1、SSPC-TU 11December 1, 20101SSPC: The Society for Protective CoatingsTECHNOLOGY UPDATE NO. 11Inspection of Fluorescent Coating Systems1. Scope Protective coating systems, when properly selected and applied, will protect the underlying substrate from corrosion and deterioration. Confirming that the co
2、ating has been applied correctly can require an extensive and lengthy inspection process. The use of fluorescent coatings in a coating system permits faster identification of holidays and areas with low film thickness. This technology update discusses the technique and the equipment required to insp
3、ect a coating system that incorporates fluorescent properties. 2. Description Fluorescent coatings, visually inspected with ultraviolet and/or violet light, assist in quickly identifying holidays and areas with low film thickness. They can be used as both primer and finish coats. This technology may
4、 also enable the inspector to detect incomplete removal of coatings. General information on ultraviolet and violet lamps and safety precautions for their use is also provided.3. Background on the Available Technology3.1 For many years, the marine industry has been trying to extend the life of vessel
5、 tanks. The failure of the coating system and subsequent failure of the underlying structure is a leading cause of ships being taken out of service. In the most extreme cases, failure of ballast tanks has caused vessels to break apart in high seas with loss of life. Fluorescent coatings were origina
6、lly developed for use in ballast tanks in large ocean-going vessels to assist in the inspection of applied coatings for holidays both during and after application. The proper use of this technology gives the ship owner further assurances that the coating system has been applied correctly and will pr
7、ovide the expected service life. The United States Navy took a leading part in the advancement of this technology when in 2003 it included ultraviolet fluorescence as a requirement for Type VII (solvent free) tank linings meeting MIL-PRF-23236.(1),1The same technology can be used for many other stru
8、ctures or pieces of equipment that are difficult to inspect. Virtually any type of coating can be made to fluoresce with the addition of fluorescent pigments or optically active additives. These addi-tives are similar to other colorants and optical effects additives in coatings. Depending on the app
9、lication, the fluorescent effect is available either as a fluorescent effects product line formulated by a coatings manufacturer, or as a concentrated colorant formulated for field addition to a coating. The coat-ings applicator should consult the coatings supplier, coatings specification and asset
10、owner to determine which products are appropriate for a specific project.3.2 Ultraviolet (UV) radiation is a part of the electromagnetic radiation spectrum just outside the visible range and adjacent to the violet color of the visible spectrum. The UV-A range is between 315 nanometers (nm) and 400 n
11、m. This is the typical UV range for fluorescent coating inspection. The UV-B range is between 280 nm and 315 nm. The UV-C range is between 180 nm and 280 nm. Visible light is generally considered to be between approximately 400 nm nanometers (nm) and 760 nm. In the visible spectrum, violet light is
12、in the range of 400 to 420 nm. This is the typical violet light range for fluorescent coating inspection (see Figure 1).(1)US Department of Defense Single Stock Point (DODSSP) for military standards may be accessed online at .Figure 1. Wavelength Chart. Wavelength (in nanometers) illustrating UV-A a
13、nd violet ranges used in fluorescent coating inspection and their relationship to the visible light spectrum.Visible LightSSPC-TU 11December 1, 201023.3 The intensity and color of fluorescence is related to the type and concentration of the fluorescent and other pigments used in the coating; the pow
14、er and wavelength of the inspection lamp; and the standoff distance. Under a suitable inspection lamp, pinhole defects can be visible at a distance of about 3 meters (10 ft), depending on ambient lighting conditions. The work area does not have to be blacked out to perform the inspection. The visual
15、 effect can be captured clearly on camera. 3.4 The addition of fluorescent pigments to a coating has no effect on the application method typically used for applying that coating. However, the applicators progress and application technique can be monitored by using a suitable inspection lamp. 4. Insp
16、ection Lamp Requirements4.1 Light wavelength must be selected to complement the optically active additive and may need to account for other light absorbing additives as well. The coating manufacturer should be consulted to select the light wavelength that best activates the fluorescent property of t
17、heir coatings. ASTM(2)E 25012and ASTM E 22973are example of industry standards that address specifying inspection lights.24.2 The most advantageous light intensity, throw distance and area illuminated depend on the size and type of the struc-ture being inspected.4.3 Environmental and safety consider
