CoatingsPro Magazine

MAR 2018

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 66 of 84

66 MARCH 2018 COATINGSPROMAG.COM for the best adhesion. A moderately flexible substrate with a 0.5 mil (12.7 microns) profile may not be adequate, especially in immersion service environ- ments, such as wastewater piping. A lthough we cannot determine whether or not the problem was due to inadequate surface prep or lack of system compatibility testing before over-coating, it is clear from our obser- vations that the new topcoating was failing prematurely. ere was insuffi- cient adhesion between the layers. Pipe Invert: The Bottom of the Wastewater Pipe Another failure area observed on this wastewater lining system was located on the pipe invert. e lining failure was total lining system delamination exposing the underlying metallic substrate, as shown in Photo 3. e invert is the very bottom of the pipe. (If you're walking in the pipe, the invert is underneath your feet.) We estimated in this case that the invert was about 1-foot (0.3 m) wide. We expected that this area would also see chemical attack as the concentration of the water decreases — and the chemical concentra- tion increases — due to evaporation into the air. Additionally, constant abrasion as the liquid and foreign material constantly slide across the invert area would be an in-service issue. e lining system could easily be worn away quicker in this area than, say, the overhead area (aka crown) of the piping. Maintenance Options Based on all the modes of failure seen in this wastewater and storm water piping and the 30+-year service life of the original lining system, removal and replacement was determined to be the best possible option. Abrasive blast cleaning using NACE No. 2/Society for Protective Coatings (SSPC) Surface Preparation (SP) 10: Near-White Blast Cleaning would be the preferred method of surface prepa- ration in this wastewater piping. is would help to achieve the first in the three legs of a successful coating system. Secondly, we recommended that the internal lining system chosen should be suitable for the chemical exposure, cyclic immersion, and sliding and impact abrasive service found in the wastewater system. irdly, as this wastewater and storm pipe was located in New York, road salt would have been used and carried into the pipe. Chloride testing and remediation before any new lining was suggested. e chloride level should be below 7 mg/cm 2 (45.2 mg/in.²) and should meet the coating manufacturer's requirements. Finally, application of the lining system along with stripe coating (in corners and sharp edges, such as the welded pipe connectors) would increase the chances of success for a new lining system's service life. Key Takeaways A lthough this article highlights a couple of types of coating failures that have happened in wastewater piping, it's worth noting that lining failures can happen in any industry. To avoid a premature coating failure such as this one, it would be wise not only to choose the right system but also to be sure to apply it properly. A lthough using support pieces over seams may be accepted in industry as a solution, the specific use of the pipe needs to be considered. In this case, employing an alternative seam solution, such as stripe coating, would have been more effective. Additionally, proper application methods should be taught and used on the jobsite. Even when applying an additional coating to a system already in place, it is crucial to employ the proper surface preparations to ensure proper adhesion. With the proper knowledge and tools, this problem can be avoided in the future. Proper coating and lining system selection, proper specification devel- opment, proper surface profile, and proper application of the coating and lining system are essential to achieve expected system performance with a well-predicted coating and lining service life. CP Adam Beers is a business manager of t he Consu lt ing and Eng ineer ing Ser v ices Depar t ment for K TA . A NACE Coat ings Inspector CIP Level 2 and an SSPC Cer t if ied Protect ive Coat ings Specia l ist, Beers lead s a staf f of e x per ienced techni- ca l consu ltants and ot her coat ings professiona ls who can assist on coat ings fa i lures, submitta l rev iews, coat ing cond it ion assessments, specif ica- t ion w r it ing , and ma intenance pa int ing pr ior it y planning. For more infor mat ion, contact: K TA , (412) 788-1300, w w Pipe Lining Failure Photo 3. The pipe invert showed a total lining system delamination, exposing the 1-foot (0.3 m) wide underlying metallic substrate.

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