US ARmy Corps of Engineers - Structural Inspection of Existi

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DEPARTMENT OF THE ARMY ETL 1110-2-346U.S. Army Corps of Engineers

CECW-ED Washington, DC 20314-1000

TechnicalLetter No. 1110-2-346 30 September 1993

Engineering and DesignSTRUCTURAL INSPECTION AND EVALUATION

OF EXISTING WELDED LOCK GATES

1. Purpose

This engineer technical letter (ETL) provides

guidance for evaluating the structural adequacy of

existing welded lock gates.

2. Applicability

This ETL applies to HQUSACE elements, major

subordinate commands, districts, laboratories, and

field operating activities having responsibilities for

civil works projects.

3. References

a. ER 1110-2-100, Periodic Inspection andContinuing Evaluation of Completed Civil Works

Structures.

b. ER 1110-2-101, Reporting Evidence of Dis-

tress of Civil Works Projects.

c. EM 1110-2-2105, Design of Hydraulic Steel

Structures.

d . EM 1110-2-2703, Lock Gates and Operating

Equipment.

4. Discussion

a. ER 1110-2-100 defines periodic inspection

requirements for completed civil works projects.

These requirements include all aspects of a project

and are general in nature. ER 1110-2-101 requires

that signs of distress in any project feature be

reported through channels to HQUSACE. Neither

of these references describes how to perform a

detailed inspection and evaluation of hydraulic steel

structures.

b. The state of the art in metal fatigue and

fracture analysis has advanced greatly in recent

years. In many industries these concepts are regu-

larly applied to new designs and to evaluation of

existing structural elements. EM 1110-2-2105

requires that fatigue and fracture be considered

when designing new hydraulic steel structures.

c. Steel structures at several civil works pro-

jects have experienced severe cracking. Some of

these incidents are discussed in Enclosure 1. This

demonstrates the need to emphasize fatigue andfracture concepts when inspecting and evaluating

such structures.

d . The six enclosures to this ETL provide

detailed methods for inspection and evaluation of

existing steel lock gates. These enclosures provide

specific recommendations for inspection techniques,

evaluation of detected flaws, and prediction of

remaining life. These concepts are also applicable

to a wide range of other structures, including almost

any steel structure in a civil works project.

5. Action

a. Periodic inspection of steel lock gates

should include close visual inspection of critical

members and connections.



ETL 1110-2-34630 Sep 93

b. If cracks are detected during periodic

inspections, the cracked elements and other critical

locations should be evaluated using the methods

defined in the enclosure.

c. These actions should also be implemented

for other steel features of civil works projects when

deemed appropriate by the structural engineer.

FOR THE DIRECTOR OF CIVIL WORKS:

6 Encl PAUL D. BARBER, P.E.

Chief, Engineering Division

Directorate of Civil Works

2



ETL 1110-2-34630 Sep 93

GENERAL DISCUSSION

1. Scope

a. Enclosures 1 through 6 include procedures to

inspect existing welded steel lock gates and evaluatethem for potential failure. The general concepts

may also be applied to new designs, riveted and

bolted gates, gates for other purposes, and even to

other types of materials.

b. This enclosure provides general discussion

and Enclosure 2 discusses causes of structural dete-

rioration. Enclosure 3 describes the level of steel

gate inspection appropriate during a periodic inspec-

tion. This includes preselecting critical locations

which require close examination, including identifi-

cation of fracture critical members and connections

and visual inspection. Enclosure 4 describes the

detailed nondestructive testing procedures which

should be used while performing a detailed struc-

tural inspection. Some of these procedures may

also be appropriate during periodic inspections.

c. When evaluating older lock gates, necessary

material information may not be available. It may

become necessary to perform material testing to

determine the chemistry, strength, ductility, hard-

ness, and toughness of the base and weld metal.

For this reason, material and weld testing tech-

niques are discussed in detail in Enclosure 5.

d. Engineering evaluation of an existing gate

should be more than an educated guess or a subjec-

tive evaluation. The gate condition should be deter-

mined numerically using proper fatigue and fracture

analysis methods. These procedures are described

in Enclosure 6. The analyses can be used to deter-

mine if the gate is safe to continue current

operation, what is a safe interval until the next

inspection, and what is the remaining life of the

gate for expected operating conditions.

2. Types of Gates

a. Currently, the U.S. Army Corps of Engineers

(USACE) operates over 250 lock chambers. The

functional requirements for lock gates vary, depend-

ing on the specific project location and operating

conditions. The primary purpose for steel gates is

to provide a damming surface across the lock

chamber; however, they can also be used as guard

gates, valves for filling and emptying the lock

chamber, for passing ice and debris, to unwater the

lock chamber, to separate salt and fresh water, andto provide access from one lock wall to the other

via walkways attached to the top of the gates. Most

existing lock gates are miter gates and vertical-lift

gates, with a small percentage being sector gates

and submergible tainter gates.

b. The majority of lock gates are of the miter

type, primarily because they tend to be more eco-

nomical to construct and operate and can be opened

and closed more rapidly than other types of lock

gates. Miter gates are categorized by their framing

mechanism into vertically or horizontally framed

gates. Water pressure acting on the skin plate of a

vertically framed gate is resisted by vertical beam

members supported by a horizontal girder at the top

and bottom of the leaf. The horizontal girders then

transmit the loads to the miter and quoin at the top

of the leaf and into the sill at the bottom of the leaf.

Horizontally framed lock gates transmit the skin

plate water load directly to horizontal girders which

then transfer the load to the quoin block and into

the walls of the lock monolith. Current design

guidance, Engineer Manual (EM) 1110-2-2703,

"Lock Gates and Operating Equipment,"1 recom-

mends that future miter gates be horizontallyframed; however, a large percentage of existing

miter gates are vertically framed.

c. Another type of lock gate is the sector gate.

This gate is framed similar to a tainter gate, how-

ever, it pivots about a vertical axis similar to a

miter gate. Sector gates have traditionally been

used in tidal reaches of rivers or canals and conse-

quently may be subject to head reversal. Sector

gates may be used to control flow in the lock cham-

ber during normal operation or close off flow dur-

ing emergency operation. Sector gates are generally

limited to lifts of 10 ft or less.

d. Vertical-lift gates differ from miter and

sector gates in that they are raised and lowered

____________________1 References for Enclosures 1 through 6 are found

in the Reference section following Enclosure 6.

Enclosure 1 1-1



ETL 1110-2-34630 Sep 93

vertically to open or close the lock chamber. The

load developed by water pressure acting on the lift

gate skin plate is transmitted along horizontal

girders into the walls of the lock monolith. Lift

gates can be operated under moderate heads but not

under reverse head conditions.

e. Submergible tainter gates are used infre-

quently as lock gates. This type of gate pivots

similar to a spillway tainter gate but is raised to

close the lock chamber and lowered into the cham-

ber to open it. The load developed by water pres-

sure acting on the submergible tainter gate skin

plate is transmitted along horizontal girders to struts

recessed in the lock wall. The struts are connected

to and rotate about trunnions anchored to each lock

wall.

3. Strength and Serviceability Requirements

a. Lock gates are designed according to

requirements of appropriate EM’s and design codes

as listed in EM 1110-2-2105, "Design of Hydraulic

Steel Structures." Lock gates are designed to have

design strengths at all sections equal, at least, to the

required strengths calculated for the critical combi-

nation of loads and forces. Various gate members

must be designed to resist axial forces, bending

forces, and combined bending and axial forces.

These members are fabricated from bars, plates,

standard rolled shapes, and built-up sections

depending on geometrical requirements, loading,and economics. Structural inspection and evalua-

tion are required to assure that adequate strength

and serviceability are maintained at all sections

during the life of the gate.

b. Serviceability is a state in which the function

of a lock gate, its maintainability, durability, and

operability are preserved for the life of the gate.

The structural inspection and evaluation must assure

that all deflections, deformations, vibrations, corro-

sion, and wear of structural members do not impair

the operability or performance of the lock gate.

4. Examples of Distressed Lock Gates

Fracture and failure of steel members and connec-

tions have occurred in several Corps of Engineers

projects. These projects received the required peri-

odic inspections. However, the inspections were

not detailed enough to detect initial cracks nor were

fatigue and fracture analyses performed for these

structures prior to, and often not subsequent to,

failure. The following brief examples, all taken

from a single district, illustrate the potential results

of casual inspection combined with inattention to

fatigue and fracture concepts during design.

a. Miter gate anchorage.

(1) The project utilized vertically framed

downstream miter gates, 45 ft high, with a 110-ft

lock width. The upper embedded gate anchorage

failed unexpectedly while the chamber was at tail-

water elevation. Failure occurred by fracture at the

gudgeon pin hole. The anchor was a structural steel

assembly of two channels and two 1/2-in.-thick

plates. The use of a channel with up-turned legs

causes ponding of water and results in pitting and

scaling corrosion. Since the anchor is a nonredun-dant tension member, failure caused the leaf to fall

to the concrete sill, though it remained vertical.

(2) The failure surfaces were disposed of

without an examination to determine the cause of

failure. To make the lock operational as quickly as

possible, repairs were implemented without any

evaluation or recommendations from the Engineer-

ing Division. These repairs consisted of butting and

welding a new channel section to the remaining

embedded section and bolting a 1-in. cover plate to

the channel webs. The bolt and plate materials are

not known.

(3) The same type of anchorage is used on at

least two other projects with a total of 16 similar

anchors.

b. Spare miter gate.

(1) The project had a spare miter gate which

consisted of five welded modules. When in use,

these modules were stacked vertically and bolted

together. The spare gate had been used several

times. However, 1 month after the last installation,

cracks were discovered in the downstream flanges

of three vertical girders. The cracks originated at

the downstream face of the flange in the heat

affected zone at the toe of a transverse fillet weld.

(This detail is category E for fatigue design.) The

cracks then propagated through the flange and into

the web. After cracking the downstream face of the

flanges was 0.5-in. out-of-vertical alignment.

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ETL 1110-2-34630 Sep 93

(2) Quick repairs were performed by operations

personnel, without input from engineering person-

nel. The web crack was filled with weld. The

flange cracks were gouged and welded, then two

small bars were fillet welded across the crack. The

bar material is unknown. These repairs served to

get the gate back into service immediately. How-ever, reliable long-term repairs also should be

developed and implemented.

c. Submersible lift gate.

(1) This project has a submersible lift gate as

the main, operational, upstream lock gate. The gate

consists of two leaves with six horizontal girders

spanning 110 ft. Several cracks were discovered in

one leaf while the lock was out of service for other

repairs. Subsequent detailed inspection identified

over 100 cracks in girder flanges and bracing mem-

bers. One crack extended through the downstreamflange of a horizontal girder and 3 ft into the

8-ft-deep web.

(2) This gate was subjected to a detailed inves-

tigation of the cause of the cracking. The study

identified several contributing factors: the original

design had ignored a loading case and had included

improper loading assumptions; limit switches were

improperly stopping the gate before it reached its

supports; the design ignored higher stresses caused

by eccentric connections on the downstream face;

most of the original welds did not meet current

American Welding Society (AWS) quality stan-dards; the steel for the gate had a low fracture

toughness, ranging from 5 ft-lb at 32 oF to 15 ft-lb

at 70 oF.

(3) Repair procedures were designed by engi-

neering personnel for this gate. However, the

specified weld procedures were not used by the

contractor, and the welders were not properly quali-

fied per AWS requirements. These facts may have

caused inadequate repair welds, which duplicates

part of the causes of the original cracking problem.

5. Summary

The preceding examples represent only a few of the

steel cracking problems which have occurred on

Corps of Engineers projects. It is evident that steel

fatigue and fracture are real problems. Engineering,

construction, and operations personnel should be

aware of this and of the preventive procedures

needed to minimize such problems. Prevention is

best accomplished through proper design and con-

struction, followed by adequate maintenance andinspection. However, many existing steel structures

may be susceptible to fatigue and fracture problems.

When cracks are discovered, engineering personnel

should evaluate the reliability or remaining life of

the structure, determine the need for repairs, and

develop adequate repair plans. When fractures

occur, operations and engineering personnel should

work together to investigate the causes and develop

reliable repair plans. Enclosures 2 through 6 pre-

sent methods for inspection and evaluation of exist-

ing steel lock gates. These procedures should be

followed to identify and correct deficiencies before

they result in serious failures.