18、ations can impose requirements for mercury-free or explosion-proof lighting. Inspection lamps that use bulbs may contain mercury in both the bulb and the lamp ballast. 5. Training Requirements5.1 A coating inspector with previous training and experi-ence can use this technology with little additiona
19、l training. The inspector should follow the instructions supplied with the lamp, especially recommended safety practices. Ultraviolet or violet lamps may require the use of appropriate contrast enhance-ment/safety eyewear.5.2 Before inspecting fluorescing coatings for the first time, the inspector o
20、r inspection team and the coating suppliers representative should examine sample panels under the lamp (2)ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. Standards are available online at that will be used to perform the inspection to learn to recognize film defects. The
21、 coating supplier should have several panels prepared showing the following:Fluorescent coat on a flat panel with pinholes Fluorescent prime coat and nonfluorescent finish coat on a flat panel with pinholes in the finish coatFluorescent coat on a weld seam, with cracks in the coatingFluorescent prim
22、e coat and nonfluorescent finish coat on a weld seam, with cracks in the finish coatFluorescent prime coat and nonfluorescent stripe coat on an angleFluorescent coat applied below recommended dry film thickness (DFT)Fluorescent prime coat applied correctly with next coating applied below recommended
23、 DFT5.3 In rare cases, individuals with certain forms of color blindness cannot see the fluorescence emitted from certain optically active pigments. The contrast enhancement provided by the fluorescence is not seen by these individuals. This possi-bility should be assessed during the training and or
24、ientation session for each new coating system encountered.5.4 The inspection of fluorescent coatings with ultraviolet or violet lamps can speed up or enhance finding and interpreting many types of coating defects. Depending on the nature of the project and the types of defects encountered, it may be
25、 appropriate to emphasize to the coatings inspector that this process is not intended to replace other inspection methods like the use of white light or yellow lamps for visual inspec-tion, NACE RP-0811(3).4for holiday detection, or SSPC-PA 25for DFT readings.6. PPE Requirements6.1 Eye Protection: U
26、V radiation is that radiation just outside the visible range, or under 400 nanometers (nm). There are three ranges of UV (see Table 1).The UV-A lamps used in fluorescent inspection contain a significant amount of invisible radiant energy that can potentially cause eye and skin damage. UV blocking gl
27、asses should be worn when using UV-A lamps. Contrast-enhancement/glare-(3)NACE International, 1440 South Creek, Houston, TX 77084. Standards are available online at http:/www.nace.org.Region Range in nmHazard PotentialDamage Mechanism (High Exposure)UV-A 315-400 LowestPossible cataracts. Traditional
28、 “black lights” emit in the range of 340-390 nmUV-B 280-315 Mid to HighCataracts, skin or eye burns. Increased risk of some types of skin cancerUV-C 180-280 Highest Skin or eye burns.TABLE 1TYPES AND HAZARDS OF UV LIGHTSSPC-TU 11December 1, 20103reduction filters are appropriate for violet lamps. Th
29、e beam from the UV-A or violet lamp should never be directed into the eyes, and needless exposure of the skin should also be avoided. The lamp manufacturers written safety instructions should be strictly followed.The ASTM standard E 2297-044is a resource for Personal Protective Equipment (PPE) for U
30、V-A lamps. For guidance in specific situations for specific sources, ACGIH(4) publishes Threshold Limit Values (TLVs)6for exposure to UV and intense visible light that can be used to evaluate work exposure and PPE.Some LED light manufacturers include an IEC(4)624717 classification statement on the p
31、roduct or in the product tech-nical data sheets. This standard classifies the eye safety of a lamp source (including LED) device based on its wavelength and power. The statements provide guidance on what kind of eye protection (if any) is required when using the light. An “Exempt” lamp device is con
32、sidered “safe under reasonably foreseeable conditions of operation” in this standard. LED light products classified before 2006 may include an IEC 60825-18 classification statement on the product or in the product tech-nical data sheets. In this standard, a Class 1 LED device was considered “safe un
33、der reasonably foreseeable conditions of operation.”At the time of this writing there is no OSHA-mandated UV exposure limit in the workplace. This information may be found at the OSHA web address:6.2 Skin Protection: Limited exposure to UV-A radiation can cause redness (erythema) on normal skin. Suc
