9TH ANNUAL AEROSPACE HAZARDOUS MATFiRIALS MANAGEMENT CONFERENCE DENVER, COLORADO TECHNICAL PAPER COVER SHEET (Please Type) SEPTEMBER 28-30,1994 PaDerTifle: Methyl Chloroform Use Reduction in RSRM Manufacture Number of Papes: L 3 Primarv Author: Neil Sagers Company: Thiokol Space Operations Address: P.0. BOX 707, M/S L C ~ Brigham City, UT 84302-0707 Phone: 801 863 6116 Fax: 801 863 2234 Presenter: Neil Sagers COEIpany: Thiokol Space Operations Address: P.O. Box 707, M/S LC2 Brigham City, UT 84302-0707 801 863 6116 801 863 2234 Phone: Fax Co-Authors: (Please give name, company, address, phone & fax) Have all necessary releases been obtained in order to present this paper at this conference? Yes . \
PaDerTifle: Methyl Chloroform Use Reduction in RSRM Manufacture
Number of Papes: L 3
Primarv Author: Neil Sagers
Company: Thiokol Space Operations Address: P.0. BOX 707, M/S L C ~
Brigham City, UT 84302-0707 Phone: 801 863 6116 Fax: 801 863 2234
Presenter: Neil Sagers
COEIpany: Thiokol Space Operations Address: P.O. Box 707, M/S LC2
Brigham City, UT 84302-0707 801 863 6116 801 863 2234
Phone: Fax
Co-Authors: (Please give name, company, address, phone & fax)
Have all necessary releases been obtained in order to present this paper at this conference? Yes .
\
. . .
Merhyl Chloroform Use Reduction in RSRM Manufacture
Methyl Chloroform Use Reduction in RSRM Manufacture
September 29, 1994
Presented by: Neil Sagers
Thiokot Corporation Space Operations
Abstract Space shuttle redesigned solid rocket motor (RSRM) case and nozzle seg- ments curently use preservative grease after launch and during the refurbishment process to prevent cor- rosion and vapor degreasers with l,l,l-trichloroethane (TCA) to re- move the preservative grease and oth- er contaminants. The purpose of the study was to reduce consumption of TCA, an ozone-depleting chemical, by elimination of preservative grease in favor of preservation in dry air. The scope of the test plan included man- ufacturing processes for the refurbish- ment of steel and aluminum case and nozzle components. The objective of the project was to demonstrate and
implement a manufacturing process which will reduce TCA use through elimination of preservative grease, a potential source of contamination.
All test results indicated that the new environmentally friendly process produced results that were equivalent to the current manufacturing process. All three TCA vapor degrease opera- tions for aluminum parts were elimi- nated, and six of the eight vapor de- grease operations on steel parts were eliminated. The new processes will eliminate 64 percent of all TCA used for RSRM manufacture and eliminate a potential source for contamination of adhesive bondlines.
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Methyl Chlorolorm Use Reductlon In RSRM Manufacture
Agenda 0 Process Overview
0
0
0
The space shuttle and RSRM configuration
RSRM uses of TCA before ODC elimination
1992 RSRM case process flow
The Previous and Demonstrated Processes 0
0 Results
0 Reduced TCA use
Bond results
0 The Future
0 Cleaners to eliminate all degreasing
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-. Methyl Chloroform Use Reductlon .
In RSRM Manufacture
Process Overview
The space shuttle and RSRM configuration Two solid rocket motors, or RSRMs, are used with every launch of the space shuttle. Each motor contains about 1.1 million pounds of propellant and produces over three million pounds peak thrust. The motors oper- ate at a maximum pressure of 950 psia and the propellant burns at 5,000 degrees Fahrenheit.
At about two minutes into the flight, the solid rocket motors drop off and are recovered in the Atlantic ocean. The motors are towed to land where they are disassembled and returned to Utah for refurbishment.
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Methyl Chloroform Use Reduction In RSRM Manufacture
Thiokol manufactures the space shuttle solid rocket motors in Utah. Nine metal cylinders are assembled with the forward and aft domes to make the entire motor chamber. The entire booster is about 12 feet in diameter and 149 feet long when the forward skirt and nose assembly are attached.
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Methyl Chloroform Use Reductlon In RSRM Manufacture .
Because of the size, each motor is manufactured in four segments: a for- ward segment, two center segments, and an aft segment. Each of the four segments is cast with propellant and sent to Kennedy Space Center where they are assembled for flight.
The cases are made of half-inch- thick D6ac steel where the nozzle structural components are made of both D6ac steel and aluminum. DGac is a high-strength steel but it corrodes very quickly. Because of the potential for corrosion, bare steel is painted or coated with preservative grease to avoid exposure of the metal to the environment.
