| 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. Be sure to have your local Industrial Health Specialist
check the air for any resident metals.
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:
- Elimination of
volatile organic compounds (VOCs) used as strippers which are associated
with the formation of smog typically regulated by state and local air
pollution control districts.
- Elimination of
hazardous air pollutants (HAPs) in strippers which are regulated by
federal, state, and local regulations including the National Emissions
Standards Hazardous Air Pollutants (40 CFR 63).
- Elimination of
all SARA Title III reporting substances from coating process (by the
Navy) (40 CFR 300, 355, 370, and 372; and EO 12856).
- Reduced volumes
of organic wastes, which must be managed as hazardous waste under 40
CFR 260 and related sections.
- Reduced occupational
exposures, which are regulated under 29 CFR 1910.
Compliance benefits
include: 1) elimination of recordkeeping and reporting requirements under
the Title V, 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 a general guideline 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: |
- Significantly
reduces in the amount of hazardous waste generated compared to chemical
stripping.
- Reduces the number
of hours required for paint stripping in comparison to chemical stripping.
- Selectively removes
individual coating layers.
- Prewashing and
masking is not required in most applications.
- No size limitations
for parts being stripped.
- Wastewater stream
may be centrifuged to reduce its volume or treated (if required) at
industrial wastewater treatment plants.
- Blast media is
usually less expensive than PMB, wheat starch, and CO2 pellets.
|
| Disadvantages: |
- Requires subsequent
washing of the item; thus, electrical components cannot be exposed to
this stripping process.
- The sodium bicarbonate
solution can not be recycled for stripping, although the water can be
separated for disposal.
- Process may require
monitoring.
- Containment may
be required.
- Not approved by
NAVAIR for depainting aircraft.
|
| 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:
- Accustrip System
cost: $20,000
- Compressor, trailer
mounted: $20,000
- Materials and
installation: $125,000
- Other significant
costs (engineering, contingency, startup): $60,000
Annual
Operating Cost Comparison for Bicarbonate of Soda Stripping and Chemical
Paint Stripping
| |
Bicarbonate
of Soda Stripping
|
Chemical
Stripping |
| Operational
Costs: |
|
|
| Labor: |
$2,200 |
$16,200 |
| Material: |
$2,600 |
$1,600 |
| Waste
Disposal: |
$2,300 |
$2,800*
|
| Total
Operational Costs: |
$7,100 |
$20,600 |
| Total
Recovered Income: |
$0 |
$0 |
| Net
Annual Cost/Benefit: |
-$7,100 |
-$20,600 |
* Figure is based
on the material cost of $1,600 for chemical paint remover at $10/gallon,
the material consumption is 160 gallons. Paint/solvent disposal is $2.10
to $14.00 per gallon, depending on the specific solvents and paint in
the waste. Using the high estimate of $14.00 per gallon, the cost for
waste disposal is $2,240. For waste water treatment an extrapolation was
based on the $8.24/1000 gallons figure from the Plastic Media Blasting
Paint Stripping data sheet, a conservative estimate of 70,000 gallons
of waste water, and a waste water treatment cost of $580. Therefore, the
total waste disposal cost is $2,800.
Economic Analysis
Summary
Annual Savings
for Bicarbonate of Soda Stripping System: $13,500
Capital Cost for Equipment/Process: $225,000
Payback Period for Investment in Equipment/Process: < 17 years
Click Here to view an Active Spreadsheet for
this Economic Analysis and Enter Your Own Values. To return from the Active
Spreadsheet, click the reverse arrow in the Tool Bar.
|
| Approving
Authority: |
Approval has not
been made by NAVAIR for application on aircraft and aircraft components
without pretreatment of aircraft substrate to remove all blast media.
This technology should be implemented only after cognizant authority has
granted engineering approval.
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.
|
| NSN/MSDS: |
| Product |
NSN |
Unit
Size |
Cost |
MSDS* |
| High
Pressure Cleaner |
4940-01-413-5627 |
ea. |
$63,368.15
|
|
| High
Pressure Cleaner |
4940-01-413-5629 |
ea. |
$51,862.55
|
|
| Waste
Water Centrifuge |
4940-01-411-9830 |
ea. |
$8,082.28
|
|
| BOSSBLAST
(Blast Media) |
5350-01-414-1894 |
49/50
lb Bags |
$621.69
|
Click me |
| Blast
Cleaning Contain. Room |
4940-01-413-5605 |
ea. |
$27,816.20
|
|
*There are multiple MSDSs for most NSNs.
The MSDS (if shown above) is only meant to serve as an example.
|
| Points
of Contact: |
Air Force:
Air Force Corrosion Prevention and Control Office
AFRL/MLS-OLR (Bldg. 165)
325 Richard Ray Boulevard
Robins AFB, GA 31098-1640
Phone: (478) 926-3284
DSN: 468-3284
Marine Corps:
Mr. Warren Akers, Code 882
USMC Logistics Base
814 Radford Boulevard, Ste 20325
Albany, GA 31704
Phone: (229) 639-5103
DSN: 567-5307
FAX: (229) 439-6150
Navy:
Steve Siens
JDMAG/JTEG
Building 280, Door 24
4170 Hebble Creek
Wright Patterson AFB, GA 45433-3653
Phone: (937) 656-2774
DSN: 986-2774
FAX: (937) 656-2233
DSN FAX: 986-2233
URL: http://www.jdmag.wpafb.af.mil/
Mr. Bob Frederickson
Naval Facilities Engineering Service Center, ESC 423
1100 23rd Avenue
Port Hueneme, CA 93043-4370
Phone: (805) 982-4897
DSN: 551-4889
FAX: (805) 982-4832
|
| Vendors: |
This is not meant
to be a complete list, as there are other manufacturers of this type of
equipment.
Carolina Equipment
and Safety
7251 Cross County Road
N. Charleston, SC 29418
Phone: (800) 394-4987
or (843) 760-3000
FAX: (843) 760-3500
Contact: Chris Fulmer
Service: Aqua Miser®
URL: http://www.blastandpaint.com/
Schmidt Manufacturing,
Inc.
P.O. Box 37
Fresno, TX 77545
Phone: (800) 231-2085
FAX: (713) 431-1717
Service: Accustrip System®
Friess Equipment
2222 Akron-Peninsula Road
Akron, OH 44313
Phone: (800) 899-7624
FAX: (216) 923-5833
Service: SOBI System
|
| Sources: |
Joint Depot Maintenance Analysis Group,
"Joint Paint Removal Study on Sodium Bicarbonate," February 1995.
Mr. Talmon Perkins, Joint Depot Maintenance Analysis Group, Wright Patterson
AFB, May 1996
Mr. Mike Seybold, Material Engineering Laboratory, NADEP, NAS North Island,
San Diego, California, April 1996.
Vendor communication, Mr. Chris Fulmer, Carolina Equipment and Supply
Co., Inc., April 1996.
Vendor communication, Ms. Annette Rodriguez, Church and Dwight Co., Inc.,
April 1996.
|
