a pad were visible and cracks had initiated at the stop holes as early as 6000 cycles. However, the remaining life was still equivalent to those of repair welded specimens. Obviously, the bonded pad was still transmitting enough load to sub­stantially reduce the rate of crack growth.

Conclusions

1. The levels of incomplete penetra­tion and gross porosity present in these specimens did not affect the fatigue strength of reinforcement intact welds.

2. Removing the weld reinforcement doubled the lives of sound welds, but greatly reduced the lives of transverse specimens containing incomplete pene­tration.

3. High residual stresses, such as would be found in actual structures, had more effect on longitudinal joints than on transverse joints.

4. Repaired welds had lives only 40%

3 -

c

%2

ro o

ro 1 -

I I I,

/

/

/ 0.280 in. (7.1 mm) dia. /

stop holes drilled /

/

rf y

o

I o

o

o o

o

-

0 H-Plate Specimen O Gross stress -

° R = +0.1 Laboratory air

l I I

15.8 ksi (109 MPa)

l

0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 N, cycles

Fig. 26 —Effect of stop hole on fatigue crack growth

to 75% those of sound welds, unless the repairs were suitably ground or peened.

5. The discontinuities generally low­ered the strengths and elongations of tensile coupons. Although the repaired welds had tensile strengths equivalent to those of sound welds, the restraint of the enlarged weld reinforcement reduced the measured elongation.

6. For relatively short fatigue cracks, insertion of interference bolts in holes at the ends of the cracks produced lives equivalent to those of sound welds. Stop­page holes —even expanded holes —did not delay propagation much.

7. Reinforcement intact repair welding of fatigue cracks was more effective for transverse joints than for longitudinal joints. Moreover, bonded or welded patches were as effective as repair welds for transverse joints.

A ckno wledgments

This work was performed under U. S. Navy Contracts N00167-80-C-0206, N00167-81-C-0186 and N00167-82-C-0183. Major contributions were made by L. N. Mueller of Alcoa's Applications Engi­neering Division, R. E. Grimm and R. S. Fyala, Alcoa Laboratories, and former Alcoa Laboratories employees: F. F. Rudolph, R. A. Kelsey and G. P. Yanok.

References

1. Slater, C. 1985. The effect of repair welds on service performance. Welding jour­nal 64(3):22-29.

2. NAVSHIPS 0900-003-9000, November 1967. Radiographic Standards for Production and Repair Welds. Change 1.

3. Ibatullin, R. L. 1976. The influence of repeated rewelds on the properties of welded

joints in aluminum alloy AlMg5. Welding Pro­duction (9):35-36.

4. Hersh, M. S. 1969. Effect of discontinui­ties on fatigue properties of aluminum welds. Welding journal 48(9).389-s to 394-s.

5. Nelson, F. C. 1961. Effects of repeated repair welding of two aluminum alloys. Weld­ing journal 40(2): 166-s to 168-s.

6. Kelsey, R. A., Mueller, L. N., and Nord­mark, C. E. April 1983. Effect of repair welding on fatigue performance of aluminum alloy 5456 butt welds. WRC Monograph.

7. Shumaker, M. B., Kelsey, R. A., Sprowls, D. O., and Williamson, I. C. 1967. Evaluation of various techniques for stress corrosion test­ing welded aluminum alloys. ASTM STP 425, p. 317-341.

8. Kelsey, R. A., and Nordmark, C. E. August 1978. Effect of residual stresses on fatigue properties of aluminum butt welds. Proc. Fifth Bolton Landing Conference, Lake George, N.Y.

9. Toyouka, T., Tsunenari, T., Ide, R., and Tange, T. 1985. Fatigue test of residual stress induced specimens in carbon steel. Welding lournal 64(1):29-s to 30-s.

10. McLester, R. 1963. Fatigue strength of welded and riveted joints in aluminum. Alumi­num in Structural Engineering; Institute of Str. Engineers and Aluminum Fed., Symposium, London, England, journal Proceedings 9-19.

11. Pense, A. W„ and Stout, R. D. July 1970. Influence of weld defects on the mechanical properties of aluminum alloy weldments. WRC Bulletin 152.

12. Sanders, W. W„ ]r. April 1972. Fatigue behavior of aluminum alloy weldments. WRC Bulletin 171.

13. ASME Boiler and Pressure Vessel Code, Section VIII.

14. Burk, |. D., and Lawrence, F. V., )r. lanuary 1978. Effects of lack-of-penetration and lack-of-fusion on the fatigue properties of 5083 aluminum alloy welds. WRC Bulletin 234.

15. Montemarano, T. W., and Wells, M. E. 1980. Improving the fatigue performance of

172-s | JUNE 1987

welded aluminum alloys. Welding journal 59(6):21-28.