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ETL 1110-2-34630 Sep 93

CAUSES OF DETERIORATION

1. Corrosion

Corrosion is degradation of a material by reaction

with its environment. All corrosion processes haveelectrochemical reactions as their bases. Some are

purely electrochemical, such as galvanic, pitting,

crevice, and general corrosion, whereas others result

from the action of chemical plus mechanical factors,

such as erosion and stress corrosion.

a. General corrosion is characterized by an

uniform attack over the entire exposed surface with

minimal variation in the depth of damage. The rate

of attack is usually predictable, and catastrophic

failure does not often result. Galvanic corrosion

occurs when two or more dissimilar metals are in

contact and placed in an electrolyte such as water.

A potential difference in the metals causes a flow

of current between them, and the more active metal

(anode) undergoes accelerated corrosion whereas

corrosion in the less active metal (cathode) is

retarded or eliminated. Galvanic corrosion can be

minimized by use of coatings and by keeping the

anode large relative to the cathode. Pitting is a

form of localized corrosion where the attack is

confined to numerous small cavities on the metal

surface. The length/depth ratio of the pit is usually

equal to or greater than 1. The pitts can act as

stress risers and promote nucleation of fatiguecracks. Failure due to pitting corrosion may be

rapid and without warning. Crevice corrosion is

associated with confined spaces (< 0.001 in.)

formed by close fitting mechanical configurations

such as tapped joints, washers, and lap joints.

b. Stress corrosion involves the occurrence of

both chemical and mechanical interactions. Four

basic requirements are necessary to cause stress

corrosion cracking: a susceptible alloy, an aggres-

sive environment, applied or residual tensile stress,

and time. The rate of attack is rapid at the crack

tip and much less rapid at the sides.

c. The paint system and cathodic protection

systems should be inspected to assure that protec-

tion is being provided against corrosion. The effect

of corrosion on the strength, stability, and service-

ability of lock gates must be evaluated. The type of

corrosion and cause should be identified to assure

that a thorough evaluation is performed. Ultrasonic

equipment and gap gauges are available to measure

loss of material. The progressive loss of materialcan increase deflections and result in failure by

overstressing, buckling, or fracture.

2. Unusual Loads

Lock gates are designed to resist loads from self

weight, hydraulic, and boat impact as discussed in

EM 1110-2-2703. Dynamic loading due to hydrau-

lic flow and impact loading due to vessel collision

is currently unpredictable. The dynamic loading

may be caused by hydraulic flow at the seals or

when lock gates are used to supplement chamber

filling or skim ice and debris. Impact loading can

occur from malfunctioning equipment on the vessel

or operator error. Furthermore, unusual loadings

may occur from malfunctioning limit switches or

debris trapped at interfaces between moving parts.

In addition, unusual loads may develop on gates

supported by walls that are settling or moving.

These unusual loads can cause overstressing and

lead to deterioration of the lock gates.

3. Fatigue

a. Most structures are subjected to repeated

cyclic loading. Fatigue is the process of cumulative

damage caused by repeated cyclic loading. Fatigue

damage occurs at stress concentrated regions where

the localized stress exceeds the yield stress of the

material. After a certain number of cyclic loads,

the accumulated damage causes the initiation and

propagation of a crack.

b. Total fatigue life is the sum of the crack

initiation and the crack propagation to a critical size

(Barsom and Rolfe 1987). The main concern infatigue assessment of welded lock gates is to deter-

mine the time required for failure to occur. The

propagation life is governed by the rate of subcriti-

cal crack growth. Refer to Enclosure 6 for

additional discussion on fatigue.

Enclosure 2 2-1



ETL 1110-2-34630 Sep 93

4. Fracture

For strength and economic reasons, EM 1110-2-

2703 recommends that lock gates be fabricated

using structural-grade carbon steel. Standards such

as American Society for Testing and Materials

(ASTM) A6 or ASTM A898 (1991a,e) have beendeveloped to establish allowable size and number of

discontinuities for base metal used to fabricate lock

gates. In addition, EM 1110-2-2703 also recom-

mends that the gates be welded in accordance with

the Structural Welding Code-Steel (American

National Standards Institute (ANSI)/AWS (1992).

This code provides a standard for limiting the size

and number of various types of discontinuities that

develop during welding. Although these criteria

exist, when a lock gate goes into service it does

contain discontinuities.

a. When tensile stresses are applied to a bodythat contains a discontinuity such as a sharp crack,

the crack tip tends to open. For cases where plastic

deformation is constrained to a small zone at the

crack tip (plane-strain condition), the fracture insta-

bility can be predicted using linear elastic fracture

mechanics (LEFM) concepts. The fundamental

principle of LEFM is that the stress field ahead of a

sharp crack in a structural member can be charac-

terized in terms of a single parameter, K . K is the

stress-intensity factor and has units of kips per

square inch-√ in. The stress-intensity factor is

related to both the nominal stress and the geometry

of the existing discontinuity. When the crack isopening with the two fracture surfaces displaced

perpendicular to each other in opposite directions,

the displacement is referred to as mode I . The

stress-intensity factor during crack opening or

mode I displacement is referred to as K I .

b. Another underlying principle of fracture

mechanics is that unstable fracture occurs when the

stress-intensity factor at the crack tip reaches a criti-

cal value. For mode I displacement and for small

crack-tip plastic deformation (plane-strain condi-

tion), the critical stress-intensity factor for fracture

instability is designated K Ic. The critical stress-

intensity factor represents the ability of the material

to withstand a given stress-field intensity at the tip

of a crack and to resist tensile crack extension.

Thus, K Ic represents the fracture toughness of a

particular material and is a function of temperature

and loading rate. When a structural member con-

tains a discontinuity, the stress-intensity factor, K I ,

should be kept below the critical stress-intensity

factor, K Ic, at all times to prevent brittle fracture.

c. Brittle fracture is a sudden catastrophic

failure which occurs suddenly without prior plastic

deformation and can occur at nominal stress levels

below yield. Brittle fracture becomes more pre-dominate as member thickness, constraint, and

loading rates increase and as temperature decreases.

Frequently, plates 1-1/2 in. in thickness and greater

are used as primary welded structural components

on hydraulic gates. It is not uncommon to see such

thick plates used as gate flanges, embedded

anchorage at the top of gates, hinge and operating

equipment connections, diagonal bracing, lifting or

jacking assemblies, or platforms to support oper-

ating equipment that actuates the gates. In addition,

thick castings, such as sector gears used for operat-

ing lock gates may be susceptible to brittle fracture.

Cracking has been experienced on lock gates duringfabrication and after the thick assemblies are welded

and placed into service.

d. For many structural applications where low-

to medium-strength steels are used, the material

thickness is not sufficient to maintain small

crack-tip plastic deformation under slow loading

conditions at normal service temperatures. Conse-

quently, the LEFM approach is invalidated by the

formation of large plastic zones and elastic-plastic

behavior in the region near the crack tip. One

method frequently used to analyze discontinuities

when elastic-plastic conditions exist is the crack-tipopening displacement (CTOD) method (British

Standards Institution 1980). The LEFM and CTOD

methods are discussed in detail in Enclosure 6.

5. Design Deficiencies

Many existing lock gates were designed during the

early and mid-1900’s. Analysis and design technol-

ogies have significantly improved to the current

methodology for gate design. Original design load-

ing conditions may no longer be valid for the exist-

ing gate operation and overstress conditions may

exist. Current information, such as fatigue and

fracture control in structures, was not available

when many of the initial designs were performed.

Consequently, low category fatigue details and low

toughness materials exist on some lock gates. In

addition, the amount of corrosion anticipated in the

original design may not accurately reflect actual

2-2



ETL 1110-2-34630 Sep 93

conditions, and structural members may now be

undersized. To properly evaluate existing lock

gates, it is important that the analysis and design

information for the gate be reviewed to assure no

design deficiencies exist.

6. Fabrication Discontinuities

Welded fabrication can contain various types of

discontinuities. Discontinuities in regions near the

weld are of special concern, since high-tensile

residual stresses develop from the welding process.

There are two reasons that fabrication discontinu-

ities reduce the strength of welded gates. First, the

presence of the discontinuities decreases the sec-

tional areas, and second, stress becomes concen-

trated around the discontinuities. The effect of

weld discontinuities on structural strength depends

upon the nature and size of discontinuities, type of material, and type of loading. Discontinuities that

exist during initial fabrication are rejectable only

when they exceed specified requirements in terms

of type, size, distribution, or location as specified

by ANSI/AWS (1992). In addition, industry stan-

dards have improved in the area of material

processing and fabrication. Therefore, existing

structures may have included joint preparation and

welds which may not be acceptable according to

current standards.

7. Operation and Maintenance

Proper operation and maintenance of lock gates isnecessary to prevent structural deterioration. If

moving connections are not lubricated properly, the

bushings will wear and result in misalignment of

the gate. The misalignment will subsequently wear

contact blocks and seals, and unforseen loads may

develop. Overstressing and vibrational loads could

then develop and reduce the life of the gate. Mal-

functioning limit switches and debris along the gate

path can also induce detrimental loads and wear.

As discussed in this enclosure, paragraph 1, it is

essential that an effective coating system be main-

tained on the gates to minimize corrosion. Further-

more, when cathodic protection is necessary, it, too,must be properly operated and maintained. In addi-

tion, to assure that necessary torsional stability is

provided during opening and closing of miter gates,

it is essential that the prestress in the diagonals be

maintained. In addition, proper maintenance of

timber fenders and bumpers is necessary to provide

protection to the gate and minimize deterioration.

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ETL 1110-2-34630 Sep 93

PERIODIC INSPECTION

1. Purpose of Inspection

Existing welded lock gates are subjected to condi-

tions which could cause structural deterioration andpremature failure. The causes of deterioration are

discussed in Enclosure 2. To assure premature

failures are averted and identify future maintenance

requirements, periodic inspections are performed as

discussed in Engineer Regulation (ER) 1110-2-100,

"Periodic Inspection and Continuing Evaluation of

Completed Civil Works Structures." Periodic

inspections on lock gates are primarily visual

inspections. If the periodic inspection indicates that

a gate may be distressed, a more detailed inspection

and evaluation may be necessary. This detailed

inspection may require nondestructive and/or

destructive testing as discussed in Enclosures 4

and 5. The information obtained from the inspec-

tions and tests will then be used to perform a struc-

tural evaluation as discussed in Enclosure 6 and

make a recommendation for future action. This

enclosure will further discuss the visual inspection

which should be performed during the periodic

inspection.

2. Inspection Procedures

The periodic inspection procedure should includethe following steps:

a. Review documentation on gate design,

operational history, and maintenance record.

b. Identify critical members and connections.

c. Develop plan for visual inspection.

d. Inspect for weld condition and surface

discontinuities.

e. Inspect for corrosion conditions.

f. Observe gate operation (and cathodic protec-

tion, if applicable).

g. Document weld, discontinuity, and corrosion

conditions.

h. Conduct initial evaluation.

3. Critical Members and Connections

a. The periodic inspection should assure that

all critical members and connections are fit for

service until the next scheduled inspection. Critical

members and connections are those structural ele-

ments whose failure would render the gate inoper-

able. Fitness for service means that the material

and fabrication quality are at an appropriate level

considering risks and consequences of failure

(Enclosure 6).

b. Critical gate members and connections can

be determined from structural analysis of the gate.

This should include local stress concentrations and

fatigue considerations. In addition, effects from

existing corrosion and reduced weld quality or

associated residual stresses should be considered.

This analysis will require information pertaining to

the existing mechanical properties of the structural

material and weld (i.e. strength, toughness, ductility)

and the location, type, size, and orientation of any

known discontinuities.

4. Visual Inspection

a. The inspector should look closely at the

members and connections and not just view them

from the top of the lock wall. Visual inspections

should be performed with an emphasis on critical

gate members and connections as discussed in para-

graph 3 of this enclosure. Historically, distressed

gate members and connections have been located in

areas subject to high structural loads or stress

ranges, geometric stress concentrations, corrosion-

promoting conditions, and thick plates.

b. Inspectors should use various measuringscales and weld gauges for checking the dimensions

of the weld bead. Boroscopes, flashlights, and

mirrors may be necessary to inspect areas of limited

accessibility. Hand-tools may be necessary for

cleaning the surface for inspection.