34、h redness is temporary and normally will not produce blistering. Inspectors and workers should be cautioned to be particularly cautious when taking medications that are photosensitizers and extra protection of the skin would be warranted.However, UV exposure is not immediately felt. The user may not
35、 realize a hazard until after the damage is done. It is best to wear gloves and a UV-resistant face shield during long term inspection processes.7. Post-Application Inspection 7.1 Visual Effect 1 Fluorescent coating over non-fluorescent substrate or coating: This scenario includes: fluorescent prime
36、r over steel; fluorescent stripe coat over non-fluorescent primer; fluorescent single coat systems, including multiple passes of the same coating.These are some of the effects an inspector may observe when the coating is illuminated by an ultraviolet or violet lamp:Black or dark spots seen under the
37、 beam of the lamp indicate holidays or undercoated areas. In some (4)International Electrotechnical Commission, 3, rue de Varemb, P.O. Box 131, CH -1211 Geneva 20 Switzerland. Standards are available online at cases, black dirt or grit has a similar look and could be misinterpreted as a holiday. Are
38、as of brighter than normal luminosity may indicate higher film thickness. Less bright areas may indicate lower film thickness.Areas where the coating is glowing white may indi- cate areas of paint detachment from the surface or hot-work damage.Organic dust and grit may show speckled bluish-white bri
39、ght spots under the light. Organic dust particles can come from rags, clothing, and protective fabric booties. In general, if the area under the lamp is not a uniform brightness, closer examination is required to determine the nature and cause of appearance.7.2 Visual Effect 2 Non-fluorescent coatin
40、g over fluorescent coating: This scenario includes: nonfluorescent topcoat over fluorescent primer; nonfluorescent stripe coat over fluorescent primer. The nonfluorescent coat has no fluorescent pigments and will not respond to the ultraviolet or violet lamp. These are some of the effects an inspect
41、or may observe when the coating is illuminated by an ultraviolet or violet lamp:Prime coat fluorescence is clearly seen through holidays, pinholes, and cracks in the topcoat (see Appendix A). Prime coating fluorescence may show through areas of thin film build in the second coat. Organic dust from r
42、ags, clothing, and protective fabric booties may show speckled bluish-white bright spots under ultraviolet or violet light. In some cases, this could be misinterpreted as a holiday.7.3 Visual Effect 3 Fluorescent coating of one color over a fluorescent coating with a different fluorescent color: Thi
43、s scenario includes:a three-coat system with a fluorescent primer and a fluorescent intermediate coat or fluorescent stripe coatThis type of coating system is uncommon. It is recom-mended that coating applicators and coating inspectors who encounter this type of system rely on application-specific t
44、raining with example panels per Section 5.Given the availability of different combinations of prime coats and topcoats, coating applicators may encounter a 2-coat system with contrasting colors under normal white light that have the same fluorescent emission color under ultraviolet or violet light.
45、These systems behave like a Visual Effect 1 system (see Section 7.1 above), not like the Visual Effect 3 system of this section. In this case, topcoat defects that are visible under white light can disappear under a UV-A or violet inspection light.SSPC-TU 11December 1, 201048. In-Process Application
46、 Inspection A fluorescent coating system can be used for in-process inspection if the applicator is supplied with a suitable lamp (explosion-proof or intrinsically safe). The fluorescent pigment is reactive in the wet film, so the applicator can easily observe and repair holidays while applying the
47、coating. This provides instant visual feedback to the operator and over time can improve worker skill by acting as a training aid.9. Preconstruction Primer RemovalIf a fluorescent primer has been incorporated into the preconstruction primer, the extent of removal of the primer can be determined by s
48、hining the ultraviolet or violet light on the surface. Any preconstruction primer remaining on the surface will be detected by the ultraviolet or violet lamp. If no fluores-cence is observed, it can be concluded that the preconstruction primer has been completely removed.10. Benefits of the Use of F
49、luorescent Primers in Coating InspectionThe use of fluorescent primers provides owners and inspectors with an additional inspection option to ensure high quality coating application to tank interiors. The main benefits of using this technology are listed below.10.1 Coating ApplicationReduces defects, re-work and job cycle time by repairing defects during application.Improves the quality of the workmanship by providing continuous instant feedback to the applicator.10.2 Newly Applied Coatings Inspection Improves coating defect detection by visu
