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Material Failures in Fire Protection Systems
March 4, 2014
University of Central Florida (UCF), Orlando, FL
Jeff Pfaendtner – Materials/Metallurgical Engineer Crane Engineering Inc., Plymouth, MN
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Forensic Engineering
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PROFESSIONAL DISCIPLINES • Mechanical Engineering • Metallurgical & Materials Eng. • Chemical Engineering • Electrical Engineering • Forensic Architecture • Structural Engineering • Fire Protection Engineering • Civil Engineering • Geotechnical Engineering
FORENSIC ENGINEERING & CONSULTING SERVICES • Fire and Explosion Investigation • Propane & Natural Gas Investigation • Materials & Process Engineering • Industrial Accident Investigation • Slip and Fall Investigations • Standards and Code Consulting • Building Science Investigations • Automotive System and Component Analysis • Accident Investigation and Crash Reconstruction
Introduction
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Failure Modes Relate to: • Design • Manufacture • Installation • Service Environment
– Water chemistry – Nominal Operating Temp & Temp extremes – Service & Maintenance – Age – Geographic location – etc.
A flaw becomes a defect when it prevents the part/system from functioning as designed.
Case Studies
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1. CPVC “Spider Lines” (M) 2. CPVC Environmental Stress Cracking (I&E) 3. CPVC Environmental Stress Cracking (I&E) 4. CPVC Other Incompatible Materials (I&E) 5. Sprinkler head: Crack in Frangible Bulb (M) 6. Sprinkler head: Casting defect (M) 7. Sprinkler head: Galvanic/Crevice Corrosion (D&M) 8. Steel pipe: Microbiologically Induced Corrosion (I&E) 9. Steel pipe: Pitting Corrosion (I&E) 10. Brass Fittings: Stress Corrosion Cracking (D, M, E) 11. Steel pipe: Light wall Pipe (D) 12. Freeze failures (I & E) 13. “Rube Goldberg” type failures (E)
Key: D – Design M – Manufacture I – Installation E – Environment
Case 1 - “Spider Lines” in PVC Pipes
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• Straight fracture observed in CPVC pipe after less than one year of service.
Scanning Electron Microscope (SEM) images of fracture
Case 1 - “Spider Lines” in PVC Pipes
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Outer Surface of Pipe
Fracture Surface
• Spider lines are “virtual cracks” in pipe • From manufacture process
Case 2 – CPVC & Glycol
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• Failure after 10 years in service.
• System was a “glycerin” filled system, but testing revealed the presence of glycol.
Environmental Stress Cracking (ESC) from residual glycol
Case 3 – CPVC & Alkane Oils
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• Wet system in condo building • Heated garage is Allied XL steel • Steel to CPVC transition (living space) • Water leaks in CPVC after ~3 years
Case 3 – CPVC & Alkane Oils
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• External view of CPVC pipe
• Through-thickness cracks
Case 3 – CPVC & Alkane Oils
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• Internal view of CPVC pipe • Multiple cracks developing on ID surface
Case 3 – CPVC & Alkane Oils
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• Internal view of CPVC pipe • Cracks developing around cement drip
Case 3 – CPVC & Alkane Oils
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Case 3 – CPVC & Alkane Oils
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Environmental Stress Cracking (ESC) from residual thread cutting oil
Summary: Environmental Stress Cracking
Environmental Stress Cracking (ESC) is a time dependent (slow) cracking mechanism
ESC has three main requirements: • Susceptible material (e.g., CPVC pipe) • Stress (either residual in the material, or applied stress) • Incompatible chemical species (certain oils, plasticizers,
glycols, etc.)
Failures are usually manifested as slow leaks, but sometimes as catastrophic breaks.
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Case 4 – Incompatible Materials
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• CPVC potable hot water line to irrigate trash chute in high rise condo.
• Pipe failure occurred after several years in service at location of contact with grommet.
Case 4 – Incompatible Materials
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• Plasticizer diffuse from one plastic into another • Pipe weakens & ruptures
Case 5 – Crack in Frangible Bulb
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• Sprinkler head deployed unexpectedly causing water damage.
• Purple staining observed on frame arms & body.
