Conservation of Historic Metals by Waterjetting Techniques

Notes

• The aircraft industry, i.e. Delta, Lufthansa, KLM, United, American, Northwest, routinely use 36,000 psig to remove coatings while retaining the original profile on aluminium without distortion. One example is Pratt and Whitney ‘Advanced Robotics Maintenance Systems (ARMS TM)’ which operates at 28,000 psig. In working with General Electric Aircraft Engineers on the cleaning of engine components, Flow International calculated that it takes 158 times more energy to erode metal than is commonly used in surface cleaning (1995). NASA testing is documented in Spinoff 1996, NASA Center for AeroSpace Information (CASI) (ed.) ‘Robotic WaterJet Systems’, available at www.sti.nasa.gov. This article describes how, in the early 1990s, similar waterjet technology was developed when NASA teamed with United Technologies to produce an automated robotic maintenance system (ARMS) that uses 28,000 psig to strip thermal protection materials, paints and primers, layer by layer.
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• In 1999, R. K. Miller and G.J. Swenson of Thiokol presented ‘Erosion of Steel Substrates when Exposed to Ultra-Pressure Waterjet Cleaning Systems’ (WJTA, 10th American Waterjet Conference, August, 1999, paper 52, p. 661). Thiokol uses waterjetting to clean critical rocket engine parts for outer space. Prior to using UHP WJ (waterjetting), they had been cleaning the surfaces pits with dental picks. UHP WJ cleans these pits. Thiokol was concerned with damage to the metal substrate. The experiment used a target of D6AC steel with different sweep rates and rotation rates (dwell time). The plate was weighed before and after the sweep and an average profile was calculated. Data had been collected in 1992 and 1995 at 36,000 psig, and in 1998 with 40,000 psig, 1,300 revolutions per minute, standoff of 2.5 inch nominal, sweep rate of 60 inches per minute nominal. Thiokol verified that the minimum allowable erosion of 0.0001 inch (2.5 micron) would not be exceeded during the cleaning process. A grit blast of zirconium silicate produced an average profile of 0.700 mil (18 micron). A single pass of 40,000 psig produced an average profile of 0.009 mil; a second pass produced 0.017 mil; three to six passes produced an average profile of 0.018 mil (0.5 micron). Thus for 40,000 psig, this paper established that two passes eroded whatever material was going to be eroded from the D6AC steel. Then the steel substrate remained constant. These results are different from the 1992 tests. Thus, UHP WJ does make a micro-profile, but not of the same magnitude as the abrasive.
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• Surface profile, roughness or anchor pattern for coatings is the maximum peak-to-valley depth created during the cleaning, blasting, and preparation stages. This term is commonly associated with abrasive blast cleaning and is the result of the impact of the abrasive on the substrate.
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• Historical reference: Bryan, E.L. ‘High Energy Jets as a new concept for wood machining,’ Forest Products Journal, Vol 13, No. 8, August, 1963, p. 305.
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• PSI (pressure measured in pounds per square inch) is referred to in the waterjetting industry more specifically as PSIG, the pressure as it is measured at the pump gauge (pounds per square inch at gauge) where the operator controls are located. By following system parameters, the gauge pressure directly relates to the stream pressure impacting the work surface. The conversion for PSI to BAR and MPa is as follows: 1,000 psig = 68.9 BAR = 6.9 Mpa.
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• Merk-Gould, L.; Herskovitz, R. and Wilson, C., ‘Field Tests on Removing Corrosion from Outdoor Bronze Sculptures Using Medium Pressure Water’, ICOM, Vol. II, 1993, pp. 772–8.
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• Draughon, R., ‘Ultrahigh-Pressure Blasting’, NACE Corrosion 89, paper 119, 28 pp.
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• David Summers, Waterjetting Technology Chapman & Hall, New York, NY (1995) is a comprehensive treatise on civil engineering applications with chapters on how abrasives and water affect surfaces.
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• The unit of measure for the North American Waterjet Industry equipment is English (inches). Metric conversions are approximated as 0.002 inch = 0.01 millimetre, 2 to 3 inches = 5 to 7.5 centimetres, and 1 sec/in2 approximately 2 sec/5 cm2.
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• www.fertan.co.uk accessed 21 September 2005.
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• www.cortecvci.com accessed 21 September 2005.
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• The coupon samples were small disks of aluminum taken from the S-IVB stage of the JSC Saturn V Rocket. Samples were sent for EDS (energy dispersive X-ray spectroscopy) analysis. All 12 disks were probed at 20 kV. Acquisition time per probe was 120 seconds at a working distance of 39mm. Each disk was given an overall probe at 10X, and (3) additional probes were taken at 5000X (thus test 1, 2, 3). The instrument used was a JEOL JXA-840A Scanning Electron Microscope (SEM) with a ThermoNORAN TN-5502 energy dispersive analytical attachment and NORAN Vantage spectrum processing software. The system is also fitted with a low atomic number detector (Pioneer Premium detector with a Norvar window). The elements in the columns are what were found on the surface after the cleaning test—quantitative results are not given in this table.
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• The unit of measure for the North American Waterjet Industry equipment is English (inches). Metric conversions are approximated as 0.001 inch = 0.03 millimetre, 2 to 3 inches = 5 to 7.5 centimetres, and 1 sec/in2 approximately 2 sec/5 cm2.
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• Joint Surface Preparation Standard, NACE No. 5/SSPC-SP12 ‘Surface Preparation and Cleaning of Steel and Other Hard Materials by High and Ultrahigh-Pressure WaterJetting’ (revised 2002).
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• Soft abrasives in a stream of pressurized water were also tested to remove paint coatings. Universal Minerals, Inc. of Houston, Texas, provided the abrasive materials as well as an abrasive induction system operating with pressurized water from 3,000 to 20,000 psig and their RIPP 3000 nozzle. The RIPP 3000 nozzle uses the Venturi effect to introduce their Maxxstrip abrasives into the WJ stream. Maxxstrip is a sodium bicarbonate in fine, medium, and coarse grades. Maxxstrip has a neutral pH and was used in the demonstration.
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• The unit of measure for the North American Waterjet Industry equipment is English (inches). Metric conversions are approximated as 0.008 inch = 0.2032 millimetre, 2 to 3 inches = 5 to 7.5 centimeters, 0.5 sec/in2 approximately 1 sec/5 cm2
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