Enclosure 3 3-1



ETL 1110-2-34630 Sep 93

5. Other Inspection Methods

Inspection methods other than visual inspection may

be used for the periodic inspection of lock gates, if

necessary. These methods may include penetrant,

magnetic particle, ultrasonic, and eddy-current

inspections. These inspection methods are dis-cussed in Enclosure 4.

6. Initial Evaluation

The most common problems identified by a visual

inspection are discovery of weld bead noncompli-

ance, with respect to the ANSI/AWS D1.1-92

(1992), Structural Welding Code-Steel, surface

cracks, fracture of structural members, and deterio-

ration from corrosion. For weld bead noncompli-

ances, the initial evaluation will be based on

checking with the ANSI/AWS D1.1-92 code accep-tance criteria. If surface cracks or fractured mem-

bers are discovered during the periodic inspections,

detailed inspection and evaluation shall be per-

formed for the entire gate. The strength and stabil-

ity of corroded members should be calculated. Loss

of material due to corrosion can often be deter-

mined using ultrasonic inspection methods. If the

strength or stability under the existing conditions

does not meet the design criteria, then the loads

must be reduced by modifying the operational pro-

cedures or the section should be replaced or rebuilt.

7. Inspection Intervals

The maximum time interval between periodic

inspections of lock gates is established in ER 1110-

2-100. Visual inspections should also be performed

if unusual loading situations occur. Such situations

include barge impact, earthquake, excessive ice

load, frictional forces increase between seals and

embedded plates, and movement of the supporting

monoliths. Additional detailed inspections may be

required to pursue concerns developed from the

periodic inspections or investigate reported distressfrom lock personnel. If discontinuities exist, frac-

ture mechanics concepts can also be applied to

determine appropriate inspection intervals as dis-

cussed in Enclosure 6.

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ETL 1110-2-34630 Sep 93

DETAILED INSPECTION

1. Purpose of Inspection

a. If distressed gate members or connections

are identified in the periodic inspection or deteriora-tion in structural performance is assessed from the

initial evaluation, then the entire gate should receive

a more detailed inspection of the distressed mem-

bers, and connections should be evaluated. This

enclosure presents a summary of various inspection

methods, guidance in selecting inspection methods,

inspector qualifications, code acceptance criteria,

and applicable source documents that may aid in

performing a detailed inspection.

b. Detailed inspections may be also used as

part of a damage-tolerance fracture control plan

which has been used to optimize the use of welded

structures in many industries. This fracture control

concept is based on the fact that presence of crack-

like discontinuities in the structural members or

connections does not necessarily mean the end of

the structure’s service life. An integrated approach

using scheduled inspections on the flawed members

and analysis of fracture/fatigue resistance of the

same members can maintain satisfactory structural

performance. The cost for repair or replacement of

the flawed members can therefore be balanced

against the inspection cost.

c. To develop schedules for inspection when

the damage-tolerance fracture control plan is used,

fracture mechanics theories must be applied. The

inspection periods can be determined by fatigue

propagation analysis of the cracked structural mem-

bers. The crack growth history from a detectable

size to the critical size can be predicted using the

propagation laws (e.g. Paris’s crack growth law).

Time interval between inspections should be a

fraction of this crack growth life. The optimum

nondestructive testing (NDT) intervals vary with

service conditions and the discontinuity conditions.

These inspection intervals should be short enoughthat the nondetectable cracks at the preceding

inspections do not have time to propagate to failure

before the next scheduled inspection.

d. A procedure for planning the inspection

schedules from the crack growth analysis is

presented in Enclosure 6.

2. Selecting Inspection Methods

a. NDT methods are essential for field inspec-

tion of existing lock gates. NDT can be used toimprove structural reliability by detecting discon-

tinuities for appropriate repair. NDT methods differ

from destructive testing methods which damage or

impair the serviceability of the items tested.

b. The six NDT methods commonly used in

today’s industries are visual (VT), penetrant (PT),

magnetic-particle (MT), radiographic (RT), ultra-

sonic (UT), and eddy-current (ET). Selection of an

NDT method for inspection depends on a number of

variables, including the nature of the discontinuity,

accessibility, joint type and geometry, material type,

detectability and reliability of the inspection

method, inspector qualifications, and economic

considerations. A general guide for selecting NDT

methods for field inspection is given in Table 4-1,

this enclosure.

3. Inspector Qualifications

For an inspection to be worth performing, the

inspector must be qualified. Corps personnel are

often not adequately trained in inspection methods;

therefore, inspections are often performed via con-tract with inspection specialists. The following

qualification requirements apply to all inspectors,

whether government or contractor employees.

a. Qualification in NDT methods.

(1) The effectiveness of NDT depends on the

capabilities of the person who performs the test.

Inspectors performing NDT should be qualified in

accordance with the American Society for Non-

destructive Testing (ASNT) Recommended Practice

No. SNT-TC-1A (ASNT 1980). The SNT-TC-1A

document is a guide to establish practices for train-ing, qualification, and certification of NDT person-

nel. Three basic levels of qualification are defined

in SNT-TC-1A as follows:

(a) NDT Level I: An NDT Level I individual

shall be qualified to properly perform specific cali-

brations, specific NDT, and specific evaluations for

Enclosure 4 4-1



ETL 1110-2-34630 Sep 93

Table 4-1

Selection Guide for Inspection Method

Method Applications Advantages Disadvantages

Visual Surface discontinuities Economical, fast. Limited to visual acuity of the inspector.

Liquid Surface cracks and porosity Relatively inexpensive and Cleaning is needed before and afterpenetrant reasonably rapid. inspection. Surface films hide defects.

Magnetic Surface discontinuities and Relatively economical and Applicable only to ferromagnetic

particle large subsurface voids expedient. materials.

Radiographic Voluminous discontinuities Provides a permanent Planer discontinuities must be favorably

Surface and internal record. aligned with radiation beam. Cost of

discontinuities equipment is high.

Ultrasonic Most discontinuiti es Sensitive to planer type Small, thi ck parts may be dif ficult to

discontinuities. High inspect. Requires a skilled

penetration capability. operator.

Eddy current Surface and subsurface Painted or coated surfaces Many variables can affect the test

discontinuities can be inspected. signal.High speed.

acceptance or rejection determinations according to

written instructions and to record results.

(b) NDT Level II: An NDT Level II individual

shall be qualified to set up and calibrate equipment

and to interpret and evaluate results with respect to

applicable codes, standards, and specifications. The

NDT Level II individual shall be able to organize

and report the results of NDT.

(c) NDT Level III: An NDT Level III indivi-

dual shall be capable of establishing techniques and

procedures; interpreting codes, standards, and proce-

dures; and designating the particular NDT methods,

techniques, and procedures to be used.

(2) Certification of all levels of NDT personnel

is the responsibility of the employer. The employer

must establish a written practice for the control and

administration of NDT personnel training, examina-

tion, and certification.

b. Qualification in weld inspection.

(1) Welding inspectors are responsible for

judging the quality of the product in relation to

some form of written specification. The following

qualifications are necessary for individuals to ade-

quately inspect welds:

(a) A welding inspector must be familiar with

engineering drawings and able to interpret

specifications.

(b) A welding inspector should be familiar

with welding processes and welding procedures.

(c) A welding inspector should be able to

maintain adequate records.

(d) A welding inspector should have passed

an eye examination with or without corrective

lenses to prove:

• Near vision acuity of Snellen English, or

equivalent, at 12 in.

• Far vision acuity of 20/40, or better.

(2) In addition, one of the following three

requirements is necessary to qualify an individual as

a weld inspector for a lock gate:

(a) Current or previous certification as an

AWS Certified Welding Inspector (CWI) in accor-

dance with the provisions of AWS QC1-88, Stan-

dard and Guide for Qualification and Certification

of Welding Inspectors (ANSI/AWS 1988).

4-2



ETL 1110-2-34630 Sep 93

(b) Current or previous qualification by the

Canadian Welding Bureau (CWB) to the require-

ments of the Canadian Standard Association (CSA)

Standard W178.2, Certification of Welding

Inspectors (CSA 1917).

(c) An engineer or technician who, by training,experience, or both, in metals fabrication, inspection

and testing, is competent to perform inspection of

the work.

4. Inspection Reporting

A report should be completed by the inspector at

the time of inspection. It should show the location,

size, orientation, and classification of each disconti-

nuity. The following information should be identi-

fied and recorded in the report:

a. Identification and location of inspected

structures.

b. Date and time of inspection.

c. Type of inspection.

d. Inspection procedure.

e. Inspection system (equipment).

f. Inspector identity and level.

g. Record of discontinuities detected.

5. Summary of NDT Methods

a. Detailed visual inspection (VT).

Detailed VT inspection uses the same inspection

tools and procedure as that described in

Enclosure 3, except that, with a knowledge of

existing discontinuities in a structural member or

connection from periodic inspections, a more con-

centrated examination is performed. The type,

geometry, size, location, and orientation of the

discontinuities must be quantitatively determined.

The entire structure may be inspected rather than

just representative members or connections.

(1) Advantages. VT inspection is useful for

checking the presence of surface discontinuities. It

is simple, quick, and easy to apply. It requires no

special equipment other than good eyesight, some-

times assisted by simple and inexpensive

equipment.

(2) Disadvantages and limitations. A major

disadvantage of VT inspection is the need for aninspector who has considerable experience and

knowledge in many different areas. Although VT

inspection is an invaluable method for detecting

surface discontinuities, it is less reliable in detecting

and quantifying small surface discontinuities or

detecting subsurface discontinuities.

(3) Applicable document. Material pertaining

to VT inspection is included in ANSI/AWS

B1.10-86, "Guide for the Nondestructive Inspection

of Welds" (ANSI/AWS 1986).

b. Penetrant inspection (PT).

PT inspection is also a method used to detect and

locate surface discontinuities. Liquid penetrants can

seep into various types of minute surface openings

by capillary action. Therefore, this process is well

suited for detecting discontinuities such as surface

cracks, overlaps, porosity, and laminations. PT

inspection can be performed using visible dye or

fluorescent dye visible with ultraviolet light. Three

different penetrants commonly used with either dye

are water washable, solvent removable, and post

emulsifiable. The various penetrant inspection

systems are listed in an order of decreasing inspec-tion sensitivity and operational cost as follows:

• Post emulsifiable fluorescent dye

• Solvent removable fluorescent dye

• Water washable fluorescent dye

• Post emulsifiable visible dye

• Solvent removable visible dye

• Water washable visible dye

(1) Advantages. PT inspection is relatively

inexpensive and reasonably rapid. Equipment

4-3



ETL 1110-2-34630 Sep 93

generally is simpler and less costly than that for

most other NDT methods.

(2) Disadvantages and limitations. The major

limitation of PT inspection is that it can detect only

discontinuities that are open to the surface. Another

disadvantage is that the surface roughness of theobject being inspected may affect the PT inspection

results. Extremely rough or porous surfaces may

produce false indications. Some substances in the

penetrants can affect structural materials. If pene-

trants are corrosive to the gate material, they should

be avoided.

(3) Applicable documents.

(a) ASTM E165-91: Standard Test Method for

Liquid Penetrant Examination (ASTM 1991h).

(b) ASTM E1316-92: Standard Terminologyfor Nondestructive Examinations (ASTM 1992 f ).

(c) AWS B1.10-86: Guide for the Nondestruc-

tive Inspection of Welds (ANSI/AWS 1986).

c. Magnetic particle inspection (MT).

MT inspection is used to detect surface or near-

surface discontinuities in ferromagnetic materials.

Magnetic fields can be generated by yokes, coils,

central conductors, prod contacts, and induced cur-

rent. When the material is magnetized, magnetic

discontinuities that lie in a direction generally trans-verse to the direction of the magnetic field will

cause a leakage field at the surface of the material.

The presence of this leakage field is detected by the

use of fine ferromagnetic particles applied over the

surface, some of the particles being gathered and

held by the leakage field. This collection of parti-

cles indicates the discontinuities. Several magnetic

particle materials commonly used for MT inspection

are dry powders (i.e. suitable for field inspection of

large object), wet magnetic particles suspended in

water or light oil (i.e. suitable for very fine or shal-

low discontinuities), magnetic slurry suspended in

heavy oil, and magnetic particles dispersed in the

liquid polymers to form solid indications.

