Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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11 NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS PERFORMANCE JUNE 2016 Continued on page 13 (DFT). Ten ask your client to specif y the critical areas where a thickness of 300 µm must not be exceeded, and ask him to compromise every where else based on the powder manufacturer's maximum DFT recommendations. A: What is the item being coated with FBE? Is it pipe or other irreg- ular shapes such as bends? What is the application method? Is it mechanized/ automatic (e.g., on line pipe), or hand- fock sprayed such as bends? You haven't advised what statistical spread of DFT readings is >300 µm. Has the applicator conducted tests to demon- strate that the properties of the FBE in the 300 µm+ areas are the same as those areas that comply with the specif ication? 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 considered by the applicator before a conclusion can be drawn. A: For most applications, a maxi- mum of 300 µm is too strict. Te only downside to having FBE too thick is that it is more susceptible to cracking. In my experience in North America with the leading powder manufacturers, FBE up to 500 µm can meet bending of 2.5 °/PD at –30 °C. Many specifcations here even allow more than 500 µm, but pipe with that thickness must be labeled "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 will be encased in concrete for bridge decks. In my experience, 250 to 300 µm is a ty pical range when complying with coating specifcations designed for this purpose. Te tight tolerance is achievable (still not easy) using automated applica- tion equipment. Te upper thickness limi- tation is important in this instance in order to pass "pull-out" test requirements (pulling coated rebar out of cured con- crete samples). It is fairly common practice to " borrow" parts of a specif ication (such as acceptable DFT range) and apply them to another specif ication when the coating ty pe and substrate are the same. This may explain why you have come across such a tight acceptable DFT range. That said, I agree with other commenters in that you check with the manufacturer for maximum DFT allowances and then discuss your f indings with your customer. Mentors Make a Difference Find a mentor. Be a mentor. nace.org/BeAMentor

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