Evaluation Of Fillet Weld Requirements (1501 S) Making Welds 1501 S

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Project Summary Report 1501-S – 1 –

The University of Texas at Austin

Center for

Transportation Research

PROJECT SUMMARY REPORT

CENTER FOR TRANSPORTATION RESEARCH

THE UNIVERSITY OF TEXAS AT AUSTIN

Project Summary Report 1501-S

Fillet Welding Procedure Qualification Research

Authors: Heather E. Gilmer and Karl H. Frank

Center for Transportation Research, The University of Texas at Austin

December 2001

Evaluation of Fillet Weld Requirements

The motivation for this

research was the desire to

develop improved procedures for

qualifying fillet welds on bridge

structures. The current procedure

qualification tests prevent the use

of active fluxes and other

consumables or procedures which

may be more applicable to fillet

welding. Active fluxes are

formulated for limited-pass

welding. They contain active

deoxidizers, such as manganese,

silicon, or both, to improve the

resistance to porosity and weld

cracking caused by contaminants

on or in the base metal. Most

fillet welds are single-pass welds

applied to unprepared surfaces.

The enhanced ability of active

fluxes to deoxidize the weld

metal is particularly important for

fillet welds. The amount of

manganese and silicon in the

weld metal varies with the arc

voltage, and so the arc voltage

must be carefully controlled

when making multipass welds

with active fluxes. The change in

the amount of silicon and

manganese when the arc voltage

is changed is used as an index to

differentiate between active and

inactive or neutral fluxes. More

active fluxes will show a larger

change in deposited weld metal

chemistry for an incremental

change in voltage.

The fillet weld qualification

requirements in the current bridge

welding code, ANSI/AASHTO/

AWS D1.5-96, henceforth “AWS

D1.5,” specify that fillet welding

procedures be qualified using a

groove weld specimen (AWS

D1.5, Section 5.10). A large

groove weld is used to produce

the test specimens. The weld is

designed to provide as near as

possible a weld that is undiluted

by the base metal. Fillet welds

are often single pass welds that

contain a considerable amount of

base metal in the cast welds. A

typical small fillet weld will have

more dilution of weld metal with

base metal than the material at

the center of the large groove

weld used in the standard test. In

addition to the difference in the

amount of dilution, the groove

weld microstructure will be

refined in subsequent passes;

single-pass fillet welds undergo

no refinement. In practice,

welding procedures that give

good test results for a groove

weld may not necessarily produce

the best fillet welds. In particu-

lar, fabricators have reported that

the heat input required to produce

a groove weld specimen that will

pass the specified tests is too high

for many fillet welds. This

requirement is particularly

problematic with T-joints welded

simultaneously on both sides,

where the total heat input to the

welded area is greatly increased.

There are anecdotal reports that

fillet welds made with procedures

that pass the qualification tests

have failed in the field.

The research investigated the

behavior of fillet welds to

determine what requirements if

any should be imposed upon the

fabricator to ensure the satisfac-

tory performance of fillet welds

used in bridges. The research was

restricted to welds made using the

submerged-arc process.

What We Did...

The research examined the

performance of fillet welds made

with a matrix of consumables and

heat inputs. Different fabricators

made the weld specimens using

consumables they normally use in

their shop. All of the consum-

ables were from the Lincoln

Electric Company. The weld

matrix is shown in Table 1. The

fabricator that provided the

weathering specimens uses this

set of consumables for all his

submerged-arc welds. This set of

consumables was included since

the fabricator does the majority

of the steel bridges in Texas. The

two heat input ranges used for

each set of consumables bound

the values that would be used in

normal fabrication. The high heat

input values used for the active

flux were much higher than the

fabricator would use in normal

practice. Two-sided as well as

single-sided welds were included

in the fabrication of the T-bend

and the fillet weld shear speci-

mens. These welds simulate the

welding of a stiffener to web. The

3/8 and 1/2 in. thick plates

Project Summary Report 1501-S – 2 –

forming the stem of the T, the

simulated stiffener, were used to

determine the influence on the

additional heat input from the weld on

the opposite side upon the weld

properties.

Each fabricator produced three

specialized fillet weld test specimens.

A transverse shear specimen similar to

the specimen in AWS B4.0-92 was

used to measure the shear strength of

the weld. A T-bend specimen, which

has been used by the Georgia and

California departments of transporta-

tion and also used to evaluate fillets

welds used on the new high perfor-

mance 70 grade bridge steel, was used

to measure the ductility of the welds.

