PAINT STRIPPING USING SODIUM BICARBONATE MEDIUM
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Overview: | Sodium bicarbonate stripping processes are used as alternatives to
traditional chemical paint stripping. Bicarbonate of soda (or sodium
bicarbonate) is a soft blast medium with a heavier specific gravity and
less hardness than most plastic abrasives. The bicarbonate of soda
stripping process can be used with or without water. It is most frequently
used with water, which acts as a dust suppressant. In this form,
compressed air delivers sodium bicarbonate media from a pressure pot to a
nozzle, where the medium mixes with a stream of water. The soda/water
mixture impacts the coated surface and removes old coatings from the
substrate. The water dissipates the heat generated by the abrasive
process, reduces the amount of dust in the air, and assists in the paint
removal by hydraulic action. Workers need to mask the surface of the
material being stripped to prevent intrusion of bicarbonate of soda blast
media. Blast media begins to decompose at 140° Fahrenheit and may become
corrosive if left entrapped within a structure. Settling or filtration can
separate the solid residue from the wastewater generated from this
process.
The effectiveness of bicarbonate of soda stripping depends on a number of operating parameters, including: nozzle pressures, standoff distance, angle of impingement, flow rate, water pressure, and traverse speed. In general, bicarbonate of soda stripping systems remove paint slower than most methods (other than chemical paint stripping) currently used. The type of equipment used in this stripping process may also influence results (e.g., Aqua Miser® vs. the Accustrip System®). Use of sodium bicarbonate in its dry form (or when not fully mixed with water) can create a cloud of dust that will require monitoring and may require containment to meet air standards. The dust generated is not an explosive hazard, nor is sodium bicarbonate toxic in this form. However, the airborne particulates generated from the stripping operation can contain toxic elements from the paint being removed. This stripping process should be performed in areas where exhaust particulates can be contained and/or exhaust ventilation system controls are present to remove hazardous airborne metals. If bicarbonate of soda stripping is operated outdoors, air monitoring of dust (e.g., for metals) may be necessary to ensure that air standards are met. However, tests have shown that lead will adhere to the sodium bicarbonate, thus reducing the risk. The waste generated from bicarbonate of soda stripping systems using the wet process is a slurry consisting of sodium bicarbonate media, water, paint chips, and miscellaneous residues such as dirt and grease. Some installations are employing centrifuges to separate the water from the contaminated waste stream, thus reducing the amount of hazardous waste being disposed. Filtered wastewater containing dissolved sodium bicarbonate may be treated at an industrial wastewater treatment plant. In the dry stripping process, waste generated includes nuisance dust, paint chips, and miscellaneous residues such as dust and grease. The solid waste may be suitable for disposal in a sanitary landfill. Analysis of wastewater and waste solids is required prior to disposal. Wastewater and bicarbonate residue disposal requirements will depend on the toxicity of the coatings and pigments to be removed. The sodium bicarbonate media can not be recycled. The paint chip and miscellaneous residue wastes may be considered a hazardous waste. Currently, bicarbonate of soda stripping is not approved by NAVAIR for depainting aircraft. NAVAIR’s primary concern is that at temperatures of 140 to 160 degrees Fahrenheit, sodium bicarbonate may convert to sodium carbonate, which is corrosive. The Air Force has expressed the same concerns with the sodium bicarbonate stripping process as NAVAIR for depainting aircraft. The process is currently only being utilized as a supplementary process to chemical paint stripping for C-130 and C-141 aircraft. With regard to component stripping, where intrusion is not a significant factor, this process offers a viable alternative to chemical stripping. This technology has been tested at the USMC Logistics Base, Albany, Georgia. They tested sodium bicarbonate media in three types of commercial off-the-shelf equipment. The cost of these systems ranged from $15,000 (Accustrip 16W) to $40,000 (Aqua Miser E25 and Jet Stripper DP-1). The Aqua Miser and Jet Stripper use medium-pressure water to remove paint with sodium bicarbonate injected to enhance removal effectiveness (with the Aqua Miser system, the sodium bicarbonate flow can be turned on and off as necessary). Accustrip uses a stream of 30 to 90-psi air and sodium bicarbonate, and is combined with a stream of blast water at the nozzle to try to eliminate the dust. In both cases, the sodium bicarbonate medium is then propelled against the surface, and the sharp edges of the media blast paint away from the base metal. | ||||||||||||||||||||||||||||||