16. Fisher, |. W., and Mertz, D. R. May 1985. Retrofitting steel bridges to extend their fatigue lives. 1985 Int. Eng. Symposium on Structural Steel.

17. Kobler, H. C , Huth, H., Schutz, D. Fatigue life improvement of riveted joints by cold working of precracked fastener holes. LBF-Rep. No. 3913, Fraunhofer.

18. Kemp, R. M. S., Murray, D. )., Butt, R. I., Wilson, R. N., and Phillips, L. N. 1984. Effects of pre-moulded woven CFRP patches on fatigue crack growth in 7475-T761 aluminum alloy sheet. Fatigue of Engineering Materials, Struc­tural, Vol. 7, No. 4, pp. 329-344.

19. Lawrence, F. V., )r., and Munse, W. H. February 1983. Effect of porosity on the tensile

properties of 5083 and 6061 aluminum alloy weldments. WRC Bulletin 181.

20. Butz, G. A., and Nordmark, G. E. Sep­tember 1964. Fatigue resistance of aluminum and its products. Paper No. 893E, presented at SAE National Farm, Construction and Industrial Machinery Meeting, Milwaukee, Wis.

21. Nordmark, G. E. November 1963. Peen­ing increases fatigue strength of welded alumi­num. Metal Progress

22. Polmear, I. J. Comparison of brush and needle peening on fatigue properties of alumi­num alloy 5083 fillet welds. AWRA Document P3-8-84, AWRA Contract No. 101.

23. Van Leeuwen, H. P., Schra, L., and Meulman, A. E. February 1970. The repair of fatigue cracks in low-alloy steel sheet. NLR TR 70029U, National Lucht-Em Ruimtevaarlabora-

torium. 24. De Rijk, P., and Otter, A. A. M. Novem­

ber 1969. Empirical investigation on some methods for stopping the growth of fatigue cracks. NLR TR 70021U.

25. Kobler, H-G., Huth, H., and Schutz, D. 1979. Fatigue life improvement of riveted joints by cold working of precracked fastener holes. LBF-Rep. No. 3913. Fraunhofer-lnstitut fur Betriebs Festigkeit, Darmstadt.

26. Mann, J. Y., Ravill, G W., and Lupson, W. F. April 1983. Improving the fatigue perfor­mance of thick aluminum alloy bolted joints by hole cold-expansion and the use of interfer­ence-fit steel bushes. Aeronautical Research Laboratories Structures Note 486, Defense Science and Technology Organization, Mel­bourne, Victoria, Australia.

WRC Bulletin 318 September 1986

The primary objective of this Bulletin, which contains two papers, is to present a comprehensive picture of the research work conducted to establish the current techniques and procedures for specifying the ferr i te content of austenitic stainless steel weld metal and measuring its level.

Factors Influencing the Measurement of Ferrite Content in Austenitic Stainless Steel Weld Metal Using Magnetic Instruments By E. W. Pickering, E. S. Robitz and D. M. Vandergriff

This report describes a program conducted under the auspices of the Welding Research Council (WRC) Subcommit tee on Welding Stainless Steel to identify the opt imum procedure for the preparation of austenitic stainless steel weld samples for Ferrite Number (FN) determinat ion.

Measurement of Ferrite Content in Austenitic Stainless Steel Weld Metal Giving Internationally Reproducible Results By E. Stalmasek

This report is a summary of the results of 14 years' work by the IIW Commission 2 in the field of ferr i te content measurement, done prior to 1978.

The publication of these reports was sponsored by the Subcommittee on Welding Stainless Steel of the High Alloys Commit tee of the Welding Research Council. The price of WRC Bulletin 318 is $24.00 per copy, plus $5.00 for postage and handling. Orders should be sent with payment to the Welding Research Council, Suite 1301, 345 E. 47th St., New York, NY 10017.

WRC Bulletin 319 November 1986

Sensitization of Austenitic Stainless Steels: Effect of Welding Variables on HAZ Sensitization of AISI 304 and HAZ Behavior of BWR Alternative Alloys 316NG and 347 By C. D. Lundin, C. H. Lee, R. Menon and E. E. Stansbury

The research described in this report was undertaken to derive a better understanding of the HAZ sensitization response of 304, 304LN, 316NG and 347 austenitic stainless steels. The results are directly applicable to both the as-welded and long-time service behavior of these austenitic stainless steels.

Publication of this report was sponsored by the Subcommit tee on Welding Stainless Steel of the High Alloys Commit tee of the Welding Research Council. The price of WRC Bulletin 319 is $24.00 per copy, plus $5.00 for postage and handling. Orders should be sent with payment to the Welding Research Council, Suite 1301 , 345 E. 47th St., New York, NY 10017.

WELDING RESEARCH SUPPLEMENT 1173-s