(1) Advantages. The MT inspection is a sensi-

tive means of detecting small and shallow surface

or near-surface discontinuities in ferromagnetic

materials. The cost of MT inspection is consider-

ably less expensive than radiographic or ultrasonic

inspection. MT inspection is generally faster and

more economical than penetrant inspection. Com-

pared to PT inspection, MT inspection has the

advantage of revealing cracks filled with foreign

material.

(2) Disadvantages and limitations. MTinspection is limited to ferromagnetic material. For

good results, the magnetic field must be in a direc-

tion that will intercept the direction of the discon-

tinuity. Large currents sometimes are required for

very large parts. Care is necessary to avoid local

heating and burning of surfaces at the points of

electrical contact. Demagnetization is sometimes

necessary after inspection. Discontinuities must be

open to the surface or must be in the near subsur-

face to create flux leakage of sufficient strength to

accumulate magnetic particles. If a discontinuity is

oriented parallel to the lines of force, it will be

essentially undetectable.


(a) ASTM E1316-92: Standard Terminology

for Nondestructive Examinations (ASTM 1992 f ).

(b) ASTM E709-91: Standard Guide for

Magnetic Particle Examination (ASTM 1991l).

(c) ANSI/AWS B1.10-86 (ANSI/AWS 1986):

Guide for the Nondestructive Inspection of Welds.

d. Radiographic inspection (RT).

RT inspection is based on differential absorption of

penetrating radiation by the material being

inspected. Radiation from the source is absorbed

by the test piece as the radiation passes through it.

The discontinuity and its surrounding material

absorb different amounts of penetrating radiation.

Thus, the amount of radiation that impinges on the

film in the area beneath the discontinuity is differ-

ent from the amount that impinges in the adjacent

area. This produces a latent image on the film.

When the film is developed, the discontinuity can

be seen as a shadow of different photographic den-

sity from that of the image of the surrounding

material. Evaluation of the radiograph is based on

a comparison of these differences in photographic

density. The dark regions represent the more easily

penetrated parts (i.e. thin sections and most types of

discontinuities) while the lighter regions represent

the more difficult areas to penetrate (i.e. thick

4-4



ETL 1110-2-34630 Sep 93

sections). An essential element to the radiographic

process is film, a thin transparent plastic base

coated with fine crystals of silver bromide

(emulsion).

(1) Advantages.

(a) RT inspection has an ability to detect sur-

face and internal discontinuities.

(b) It is generally not restricted by the type of

material or grain structure.

(c) It provides a permanent record for future

review.

(2) Disadvantages and limitations.

(a) Discontinuities must be favorably aligned

with the radiation beam for reliable detection.

(b) It presents a potential radiation hazard to

personnel.

(c) The cost of radiographic equipment, facili-

ties, and safety programs is relatively high.

(d) Accessibility to both sides of the parts to be

inspected is required.

(e) It is difficult to apply for field inspections.

(f) It is a time consuming process compared toother NDT methods.


(a) ASTM E 94-91: Standard Guide for

Radiographic Testing (ASTM 1991g).

(b) ASTM E142-92: Standard Method for

Controlling Quality of Radiographic Testing (ASTM

1992c).

(c) ASTM E242-91: Standard Reference

Radiographs for Appearances of Radiographic

Images as Certain Parameters are Changed (ASTM

1991k ).

(d) ASTM E1316-92: Standard Terminology

for Nondestructive Examination (ASTM 1992 f ).

(e) ASTM E747-90: Standard Test Method

for Controlling Quality of Radiographic Examina-

tion Using Wire Penetrameters (ASTM 1990h).

(f) ASTM E999-90: Standard Guide for Con-

trolling the Quality of Industrial Radiographic Film

Processing (ASTM 1990i).

(g) ASTM E1025-84: Standard Practice for

Hole-Type Image Quality Indicators Used for

Radiography (ASTM 1989c).

(h) ASTM E1032-92: Standard Method for

Radiographic Examination of Weldments (ASTM

1992e).

(i) ANSI/AWS B1.10-86: Guide for the Non-

destructive Inspection of Welds (ANSI/AWS 1986).

(j) ANSI/AWS D1.1-92: Structural WeldingCode-Steel (Chapter 6: Inspection) (ANSI/AWS

1992).

e. Ultrasonic inspection (UT).

UT inspection is a nondestructive method which

uses high-frequency sound waves to detect surface

and internal discontinuities. The sound waves

travel through the materials to be inspected and are

reflected from surfaces refracted at a boundary

between two substances and diffracted at edges or

around obstacles. The reflected sound beam is

detected and analyzed to define the presence andlocation of discontinuities. Cracks, laminations,

shrinkage cavities, pores, and other discontinuities

that act as metal-gas interfaces can be easily

detected. Inclusions and other inhomogeneities in

the metal can also be detected. All surfaces of the

part to be examined should be free of weld spatter,

dirt, grease, oil, paint, and loose scale. UT inspec-

tion is usually performed with longitudinal waves or

shear waves (i.e. angle beam). Most UT inspec-

tions for discontinuities are performed using angle-

beam technique. The pulse-echo method with

A-scan is most commonly used for inspection of

welds. The most commonly used frequencies are

between 1 and 5 MHz, with sound beams at angles

of 0, 45, 60, and 70 deg.

(1) Advantages.

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ETL 1110-2-34630 Sep 93

(a) Superior penetrating power allows the

detection of discontinuities deep in the part.

(b) High sensitivity permits the detection of

small discontinuities.

(c) Great accuracy in determining the size,position, and the shape of discontinuities.

(d) Almost instantaneous indications of dis-

continuities provided.

(e) Ultrasonic inspection is not hazardous to

personnel and has no effect on materials.


(a) Manual operation requires careful attention

by experienced technicians.

(b) Parts that are rough, irregular in shape, very

small, or inhomogeneous are difficult to inspect.

(c) Reference standards are needed for cali-

brating the equipment and for characterizing

discontinuities.

(d) Interpretation requires experienced

technicians.


(a) ASTM A435/A435M-90: Standard Speci-fication for Straight-Beam Ultrasonic Examination

of Steel Plates (ASTM 1990a).

(b) ASTM A577/A577M-90: Standard Speci-

fication for Ultrasonic Angle-Beam Examination of

Steel Plates (ASTM 1990c).

(c) ASTM E114-90: Standard Practice for

Ultrasonic Pulse-Echo Straight-Beam Examination

by the Contact Method (ASTM 1990d ).

(d) ASTM E164-90: Standard Practice for

Ultrasonic Contact Examination of Weldments

(ASTM 1990e).

(e) ASTM E214-68: Standard Practice for

Immersed Ultrasonic Examination by the Reflection

Method Using Pulsed Longitudinal Waves (ASTM

1991 j).

(f) ASTM E1316-92: Standard Terminology

for Ultrasonic Examination (ASTM 1992 f ).

(g) AWS B1.10-86: Guide for the Nonde-

structive Inspection of Welds (ANSI/AWS 1986).

(h) ANSI/AWS D1.1-92: Structural WeldingCode-Steel (Chapter 6: Inspection) (ANSI/AWS

1992).

f. Eddy-current inspection (ET).

ET inspection is an electromagnetic NDT method

which is based on the principles of electromagnetic

induction. When an alternating current is passed

through a coil, eddy current is created in the mater-

ial being tested by an alternating magnetic field.

The test coil is electronically monitored to detect

the changes of magnetic field caused by the inter-

action between the eddy currents and the initialfield. Any changes in the eddy currents due to

inhomogeneities in the material are detected; there-

fore, any surface or subsurface discontinuities that

appreciably alter the normal flow of eddy currents

can be detected by ET inspection. Because ET

inspection is an electromagnetic induction tech-

nique, it does not require direct contact between

probe and the material being tested. The method is

based on indirect measurement, and the correlation

between the instrument readings and the structural

characteristics of the material being inspected must

be carefully established.

(1) Advantages.

(a) Since direct contact between probe and the

material is not required, painted, or coated, mater-

ials can be inspected.

(b) ET inspection is adaptable to high-speed

inspection.


(a) The test material must be an electrical

conductor.

(b) Some internal discontinuities cannot be

detected by eddy-current inspection.

4-6



ETL 1110-2-34630 Sep 93

(c) Since many variables can affect an eddy-

current signal, variables of no concern must be

separated from those of interest.


(a) ASTM E1316-92: Standard Terminologyfor Nondestructive Examination (ASTM 1992 f ).

(b) ANSI/AWS B1.10-86: Guide for the Non-

destructive Inspection of Welds (ANSI/AWS 1986).

6. Acceptance Criteria for NDT Results

a. The common weld discontinuities detected

from various NDT methods can be classified into

planar and nonplanar types. Planar type discontinu-

ities include cracks, delaminations or laminar tear-

ing, and sometimes incomplete joint penetration orincomplete fusion. The nonplanar type discontinu-

ities are volumetric weld discontinuities which

include porosity, slag or tungsten inclusions, under-

cut, underfill, and overlap. Figure 4.1 shows these

common types of weld discontinuities defined by

ANSI/AWS B1.10-86, Guide for the Nondestructive

Inspection of Welds (ANSI/AWS 1986).

b. The results obtained from various NDT

inspections are usually assessed according to the

code acceptance criteria. The recommended accep-

tance criteria for weld discontinuities are presented

in the ANSI/AWS D1.1-92 Structural WeldingCode (ANSI/AWS 1992). Repair or replacement of

structural members or connections which contain

unacceptable discontinuities (i.e. flaws) may be

required. However, fracture mechanics analysis

may be conducted to reassess these unacceptable

discontinuities. A maintenance schedule may be

developed in lieu of immediate repair or replace-

ment of the distressed members or connections

using the damage-tolerance fracture control plan

(Enclosure 6).

c. The ANSI/AWS D1.1-92 Structural Welding

Code acceptance criteria for various NDT inspection

results can be summarized in three perspectives:

weld profile, static loading case, and dynamic

loading case. Weld profile is a code compliance for

Figure 4-1. Weld discontinuities (ANSI/AWS

1986; copyright permission granted by American

Welding Society)

weld quality. Inspection for this code compliance is

usually made by visual inspection with the aid of a

weld gauge. The purpose of this code compliance

is to provide information on the structural fitness of

the welds. However, weld profile noncompliance

may be acceptable if an engineering assessment isconducted.

d. The code acceptance criteria recognize the

effect of dynamic loading on the structures as

opposed to the statically loaded case. Planar type

discontinuities are not acceptable in either case.

Permissible conditions on nonplanar type disconti-

nuities are specified in the code criteria with smaller

allowances for the dynamically loaded structures.

Engineering analyses may be conducted to assess

the structural significance of the unacceptable

discontinuities in both instances. A damage-

tolerance fracture control plan may be used rather

than repair or replacement of the distressed

members or connections.

4-7



ETL 1110-2-34630 Sep 93

MATERIAL AND WELD TESTING

1. Purpose of Testing

a. Distressed gate members and connections

identified from NDT inspection may continue toperform the structural functions with adjustments in

load conditions or under a reduced safety factor

without load adjustment. Engineering assessments

should include fracture and fatigue analysis as

discussed in Enclosure 6. Mechanical properties of

the structural members and welds are usually

needed in the analysis.

b. For lock gates fabricated in recent years, the

materials used for the structural members and welds

are usually well documented and can be identified

from the design drawings. For older gates, how-

ever, information on mechanical properties of the

structural materials or welds may not be readily

available. Mechanical tests of these materials and

welds are sometimes required to determine neces-

sary information for fracture and fatigue analyses.

In addition, it may be required to determine the

chemical composition of unknown materials to

assist in selecting the appropriate NDT inspection

method, performing corrosion assessment, and con-

ducting fracture evaluation.

2. Selection of Samples from ExistingStructure

Material information that is frequently required to

structurally evaluate a welded gate includes chemi-

cal composition, tensile strength, bend ductility,

fillet weld shear strength, hardness, and fracture

toughness. The test samples may be taken from the

materials left from original fabrication, removed

from existing gate members or connections, or

obtained from weldments made of similar materials

with welding procedures similar to those used in the

original fabrication.

3. Chemical Analysis

When the chemical composition of an existing gate

material is not available, it may be necessary to

perform a chemical analysis. This is an important

initial task in the overall material and weld testing

program. The information from this analysis will

provide a basis of similarity to other known struc-

tural materials for characterizing the properties of

the unknown gate materials. This information can

be used to assist in selecting appropriate NDTmethods, assessing corrosion problems, conducting

fracture analyses, and assessing material weldability

for possible repair. A chemical analysis for mate-

rial compositions should be in conformance with

ASTM E30-89 and E350-90 (1989b, 1990 f ).