Compliance Benefit: |
Use of sodium bicarbonate paint stripping as a replacement for chemical paint strippers results in the following compliance benefits:
Compliance benefits include: 1) reduction or elimination of recordkeeping and reporting requirements under the Title V Operating Permits Program, NESHAP Program and SARA programs; 2) reduce administrative burden associated with hazardous waste (i.e., tracking, plans, reports, training); and 3) reduced administrative burden associated with OSHA (i.e., training and recordkeeping). The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved. | ||||||||||||||||||||||||||||||
Materials Compatibility: |
Material compatibility must be evaluated with respect to the item being cleaned. Uninhibited sodium bicarbonate and water residue can corrode substrates; however, current testing indicates that the corrosion potential of inhibited formulations is similar to that of organic solvent strippers. Results from an Air Force test program (Tasking Directive I-90) indicated that there was excessive corrosion of aluminum cladding materials when sodium bicarbonate and water slurry were used. | ||||||||||||||||||||||||||||||
Safety and Health: |
Health concerns are dependent on the variety of paint to be removed. Inhalation of lead- and zinc chromate-based paints can lead to irritation of the respiratory system. Some lead compounds are carcinogenic. Solvent-based paints can irritate the lungs and mucous membranes. Prolonged exposure can affect respiration and the central nervous system. Because of the noise and dust produced (the amount of dust produced will vary from system to system), a sodium bicarbonate stripping system should only be operated in an isolated area outdoors or indoors in a confined or remote area. Operators must wear double hearing protection - an air-hood blast helmet with an air-supplied respirator and optional half mask (for those blasting systems that generate large amounts of dust), or a full-faced air purification respirator with HEPA filters - and protective clothing (e.g., rain suits, rubber gloves, and safety-toed rubber boots, depending upon the substrate coating). Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology. | ||||||||||||||||||||||||||||||
Benefits: |
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Disadvantages: |
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Economic Analysis: | Annual operational costs for depainting 228 aircraft wheels with
bicarbonate of soda stripping system (Accustrip) compared to chemical
paint stripping were evaluated at the Lyndon B. Johnson Space
Center, Houston, Texas, as shown below.
Assumptions:
Annual Operating Cost Comparison for Bicarbonate of Soda Stripping and Chemical Paint Stripping
Economic Analysis Summary:
Click Here to view an Active Spreadsheet for this Economic Analysis and Enter Your Own Values. To return from the Active Spreadsheet, click the Back arrow in the Tool Bar. | ||||||||||||||||||||||||||||||
NSN/MSDS: |
*There are
multiple MSDSs for most NSNs. The MSDS is only meant to serve as an example. | ||||||||||||||||||||||||||||||
Approving Authority: |
Appropriate authority for making process changes should always be sought and obtained prior to procuring or implementing any of the technologies identified herein. This process is contained in T.O.1-1-8, but the use of it requires approval by the engineering authority of the specific Weapon System Manager or Equipment Item Manager with the Air Force. Approval has not been granted by NAVAIR for application on aircraft and aircraft components without pretreatment of aircraft substrate to remove all blast media. | ||||||||||||||||||||||||||||||
Points of Contact: | For more information | ||||||||||||||||||||||||||||||
Vendors: |
This is not meant to
be a complete list, as there may be other manufacturers of this type of
equipment. Schmidt
Manufacturing, Inc. Friess
Equipment | ||||||||||||||||||||||||||||||
Related Links: |
Do You Remove Paint Using Chemical Paint Stripping or Sand Blasting? - Navy Environmental Quality Initiative (EQI) Sodium Bicarbonate Blasting System (Walk - In) - P2 Equipment Program Sodium Bicarbonate Blasting System (4ft x 4ft) - P2 Equipment Program
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Sources: |
Joint Depot Maintenance Analysis Group,
"Joint Paint Removal Study on Sodium Bicarbonate," February 1995. | ||||||||||||||||||||||||||||||
Supplemental: | Picture of Sodium Bicarbonate Blasting System (Walk-In)
![]() Picture of Sodium Bicarbonate Blasting System (4 ft X 4 ft)
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