CoatingsPro Magazine

MAY 2016

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22 MAY 2016 COATINGSPROMAG.COM Recommended Thickness of FBE Coating Q: I have a client who requires the thickness of a fusion-bonded epoxy (FBE) coating to be minimum 250 µm (9.8 mils) and maximum 300 µm (11.8 mils). If I apply more than a 300 µm (11.8 mils) thickness, what would the efect be? A: We apply FBE on a daily basis. FBE applied to 250 µm (9.8 mils) is a single layer coating process applied on preheated surfaces. Based on my experience, application of FBE up to 700–800 µm (27.6–31.5 mils) has little to no noticeable efects other than powder consumption (depending on your specifc application). Tat said, I recommend you contact the powder manufacturer for consult for his recom- mendations for maximum allowable dry flm thickness (DFT). Ten ask your client to specify the critical areas where a thickness of 300 µm (11.8 mils) must not be exceeded, and ask him to compromise everywhere else based on the powder manufacturer's maximum DFT recommendations. A: W hat is the item being applied with FBE? Is it pipe or other irregular shapes, such as bends? W hat is the application method? Mechanized/automatic (e.g., on line pipe), or hand-fock sprayed, such as bends? You haven't advised what statis- tical spread of DFT readings is greater than 300 µm (11.8 mils). Has the appli- cator conducted tests to demonstrate that the properties of the FBE in the 300 µm+ (11.8+ mils) areas are the same as those areas that comply with the specifcation? Apart from wasting FBE powder material and adding to the cost for your supplier, does the excess DFT really matter? A ll these things must be consid- ered by the applicator before a conclusion can be drawn. A: For most applications, a maximum of 300 µm (11.8 mils) is too strict. Te only downside to having FBE too thick is that it is more susceptible to cracking. In my experi- ence in North America with the leading powder manufacturers, FBE up to 500 µm (19.7 mils) can meet bending of 2.5 °/PD at -30° C (-22° F). Many specif- cations here even allow more than 500 µm (19.7 mils), but pipe with that thick- ness must be labelled "do not bend " so that they are not cold bent in the feld. If the FBE is not going on a pipe, but some ftting, I don't really see a maximum other than what can be cured according to the manufacturer. A: I just wanted to add that FBE is often used over reinforcing steel that w ill be encased in concrete for bridge decks. In my experience, 250 to 300 µm (9.8 –11.8 mils) is a ty pical range when comply ing w ith coating specifications designed for this pur pose. T he tight tolerance is achievable (still not easy) using automated application equipment. T he upper thickness limitation is important in this instance in order to pass "pull-out" test requirements (pulling coated rebar out of cured concrete samples). It is fairly common practice to " bor row" par ts of a specif ication (such as acceptable DFT range) and apply them to another specif ication when the coating t y pe and substrate are the same. Tis may explain why you have come across such a tight acceptable DFT range. Tat said, I agree with other commenters in that you check with the manufacturer for maximum DFT allow- ances and then discuss your fndings with your customer. Difference Between Painting and Coating Q: W hat is the diference between painting and coating? A: Tere are lots of diferent ways to look at this. Te terms are often used interchangeably, but some people attach specifc meanings. "Painting" is the most generic, but some people refer to it specifcally for decorative uses. Many people use painting to ®The DOW Diamond Logo is a trademark of The Dow Chemical Company © 2016 Learn how we can tailor a solution for even the most aggressive conditions. dowpolyurethanes.com Protect Your Assets for the Long Haul Extending the life of your pipes, tanks, reservoirs and other infrastructure will pay big dividends down the road. From fexible elastomers to high-hardness, chemically resistant coatings, our polyurethane solutions can be applied to concrete, steel or other substrates to provide durable, long-lasting protection that pays. Wr i te in Re ad e r In q u ir y #352

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