Transcript Unit 6 Coating Failure Case Histories

Coating Failure
Analysis
 An overview
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Coating Failure Consequences
 Damage to substrate
 Costly rework
 Downtime
 Product contamination
Coating Failure Consequences :
Damage to Substrate
 Substrate repair
 Substrate replacement
Pedestrian
Bridge
Coating Failure Consequences:
Costly Rework
 Condition of the existing system?
 Field repairing a shop applied system
Coating Failure
Consequences: Downtime
 Can cost more than the coating failure
Examples areas where corrosion has developed
and may be difficult to address.
5a– The surfaces above grating slots are below motor and lock pin assemblies.
5b– Grating strips and angle iron beneath sidewalk grating and curb.
5c– Corrosion above lift span girder below the steel curb over deck/sidewalk grating.
5d- Back to back angles of a counterweight.
5e– Rusted fasteners behind electric (latch pin) motor.
5f– Steel above a lift span girder -the underside of various steel elements deck surface.
SCRUB COLUMNS
Coating Failure Consequences:
Product Contamination
 Tanks, vessels, pipelines
 Product contact with disbonded coating
 Product contact with exposed substrate
Coating Failure Analysis
 Receiving the “telephone call”
(Background)
 Field Investigation
 Laboratory analysis
 Report and Recommendations
Background
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Location
Substrate
Age of Site and of Coating
Location,storage, or exposure of coating
Coating Specification
Coating Product Data Sheets
Coating Inspection
Background
 Substrate preparation
 Environmental conditions during coating
application
 Time reference between failure and
application of coatings
 Description of failure including any
noticeable patterns
Field Investigation
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View condition of the applied coatings
Investigate the nature of the failure
Dry film thickness of the coating
Field testing of coating; physical parameters
Condition of the substrate
Obtain samples from “failing” areas that are
representative of the failure
Field Investigation
 Obtain samples from “non-failing” areas that
are representative
 Note any patterns
Laboratory Techniques
for Coatings Failure
Analysis
Laboratory Testing
 Optical / Digital Microscopy
 Infrared Spectroscopy
 Gas Chromatography / Mass
Spectroscopy / Pyrolysis
 High Performance Liquid Chromatography
 SEM / EDS
 Atomic Absorption Spectroscopy
 Differential Scanning Calorimetry
 Electrochemical Impedance Spectroscopy
Optical / Digital Microscopy
 Visual examination of coating samples
 20X to 1000X magnification
 Inexpensive, rapid gathering of information
 May change the course of a failure analysis
Cross-section Diamond Blade
50X
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Cross-section at Edge/Corner
Tank lining –cross-section
Coating Thickness
Fourier Transform Infrared
Spectroscopy (the IR)
 Produces a fingerprint of an individual paint
 Can determine if the paint specified was the
one actually applied
How an IR Works
 A spectrometer passes infrared light through
a coating sample
 Molecules absorb light at different rates
 An IR produces a spectrum
 Each coating type has its own spectrum
Amine Cured Epoxy Coating
Gas Chromatography
 Detects the presence of solvents trapped in a
coating
 Gas Chromatography works on the principle
of attraction
 Each solvent eludes (comes out) at a
different rate
Solvent Entrapment
 Entrapped solvents can cause serious
problems
 Solvent entrapment can be detected years
after application
Pyrolysis / Gas Chromatography /
Mass Spectroscopy
 Pyrolysis- allows for vaporization of a solid
sample
 Mass Spectroscopy- allows universal
identification of separated components
 Review-Gas Chromatography- allows for
separation of components within a mixture
High Performance Liquid
Chromatography (HPLC)
 Wide range of testing
 Employs a liquid, rather than a gas, to carry
a sample through the testing columns
 HPLC includes:
 Ion chromatography
 Gel permeation chromatography
Ion Chromatography
 Six salts can be identified through a single test
1. Chloride
4. Nitrite
2. Phosphate
5. Nitrate
3. Sulfate
6. Bromide
Gel Permeation
Chromatography
 Looking for problems within a resin system
 Allows separation of coating components by
molecular weight
SEM/EDS
 Uses magnification up to 5000X and beyond,
if necessary
 Examines defects in the coating surface
 Compares failing and non-failing areas
 Provides Elemental Information
SEM – EDS of Zinc Layer - Elemental Analysis of Filler
 filler
consisted
elementally
of calcium
and
silicon……
most likely
calcium
silicate
Differential Scanning
Calorimetry
 Used to determine if a product has
properly cured
 Useful for product with high mix ratios
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Electrochemical Impedance
Spectroscopy
 AC (alternating current) electricity to measure
electrical resistance (impedance)
 Impedance used to assess coating integrity
and to follow deterioration
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Excellent
Results of Laboratory
Techniques
 Optical Microscopy
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Starting point /Observation/ Determine
path of investigation
Infrared spectroscopy Resin types/mix ratios
Gas chromatography Solvent identification
Ion chromatography
Salt identification
GPC
Separation / formulation discrepancy
SEM/EDS
High magnification / elemental analysis
AA spectroscopy
Toxic Metals/ Environmental issues
DSC
Degree of cure
EIS
Barrier properties / track degradation