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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8 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 Continued on page 10 THE BLOG EDITORIAL D I R E C TO R, CO N T E N T D E V E LO P M E N T/ Gretchen A. Jacobson MA N AG I N G E D I TO R T E C H N I C A L E D I TO R John H. Fitzgerald III, FN AC E T E C H N I C A L E D I TO R Norman J. Moriber, Mears Group, Inc. A S S O C I AT E E D I TO R Kathy Riggs Larsen CO N T R I B U TO R Husna Miskinyar GRAPHICS E L E C T R O N I C P U B L I S H I N G Teri J. Gilley CO O R D I N ATO R G R A P H I C S D E S I G N E R Michele S. Jennings ADMINISTRATION C H I E F E X E C U T I V E O F F I C E R Rober t (Bob) H. Chalker G R O U P P U B L I S H E R William (Bill) Wageneck ADVERTISING S A L E S MA N AG E R Diane Gross diane.gross@nace.org, +1 281-228-6446 A S S I S TA N T S A L E S MA N AG E R Teresa Wright t.wright@nace.org, +1 281-228-6472 ACCO U N T E X E C U T I V E S Erica R. Cor tina erica.cor tina@nace.org, +1 281-228-6473 Brian Daley brian.daley@nace.org, +1 281-228-6455 Pam Golias pam.golias@nace.org, +1 281-228-6456 Jody Lovsness jody.lovsness@nace.org, +1 281-228-6257 Leslie Whiteman leslie.whiteman@nace.org, +1 281-228-6248 A DV E RT I S I N G/B O O K S Brenda Nitz CO O R D I N ATO R brenda.nitz@nace.org, +1 281-228-6219 R E G I O N A L A DV E RT I S I N G S A L E S The Kingwill Co. R E P R E S E N TAT I V E S Chicago/Cleveland/ New York Area– jim@kingwillco.com, +1 847-537-9196 NACE International Contact Information Tel: +1 281-228-6200 Fax: +1 281-228-6300 E-mail: Firstser vice@nace.org Web site: w w w.nace.org EDITORIAL ADVISORY BOARD John P. Broomfield, FNACE Broomfield Consultants Raul A. Castillo Consultant Ir vin Cotton Ar thur Freedman Associates, Inc. Ar thur J. Freedman Ar thur Freedman Associates, Inc. David D. He PG&E Orin Hollander Holland Technologies W. Brian Holtsbaum Corsult Associates (1980), Ltd. Russ Kane iCorrosion, LLC Ernest Klechka CITGO Petroleum Corp. Kur t Lawson Mears Group, Inc. Lee Machemer Jonas, Inc. John S. Smar t III John Smar t Consulting Engineer L.D. "Lou" Vincent L.D. "Lou" Vincent PhD LLC NACE INTERNATIONAL: VOL. 53, NO. 11 The following are excerpts f rom the NACE International Corrosion Net work (NCN) and NACE Coatings Net work . These are e-mail-based discussion g roups for corro- sion professionals , with more than 3 ,000 participants . The excerpts are selected for their potential interest to a large number of NACE members . They are edited for clarit y and leng th . Authors are kept anony mous for publication . Please be advised that the items are not peer-reviewed , and opinions and sug gestions are entirely those of the inquirers and respondents . NACE does not g uarantee the accuracy of the techni- cal solutions discussed . MP welcomes additional responses to these items . They may be edited for clarit y. For information on how to subscribe to these f ree list ser vers , click on the "Corrosion Central " link and then "Online Corrosion Communit y List Ser vers" on the NACE Web site: www.nace .org. Galvanic corrosion and inhibitors in fresh cooling water heat exchangers Q: Would one expect signif icant galvanic corrosion between carbon steel (CS) and Ty pe 316L stainless steel (SS) (UNS S31603) in a treated, fresh- water recirculated cooling water heat exchanger? With a bundle of Ty pe 316L SS tubes and bare CS tube sheet, would the CS be subject to serious galvanic corro- sion? Are there guidelines or rules of thumb for controlling galvanic corrosion in freshwater systems? A: From my experience with several such couples, galvanic corrosion is very possible, even in a wet atmosphere (e.g., humidity). A: If you are concerned about inter- nal corrosion where parts are in intimate contact with the recirculating cooling water, it will depend on the water treatment regime being used. Your water treatment organization should overcome any likely problems. With proper manage- ment there should be no problems. With poor management there will be! A: One would expect a signifcant galvanic efect under these condi- tions. Steel is a fairly good cathode for oxygen reduction, and the potential diference between Ty pe 316L SS and low CS is ~600 to 800 mV depending on water chemistry, temperature, and fow. I would expect severe corrosion at the tube-to- tube sheet junction, mostly in the crevice formed at the roll into the tube sheet. If a good inhibitor program is in use, like the stabilized phosphate treatments that promote a thin passivating f ilm of ferric phosphate (FePO 4 ) or (as some claim) ferric oxide (Fe 2 O 3 ), then the galvanic effect might be attenuated signif icantly. A: Probably, yes. Recirculating indicates a potential buildup of solids in the water. Is there a CS bonnet also associated with the CS tube sheet? Te ratio of anode to cathode may be in your favor. One could always coat the CS and add anodes to the water box. A: Recirculation, especially open recirculation, would add to problems as it increases the dissolved oxygen (DO) content. Coupled with high fow rates as are expected in a heat exchanger, this enhances the corrosion behavior of cooling waters from fresh water to nearly the same as seawater. A: I agree with the other responses. My experience on the Texas Gulf Coast years ago showed a severe galvanic efect of Ty pe 300 series austenitic SS in open recirculated cooling water systems. Te potential diference essentially is the same as for seawater and the corrosion of steel is dependent upon the cathode-to- anode ratio. Even the chromate/ poly phosphate treatments permitted then, although efective on corrosion of steel alone, could not surmount the galvanic corrosion. Tip: Do not coat the steel without also coating the internal diameter of the SS tubes for at least four to six tube diame- ters. Otherwise, because the galvanic current is determined by the area of the cathode, you will simply focus the same amount of galvanic current f low on "holidays" in the coating. A: Tere are several heat exchangers in ammonia (NH 3 )/urea plants in India with Ty pe 304 SS (UNS S30400) tubes and CS shell, channel, etc. with circulating cooling water on the shell side

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