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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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200F 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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