Brittle Fracture the Cold Hard Facts Vern Ragle Final

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BRITTLE FRACTURE

The Cold, Hard Facts

by Verne Ragle


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Verne Ragle, P.E.

45 years in the Petrochemical business with primaryemphasis on equipment integrity, inspection,materials, corrosion and failure analysis.

n 25 year member of NACEn Active in numerous NACE and API Standards

Committees

n Worked in all areas of Process SafetyManagementn Mechanical Integrityn PSM Compliance

Current job

l Support company operations worldwide onCorrosion and Materials issues. Specific focus onDownstream Mechanical Integrity Issues.

l Pressure Equipment Mech. Integ. Assessment

l Fitness for Service

Energy


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l Create and awareness of Brittle

Fracture and the factors that cause

it.

l Notable Brittle Fracture Failures

l Variables that Cause Brittle

Fracture

l Effect on Codes an Standardsl API RP 579

l Assessing Existing Facilities

Purpose of

Presentation


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Example: Brittle vs

Ductile

(a) (b) (c)

(a) Highly ductile fracture in which the specimennecks down to a point.

(b) Moderately ductile fracture after some necking.

(c) Brittle fracture without any plastic deformation.


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Notable Brittle FractureFailures

Great Boston Molasses Flood

1919

Liberty Ships Breaking apart

1943

Oil Storage Tank Failure -1988


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The Great BostonMolasses Flood


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Boston Molasses FloodDataDate: January 15, 1919Location: Boston, Massachusetts

Temperature: -2 to 41F (temp. rise over previousseveral day)

Construction: RivetedMaterial: Steel- type unknown (one report saidcast iron)

Significant Characteristics: Poor construction quality

Point of Origin: Manhole near the base of the tank

Commodity: Molasses

Amount Lost: 2,300,000 gallons ( 50ft tall by 90 ftdiam.)

Deaths: 21

Injuries: 150


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Boston Molasses FloodDataWitness ReportsSome say it collapsed, others say it exploded.

Reported loud rumbling like a machine gun as rivetsshot out of the tank.

The ground shook like a train going by.

Eight to fifteen foot wave of molasses at 35 MPH.

Girders of Boston Elevated Railway broke trainlifted off the tracks

Buildings swept off of their foundation

Several blocks flooded to a depth of 2 to 3 feet withmolasses.

Moving masses investigated to determine if man oranimal.

Truck blown into Boston Harbor.


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The Great BostonMolasses Flood


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Boston Molasses FloodDataContributing factors reported andspeculated

Poor construction and insufficient testing

People reportedly filled their molasses jarsfrom home from leaks

Filled to highest level (also filled to max on 8 otheroccasions)

Cyclic stress and fatigue?

Pre-stressed cracks?

Speculation of Carbon Dioxide pressure due tofermentation

Vents Plugged?

Initiated from a manhole near the base of the tank

Maximum hoop stress


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LibertyShip

Failures


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USS Schenectady


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Liberty Ships BreakingApartDate: January 16, 1943Location: Portland Oregon

Temperature: Water 29.2F : Air 37F

Construction: Welded

Material: Steel- type unknown

Significant Characteristics: Rapidconstruction, No Crack arresting plates,Inexperienced welders Poor constructionquality

Point of Origin: Corners of Hatch opening,

Number of ships that failed; 1943 -20

1944- 120


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Liberty Ships BreakingApartSignificant contributors to failure:

Poor quality steel

New construction methods (welding)-

thought to be an unsuitable method of

construction

Lack of knowledge of fracture characteristics

of steel,

Cold, North sea water,

Overloading.


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Add text

USS Ponaganset

Liberty Ship Failures


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OilStorage Tank

Failure


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Oil Storage Tank FailureDate: January 2, 1988

Location: Floreffe , Pennsylvania

Temperature: 12 to 26F (12 hours before to time offailure)

Construction: Welded

Material: Steel type: Carbon Steel Gradeunknown

Significant Characteristics: Reconstructed Tank

Point of Origin: Flaw near a weld

Commodity: Diesel fuelAmount Lost: 2,500,000 gallons

Deaths: none Injuries: none

Significant factor: Filled to highest level everattained


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* Photograph source:http://www.epa.gov/superfund/programs/er/resource/d1_07.htm


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Oil Storage Tank Failure

Witness comments:Eyewitness accounts of the failure indicated thatthere were no warnings.