The preservative grease is re- moved in a vapor degreaser with methyl chloroform (TCA). With the passage of the Clean Air Act of 1990, Thiokol began the project to eliminate the use of TCA and all other ozone- depleting compounds (ODCs) from the manufacturing processes. The primary focus was on elimination or replacement of TCA since there was little use of other ODCs at Thiokol.
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Methyl Chloroform Use Reduction In RSRM Manufacture ’
1992 RSRM case process flow 1. Receive 2. Washout 3. Grease preservation 4. Disassemble 5. Degrease 6. Grit blast 7. Degrease 8. Pressure test 9. Degrease
10. Glass bead blast 11. Degrease 12. Magnetic particle imp. 13. Degrease 14. Grit blast 15. Inspect wall thickness 16. Degrease 17. Grease 18. Ship 19. Degrease 20. Grit blast 21. Degrease 22. Assemble and paint Since we knew where the majority of the TCA was used, the next question was “why do we use grease and vapor degreasing?” A quick look at the process flow for case refurbishment and preparation showed that the parts
were cleaned after almost every major process step for a total of eight vapor degrease operations in the normal process. If the refurbishment process was delayed for any length of time, another grease and degrease cycle was performed.
Grease was applied to metal parts between process steps and for long- term storage between the refurbish- ment of the separate components and the manufacture of the RSRM. Vapor degreasing was used mostly to remove the grease, but also to remove inspec- tion fluids or grit blast dust.
A proposal was made to the cus- tomer, NASA in this case, and a study was funded for a full-scale demon- stration which included:
1. Manufacture of both the case and nozzle components.
2. Minimum use of TCA without major facility costs.
Because the case and nozzle man- ufacture are similar in many respects, I will concentrate on the case man- ufacturing process.
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Methyl Chlorclorm Use Reductton in RSRM Manufacture
The Previous and Demonstrated Processes Washout. The first step in the refur- bishment process is to remove the rubber insulation with 9,000 psi wa- ter. Because the D6ac steel corrodes very quickly, Barochem C430 corro- sion inhibitor is added to the water. In the previous process, the insulation washout was followed by a rinse with potable water to remove any remain- ing corrosion inhibitor. Since there was no inhibitor on the steel, Conoco HD-2 preservative grease was applied immediately after the washout proc- ess to stop any rust which might form.
After the grease application, it was necessary to degrease the case before the next process step.
The demonstration showed that if the inhibited water was allowed to dry on the steel parts, no rust would form. Elimination of the grease preservation after washout streamlined the process and saved the labor and materials required to grease and degrease case and nozzle parts. The trade-off for this savings was that the steel parts could not be stored for more than a few weeks between process steps. The storage limitation did not impair manufacturing operations.
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Methyl Chloroform Use Reduction . in RSRM Manufacture
Disassemblelgrit blast. After the insulation has been washed out, the segments are disassembled, de- greased, and grit blasted to remove the external paint and any remaining traces of adhesive on the inside. The grit blast operation leaves some dust on the surface of the metal.
In the past, dust from the grit blast
was removed in the vapor degreaser so that the grit would not interfere with the pressure-test equipment in the next step. In order to eliminate the dust-removal degrease, a filter was added to the pressure-test equipment to remove any particles which entered the system. Addition of the filter elim- inated the need to degrease the hard- ware after grit blast operations.
Pressure test. Because a hydraulic oil 36,000 psi water can remove contami- is used as the pressure-test fluid, a nants and leave a water-break-free vapor degrease was necessary to surface. The facility for the high remove the oil. Future operations will pressure water blast is now being built use 36,000 psi water to remove both and will be completed by January paint and oil in the refurbishment 1995. operations. It has been found that the
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Mefhyl Chloroform Use Reducflon In RSRM Manufacrure
Glass bead blast. Various inspections are performed in addition to the pressure test to ensure that the hardware is flight worthy and ready to be put back into service. One of the operations is magnetic particle inspec- tion. Since several inspections have occurred since the grit blast for paint removal, the case is glass bead blasted to ensure that any oxide formation is removed.
Magnetic particle inspection. Glass bead blasting leaves a small amount of dust on the case which is removed before the magnetic particle inspec- tion. Previously, the glass bead blast was followed by a vapor degrease to remove the glass bead dust. The demonstration showed that a rinse with the detergent-water solution
from the magnetic particle inspection effectively removed the glass-bead dust; and thus, eliminated another vapor degrease operation.