A weld root Charpy V-notch,

WRCVN, specimen was utilized to

measure the notch toughness of a

simulated fillet weld. In addition, a

standard AWS groove weld qualifica-

tion specimen was made using

weathering consumables at the high

and low heat input in order to com-

pare the results of the specialized

fillet weld tests with the standard

AWS specimen. Three replicate

specimens were tested for each

condition. The factorial experimental

results were analyzed using analysis

of variance method.

What We Found...

The results of the tests indicated

that the strength and ductility mea-

sured in the shear and T-bend speci-

mens were similar. The T-bend

specimen did not provide meaningful

test results. However, it did provide a

means of assessing the depth of

penetration of the weld procedure.

High heat input double-sided dart

welds with an active flux produced

complete penetration with a 3/8 in.

web. Cracking across the weld

occurred in these specimens. How-

ever, the ductility of the single-sided

high heat input weld was the least

cracked. The hardness of the higher

heat input welds was less than the

lower heat input and the double-sided

welds produced the lowest hardness.

The variation of hardness with heat

input was largest in the welds using

an active flux. The double-sided high

heat input fillet weld on a 3/8 in. stem

produced the lowest weld hardness

with active and neutral fluxes. The

specimens using the weathering flux

showed smaller variation in weld

hardness with changes in heat input.

The estimated tensile strength for the

weld with lowest hardness is 84 ksi,

far above the required strength of 70

ksi.

The results of the weld shear

strength tests showed for all consum-

ables that the low-heat welds are

stronger and harder than high-heat

welds and single-sided welds are

stronger and harder than dart welds.

Both the calculated shear strength and

the tensile strength corresponding to

the hardness are well above the

nominal tensile strength of 70 ksi for

all speci-mens tested. The measured

shear strengths were as large as two to

four times the nominal value of 0.6 x

70 = 42 ksi.

For all three sets of consumables,

no effect of heat input was found

within the dart-welded specimens.

This finding may have to do with the

effect of dart welding on actual heat

input. It is possible that although

raising the heat input may change

weld strength, once a “saturation”

heat input is reached there will be no

more effect from further heat input

increases. If this is so, then dart

welding will have no additional effect

on a weld whose heat input is already

high.

The active flux specimens gave

the lowest absorbed energy in the

WRCVN tests. A comparison of the

low heat input results is shown in

Figure 1.

The WRCVN, PQR, and certifi-

cate Charpy that the consumable

manufacturer reported results are

essentially the same for the active and

neutral fluxes. Only the weathering

consumables show a significant

difference between the WRCVN

specimens and the groove weld test

plate specimens performed for PQR

and certification testing. The heat

input had little effect on the results

from either the WRCVN or the

normal CVN test specimens.

The weathering consumable

WRCVN specimens had different

properties from standard AWS CVN

specimens. The pattern of results

from WRCVN tests was shifted

approximately 20C to 40C (35F to

70F) higher then the standard AWS

CVN specimens. The WRCVN

specimens should reflect fillet weld

properties more accurately because

they are taken from the root of what is

in essence a multiple-pass fillet weld.

If the pattern seen among the weather-

ing specimens can be extrapolated to

other consumables, then the standard

test overestimates weld toughness.

Medlock (1998) demonstrates that

standard AWS CVN test results are

not representative of production

groove welds, and typically have

higher toughness values than produc-

tion welds. Fillet welds differ even

more from the standard test weld, and

so are even less likely to be ad-

equately represented by the standard

test.

Table 1: Welding parameters

Consumable

Designation Flux Electrode Heat Inputs(kJ/in)

Low High

Neutral Flux 960 L-613/32"

wire 35.7 50.4

Active Flux 780 L-615/64"

wire 32.9 48.7

Weathering 860 LA-753/32"

wire 34.6 48.0

Project Summary Report 1501-S – 3 –

.

The Researchers

Recommend...

The results of this research

indicate that the tensile strength

requirements of the weld certification

tests are adequate to ensure the

strength of fillet welds. Based upon

these results, the weld qualification

tests presently required in AWS D1.5

are not necessary to ensure the

strength of a fillet weld. The T-bend

specimen did not provide a useful

measure of the strength or ductility of

a fillet weld. The T-weldment does

provide a simple means to evaluate

the influence of double-sided weld

upon the geometry of the weld and

melt-through of the stem. The

WRCVN specimen provides a

convenient method of characterizing

the toughness of the fillet weld root

material. The WRCVN toughness

may be comparable to or less than the

toughness measured in the standard

all-weld metal tests. The WRCVN

test is recommended as a simple

means to ensure that the fillet weld

toughness is adequate. Toughness

comparable to the base metal should

be sufficient for the root of the fillet.

