1. BRITTLE FRACTURE
The Cold, Hard Facts
by Verne Ragle

2. Verne Ragle, P.E. Energy
45 years in the Petrochemical business with primary
emphasis on equipment
integrity, inspection, materials, corrosion and failure
analysis.
 25 year member of NACE
 Active in numerous NACE and API Standards
Committees
 Worked in all areas of Process Safety Management
 Mechanical Integrity
 PSM Compliance
Current job
 Support company operations worldwide on Corrosion
and Materials issues. Specific focus on Downstream
Mechanical Integrity Issues.
 Pressure Equipment Mech. Integ. Assessment
 Fitness for Service

3. Purpose of Presentation
 Create and awareness of Brittle Fracture and
the factors that cause it.
 Notable Brittle Fracture Failures
 Variables that Cause Brittle Fracture
 Effect on Codes an Standards
 API RP 579
 Assessing Existing Facilities

4. Example: Brittle vs Ductile
(a) (b) (c)
(a) Highly ductile fracture in which the specimen necks down
to a point.
(b) Moderately ductile fracture after some necking.
(c) Brittle fracture without any plastic deformation.

5. Notable Brittle Fracture Failures
•Great Boston Molasses Flood 1919
•Liberty Ships Breaking apart – 1943
•Oil Storage Tank Failure -1988

6. The Great Boston Molasses Flood

7. Boston Molasses Flood Data
Date: January 15, 1919
Location: Boston, Massachusetts
Temperature: -2 to 41°F (temp. rise over previous several day)
Construction: Riveted
Material: Steel- type unknown (one report said cast 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 ft diam.)
Deaths: 21
Injuries: 150
Significant event prior to rupture: Filled to maximum level

8. Boston Molasses Flood Data
Witness Reports
•Some say it collapsed, others say it exploded.
•Reported loud rumbling like a machine gun as rivets shot 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 – train lifted off the
tracks
•Buildings swept off of their foundation
•Several blocks flooded to a depth of 2 to 3 feet with molasses.
•Moving masses investigated to determine if man or animal.
•Truck blown into Boston Harbor.

9. The Great Boston Molasses Flood

10. Boston Molasses Flood Data
Contributing factors reported and speculated
Poor construction and insufficient testing
• People reportedly filled their molasses jars from home
from leaks
Filled to highest level (also filled to max on 8 other occasions)
• Cyclic stress and fatigue?
• Pre-stressed cracks?
Speculation of Carbon Dioxide pressure due to fermentation
• Vents Plugged?
Initiated from a manhole near the base of the tank
• Maximum hoop stress
• Stress riser

11. Liberty
Ship
Failures

12. USS Schenectady

13. Liberty Ships Breaking Apart
Date: January 16, 1943
Location: Portland Oregon
Temperature: Water 29.2°F : Air 37°F
Construction: Welded
Material: Steel- type unknown
Significant Characteristics: Rapid construction, No
Crack arresting plates, Inexperienced welders Poor
construction quality
Point of Origin: Corners of Hatch opening,
Number of ships that failed; 1943 -20 1944- 120

14. Liberty Ships Breaking Apart
Significant 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.

15. Liberty Ship Failures
Add text
USS Ponaganset

16. Oil
Storage Tank
Failure

17. Oil Storage Tank Failure
Date: January 2, 1988
Location: Floreffe , Pennsylvania
Temperature: 12 to 26°F (12 hours before to time of
failure)
Construction: Welded
Material: Steel type: Carbon Steel Grade unknown
Significant Characteristics: Reconstructed Tank
Point of Origin: Flaw near a weld
Commodity: Diesel fuel
Amount Lost: 2,500,000 gallons
Deaths: none Injuries: none
Significant factor: Filled to highest level ever attained

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

19. Oil Storage Tank Failure
Witness comments:
Eyewitness accounts of the failure indicated that there 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 that it was
nearly full just five minutes before the tank ruptured.
Sounds like thunder were described as emanating from the
tank for about 30 seconds at the time of the failure.

20. Oil Storage Tank Failure
R.M. Keddal & Assoc., Library, PA

21. 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 of the tank
wall.
The bottom of the failed tank remained intact.
Collateral damage included a fifty ft high adjoining tank that
had oil on its roof and another tank some distance away that
had oil all over it and was physically damaged
The tidal wave effect of the sudden release of a column of
diesel oil 120 ft in diameter and 50 ft high caused the oil to
flow over the dike wall, into storm drain at an adjacent power
plant that flowed directly to the Monongahela River.
An estimated 500,000 gallons of oil went into the river.

22. Oil Storage Tank Failure
R.M. Keddal & Assoc., Library, PA

23. Contributing Factors to Tank Failure
• Tank was built in 1940
• Poor quality steel
• Welding Technology was not what it is today
• Tank was cut apart and rewelded
• Flaw existed
• From original Welding
• Service Change
• Old service required Heating and Insulation
• New Service did not required heating and
insulation

24. Contributing Factors to Tank Failure
Battelle; Columbus ,Ohio
Flaw in bottom shell course from original construction.

25. Factors Contributing to Brittle Fracture
Common factors that are very consequential.
•All of the failures were associated with cold
weather
•All 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 very little
was known concerning fracture mechanics and
the effect low temperature could have on the
toughness of steel.

