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April 22 - April 26, 2019

How do you properly coat welded joints?

Selected Answers

From Ron Berry of NZ Corrosion Services Ltd on May 23, 2019:
Blast and paint the same spec as the pipe.  If dust and debris are an issue, the bristle blaster is a great option but is slower than conventional blasting.

From Per Gabrielsson of Free Lance Consultations and Inspections on April 29, 2019:
I thought the question was just concerning painting and not surface preparation.  Free blasting in tanks after erection cannot be done due to ricocheting and dust formation. If blasting in tanks is specified, a blasting media surrounded by polyurethane foam can be used very easily. The slight dusting and ricocheting when blasted at angle may easily be stopped by using plastic sheeting around the areas to be blasted. The Bristle Blaster is a very good device, but cannot reach the really corrosive points in corners and in scallops, as well as sniped flatbars. Special care needs to be given to remove the black, hard deposit from high current welding of erection joints. Disking cannot remove this material properly.

From Derek Gerard Rodrigues of Flakecoat Technology pte Ltd on April 24, 2019:
Use a bristle blaster to prepare welded seams to achieve a minimum SSPC-SP 10 with a surface profile of a minimum 70 microns. Apply a suitable high quality coating system. The key is the surface preparation with the bristle blaster industrial.

From Sasha A. Bacic of None on April 22, 2019:
The welds should be checked and all welding defects repaired prior to any surface preparation and coating. Depending on where the welds are located, the surface preparation should be doneas follws: for immersed areas, fresh water washing followed by abrasive blasting to at least Sa2 1/2 and soluble salts measurement below 5 ppm.  This should be followed by brush application of paint for a first full coat and brush application for a second full coat. In atmospherically exposed areas, use the same treatment but without a second application by brush.  It is understood that all irregularities of the weld shall be repaired, notably undercuts and blow holes. Never accept t repairs with epoxy putty!!

From Per Gabrielsson of Free Lance Consultations and Inspections on April 22, 2019:
Especially manual welds should be coated with round brushes, working the paint well into irregularities. The coat should not  be too heavy. Rollers should never be used and spray t/u does not really do the work.

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Tagged categories: Coating Application; Coating Materials

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