Coating Failure Analysis An overview © KTA-Tator, Inc. 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 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 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 © KTA-Tator, Inc. 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 © KTA-Tator, Inc. Electrochemical Impedance Spectroscopy AC (alternating current) electricity to measure electrical resistance (impedance) Impedance used to assess coating integrity and to follow deterioration - Excellent Results of Laboratory Techniques Optical Microscopy 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