26. Factors Contributing to Brittle Fracture
.
•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

27. Similar Traits of Failures
Molasses Oil Tank Ships
Tank
Low -2 to 41°F 12 to 26°F 29/37°F
temperature
Flaws, Leaks Yes Stress Risers
Stress Maximum fill Maximum fill Movement
and
overload
Susceptible Yes Yes Yes
Metal
New NO Yes Yes
Technology
(welding)

28. 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

29. Effect on Codes and Standards
Molasses 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 -20°F

30. Effect on Codes and Standards
1980s & 90s
API – In response to industry needs was In a
period of unprecedented development of
documents
RP 570 Piping Inspection Code:
RP 571 Damage Mechanisms Affecting Fixed Equipment
RP 572 Inspection of Pressure Vessels
RP 573 Inspection of Fired Boilers and Heaters
RP 574 Inspection Practices for Piping System Components
RP 575 Inspection of Atmospheric & L P Storage Tanks
RP 576 Inspection of Pressure-Relieving Devices
RP 577 Welding Inspection and Metallurgy
RP 578 Material Verification Program
Std 579-1/ASME FFS-1 Fitness-For-Service
RP 580 & 581 Risk-Based Inspection

31. Effect on Codes and Standards
ASME data on Brittle Fracture and Low
temperature
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 Std
Appendix Q and R related to Low Temperature

32. Considerations for Existing Equipment
The brittle fracture resistance of the material of construction
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 for Brittle Fracture
•Variables
• Material Type
• Thickness
• Stress
• Applied Stress
• Known flaws
• Credit for PWHT
• Temperature -Limit Exposure

33. Assessment Considerations
Three Levels of Assessment
Level 1 Can be satisfied based on:
• Impact test results or impact test exemptions curves
from the code
• Accomplished by a scrutiny of existing equipment
data
• Comparing the CET (critical exposure temperature) to
the MAT (minimum allowable temperature).
The methodology of RP 579 is quite thorough in the
guidelines provided for determining the CET and the MAT.
Equipment that has a CET equal to or greater than the MAT
are exempt from further brittle fracture assessment unless
conditions change.
.

34. Assessment Considerations
A good Management of Change program should be in place
to trigger an action item should changes occur that might
affect the CET.
One level 1 assessment of a plant resulted in 15% of the
equipment being exempt from further assessment.
.

35. Assessment Considerations
Level 2 assessment takes into consideration:
• Operating pressure/temperature envelope
• Compared to the component design stress and MAT.
Adjustments are permitted to the MAT providing proper
impact test documentation is present.
Credit is also given for fabrication conditions such as PWHT
(post weld heat treatment).

36. Assessment Considerations
Level 2 assessment (cont’d):
When determining the stress conditions, consideration is
given to:
• Excess material above the required minimum
thickness
• The effect of joint efficiency
• Wall thickness
In the aforementioned assessment, 51% of the equipment
met the required criteria after a level 1 and level 2
assessment..

37. Assessment Considerations
Level 3 Assessment
Normally involves more detailed determinations of one or
more of the three factors that control the susceptibility to
brittle fracture:
• stress
• flaw size
• material toughness.
Many factors affect the outcome.
Significant amounts of inspection data may be available and
other problems may be on record that must be considered in
the brittle fracture assessment.
Example--Equipment that was in amine service --possibly
susceptible to cracking or blistering.
Many parts of RP 579 specifically address many of these
issues and can be effectively utilized to enhance the brittle
fracture assessment.

38. Assessment Considerations
There are many ways to present the results of the brittle
fracture assessments.
A very effective way is to provide a graph of each
component showing the minimum allowable temperature 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 the equipment.

39. Nature of Brittle Fracture & Assessment
•Most variables are not exact
•Stress levels are based on overall stress
• No accountability for stress concentrations such as
residual stress in welds, stress at connections
• Concentrated stresses act as crack initiators that
cannot be arrested
•Hydrotest in ductile range can blunt cracks and flaws to
resist BF
•All three components must be present at the same time
• Susceptibility- Cannot be changed
• Stress – Must be controlled
• Temperature—be aware of sources of low
temperature

40. Sources of Low Temperature
•Weather--can’t be controlled; must provide protection
• False sense of security in warm parts of the
country.
•Process related situations
• Autorefrigeration due to Relief Valve
• Relief valve open- Cool down below CET
• Relief valve close- repressurization while cold.
• Depressurization for other reasons
• Mixed phase flow- cooling of piping from Vessel
stream
• Cold start-up or repressurization procedures must be
considered
• Shock chilling

41. Summary
•Older equipment is more likely to be susceptible.
•Failure is usually catastrophic with no warning
•Stress and Temperature are only controllable factors
•Stress from applied pressure or flaws
•Fabrication Practices
•Temperature from weather
•Low temperature sources can come from process even in
warm weather
•Codes and Recommend Practices provide Guidance
• Continually being revised

42. Energy
Questions??
Verne Ragle, P.E.
Mechanical Integrity Consultant
Siemens Energy
Oil & Gas Division
Engineering Consulting Business Unit
4615 Southwest Freeway, Suite 900
Houston, TX 77027
Tel.: (281)-220-1701
Fax: (713)-570-1230
Mobile: (850) 398-7097
Email: verne.ragle@siemens.com
http://www.sea.siemens.com