4. Tension Test

a. Tension tests on the base metal and weld

metal can provide information on the strength and

ductility of materials under uniaxial tensile stress.

Transverse rectangular tension tests of weld samples

show the effect of material inhomogeneity and weld

quality on the test results. The pertinent data

obtained from a tension test are ultimate tensile

strength, yield strength, Young’s Modulus, percent

elongation, percent reduction of cross-sectional area,

stress-strain curve, and location and mode of final

fracture.

b. The transverse rectangular tension speci-

mens are machined from a butt welded plate, with

the weld crossing in the midsection of the specimen

(AWS B4.0-85 (AWS 1985), Figure C-2). Whenweldment thickness is beyond the capacity of test

equipment, the weldment is divided through its

thickness into as many specimens as required to

cover the full weld thickness. The results of the

partial thickness specimens are averaged to deter-

mine the properties of the full thickness joint.

c. Excessively deep machine cuts that will

cause specimen bending during testing or that leave

tears in the surface of the finished dimensions

should be avoided. Imperfections present in the

guage length, which are incidental to welding,

should not be removed.

d. The base metal and weld metal tests are

performed on a tensile testing machine in accor-

dance with the requirements of ASTM E8-91

(1991f). The machine should be calibrated in

accordance with ASTM E4-89 (1989a). The

testing procedure is as specified in ASTM E8-91

(1991 f ). The rate of straining should be

Enclosure 5 5-1



ETL 1110-2-34630 Sep 93

between 0.05 and 0.5 in. per inch of guage length,

per minute.

e. Material properties are calculated as follows:

(1) Ultimate tensile strength = maximum

load/original cross-sectional area in the guagelength.

(2) Yield strength = load at 0.2% offset/original

cross-sectional area in the guage length.

(3) Percent elongation = (Final guage length -

original guage length)/original guage length × 100.

(4) Reduction of area: Fit the ends of the frac-

tured specimen together and measure the thickness

and width at the minimum cross section. Calculate

the reduced area.

At least two specimens should be tested for each

sample type. The result of the tension test is the

average of the results of the specimens.

f. Applicable documents.

(1) ANSI B46.1-85: Surface Texture (ANSI

1985).

(2) ASTM E4-89: Standard Practices for Load

Verification of Testing Machines (ASTM 1989a).

(3) ASTM E8-91: Standard Test Methods forTension Testing of Metallic Materials (ASTM

1991 f ).

(4) AWS A2.4-86: Standard Symbols for

Welding, Brazing, and Nondestructive Examination

(AWS 1986).

(5) AWS A3.0-89: Standard Welding Terms

and Definitions (AWS 1989).

(6) AWS B4.0-85 - Part C: Tension Testing of

Welded Joints (AWS 1985).

5. Bend Test

a. Guided bend tests are used to evaluate the

ductility and soundness of welded joints and to

determine incomplete fusion, cracking, delamina-

tion, effect of bead configuration, and macrodefects

of welded joints. The quality of welds can be eval-

uated as a function of ductility to resist cracking

during bending. The top and bottom surfaces of a

welded plate are designated as the face and root

surfaces, respectively. Face bends have the weldface on the tension side of the bent specimen, and

the weld root is on the tension side for root bends.

For thick plates, transverse slices are cut from the

welded joint, and one of the cut side surfaces

becomes the tension side of the bent specimen.

b. When the plate thickness is less than or

equal to 3/8 in., two specimens are tested for face

bend and two specimens are tested for root bend.

When the thickness of the plate is greater than

3/8 in., four specimens are tested for side bend.

c. Transverse side bend test specimens (AWSB4.0-85 (AWS 1985), Figure A-5) are used for

plates that are too thick for face bend or root bend

specimen. The weld is perpendicular to the longitu-

dinal axis of the specimen. The side showing more

significant discontinuities should be the tension sur-

face of the specimen.

d. For a transverse face bend specimen (AWS

B4.0-85 (AWS 1985), Figure A-6a), weld is perpen-

dicular to the longitudinal axis of the specimen. The

weld face becomes the tension surface of the speci-

men during bending. For transverse root bend

specimen (AWS B4.0-85, Figure A-6b), weld isperpendicular to the longitudinal axis of the speci-

men. The root surface of the weld becomes the

tension surface of the specimen during bending.

For all types of bend tests, face, root, and side, the

specimen is tested at ambient temperature, and

deformation should occur in a time period between

1/2 and 2 min.

e. During the test, the convex surface of the

bent specimen should be examined frequently for

cracks or other open defects. If a crack or open

defect is present after bending, exceeding a speci-

fied size measured in any direction, the specimen is

considered to be failed (AWS B4.0-85 (AWS

1985)). Cracks occurring on the corners of the

specimen during testing are not considered to fail a

specimen unless they exceed a specified size or

show evidence of defects (AWS B4.0-85).

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ETL 1110-2-34630 Sep 93

f. Applicable documents.

(1) ANSI B46.1-85: Surface Texture (ANSI

1985).

(2) ASTM E190-92: Standard Test Method for

Guided Bend Test for Ductility of Welds (ASTM1992d ).



(AWS 1986).



(5) AWS B4.0-85 - Part A: Bend Testing of

Welded Joints (AWS 1985).

6. Fillet Weld Shear Test

a. The fillet weld shear test is used to deter-

mine the shear strength of fillet welds. The test

specimens are usually made from a weld sample

with welding procedures similar to that used in the

original fabrication. During testing, a tensile load is

placed on the specimen to shear the fillet welds.

The shear strength of the weld is reported as load

per unit weld length.

b. For longitudinal shear strength, the specimen

is prepared in accordance with AWS B4.0-85 (AWS1985), Figure E-1. For transverse shear strength,

the test specimen is prepared in accordance with

AWS B4.0-85, Figure E-2. The surface contour

and size of the fillet welds should be in accordance

with the applicable code or standards.

c. The test is performed on a tensile machine in

accordance with the requirements of ASTM E8-91

(ASTM 1991 f ). The machine should be calibrated

in accordance with ASTM E4-89 (ASTM 1989a).

The specimen is positioned in the testing machine

so that the tensile load is applied parallel to the

longitudinal axis of the specimen. The length,

average throat dimension, and legs of each weld

should be measured and reported. The welds are

sheared under tensile loads and the maximum ten-

sile loads are reported.

d. Shear strength in pounds per square inch is

calculated by dividing the maximum load by the

effective weld throat area (i.e. theoretical throat

thickness times total length of fillet weld sheared).

At least two specimens are tested. The result of the

shear test is the average of the results of the speci-

mens. A test is considered invalid if the failure is

caused by a base metal defect. The fracture loca-

tion must also be included in the report.

e. Applicable documents.

(1) ASTM E4-89: Standard Practices for

Load Verification of Testing Machines (ASTM

1989a).

(2) ASTM E8-91: Standard Test Methods for

Tension Testing of Metallic Materials (ASTM

1991 f ).


Welding and Nondestructive Testing (AWS 1986).



(5) AWS B4.0-85 - Part E: Fillet Weld Shear

Test (AWS 1985).

7. Hardness Test

a. Hardness tests are used in weld evaluations

to provide information on the generic weld proper-

ties. Hardness measurements provide indications of metallurgical changes caused by welding, metallurg-

ical variations and abrupt microstructural discon-

tinuities in weld joints, brittleness, and relative

sensitivity to cracking under structural loads.

b. Specimens for hardness testing include

as-welded partial or complete assemblies, weld-

ments from which the reinforcement has been

removed, and weld joint cross sections. For hard-

ness tests of existing lock gates, the weld reinforce-

ment may or may not be removed. When it is

removed, a local area of the reinforcement is

ground smooth before testing. For large assemblies,

portable hardness testers are available that can be

transported for use in the field. Microhardness

testing of weld is usually performed on ground,

polished, or polished and etched transverse cross

sections of the weld joints.

5-3



ETL 1110-2-34630 Sep 93

c. Hardness testing methods include Brinell,

Rockwell, Vickers, and Knoop tests. Selection of

test method depends on hardness or strength of the

material, the size of the welded joints, and the type

of information desired. The Brinell test produces a

large indentation and is suited for large welds in

heavy plates, which is suitable for field evaluations.The Rockwell test produces much smaller indenta-

tions than the Brinell test and is more suited for

hardness traverses. The Rockwell hardness test is

also suitable for field inspection if a portable tester

is used. The Vickers and Knoop tests make rela-

tively small indentations and are suited for hardness

measurements of the various regions in the weld

heat-affected zone and for fine-scale traverses. The

Brinell and Rockwell tests are generally used for

hardness measurements of fusion-welded joints in

laboratory condition or field environment.

d. The Brinell hardness test is performed inaccordance with the requirements of ASTM E10-84

(ASTM 1984). It is an indentation hardness test

using calibrated machines to force a hard ball into

the surface of the material and to measure the diam-

eter of the resulting impression after removal of the

load. The Brinell hardness number, HB, is related

to the applied load and to the surface area of the

permanent impression made by a ball indenter.

e. The Rockwell hardness test is performed in


(ASTM 1992a). This test is an indentation hard-

ness test to force a diamond spheroconical indenteror hard ball indenter into the surface of the material

in two operations and to measure the difference in

depth of the indentation. The Rockwell hardness

number, HR, is a number derived from the net

increase in the depth of indentation as the force is

increased from a preliminary test force to a total

test force and then returned to the preliminary test

force. The higher the number the harder the

material.

f. The Vickers hardness test is performed in


(ASTM 1987a). The Vickers hardness test is an

indentation hardness test to force a squarebased

pyramidal diamond indenter with specified face

angles into the surface of the material to measure

the diagonals of the resulting impression after

removal of the load. Vickers hardness number is

related to the applied load and the surface area of

the permanent impression. The hardness values

from different test methods can be correlated

through a conversion chart (ASTM E140-88

(ASTM 1988)).

g. For each type of hardness test performed, at

least five indentations should be made for each

region. The result of the hardness test is the aver-age of the indentations.

h. Applicable documents.


Brinell Hardness of Metallic Materials (ASTM

1984).

(2) ASTM E18-92: Standard Test Methods

for Rockwell Hardness and Rockwell Superficial

Hardness of Metallic Materials (ASTM 1992a).

(3) ASTM E92-82: Standard Test Method forVickers Hardness of Metallic Materials (ASTM

1987a).

(4) ASTM E110-82: Standard Test Method

for Indentation Hardness of Metallic Materials by

Portable Hardness Testers (ASTM 1987b).

8. Fracture Toughness Test

Fracture toughness is a material property which

indicates its resistance to fracture. Fracture tough-

ness testing provides a measure of resistance tocrack initiation or propagation. Test methods

include Charpy V-notch test (CVN), Plane-Strain

Fracture Toughness test (K Ic), and Crack-Tip

Opening Displacement test (CTOD). The CVN test

is used to measure the ability of a material to

absorb energy. The K Ic or CTOD tests are used to

determine critical crack size that a material can

tolerate without fracture when loaded to a specific

stress level. The welding process and welding

procedure have a significant effect on the fracture

toughness of a weld joint. The same welding pro-

cess and procedure must be used for the structure

and test specimens. Fracture toughness test speci-

mens should be selected from a distressed gate

member or connection so that the test results are

representative of the gate. As an alternative, test

samples may be made of similar materials and

welding procedures to that used in the original

fabrication. Orientations of the test specimens

taken from gate samples should follow the

5-4



ETL 1110-2-34630 Sep 93

provisions specified by AWS B4.0-85 (AWS 1985),

Figure D-3. Test specimens should not contain

metal that has been affected thermally as a result of

cutting or preparation nor welding stops or starts.

The weld metal width-to-specimen thickness rela-

tionship provisions are given in AWS B4.0-85,

Figure D-4. When an evaluation of the base metalor heat affected zone is required, the location of the

notch should be specified.

a. Charpy V-notch test.

(1) The CVN test provides information about

behavior of metal when subjected to a single appli-

cation of a load resulting in multiaxial stresses

associated with a notch coupled with high rates of

loading. For some materials and temperatures,

impact tests on notched specimens have been found

to predict the likelihood of brittle fracture better

than tension tests or other tests used in materialspecifications.