At the time of failure the tank was nearly full.

There was no explosion.

An operator was on the roof of the tank to verify thatit was nearly full just five minutes before the tankruptured.

Sounds like thunder were described as emanatingfrom the tank for about 30 seconds at the time of thefailure.


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R.M. Keddal & Assoc., Library, PA


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The Aftermath

Observations of the failure site revealed that the

tank had moved about 120 feet.

The roof of the tank was still attached to portions ofthe tank wall.

The bottom of the failed tank remained intact.

Collateral damage included a fifty ft high adjoiningtank that had oil on its roof and another tank somedistance away that had oil all over it and wasphysically damaged

The tidal wave effect of the sudden release of acolumn of diesel oil 120 ft in diameter and 50 ft highcaused the oil to flow over the dike wall, into stormdrain at an adjacent power plant that flowed directlyto the Monongahela River.

An estimated 500,000 gallons of oil went into the


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R.M. Keddal & Assoc., Library, PA


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Contributing Factors to TankFailure Tank was built in 1940

Poor quality steel

Welding Technology was not what it istoday

Tank was cut apart and rewelded Flaw existed

From original Welding

Service Change

Old service required Heating andInsulation

New Service did not required heatingand insulation


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Contributing Factors to TankFailure

Flaw in bottom shell course from originalconstruction.

Battelle; Columbus ,Ohio


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Factors Contributing to BrittleFractureCommon factors that are very

consequential.

All of the failures were associated with coldweatherAll of the failed structures were subjected to

high stress levels. The tanks were at their maximum fill

height The ships were subjected to the

stresses of the pounding of waves and,in many cases overloading.

They were fabricated during times that verylittle was known concerning fracturemechanics and the effect low temperature

could have on the toughness of steel.


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Factors Contributing to BrittleFracture.

Stress risers were present The molasses tank was noted to have

many flaws Revealed by the leaks

Initiated at a lower manway

The oil tank had a flaw that was attributed to

be the triggering mechanism for the failure.

Many of the ship failures initiated in corners

of hatches or other locations that are know

now to be points of high stress concentration


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Similar Traits of Failures

Molasses

Tank

Oil Tank Ships

Lowtemperature

-2 to 41F 12 to 26F 29/37F

Flaws, Leaks Yes Stress

Risers

Stress Maximum fill Maximum fill Movementandoverload

Susceptible

Metal

Yes Yes Yes

NewTechnology(welding)

NO Yes Yes


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Common Factors

Three things are necessary for brittle fracture to

occur:

1) A material that is susceptible to brittle fracture High NDT Low Charpy Values

2) Stress Uniform stress Concentrated Stress due to flaws or

discontinuities

3) Low metal temperature Below or near the NDT


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Effect on Codes andStandardsMolasses Flood Era

No active organization such as API-AME

Minimal failures

Lack of attention

Liberty Ship Era New technology

War Effort

Early Refineries

No significant incidents

Early ASME Codes 1951 API-ASME

Listed allowable stress down to -20F


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Effect on Codes andStandards1980s & 90s

API In response to industry needswas In a period of unprecedenteddevelopment of documentsRP 570 Piping Inspection Code:RP 571 Damage Mechanisms Affecting Fixed

EquipmentRP 572 Inspection of Pressure VesselsRP 573 Inspection of Fired Boilers and HeatersRP 574 Inspection Practices for Piping SystemComponentsRP 575 Inspection of Atmospheric & L P Storage

TanksRP 576 Inspection of Pressure-Relieving DevicesRP 577 Welding Inspection and MetallurgyRP 578 Material Verification ProgramStd 579-1/ASME FFS-1 Fitness-For-ServiceRP 580 & 581 Risk-Based Inspection


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Effect on Codes andStandardsASME data on Brittle Fracture and Lowtemperature

In UCS 65, UCS 66 ASME 1988 -- 3 by 8 column

ASME 1989 -- 6 pages

API Std 650

Extensive section on Low Temperature

API 620 StdAppendix Q and R related to Low Temperature


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Considerations for ExistingEquipmentThe brittle fracture resistance of the material ofconstruction is fixed for any existing piece of

equipment and cannot be altered .

