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October 19 - October 26, 2017

There are ways to increase the pressure for waterjetting to levels above 20,000 psi. What are the effects of different pressures (below and above 20,000 psi) on cleaning ratios?

Selected Answers

From Andreas Momber of Muehlhan AG on October 27, 2017:
The reader interested in effects of pressure, stand-off distance, orifice number/diameter, rotational speed, etc. on efficiency and quality of UHP waterjetting processes may refer to the following three publications: 1. Momber, A.W.: Hydroblasting and Coating of Steel Structures. Elsevier Applied Science, London, 2003 (eBook ISBN: 9780080508412 Hardcover ISBN: 9781856173957) 2. Teimourian, H., Shabgard, M.R., Momber, A.W.: De-painting with high-speed water jets: Paint removal process and substrate surface roughness. Progress in Organic Coatings, 69 (2010), 455-462. 3. Momber, A.W.: Image processing as a tool for high-pressure water jet coating removal assessment. International Journal of Advanced Manufacturing Technology, 87 (2016), 571-578.

From Lydia Frenzel of Advisory Council on October 25, 2017:
Look at the revision of NACE No 5/SSPC SP 12, which was published before we split the standard into the current version(s). It gives some wording for energy density, flow, pressures for the various pressure levels. You go from hydraulic lifting (shearing) to drilling (cutting) through the coating with a minimal amount of shearing. That wording in the CIP2 manual is loosely related to my "white paper" written in ca. 1985. We have many more choices of equipment, nozzles, and containment and recycling systems today. We routinely clean around 36,000 psi. Today,October 25, I sat through the 8 hours WJTA "basics course" on many aspect of WJ cleaning at the WJTA-IMCA conference.. It is the combination of pressure, flow, rotation, standoff, transverse speed that  determines productivity. Several presenters included productivity rates. This is the short answer. Depending upon the coatings type, it is sometimes more productive to have a lower pressure and higher flow; other times you want the higher pressure and lower flows. One thing to watch out for: Because some people want a fast production rate, you can move the head across the surface (transverse rate) so fast that the dwell time of the droplet is so short you don't get the full benefit of the cleaning mechanism.

From Greg Thorpe of Hertel Modern on October 19, 2017:
The NACE CIP 2 Manual clarifies the degree of cleanliness achieved at different pressures as follows: At pressure lower than 10,000 psi, loose rust, debris and material in pits/depressions are removed, but the black iron oxide (magnetite) remains. A matte finish is not achieved. At pressures of 10,000 psi, a matte finish is obtained that quickly turns to a golden hue (unless an inhibitor or dehumidification is used). Magnetite is removed but at a rate too slow to be considered practicable. At pressures of 20,000 psi, a matte finish is obtained that quickly turns to a golden hue (unless an inhibitor or dehumidification is used). Magnetite, paint, elastomeric coatings, enamel, red oxide and polypropylene sheet linings are removed. Chemical contaminants will be removed but with varying degrees of success. At pressures of 34,000 to 36,000 psi, a matte finish is obtained that quickly turns to a golden hue (unless an inhibitor or dehumidification is used). Surface materials, including most mill scale, are removed. (All credit to NACE)

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Tagged categories: Surface Preparation; UHP waterjetting; Waterjetting

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