(2) The specimen preparation and test proce-

dure for the CVN test is described by ASTM

E23-92 (ASTM 1992b). When specified, the sur-

face finish of the V-notch of the Charpy impact

specimen is 20 µin., or less. The testing machine is

a pendulum type of rigid construction and of capac-

ity more than sufficient to break the specimen in

one blow. The test is performed at various speci-

fied temperatures.

(3) Five specimens should be tested for eachtest condition and the amount of energy absorbed

by the specimen at fracture should be recorded.

The highest and lowest values are discarded, and

the result is taken as the average of the remaining

three specimens tested. If any specimen fails to

break or jams in the machine, the data of that speci-

men is not included in the calculation of the

average.

(4) In addition to the absorbed energy, other

test indicators, such as lateral expansion of the

fractured specimen and appearance of the fractured

surfaces, can also be used to characterize the

fracture toughness of the test material. The amount

of expansion on each side of each half can be

measured using a lateral expansion gage. The two

broken halves must be measured individually and

the larger value is used.

(5) The fracture appearance can be quantified

by measuring the length and width of the cleavage

portion of the fracture surface or comparing the

appearance of the fractured surface with a fracture

appearance chart (ASTM E23-92 (1992b)).

b. Plane-strain fracture toughness test.

(1) The property K Ic characterizes the resis-

tance of a material to fracture in the presence of a

sharp crack under severe tensile stress. This value

may be used to estimate the relation between failure

stress and defect size for a material in service

wherein the conditions of high tensile stress would

be expected. The values of K Ic can be used for

inspection and discontinuity assessment criteria,

when used in conjunction with fracture mechanics

analyses.

(2) The plane-strain fracture toughness can beexperimentally determined using compact tension

test specimen or bend test specimen. The specimen

preparation and test procedures must be in accor-

dance with ASTM E399-90 (ASTM 1990g), Figures

A4-1 and A3-1, respectively. For a result to be

considered valid, it is required that both the speci-

men thickness and the crack length exceed

2.5(K Ic / σ ys), where σ ys is the 0.2-percent offset yield

strength and K Ic is the fracture toughness of the

material at test temperature and loading rate. The

initial selection of a size of specimen may be based

on an estimated value of K Ic for the material to be

tested.

(3) The ASTM requirement for plane-strain

condition can be expressed in terms of Irwin’s

plane-strain β Ic value (ASTM E399-90 (ASTM

1990g)) as follows:

(5-1)β Ic

1

t

K Ic

σ ys

2

≤ 0.4

where

t = thickness

σ ys = material yield strength

If β Ic is 0.4, or less, the specimen size is sufficiently

large to ensure plane-strain behavior and LEFM can

5-5



ETL 1110-2-34630 Sep 93

be applied. Otherwise, elastic-plastic fracture

mechanics (EPFM) must be employed in the frac-

ture analysis. The crack-tip opening displacement,

as discussed in the following section, is usually the

material toughness parameter for EPFM assessment.

c. Crack-tip opening displacement test.

(1) CTOD is the displacement of the crack

surfaces normal to the original (unloaded) crack

plane at the tip of the fatigue precrack. The CTOD

values vary with material toughness depending upon

the amount of plastic deformation at the crack tip

under load. Therefore, CTOD at fracture incipient

load indicates the fracture toughness of the test

material.

(2) The CTOD values may be used to charac-

terize the toughness of materials that are too ductile

or lack sufficient size to be tested for K Ic. Thedifferent values of CTOD characterize the resistance

of a material to crack initiation and early crack

extension at a given temperature. The values of

CTOD can be used for inspection and fracture

assessment criteria, when used in conjunction with

fracture mechanics analyses.

(3) CTOD tests use three-point bend specimens.

Preparation of test specimen and test procedure is

described in ASTM E1290-89 (ASTM 1989d ). The

critical CTOD values are derived from measure-

ments of load and clip gauge displacement.

d. Applicable documents.

(1) ASTM E23-92: Standard Test Methods for

Notched Bar Impact Testing of Metallic Materials

(ASTM 1992b).


Plane-Strain Fracture Toughness of Metallic Mater-

ials (ASTM 1990g).

(3) ASTM E1290-89: Standard Test Method

for Crack-Tip Opening Displacement (CTOD) Frac-

ture Toughness Measurement (ASTM 1989d ).



(AWS 1986).



(6) AWS B4.0-85 - Part D: Fracture Tough-

ness Testing of Welds (AWS 1985).

e. CVN-K Ic correlations.

Due to ease of testing and cost considerations, CVN

test results are more available than K Ic test results.An approximation of K Ic may be obtained through

the two-stage CVN-K Ic transition method as discus-

sed by Barsom and Rolfe (1987).

(1) Determine impact CVN test results in the

transition temperature region at test temperatures

approximately T s above the expected minimum ser-

vice temperature, T o. T s is the temperature shift

(expressed in degrees Fahrenheit) between fracture

toughness under dynamic loading, K Id , and fracture

toughness at slow loading rate, K Ic. Transition

temperatures and T s are described in Enclosure 6.

(5-2)T s

215 1.5 σ ys

where

T s = degrees Fahrenheit

σ ys = yield strength expressed in kips per

square inch

(2) Determine K Id by the following

relationship

(5-3)K Id

5 E (CVN IMP

)

where

E = Young’s modulus expressed in units of

pounds per square inch

K Id = critical stress-intensity factor under

dynamic loading (dynamic fracture

toughness) expressed in units of

pounds per square inch-√ in.

CVN IMP = Impact CVN test result in units of

foot-pounds

(3) Shift the K Id values at each temperature by

T s (Equation 5-2) to determine the K Ic values as a

function of desired minimum service temperature:

K Ic(T o) = K Id (T o+T s).

5-6



ETL 1110-2-34630 Sep 93

Figure 5-1 illustrates the method graphically. This

procedure is limited to the lower end of the transi-

tion curve, where the impact CVN value in

foot-pounds is less than about one-half of the yield

strength in kips per square inch.

Figure 5-1. Two-stage CVN-K Ic

correlation process

5-7



ETL 1110-2-34630 Sep 93

FRACTURE AND FATIGUE EVALUATION

1. Purpose of Evaluation

a. When inspections reveal discontinuities (i.e.

cracks or flaws), it is necessary to establish accep-tance levels to determine if repairs are needed to

prevent fracture. The critical discontinuity (i.e.

defect) size may be determined through a fracture

mechanics evaluation for a given set of loads, envi-

ronmental factors, geometry, and material proper-

ties. If the size of the discontinuity (crack or flaw)

is less than the critical defect size, the expected

remaining life and rate of crack propagation may be

determined by a fatigue analysis. Fracture and

fatigue evaluation requires identification of discon-

tinuity parameters, material properties, and accep-

tance levels. The engineering decision on appropri-

ate repair or planned maintenance is based on the

concept of fitness for service of the distressed gate

structure.

b. A lock gate is fit for service when it func-

tions satisfactorily during its lifetime without reach-

ing any serious limit state. The repair of harmless

discontinuities may introduce more harmful, and

less easily detectable discontinuities. Repair welding

is often difficult to carry out satisfactorily, since the

repair welds are usually made under unfavorable

conditions. The needs to repair detected discontinu-

ities must be determined in accordance with fitness-for-service concepts.

2. Fracture Behavior of Steel Materials

a. The service temperature under which a lock

gate operates has a significant effect on the fracture

behavior of the steel. For low and intermediate

strength steels, the material changes from brittle

fracture behavior (i.e., K Ic applies) to ductile frac-

ture behavior (i.e., K c or CTOD applies) at a certain

transition temperature. This temperature is called

the nil-ductility transition (also abbreviated as NDTwhich should not be confused with nondestructive

testing) temperature and is measured by the drop

weight test (ASTM E208-91 (ASTM 1991i)). The

NDT temperature is defined as the highest tempera-

ture at which a standard specimen breaks in a brittle

manner under dynamic loading. At temperatures

above the NDT temperature, the material has suffi-

cient ductility to deflect inelastically before total

fracture. Below the NDT temperature, the fracture

toughness remains relatively constant with changing

temperature. For impact loading, the NDT tempera-

ture approximately defines the upper limit of theplane-strain condition as shown in Figure 6-1.

Figure 6-1. Relation between notch toughness

and loading rates (Barsom/Rolfe, FRACTURE

AND FATIGUE CONTROL IN STRUCTURES:

Applications of Fracture Mechanics,©1987, p 110.

Reprinted by permission of Prentice-Hall, Inc.,

Englewood Cliffs, NJ.)

b. For steel, the NDT temperature depends on

material thickness and applied loading rate. The

anticipated level of structural performance (i.e.

brittle or ductile) can be determined from the frac-ture toughness test results performed at tempera-

tures around the transition temperature. With an

additional consideration of the geometric constraint

effect due to material thickness (i.e. β factor,

Equation 5-1), the appropriate fracture parameter

K Ic, K c, or CTOD can be selected for fracture

analysis. For structures subject to static or dynamic

loading, the respective fracture toughness-to-

temperature relations (i.e. K Ic for static loading and

K Id for dynamic loading) must be used to charac-

terize the fracture behavior. Figure 6-1 shows the

schematic relationships between level of structural

performance and service temperature for various

loading rates (Barsom and Rolfe 1987).

3. Fracture Analysis

a. For lock gates operating under the mini-

mum service temperature below the nil-ductility

Enclosure 6 6-1





ETL 1110-2-34630 Sep 93

Figure 6-2. Fracture and fatigue assessment procedure

6-3



ETL 1110-2-34630 Sep 93

estimated from CVN test values by the transition

Figure 6-3. Required dimensions of a discontinuity (after British Standards Institution 1980)

Figure 6-4. Resolution of a discontinuity (after

British Standards Institution 1980)

method (Enclosure 5, paragraph 8) if direct K Ic test

data are not available.

(5) Perform fracture assessment to determine

the critical discontinuity size.

(6) If the discontinuity is noncritical, determine

the remaining life using a fatigue analysis in this

enclosure, paragraph 6.

These steps are further discussed in the following

sections.

d. Fracture mechanics may be used to establish

acceptance levels for various discontinuities by

comparing the discontinuity(ies) size with the criti-

cal discontinuity (defect) size. Each case is unique

depending on a given set of loads, environmental

factors (e.g. temperature), geometry, and material

properties. The critical discontinuity size is deter-

mined using fracture mechanics principles which

relate stress, discontinuity size, and fracture tough-

ness to existing conditions. The stress-intensity

Figure 6-5. Interaction of coplanar discontinu-

ities (Extracts from PD 6493: 1980 are repro-

duced with the permission of BSI. Completecopies of the standard can be obtained by post

from BSI Publications, Linford Wood,

Milton Keynes, MK14 6LE)

factor K I or CTOD should always be less than the

critical stress-intensity factor K Ic , K c , or the critical

CTOD value δcrit , respectively.

6-4



ETL 1110-2-34630 Sep 93

Figure 6-6. Interaction of noncoplanar

discontinuities

Figure 6-7. Interaction of discontinuities with

surfaces

4. Linear-Elastic Fracture Mechanics

a. Fundamental concepts of LEFM are

described by Barsom and Rolfe (1987). LEFM is

valid only under plane-strain conditions, when

β Ic ≤ 0.4. The basic principle of LEFM is that

incipient crack growth will occur when the stress-

intensity factor K I (the driving force) equals or

exceeds the critical stress-intensity factor K Ic (the

resistance). K I characterizes the stress field in front

of the crack and is related to the nominal stress σand crack dimension a for a given load rate and

temperature by

(6-2)K I

C σ a

where

C = dimensionless correction factor for a given

geometry

If C is known, K I can be computed for any combi-

nation of σ and a. Stress-intensity factors for vari-

ous types of geometries can be calculated using the

information included in Figures 6-8 through 6-16

(Barsom and Rolfe 1987). Barsom and Rolfe and

Tada, Paris, and Irwin (1985) contain compilations

of solutions for a wide variety of configurations.

