CoatingsPro Magazine

MAR 2016

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 20 of 84

20 MARCH 2016 COATINGSPROMAG.COM Notes From the Blog Editor's Note: Looking for " in the feld " information about the latest coating appli- cation techniques? We invite you to join the discussion. Te following are excerpts from the NACE Corrosion Network's (NCN) and NACE Coatings Network's email-based discussion groups for corrosion profession- als, with more than 1,000 participants. Te following excerpts have been selected for their potential interest to CoatingsPro readers. Tey have been edited for clarity and length. Authors are kept anonymous for publication. Please be advised that the items are not peer-reviewed, and opinions and sug ges- tions are entirely those of the inquirers and respondents. CoatingsPro and NACE do not guarantee the accuracy of the technical solutions discussed. You' ll enjoy a variety of opinions in this practical information exchange forum. For information on how to subscribe to these free list servers, click on the "Community" link on the NACE Website: Coating system for carbon steel pipelines Q: We have three parallel crude oil carbon steel pipelines, 50 km (31.1 miles) in length, with no protective internal or external coating. Approximately 34 km (21.1 miles) of the pipe's length are partially to totally covered with sand because of frequent sandstorms. Te lines are heavily corroded. No cathodic protection (CP) is provided because the pipeline was installed as an above-ground structure without taking into consideration the sand accumulation during sandstorms that commonly occur in this Kuwait desert location. We are going to repair parts of the line with <4.9 mm (0.193 in.) wall thickness remaining, maintaining a minimum wall thickness of 5 mm (0.197 in.) and applying an external protective coating. We plan to do a very thorough blast cleaning (near white metal blast). Te frst coat is a solvent-borne inorganic zinc (IOZ) silicate primer, at 75 µm (3.0 mils) dry flm thickness (DFT). Te second coat is a high-build, polyam- ide-cured, two-component grey epoxy at 125 µm (4.9 mils) DFT. Te third coat is a two-component, high-solids, self-priming, aluminum-pigmented epoxy coating with good wetting properties at 125 µm (4.9 mils) DFT. We believe the painting system is suitable for an above-ground pipe instal- lation. We are concerned, however, that a few months after the coating has been applied, sand will again accumulate, cover the pipelines, and initiate corrosion. We need a good recommendation on the painting system suitable to protect our pipelines that will be in contact with sand when it accumulates again after applying the coating. A: I can see several problems with your suggested coating system. W hile the IOZ and epoxy system would have good corrosion prevention proper- ties, there are two problems to consider. Can your applicator apply IOZ properly? In the predominantly hot climate of Kuwait, it will dry very quickly, and if applied too thickly, it will mud crack. Te cracking will not be a good substrate for the epoxy topcoat. Tere is a very good possibility of getting contamination between coats from blowing sand and chlorides in the atmosphere while waiting for each coat to cure before applying the next coat. Any contaminant of this nature can cause delamination or disbonding of the organic coating applied over it. Since your lines are heavily corroded, you will need a coating system that has good adhesion to heavily pitted metal that is blasted to SA 2.5 condition. Tere are several high-solids, abrasion-re- sistant epoxy coatings that can be applied in one coat to a DFT of 500 µm (19.7 mils), which should be enough to withstand both windblown sand and the expected immersion in sand dunes. A: I suggest you skip the zinc and go with a 100 percent solids, one-layer coating. I personally like the immersion-rated epoxy system for preventing corrosion for long periods, but it has the disadvantage of sufering ultraviolet (UV) degradation when the sand is not covering the pipeline. Te thick-flm urethane doesn't have this problem and does cure fast. I do know of one company that makes the epoxy product with UV resistance for large orders, and for smaller orders even makes a topcoat that is 100 percent solids and UV stabilized. Tis, of course, requires two coats. A: High-solids, high-build polyes- ter glass fake at 1 by 1,000 µm (0.04 by 39.4 mils) or 2 by 750 µm (0.08 by 29.5 mils) would be a good option in your case. Polyester glass fakes are quick-drying and have excellent abrasion resistance, good thermal expansion coefcient, minimal water absorption, and excellent immersion properties. A: To protect the pipe when it is covered with sand, you should use CP. Te sands in the Middle East, when wet, can be of low resistivity and high chloride content. Depending on resistivity, a galvanic anode system would probably work. Coating by itself does not adequately protect under- ground structures. CP Coating for Pipelines

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