The base metal is directly adjacent to

the weld metal at the root of the weld.

Consequently, a fracture will propa-

gate in either the weld or base metal,

whichever has the lowest toughness.

There is no benefit to having the weld

metal toughness significantly tougher

than the base metal. A weld root

toughness corresponding to the non-

fracture-critical base metal require-

ment for 4-inch plates in Temperature

Zone III should be adequate for all

bridges. For example, the required

toughness for Gr. 50 steel would be

20 ft-lbs at 10o F, per ASTM A 709

Table S1.2.

Based upon the results of this

study, the following recommended

changes to the specifications are

proposed:

1. The consumable supplier shall

perform the following tests

annually:

a. Two weld certification tests,

one at the highest and the other

at the lowest weld heat input

recommended by the manufac-

turer. If the fabricator stays

within these heat inputs, no

groove weld qualification

testing is required by the

fabricator. The essential

variables are those defined in

AWS D1.5-96 Section 5.12.2,

“Maximum-Minimum Heat

Input.”

b. A WRCVN test plate shall be

welded using the maximum and

minimum heat input recom-

mended. The average of three

specimens from each test weld

should be equal to or greater

than the non-fracture-critical

base metal requirement for

4-inch plates in Temperature

Zone III. For 36-ksi material,

the requirement for 50-ksi

material should be used.

2. The fabricator shall perform the

T-weldment test described below

every 5 years or whenever the

essential variables are changed.

The fillet weld T-weldment is

similar to the fillet weld soundness

test required in AWS D1.5-96

Section 5.10, with the following

exceptions.

a. The plate thickness shown in

AWS D1.5-96 Figure 5.8 shall

be the maximum rather than the

minimum plate thickness.

b. The welds shall be made at the

highest heat input in the WPS.

c. If two-sided dart welding will

be used in the production weld,

the same method should be used

for fabricating the T-weldment.

d. The spacing of the electrodes in

a two-sided weld shall be the

minimum specified in the WPS.

e. A T-weld test is required for

each weld size, or for the

minimum and maximum weld

sizes.

f. The welds are to be sectioned in

accordance with AWS D1.5-96

Section 5.10.3 and tested in

accordance with Section 5.19.3.

In addition, the maximum

penetration of each weld shall

not exceed 1/3 of the thickness

of the T-stem (dimension T2 in

AWS D1.5-96 Figure 5.8).

140

120

100

80

60

40

20

0

-60 -40 -20 0 20 40 60 80 100 120 140 160

Temperature (F)

Weathering, 34.6 jK/in heat input

Active Flux, 34.0 jK/in heat input

Neutral Flux, 35.6 jK/in heat input

Unusual Break

Toughness (ft-lb)

Figure 1: WRCVN Test Results

Project Summary Report 1501-S – 4 –

The University of Texas at Austin

Center for Transportion Research

3208 Red River, Suite #200

Austin, TX 78705-2650

Disclaimer

Research Supervisor: Karl H. Frank, P.E., (512) 471-4590

email: kfrank@uts.cc.utexas.edu

TxDOT Project Director: Ronnie Medlock, P.E., (512) 416-2456

email: rmedloc@dot.state.tx.us

The research is documented in the following report:

1501-1 Evaluation of Fillet Weld Qualification Requirements, October 1999.

To obtain copies of a report: CTR Library, Center for Transportation Research,

(512) 232-3138, email: ctrlib@uts.cc.utexas.edu

The results from this research will be formally presented to the AASHTO/AWS committee that writes the

AASHTO/AWS D1.5 Bridge Welding Code. This Code governs bridge welding in the US and includes require-

ments for qualification of fillet welding procedures. Dr. Karl Frank has already made a preliminary presentation to

the committee, and the committee has been provided with copies of the research results. It is expected that the

results from this research effort will be adopted to facilitate improvement of the way fillet welding procedures are

covered under this Code.

For more information please contact Tom Yarbrough, P.E., RTI Research Engineer, at (512) 465-7685 or email at

tyarbro@dot.state.tx.us.

This research was performed in cooperation with the Texas Department of Transportation and the U. S.

Department of Transportation, Federal Highway Administration. The content of this report reflects the views of

the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not

necessarily reflect the official view or policies of the FHWA or TxDOT. This report does not constitute a

standard, specification, or regulation, nor is it intended for construction, bidding, or permit purposes. Trade

names were used solely for information and not for product endorsement. The engineer in charge was Karl H.

Frank, P.E. (Texas No. 48953).

Your Involvement Is Welcome!

For More Details...

TxDOT Implementation Status

January 2002

The University of Texas at Austin

Center for

Transportation Research