API 579-1/ASME FFS-1, JUNE 5, 2007

Part 3 - based on ASME Section 8 Div 1,Para UCS-66

Screening tool for determining propensity forBrittle FractureVariables

Material Type Thickness Stress

Applied Stress Known flaws

Credit for PWHT Temperature -Limit Exposure


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AssessmentConsiderationsThree Levels of Assessment

Level 1 Can be satisfied based on:

Impact test results or impact test exemptionscurves from the code

Accomplished by a scrutiny of existing

equipment data Comparing the CET (critical exposure

temperature) to the MAT (minimum allowabletemperature).

The methodology of RP 579 is quite thorough in the

guidelines provided for determining the CET and theMAT. Equipment that has a CET equal to or greaterthan the MAT are exempt from further brittle fractureassessment unless conditions change.

.


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AssessmentConsiderationsA good Management of Change program should be inplace to trigger an action item should changes occurthat might affect the CET.

One level 1 assessment of a plant resulted in 15% ofthe equipment being exempt from further

assessment..


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AssessmentConsiderationsLevel 2 assessment takes into consideration:

Operating pressure/temperature envelope Compared to the component design stress and

MAT.

Adjustments are permitted to the MAT providingproper impact test documentation is present.

Credit is also given for fabrication conditions such asPWHT (post weld heat treatment).


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AssessmentConsiderationsLevel 2 assessment (contd):When determining the stress conditions,consideration is given to:

Excess material above the required minimumthickness

The effect of joint efficiency

Wall thickness

In the aforementioned assessment, 51% of theequipment met the required criteria after a level 1

and level 2 assessment..


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AssessmentConsiderationsLevel 3 AssessmentNormally involves more detailed determinations of

one or more of the three factors that control thesusceptibility to brittle fracture:

stress flaw size material toughness.

Many factors affect the outcome.Significant amounts of inspection data may beavailable and other problems may be on record thatmust be considered in the brittle fractureassessment.Example--Equipment that was in amine service

--possibly susceptible to cracking or blistering.

Many parts of RP 579 specifically address many ofthese issues and can be effectively utilized toenhance the brittle fracture assessment.


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AssessmentConsiderationsThere are many ways to present the results of thebrittle fracture assessments.

A very effective way is to provide a graph of eachcomponent showing the minimum allowabletemperature as a function of percent of design

pressure.

This method provides:

A rapid assessment of the permitted pressure

for all temperatures Permitted temperature for all pressures within

the limits of the design pressure of theequipment.


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Nature of Brittle Fracture &AssessmentMost variables are not exactStress levels are based on overall stress

No accountability for stress concentrationssuch as residual stress in welds, stress atconnections

Concentrated stresses act as crack initiators

that cannot be arrestedHydrotest in ductile range can blunt cracks andflaws to resist BF

All three components must be present at the sametime

Susceptibility- Cannot be changed

Stress Must be controlled

Temperaturebe aware of sources of lowtemperature


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Sources of LowTemperatureWeather--cant be controlled; must provideprotection

False sense of security in warm parts ofthe country.

Process related situations

Autorefrigeration due to Relief Valve

Relief valve open- Cool down below CET

Relief valve close- repressurization whilecold.

Depressurization for other reasons

Mixed phase flow- cooling of piping from Vesselstream

Cold start-up or repressurization proceduresmust be considered

Shock chilling


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Questions??

Verne Ragle, P.E.Mechanical Integrity ConsultantSiemens EnergyOil & Gas DivisionEngineering Consulting Business Unit

4615 Southwest Freeway, Suite 900Houston, TX 77027

Tel.: (281)-220-1701Fax: (713)-570-1230Mobile: (850) 398-7097Email: [email protected]://www.sea.siemens.com

Energy
mailto:[email protected]:[email protected]

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Brittle Fracture the Cold Hard Facts Vern Ragle Final