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March 25 - March 31, 2013

How do you properly coat welded joints?



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Selected Answers

From Lauren Fabian of ACT Test Panels LLC on May 28, 2013:
An option that may not have been considered yet is to use test panels. My company manufactures weld-bead panels and also L- Angle panels that can simulate the best way to coat the weld. By performing the various methods mentioned above on a panel, you could evaluate and determine the best way to do it without jeopardizing your project. Once you have established the particular way that works best for you, the panels can also be used to train others on how to properly coat the welded joint.

From Atanas Cholakov of ACT on May 25, 2013:
Welded joints shall be properly dressed prior to release for blast/paint. (Duty of the welding inspector). If the surface prep (abrasive blast) reveals problems, the welding inspector (construction manager) should be consulted. Brush-apply a stripe coat followed by spray application.

From Kees van Hooijdonk of van hooijdonk B.C.& I on April 7, 2013:
     The problem is that almost all specificatons require the weld joints surface preparation to be by power tool cleaning, ST3. The result is a very smooth surface that will lead to premature coating failure.

From Aldrin Cordovez of Kuwait Oil Company on April 6, 2013:
     Regardless of the type of weld and its radius, it is important that welds are free from porosity, sharp edges, and contamination. From my point of view, it is best to stripe coat by brush, with subsequent application by  air spray or airless spray.  The quality of the brush-applied stripe coating depends entirely to the skills of the applicator.

From Martin Neumann of Neumann Co. on April 5, 2013:
     While most agree that standard operating procedure should be to  stripe coat welds by brush before applying full coats, it depends on the coating to be applied as the primer, in my opinion. Some zinc-rich polyurethane primers dry much too quickly to be properly applied by brush, and when brushing is required, it leaves a surface that is not smooth. Applying the zinc-rich primer by spray over the weld and applying the next coat with striping is a proven technique based on our track record.

From James Albertoni of CA Department of Water Resources on April 4, 2013:
     I did mean radius, and it should have been > 1/16" radius. Sorry, I rushed my response.

From Per Gabrielsson of Free Lance Consultations and Inspections on April 3, 2013:
     Manual weld ripple should be ground only when it comes to sharp edges.Too much grinding may interfere with the strength of the welds. Weld spatter must be removed by grinding and not chipping. Manual welds should always be stripe-coated with good quality round brushes, working the coating well into the "valleys" of the ripple. This also enhances the mechanical adhesion of following coats. Flat brushes  give only a superficial coat and cannot  be properly worked into the ripple. Utmost care must be taken to remove the hard, black matrix around the manual welds. If power-tooled, those are impossible to remove properly. Abrasive blast to SSPC-SP10!

From Robert Cameron of Belzona Houston on April 1, 2013:
     For immersion service, all welds should be as per NACE SP0178-2007, Weld Preparation Designation Grade C, or better. For atmospheric service, I think the bases are covered already (below).

From Donald L Crusan of Marcellus Independent Technical Solutions on March 27, 2013:
     Did you perchance mean 1/16" radius James, to alleviate possible stress risers?

From Raymond Merrill of Texas Department of Transportation on March 26, 2013:
     1. Remove weld spatter. 2. Grind down welds. I'll leave it to the specification as to how much grinding the welds need. 3. Abrasive blast ground down welds to achieve a surface profile on them. This can be done at the same time as the rest of abrasive blasting is being done on the remaining structure. 4. Stripe coat the ground-down, blasted welds with primer, using a brush. 5. Apply full coat over the remainder of the structure.

From Peter Godfrey of cives steel on March 26, 2013:
     James, not sure why you would grind a weld to <1/16 in. (unless you are referring to excessive weld reinforcement). Kind of defeats putting the weld there in the first place. Also, after removing spatter, you should clean the weld with a thinner that evaporates (MEK, etc.). Then, as you said, brush the welds with paint and then spray what is required.

From James Albertoni of CA Department of Water Resources on March 25, 2013:
     All weld spatter should be removed, and welds should be ground down to < 1/16 inch. The weld should be stripe-coated with a brush. Then apply full coats as specified over the entire structure.

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