CoatingsPro Magazine

NOV 2017

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50 NOVEMBER 2017 COATINGSPROMAG.COM materials, such as solvents • Often used to identify improper or contaminated thinners and solvents • The GC instrument is an oven containing a special column • More volatile compounds pass through the column more rapidly than less volatile compounds C. Ion Chromatography • Primary use in paint/coating failure analysis is to identify salts that may have led to failure • The instrument uses ion-exchange resins to identify the presence of ionic contaminants, such as chloride, sulfate, and phosphate D. Differential Scanning Calorimetry (DSC) • Used to thermally analyze paint/ coating samples • Little or no sample preparation is required • Instrument is basically an oven — heated sample properties are compared to sample at ambient temperature • Provides information concerning the sample's degree of cure and/or cross-link density E. Physical Properties Test Methods • Adhesion • Flexibility and impact resistance • Solvent resistance • Weathering resistance • Chemical resistance • Freeze-thaw levels • Application variations and tolerances 6. Examination of the Actual Protective Coatings Involved is step is usually performed in two distinct parts. First, the inspector reviews available data sheets and batch tickets supplied by the protec- tive coating manufacturer. Protective coating batches may consist of 100 to 500 gallons (378.5‒1,892.7 L) of material, depending upon the product being manufactured. Each batch will have documentation associated with it that will likely be reviewed. Second, the inspector will review results of the chemical analysis and physical testing of the failed protective coating with the chemical analysis and physical testing of properly formulated, mixed, and applied coating (from manufacturer batch retain samples). See Step 5 for physical tests that can be performed. Actual batch samples are typically retained by the protective coating manufacturers for two to five years. 7. Literature Survey e failure analyst should review avail- able technical literature to determine whether the protective coating failure being analyzed had been observed previously at the facility involved or at other facilities. is information may shed light on how and why the prema- ture coating failure occurred. 8. The Hypothesized Failure Mechanism If possible, the inspector will identify the failure mechanism(s) involved. If not possible, he or she will postulate a failure mechanism(s) based on the results of Steps 1 through 7. In both cases, the hypothesis should be vetted with an independent third party, if possible. is is not rocket science. e approach that I use is first to make a list of the steps to be performed in the surface preparation of the substrate and mixing/application/cure of the coating or lining as required by the project specifications, product data sheets, and referenced codes and standards. Next, I make a list of the steps that were actually performed during the work (this may not be based on documen- tation but on physical examination of the coating failure sites combined with interviews with involved person- nel). I then compare the two lists to identify discrepancies. After finding the discrepancies, I am then in a position to hypothesize the failure mechanism(s). 9. Reconstruction and Testing If possible and necessar y, the inspec- tor w ill prepare " bench batch(es)" using the formulation(s) of the actual coatings batch(es) involved in the failure and w ill recreate the failure to validate the failure hy pothesis. T his step is not always possible, usually because all variables connected w ith the failure may not be know n. A lso, some of the raw materials (particu- larly resins) used in formulation of the original protective coating may no longer be available. is step is normally only neces- sary if the results of the previous eight steps indicate that a component or multiple components of the actual batches of coating or lining materials may have been defective when they left the factory or were defective due to improper storage after formulation. Conclusion W hen performing protective coating failure analyses, keep in mind that the failure investigator's work w ill ty pically involve 90 percent logic and 10 percent science. If all parties involved in a coating or lining failure investigation (contractor, ow ner, coating / lining manufacturer) honestly and impartially follow the process that I have outlined in this article, the parties should come up w ith approximately the same conclusion(s) regarding the cause(s) of the failure. T his process should also allow the various parties involved in the failure to develop a technically acceptable and equitable resolution to the failure and w ill often preclude extended arguments and litigation. CP Jon R. Cavallo, PE, FASTM, is a reg istered professiona l eng ineer in t hree states and hold s a Bachelor of Science Deg ree f rom Nor t heaster n Eng ineer ing in Boston, Massachusetts. Act ive in many nat iona l technica l societ ies, inc lud ing SSPC, NACE , and A STM , Cava l lo received t he A STM Award of Mer it in 2010 and is an A STM Fel low. He has worked in t he coat ings and cor rosion mit igat ion f ield for 40 years. For more infor ma- t ion, contact: Jon R . Cava l lo, PE , FA STM , (603) 431-1919, jrc pe@aol.com Failure Analysis 101

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