After the stress-intensity factor is determined by

Equation 6-2, it should be compared to the critical

stress-intensity factor, K Ic (determined as described

in Enclosure 5, paragraph 8). An FS = 2.0 applied

to crack length is considered appropriate to prevent

fracture. Therefore, the crack is considered to be

acceptable if K I < K Ic / √ 2. To determine the allow-

able maximum crack size or nominal stress for a

given K Ic, substitute K Ic for K I and solve for a or σusing Equation 6.2. The critical discontinuity size a

structural member can tolerate at a given stress σand K Ic with FS of 2.0 is:

(6-3)a

cr

1

2

K Ic

C σ

2

b. An approximate method to account for

stress gradients is to linearize the stress distribution,

and divide it into membrane stress σm and bending

stress σb. The stress-intensity factor for each com-

ponent of stress can be calculated separately and

then added together. The total applied stress (σ p

and σs) can be linearized and resolved into σm and

σb as shown in Figure 6-17.

5. Elastic-Plastic Fracture Assessment

Rearranging Equation 5-1 (Enclosure 5, paragraph8b(3)), the upper limit of plane-strain behavior may

be determined as

(6-4)K Ic

σ ys

t

2.5

6-5



ETL 1110-2-34630 Sep 93

Figure 6-8. Through-thickness crack (copyright

ASTM. Reprinted with permission)

Figure 6-9. Double-edge crack (Barsom/Rolfe,

FRACTURE AND FATIGUE CONTROL IN STRUC-

TURES: Applications of Fracture Mechan-

ics,©1987, p 40. Reprinted by permission of

Prentice-Hall, Inc., Englewood Cliffs, NJ.)

6-6



ETL 1110-2-34630 Sep 93

Figure 6-10. Single-edge crack (copyright ASTM.

Reprinted with permission)

Figure 6-11. Cracks growing from round holes

(copyright ASTM. Reprinted with permission)

6-7



ETL 1110-2-34630 Sep 93

Figure 6-12. Cracks growing from elliptical holes

(Barsom/Rolfe, FRACTURE AND FATIGUE CON-

TROL IN STRUCTURES: Applications of Fracture

Mechanics,©1987, p 43. Reprinted by permission

of Prentice-Hall, Inc., Englewood Cliffs, NJ.)

When this upper limit is exceeded, extensive plasticdeformation occurs at the crack tip (crack tip blunt-

ing) and a nonlinear EPFM model must be used for

analysis. (LEFM analysis using K c may be used if

the applied stress is less than yield stress.) Crack

growth criteria for nonlinear fractures can be

modeled by an R-curve, J-integral, or CTOD analy-

sis (Barsom and Rolfe 1987). The CTOD method

is the recommended method of EPFM analysis for

evaluating steel lock gates. The recommended

procedure for cases where the applied stress

(σ p + σs) is greater than the yield stress (British

Standards Institution 1980) is as follows:

a. Determine the effective discontinuity

parameter a. This is the equivalent through thick-

ness dimension which would yield the same stress

intensity as the actual discontinuities under the same

load.

(1) For through-thickness discontinuities,

a = /2.

(2) For surface discontinuities, a is deter-

mined by Figure 6-18.

(3) For embedded discontinuities, a is deter-

mined by Figure 6-19.

b. Determine allowable discontinuity parame-ter am which is calculated by:

(6-5)am

C

δcrit

ε y

where

ε y = yield strain of the material

δcrit = critical CTOD (determined according to

Enclosure 5, paragraph 8)

C = values determined by Figure 6-20

In determination of C , if the sum of primary and

secondary stresses, excluding residual stress, is less

than 2σ ys, the total stress ratio (σ p + σs)/ σ ys (includ-

ing residual stress) is used as the abscissa in

Figure 6-20. If this sum exceeds 2σ ys, an elastic-

plastic stress analysis should be carried out to deter-

mine the maximum equivalent plastic strain which

would occur in the region containing the discontinu-

ity if the discontinuity were not present. The value

of C may then be determined using the strain ratio,

ε / ε y as the abscissa in Figure 6-20.

c. If the effective discontinuity parameter a is

smaller than the allowable discontinuity parameter

am, then the discontinuity is acceptable. Using the

procedure described in paragraph 5b, this enclosure,

results in an FS of approximately 2.0 in the deter-

mination of am; Figure 6-20 was developed as a

design curve. Therefore, the calculated critical

crack size would be equal to 2.0 am (British Stan-

dards Institution 1980).

6. Fatigue Analysis

a. Fatigue is the process of cumulative dam-

age caused by repeated cyclic loading. Fatigue

damage occurs at stress-concentrated regions where

the localized stress exceeds the yield stress of the

material. After a certain number of cyclic loads,

the accumulated damage causes the initiation and

propagation of a crack.

6-8



ETL 1110-2-34630 Sep 93

Figure 6-13. Edge-notched beam in bending (Barsom/Rolfe, FRACTURE AND FATIGUE CONTROL IN

STRUCTURES: Applications of Fracture Mechanics,©1987, p 45. Reprinted by permission of Prentice-Hall,

Inc., Englewood Cliffs, NJ.)

b. The total fatigue life is the sum of the

fatigue crack-initiation life and the fatigue crack-

propagation life to a critical size (Barsom and Rolfe

1987).

N T = N i + N p (6-6)

where

N T = total fatigue life

N i = initiation life

N p = propagation life

c. All steels have microscopic discontinuities,

and welded structures always contain larger discon-

tinuities due to the welding process. Thus, the main

concern in fatigue assessment of welded structures

is to determine the crack-propagation life before

reaching the critical crack size which results in

brittle fracture. The life of a structural component

which contains a crack is governed by the rate of subcritical crack propagation.

d. Fatigue analysis methods described in para-

graphs 7 and 8 are based on extensive analyses of

test results from numerous specimens. Variation in

test data is large, and inherent uncertainty exists in

defining load and strength parameters. Therefore,

fatigue life predictions should be used as a means to

evaluate a reliable service life, not to actually pre-

dict when a structure will fail.

7. Fatigue Crack-Propagation (Barsom and

Rolfe 1987)

The fatigue crack-propagation behavior for metals is

shown in Figure 6-21. Figure 6-21 is a plot (log10

scale) of the rate of fatigue crack growth per cycle

of load (da/dN) versus the variation of the stress-

intensity factor (∆K I ). The parameter a denotes

crack length, N the number of cycles, and ∆K I the

stress-intensity factor range, K Imax to K Imin. Based on

Figure 6-21, fatigue-crack behavior for steel can be

characterized by three regions:

a. Region I: In region I, for levels of ∆K I

below a certain threshold, cracks do not propagateunder cyclic stress fluctuations. Conservative esti-

mates of fatigue threshold, ∆K th, can be determined

by

∆K th = 6.4(1 - 0.85R) ksi-√ in. for R > 0.1

∆K th = 5.5 ksi-√ in. for R < 0.1 (6-7)

6-9



ETL 1110-2-34630 Sep 93

Figure 6-14. Embedded elliptical or circular crack (Barsom/Rolfe, FRACTURE AND FATIGUE CONTROL IN

STRUCTURES: Applications of Fracture Mechanics,©1987, p 47. Reprinted by permission of Prentice-Hall,

Inc., Englewood Cliffs, NJ.)

6-10



ETL 1110-2-34630 Sep 93

Figure 6-15. Surface crack (Barsom/Rolfe, FRACTURE AND FATIGUE CONTROL IN STRUCTURES: Appli-

cations of Fracture Mechanics,©1987, p 48. Reprinted by permission of Prentice-Hall, Inc.,


where

R = stress ratio (i.e. fatigue ratio)

expressed as

R = σmin / σmax (6-8)

Residual stress should be considered for a crack

near weld area. If ∆K I is less than ∆K th, cracks do

not propagate.

b. Region II: The fatigue crack-propagation

behavior for ∆K I > ∆K th in region II (i.e. linear

portion of the plot on Figure 6-21) may be repre-

sented by

da/dN = 3.6x10-10 (∆K I )3 (6-9)

for ferrite-pearlite steels

and

da/dN = 0.66x10-8 (∆K I )2.25 (6-10)

for martensitic steels

(1) For Equations 6-9 and 6-10, a is in units

of inches, and ∆K I in units of kips per square

inch-√ in. ASTM A36-91 and A572-91 (1991b andd) Grade 50 steels are classified as ferrite-pearlite

steels, while ASTM A514-91/517 (ASTM 1991c

and 1990b, respectively) steels are martensitic

steels. The above equations were based on analyses

in air, at room temperature.

6-11



ETL 1110-2-34630 Sep 93

Figure 6-16. Cracks with wedge forces (Barsom/Rolfe, FRACTURE AND FATIGUE CONTROL IN STRUC-

TURES: Applications of Fracture Mechanics,©1987, p 52. Reprinted by permission of Prentice-Hall, Inc.,


Figure 6-17. Linearization of stresses (Extracts from PD 6493: 1980 are reproduced with the permission of

BSI. Complete copies of the standard can be obtained by post from BSI Publications, Linford Wood, Milton

Keynes, MK14 6LE)

6-12





ETL 1110-2-34630 Sep 93

Figure 6-19. Relation between dimensions of a discontinuity and the parameter a for embedded disconti-

nuities (Extracts from PD 6493: 1980 are reproduced with the permission of BSI. Complete copies of the

standard can be obtained by post from BSI Publications, Linford Wood, Milton Keynes, MK14 6LE)

6-14



ETL 1110-2-34630 Sep 93

Figure 6-20. Values of constant C for different

loading conditions (Extracts from PD 6493: 1980

are reproduced with the permission of BSI. Com-

plete copies of the standard can be obtained by

post from BSI Publications, Linford Wood, Milton

Keynes, MK14 6LE)

Figure 6-21. Fatigue-crack growth in steel

(2) Extensive fatigue-crack growth rate data

for weld metals and heat-affected-zones (HAZ)

show that the fatigue rate in weld metals and HAZ

are equal to or less than that in the base metals.

Thus, the above equations can be used for conserva-

tive estimates of fatigue-crack growth rates in base

metals, weld metals, and HAZ’s.

c. Region III: Region III is characterized by a

significant increase in the fatigue-crack growth rate

per cycle over that predicted for Region II. At a

certain value of ∆K I , the crack growth rate acceler-

ates dramatically. For materials of high fracture

toughness, the stress-intensity factor range value

corresponding to acceleration in the fatigue-crack

growth rate (i.e. transition from Region II to

Region III) for zero to tension loading can be

determined by

K T = 0.04 ( E σ ys)1/2

(6-11)

When the K Ic of the material is less than K T , accel-

eration in the fatigue rate occurs at a stress-intensity

factor value slightly below K Ic. Due to the acceler-

ation in crack growth rate, a significant increase in

fracture toughness of a steel above K T may have a

negligible effect on total fatigue life. Additionally,

extrapolation of Region II behavior to Region III

may overestimate the total fatigue life significantly.

8. Fatigue Assessment Procedures

The procedure to analyze Region II crack growth

behavior in steels and weld metals using fracture

mechanics concepts as recommended by Barsom

and Rolfe (1987) is as follows:

a. On the basis of the inspection data, deter-

mine the maximum initial discontinuity size ao

present in the member being analyzed and the

associated K I .

b. Knowing K Ic and the nominal maximum

design stress, calculate the critical discontinuity

size, acr (Equation 6-1), that would cause failure by

brittle fracture.

c. Determine fatigue crack growth rate for

type of steel (Equations 6-9 and 6-10) (i.e

ferrite-pearlite or martensitic steel).

6-15



ETL 1110-2-34630 Sep 93

d. Determine ∆K I using the appropriate expres-

sion for K I , the estimated initial discontinuity size

ao, and the range of live load stress ∆σ (i.e. cyclic

stress range). For cases of variable amplitude load-

ing, a spectrum of various discrete stress ranges ∆σi

exists. In these cases, an effective stress range ∆σe

should be used in determining ∆K I . ∆σe can becalculated as the root-mean-cube of the discrete

stress ranges ∆σi,

(6-12)∆σe

m

i 1

ni

(∆σi)3

N

1/3

where

ni = number of cycles corresponding to ∆σi

N = total number of cycles considered

m = number of discrete stress ranges considered

A live load stress range ∆σ, which is due to cyclic

compression stresses, may be detrimental in regions

where tensile residual stress exists. In these

regions, cracks may propagate, since the addition of

tensile residual stresses will result in an applied

stress range of tension and compression.

e. Integrate the crack growth rate expression

(i.e. Equations 6-9 and 6-10) between the limits of

ao (at the initial K I ) and acr (at K Ic) to obtain the

life of the structure prior to failure. To identify

inspection intervals, integration may be applied withthe upper limit being tolerable discontinuity size at .

