Materials Performance

NOV 2014

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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Page 12 of 92

10 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 Continued f rom page 8 YOU KNOW IT WHEN YOU SEE IT NO FLASH RUST = A CLEAN SURFACE HoldTight®102 is the standard of performance for preventing f ash rust. ◗ NO SALT. Removes all contaminants ◗ NO RUST. Leaves a rust-free surface for 48 hours or more—often 3 to 5 days ◗ NO DETECTABLE RESIDUE. There is nothing left on the surface that might interfere with your coating. Among rust preventers and salt removers, HoldTight®102 is the most widely used, reliable, time-proven, lab- tested, f eld-tested, recommended and approved by coating companies. Call, email or visit our website today to see why HoldTight®102 is the best option for lowcost, easy-to-achieve, and easy-to-measure contaminant-free surface preparation. Contact us today! International +1 713 266 9339 1 800 319 8802 (Toll Free in N. America) THE BLOG or channel side. Tey have poly phosphate treatment and circulation ratios of 5 to 6. I have not come across any case of galvanic corrosion. Tere are a few cases of chloride stress corrosion cracking where chlorides were >200 ppm and temperatures were >60 °C. Caustic gouging of boiler tubes Q: I am investigating a failure of a boiler tube that shows clear signs of being a victim of "caustic gouging." The boiler feedwater is treated with a coordinated phosphate program. Is it possible to develop a localized concentration of caustic high enough to cause corrosion of carbon steel (CS) in water treated with a coordinated phosphate program? I thought that coordinated phosphate programs were developed specif ically to eliminate this problem. A: Caustic gouging can occur whenever the sodium-to- phosphate molar ratio exceeds 3:1 in boiler water, or under a deposit resulting from incongruent hideout. Since the concentration factors can easily exceed 10,000:1 under a deposit in a boiler, even low ppm levels of free caustic (sodium in excess of the 3:1 molar ratio) can result in pH levels of 12 to 16 under the deposit. Even a well-run coordinated phosphate program can experience such problems if hideout is occurring, or if impurities in the boiler water mask the true ratio, leading the operator to wrongly conclude a proper ratio from the available data. It also is possible that the caustic gouging was incorrectly diagnosed, and the failure was caused by acid attack. The situation can arise from the same set of problems noted above. Use of threaded fittings on hydrogen pipeline Q: I am getting conf licting view points on the use of threaded f ittings such as for electrical resistance corrosion probes on a pipeline in hydrogen service. Some indicate that there are no reasons to exclude threaded f ittings. Others indicate that threaded f ittings are not used on hydrogen lines but do not provide reasons as to why not or whether there is a specif ic concern. My application will be hydrogen between 80 and 100 °F (28 and 39 °C) and "dry." A: Hydrogen is a very small molecule and it would be very difcult to keep a threaded ftting from leaking. Because of hydrogen fammability limits, any leaking hydrogen would be very dangerous. Furthermore, a hydrogen fame is difcult to see, especially outdoors in bright light, making leak detection both hazardous and difcult to detect.

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