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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Oil Storage Tank Failure
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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Oil Storage Tank Failure
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: verne.ragle@siemens.comhttp://www.sea.siemens.com
Energy
mailto:verne.ragle@siemens.commailto:verne.ragle@siemens.com
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