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October 29 - November 4, 2012

Is it cost-effective to grind steel edges before coating for atmospheric service? Why or why not?



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Selected Answers

From Katheravan Arumugam of Lion Offshore on November 26, 2012:
     Grinding of edges should specified in the steel construction specification instead of paint specification. It is a very labor- intensive exercise which should not be the responsibility of the blasting and painting team. Blaster s are trained to blast and so are spray painters trained to spray. Grinding of edges should be under the skills of steel work and not painting. There are a lot of disputes when it comes to this, who will be responsible to do it.

From James Albertoni of CA Department of Water Resources on October 29, 2012:
     In atmospheric service, I think the grinding of edges is more of an aesthetics issue. Grinding the edges will certainly give you a longer lasting coating; however, in a mild atmosphere, the ensuing corrosion will likely not be significant, but will likely be an eye-sore.

From terry wolfe of v&s on November 7, 2012:
     What that cost must be to use zinc-rich primers, inorganic zinc silicates, and also the grinding to protect from coating "shrinkage". The cost to hot dip galvanize the steel and coat with a epoxy/urethane surface would be minimal. No grinding, better edge protection, and documented longer corrosion protection for the steel.

From trevor neale of TF Warren Group on October 29, 2012:
     Absolutely essential in order to meet any expectations for exterior durability, therefore making it cost effective. Simple reason: coatings shrink as they cure, resulting in low or zero coating thickness over sharp edges.

From Atanas Cholakov of ACT on January 29, 2013:
     Steel edges should be rounded (2mm) for any coating in any environment. If the spec doesn't say anything about that, it is contractor's duty to clarify that in the pre-job conference. Organic coatings shrink as they dry and will pull from sharp edges. Stripe coat is essential on edges, welds, etc.

From Vyacheslav Volosiuk of Polymerprotection Ltd. on November 3, 2012:
Grinding of the corners in the shop, for the purpose of improving the surfaces for coating coverage and ultimately corrosion protection, is unnecessary when employing ethyl silicate inorganic zinc-rich primer systems. See "The Same Old Grind...An Investigation of Zinc-Rich Primer Performance Over Steel Corners" By William D. Corbett BRIDGE CROSSINGS No. 17, June 2000 National Steel Bridge Alliance 1405 Lilac Drive North, Suite 212 Golden Valley, MN 55422-4528 ph: 612/591/9099 • fax: 612/591/9499

From robert turner of Newport News Shipbuilding on November 6, 2012:
The question is "Is it cost-effective?" The answer is that it depends. How long is the structure required to last? What kind of environment is it in? What are the specification requiremtents? How many edges? If the stucture is only required to be in service for a short term, say 10 years, then probably no. If the answer is long term, say 50 years, like an aircraft carrier, then possibly yes. The environment also plays a role. Is it an immersion service application? Is it in a highly corrosive environment? There are lots of factors that need to be evaluated. And there are also innovative solutions, such as cathodic protection systems and higer solids coatings that do not shrink as much.

From Per Gabrielsson of Free Lance Consultations and Inspections on November 5, 2012:
Presently yards do not grind external steel edges. It's then all up to the owner to specify an edge grinding, with radius min. 2 mm in their contract specification. Also paint makers should emphasize the necessity of feathering sharp steel edges, but the question remains; will they do that!? Anyhow, they are supposed to be the specialists, but will they take the risk of displeasing the yards? Competition!

From david cuthbertson of savcor on October 31, 2012:
I would agree with grinding, but who will bear the additional cost of this engineering? Should it be the responsibility of the coating firm to make good? Or that of the steel manufacturer? If it were my project, I would expect that any modifications to make good on my part would be cost plus.

From Arnold McElroy of mcelroyarnold@yahoo.com on October 28, 2012:
     Yes, the coating becomes a longer lasting barrier.

From Vyacheslav Volosiuk of Polymerprotection Ltd. on November 4, 2012:
Absolutely inessential that edges are radiused if you use waterborne inorganic zinc silicates. They provide superior undercutting corrosion performance both at scribes and sharp edges.

From Donald L Crusan of Marcellus Independent Technical Solutions on January 29, 2013:
     Yes, it is cost-effective, as this is a metallurgical/mechanical integrity issue. Proper grinding relieves stress risers and the often found indications in fabrications that result in premature coating failure.

From Simon Hope of Bilfinger Salamis on November 1, 2012:
     Absolutely essential that edges are radiused!! European standards require a minimum radius of 2 or 3mm depending. Sharp edges allow coatings to pull back due to the effects of surface tension leading to severely compromised film thickness. This is a classic coating failure ,and there have been a string of well documented, high profile cases of massive failure due to the lack of, or incorrectly done, fettling along with improper coating application.

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Tagged categories: Edges; Surface preparation


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