An arbitrary safety factor based on analysis uncer-

tainties may be applied to acr to obtain at (for

example, FS = 2.0 was used in Equation 6-3).

Another consideration to specifying a tolerable

discontinuity size is crack growth rate. The at

should be chosen so that da/dN is relatively small

and a reasonable length of time remains before the

critical size is reached.

f. For a determination of ao.

(1) See Figure 6-3a for through-thickness

discontinuities.

(2) For embedded discontinuities (Figure 6-3b),

assume that the discontinuity grows until it reaches

a circular shape (b= /2). Subsequently, it grows

radially and eventually protrudes a surface at which

time it should be treated as a surface discontinuity

of length .

(3) See Figure 6-3c for surface discontinuities.

Initial propagation will result in a semicircular

shape. Further propagation will result in the dis-continuity reaching the other surface at which time

it should be treated as a through thickness

discontinuity.

9. Development of Inspection Schedules

Inspection schedules can be developed from crack

length versus fatigue life curves. Figure 6-22

shows a typical crack length-fatigue life (a - N)

curve, which can be obtained from Equation 6-9

or 6-10. Critical crack length is determined based

on K Ic and maximum design stress as discussed inparagraph 8, this enclosure. The time when repair

is needed can be determined considering FS, i.e.,

ar = acr /(FS). Remaining loading cycles before

repair are then determined from ai and ar using an

a-N curve as shown in Figure 6-22. Inspection

intervals for a gate can be determined from the

remaining fatigue life of the members (Common-

wealth of Pennsylvania, Department of Transporta-

tion 1988).

Figure 6-22. Development of maintenance

schedule

6-16



ETL 1110-2-34630 Sep 93

10. Example Fracture Analysis

Cracks of various shapes were revealed on two

tension members on a lock gate by NDT inspection.

One member has the cross-sectional dimensions of

4 in. thick by 12 in. wide. The other member is

1 in. thick by 12 in. wide. The crack types andshapes include: a) single-edge crack; b) through-

thickness center crack; c) surface crack along the

12-in. side (a/2c = 0.1 and 0.2), and d) embedded

circular cracks.

The material properties at the minimum service

temperature of 30 oF were determined by material

testings and are summarized as follows:

σ ys = 50 ksi σult = 80 ksi

E = 30,000 ksi K Ic = 60 ksi-√ in.

K Id = 40 ksi-√ in. δcrit = 0.002 in. (static)

δcrit = 0.001 in. (dynamic)

From structural analysis, the maximum applied

tensile stress is 30 ksi. For each cracked member,

the critical crack size will be determined for each

cracking condition under static loading and dynamic

loading, respectively:

a. Example for 4- by 12-in. plate:

β Ic

1

t

K Ic

σ ys

2

1

4

60

50

2

0.36 (Equation 5 1)

β Ic

<0.4; therefore, LEFM is applicable.

(1) Single-edge crack (see Figure 6-10).

K I

1.12σ πa k

a

b

C 1.12 π k

a

bin Equation 6 2

assume k

a

b1.0

acr

1

π

K Ic

1.12σ

2

1.02 in.

(Equation 6 1 with no FS)

a/b = 0.17 and = 1.06; therefore,k

a

b

iteration is needed for acr and . Afterk

a

b

iteration, acr = 0.92 in. ( = 1.05)k

a

b

With FS = 2.0, acr = 0.5 (0.92) = 0.46 in.

for dynamic loading:

acr

0.5

π

K Id

1.12σ

2

0.23 in.

(2) Through-thickness center crack

(Figure 6-8).

K I

σ πa2b

πatan

πa

2b

assume 2b

πatan

πa

2b1.0

acr

1

π

K Ic

σ

2

1.27 in.;

2bπ a

tan πa2b

1.02

After iteration, acr = 1.22 in.

With FS = 2.0, acr = 1.22/2 = 0.61 in.

for dynamic loading:

acr

0.5

π

K Id

σ

2

0.28 in.

(3) Surface crack along the 12-in. side (see

Figure 6-15).

K I

1.12σ π a

Q M

K

(a) a/2c = 0.1

6-17





ETL 1110-2-34630 Sep 93

The maximum stress level is 30 ksi and the mini-

mum stress is 0 ksi. A curve relating the initial

surface flaw size ai to number of cycles to failure

N p will be developed. From Figure 6-15

K I

1.12

σ π

a

Q M

K

σσ

ys

30

500.6 and Q 1.39 ( Figure 6 14)

assume M k = 1.0.

With FS 2.0, acr

0.5Q

π

K IC

1.12σ

2

0.71 in.

(for crack sizes up to a = 0.71 in., M k = 1.0)

for ferrite-pearlite steel, da/dN = 3.6×10-10 (∆K I )3

(Equation 6-9)

∆K I

1.12 ∆σ π a

Q50.5 a

Fatigue life can be determined as:

N ⌡⌠ acr

ai

da

(3.6×10 10)(∆K I )3

N 1

(3.6×1010

)(50.5)3

⌡

⌠ acr

ai

a 3/2 da

N (4.31×104)

1

ai

1

acr

The curve for fatigue life N as a function of initial

crack length ai for this example is shown in

Figure 6-23.

12. Example of Fracture and Fatigue

Evaluation

a. Single-edge crack. Figure 6-24 shows a

horizontal girder with a single-edge crack. The

initial crack length is assumed to be 1/8 in.. The

flange plate containing the edge crack is assumed to

be under a cyclic load from zero to maximum ten-

sion (i.e., fatigue ratio R = 0). The stress ranges

Figure 6-23. Fatigue life (N )-initial crack-length

(a i ) curve

vary from 18 ksi to 27 ksi. The fatigue life can be

calculated using the following crack growth equa-

tion (Equation 6-9):

da

dN 3.6 × 10 10(∆K

I )3

where

K I

1.12σ πa k

a

b

By integrating the crack growth equation, the life of

the propagating crack can be determined for any

crack length.

N ⌡⌠ acr

ai

da

(3.6×10 10)(∆K I )3

where

K I = stress-intensity factor which is a function

of crack length

ai = initial crack length

acr =1

π

K Ic

1.12σk (a / b)

2

(Equation 6 1)

With K Ic assumed to be 35 ksi-√ in. and a maximum

stress of 18 ksi, acr = 0.89 in. using the procedure

described in paragraph 10a(1).

6-19



ETL 1110-2-34630 Sep 93

Figure 6-24. A single-edge cracked girder

6-20



ETL 1110-2-34630 Sep 93

Figure 6-25a shows the calculated crack growth

versus life cycle for a stress range of 18 ksi

(1/2 σ ys). The remaining life N , calculated by the

above equation, is 207,700 cycles. If the structure

operates 10,000 times per year, then the remaining

life of the girder is:

Critical crack length (determined by Equation 6-1)

207,700

10,00020.8 years

is a function of external loading as shown in

Figure 6-25b. Figure 6-25c shows the fatigue life

for stress ranges varying from 18 ksi to 27 ksi

calculated using the crack growth equation with

variable stress and acr . The remaining life of the

girder flange containing a 1/8-in. initial crack is

shown in the figure as a function of stress.

b. Double-edge crack. A girder flange contain-

ing double-edge cracks is shown in Figure 6-26.

The crack growth curves were calculated for stress

ranges varying from 10 to 20 ksi. The same inte-

gration procedure as used for the single-edge crack

case is employed for calculating the fatigue life. A

1/8-in. initial crack length is also assumed in this

case. The predicted crack growth curve for stress

range of 18 ksi is shown in Figure 6-27a. The

remaining life of the girder flange plate for various

stress ranges is also shown in Figure 6-27c.

c. Surface crack. Figure 6-28 shows a crack

for which it is assumed initiated in the diagonalbracing member from a surface crack at the corner

of the bracket. It is assumed that the crack propa-

gated through the thickness of the bracing member

and then grew toward the edge of the flange plate.

A single-edge crack condition similar to the first

example case was developed. The fracture and

fatigue analysis of this example consists of three

propagation steps.

(1) The first step is to analyze the crack prop-

agation of a hemispheric surface crack having an

initial radius of 1/16 in. When the surface crack

breaks through the surface on the other side of theplate (i.e., the radius of hemispheric crack becomes

the same as the plate thickness, 3/8 in.), a through-

thickness crack condition is reached.

(2) The second step is to analyze crack growth

of a plate containing a through-thickness crack.

Once the through-thickness crack reaches the edge

Figure 6-25. Curves for fatigue life of a girder

with a single-edge crack

of the plate, the single-edge crack condition is

developed.

(3) The third step is to analyze crack growth

of the edge crack. The total remaining life of the

6-21



ETL 1110-2-34630 Sep 93

Figure 6-26. A double-edge cracked flange

6-22



ETL 1110-2-34630 Sep 93

Figure 6-27. Curves for fatigue life of a flange

with a double-edge crack

diagonal bracing member from the initial hemi-

spheric surface crack can be determined by adding

the three propagation lives. The calculated crack

growth curve for a stress range of 18 ksi is shown

in Figure 6-29a. The total remaining life and criti-

cal crack length are also shown in Figures 6-29b,

and c, for stress ranges varying from 10 to 20 ksi.

13. Recommended Solutions

a. The recommended solutions to the cracking

problems can be addressed in short- and longterm

solutions. The short-term solution is to repair the

fractured members using qualified welding proce-

dures and improved fatigue details or bolted coverplates. This temporary measure will ensure contin-

uous operation of the structure without catastrophic

failure.

b. A long-term solution will involve detailed

inspection and evaluation of the critical members

and connections. Structural analysis using a finite

element model may be necessary to identify the

critical structural members and connections. Vari-

ous loading conditions determined during the course

of previous activities need to be considered in the

analysis. The fatigue category of various welded

connections should be assessed according to theAmerican Association of State Highway and Trans-

portation Officials (AASHTO) Standard Specifica-

tion for Highway Bridges (AASHTO 1989) or the

ANSI/AWS D1.1-92 Structural Welding Code

(ANSI/AWS 1992). The expected life of the criti-

cal connections can be estimated in accordance with

the respective fatigue category.

c. To maintain satisfactory performance of a

structure, a maintenance plan needs to be devel-

oped. This maintenance plan should include peri-

odic inspections and evaluations. For the worst

loading situation, the maximum stress range can bepredicted from an appropriate structural analysis.

The inspection intervals can be determined from a

crack growth curve of maximum stress range. The

inspection intervals shall be a fraction of the

remaining life cycles of the critical members and

connections. These fraction life cycles shall corre-

spond to a crack size less than one-half of the criti-

cal crack length (i.e. FS = 2.0).

d. Recommended inspection intervals may be

computed using fatigue principles as described in

paragraph 9, this enclosure. Using the example

found in paragraph 12a of this enclosure, the

inspection schedule can be determined from the

fatigue life curve of the single-edge crack in the

primary member. The maximum stress range is

assumed as 18 ksi. The procedure is shown in the

following steps.

6-23



ETL 1110-2-34630 Sep 93

Figure 6-28. A stiffening member with a crack

6-24



ETL 1110-2-34630 Sep 93

Figure 6-29. Curves for a fatigue life of a stiffening member with a

surface crack

6-25



ETL 1110-2-34630 Sep 93

(1) Determine critical crack length:

acr = 0.89 in. (this enclosure, paragraph 12a)

(2) Determine crack length when repair is

needed (Figure 6-22):

ar = 0.89/2 = 0.45 in. (FS = 2.0)

(3) Determine fatigue life from fatigue life N

versus crack length a curve:

N = 160,000 cycles

160,000/10,000 = 16 years (10,000 cycles/year)

Therefore, the girder should be inspected within

16 years after the initial crack (ai = 1/8 in.) was

found.

6-26



ETL 1110-2-34630 Sep 93

REFERENCES FOR ENCLOSURES

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R-1



ETL 1110-2-34630 Sep 93

plates, alloy steel, high-strength, quenched, and

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R-2



ETL 1110-2-34630 Sep 93

mm. American Society for Testing and Materials.

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examination," Designation: E709-91, Philadelphia,

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nn. American Society for Testing and Materials.

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yy. Headquarters, Department of the Army.

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zz. Headquarters, Department of the Army.

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aaa. Headquarters, Department of the Army.

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(1985). "The stress analysis of cracks handbook,"

Paris Productions, Inc., Saint Louis, MO.

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