Case 5 – Crack in Frangible Bulb
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• Crack develops & propagates • Fluid leaks from bulb over time • Bulb breaks; water flows
Case 6 – Casting Defect in Sprinkler Head
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200°F Attic head
• Unexpected deployment of attic sprinkler head • Deformed load screw
Case 6 – Casting Defect in Sprinkler Head
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• SEM & X-ray imaging shows evidence of cracks in one frame arm
Case 6 – Casting Defect in Sprinkler Head
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• Difference in compliance between frame arms creates mechanical imbalance
• Frangible bulb “walks” off set screw w/ thermal cycling
Case 7 – Galvanic/Crevice Corrosion
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• Sprinkler head leaked after 3 years in service. • Water damage to condo.
Case 7 – Galvanic/Crevice Corrosion
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• Pinhole leak in Belleville spring (under seal) • Corrosion over months/years
Case 7 – Galvanic/Crevice Corrosion
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Area C O F Na Al Si S Cl Ca Ti Mn Fe Ni Cu Zn
A 3.65 2.06 0.38 0.43 93.47
B 9.68 23.53 0.62 0.78 0.48 1.50 0.32 0.30 0.78 8.01 48.98 2.17 2.83
C 7.75 42.56 0.18 1.07 0.44 0.16 0.18 0.38 42.52 3.27 1.49
D 9.55 29.86 1.46 0.21 0.47 11.00 0.48 20.54 0.96 2.16 18.71 1.72 2.88
E 7.19 50.96 0.54 0.88 1.37 0.58 11.70 0.24 8.68 14.11 0.75 3.00
• Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS)
Case 8 – Microbiologically Induced Corrosion (MIC)
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• “Dry” system developed pinhole leaks 5 years after installation. • Tubercles observed on pipe ID. • Water supply not “corrosive”.
• High levels of aerobic bacteria, low nutrient bacteria, and acid producing bacteria found
Case 9 – Pitting Corrosion
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• A wet system developed pinhole leaks after 25 years. • Water testing showed high levels of dissolved oxygen,
high hardness, and high levels of dissolved solids. • Bacterial cultures showed low or undetectable levels
of bacteria
Case 10 – Stress Corrosion Cracking (SCC)
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• Catastrophic failure of brass hose valve • $1M+ water damage to large commercial
building
Case 10 – Stress Corrosion Cracking (SCC)
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• Catastrophic failure of brass hose valve • Multiple cracks
C37700 Forging Brass Copper: 58.0 – 62.0 wt.% Lead: 1.5 – 2.5 wt.% Iron: 0.3wt% max Other impurities: 0.5% max Zinc: Balance
Raw material costs: Copper: $3.32/lb. Zinc: $0.85/lb.
Case 10 – Stress Corrosion Cracking (SCC)
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• Brass alloy defective • Zinc too high; Iron impurity too high
Case 11 – Light wall Pipe
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• Leaking NPT joints in factory producing printed circuit boards
Case 11 – Light wall Pipe
0.5mm = 0.02 inch
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Case 11 – Light wall Pipe 2" Pipe
R2 = 0.8983
R2 = 0.6746
0
50
100
150
200
250
300
350
1 2 3 4 5
# wrench turns
To
rqu
e (
ft-l
b)
Schedule 40
2in. BLT
Linear (Schedule 40)
Linear (2in. BLT)
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Case 12 – Freeze Damage
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• Component failure due to volumetric expansion of freezing water (~9 vol%)
Case 12 – Freeze Damage
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• Freeze failures often yield multiple cracks
Case 12 – Freeze Damage
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• Freeze failures often yield multiple cracks
Case 12 – Freeze Damage
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• Freeze-up can induce large scale deformation
Case 12 – Freeze Damage
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• Freeze-up can induce large scale deformation
Case 13 – Special Environmental Effects
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• All materials have their own vulnerabilities, and therefore their own application issues.
• No component is immune to failure.
• A variety of failure modes are operable in fire protection systems.
• Failures can occur in all stages of life of the system.
• Failure prevention involves good system design, material choice, good installation & maintenance
taking local environments into account
Summary & Final Thoughts
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