Grit blast. The magnetic particle in- spection leaves stains on the case which must be removed before bond- ing. In the previous process, the hard- ware was vapor degreased and then grit blasted. With the demonstration process, it was shown that a grit blast alone would remove the stains from the magnetic particle inspection and another vapor degrease was elimi- nated. In addition, the grit blast was moved so that it was performed just before bonding. The move of the grit blast ensured that a freshly grit- blasted surface was available for bonding operations.
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Methyl Chloroform Use Reduction In RSRM Manufacture
Wall thickness inspection. Before the TCA elimination effort, 3-in-1 oil was used as the ultrasonic couplant for the case wall thickness measure- ment. To remove the oil used as a couplant, the case was again vapor degreased. It was demonstrated that isopropyl alcohol made an acceptable couplant which completely evaporated and did not contaminate the bonding surface. Use of the isopropanol has eliminated another vapor degrease, reduced methyl chloroform emis- sions, and streamlined the process.
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Methyl Chloroform Use Reduction In RSRM Manufacture
Grease elimination. After the refur- bishment process was complete and the cylinder was free from all contam- inants, preservative grease was applied to all surfaces of the case. The preservative grease, Conoco HD-2, was first thinned with TCA and was then sprayed on the cylinder. The TCA would evaporate and the parts were ready for shipping or storage.
As an initial first step to reduce the TCA consumption, the grease was applied, undiluted, with paint rollers. Elimination of the thinner reduced TCA emissions by 44,000 pounds per year. A little more labor was required for grease application.
Probably the most significant change from this demonstration pro- gram was the complete elimination of grease application prior to shipping the parts from the refurbishment area to the manufacturing area. The environment in Utah is so dry that there is generally not a significant amount of corrosion for D6ac steel if it is stored indoors. The average humidity in the refurbishment area over two years is about 26 percent. It is unusual for the humidity to exceed 40 percent in the refurbishment area and it is about 40 percent relative humidity where steel corrosion occurs.
Preparation to ship. Flexible water- proof covers were used to demon- strate the concept of shipping the components in a .dry environment without grease. The covers prevented water from passing through to the steel hardware, but the seals were not able to stay closed at freeway speeds.
Even though the seals did open during transportation on the freeway and some water entered the covers, the test was considered successful be- cause the case and nozzle did not show any ill effects where the covers had protected them.
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Methyl Chloroform Use Reduction in RSRM Manufacture .
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Ship. The covers served the purpose of demonstrating the concept of ship- ping the parts in an environmentally controlled trailer. A special trailer was built because of the size of the parts. The trailer was equipped with a heating and refrigeration system which will maintain the temperature at 75 f 15 degrees Fahrenheit and keep the relative humidity below 40
percent. Oxidation of steel is very slow below 40 percent relative humid- ity as verified by tests at Thiokol and ASM books.
Smaller shipping containers have been purchased for nozzle and igniter parts. The smaller shipping contain- ers use desiccant to maintain a low relative humidity and can be carried by a flat-bed truck or on a trailer.
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Grit blast. Because the hardware is shipped without grease, the first vapor degrease operation upon arrival in the manufacturing area is not needed. Now when the hardware arrives in the manufacturing area, the first opera- tion is a light grit blast to remove process contaminants and prepare the metal surface for adhesive bonding operations.
Assemble and paint. Tests have shown that the dust from the grit blast operations does not degrade the adhesive bonds or paint adhesion.
The dust does hinder some of the inspection operations and work is in progress to remove dust from the surface before manufacturing opera- tions.
To remove dust, and as a contin- gency for contaminated hardware, an aqueous cleaning system will be in place before the vapor degreaser is shut down. Currently the vapor de- greaser is used to ensure that 100 percent of the case hardware has been cleaned and to remove dust before assembly and paint operations.
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Methyl Chloroform Use Reduction in RSRM Manufacture
This table is a comparison of RSRM case process as it was performed in 1992 and the way we will manufacture rocket motors in 1996. As you can see, the 1992 process included a vapor
1. Receive 2. Washout
3. Disassemble
4. Water blast (1995)
5. Pressure test 6. Water blast (1995) 7. Glass bead blast
degrease operation after almost every process step. The 1996 process will either eliminate or replace all de- grease operations and reduce the number of major processes from 22 to
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Methyl Chloroform Use Reductlon In RSRM Manufacture
14. The grease and degrease opera- tions have been eliminated where storage in dry air is adequate and replaced with 36,000 psi water or aqueous cleaning where cleaning operations are absolutely necessary.
Process contaminants have been removed wherever possible. The grease preservation has been elimi- nated and replaced with dry-air shipping. Just-in-time processing has also helped to reduce the need to store
hardware before the manufacturing process.
The major process changes are the high-pressure water and the aqueous cleaning to remove contaminants. Since these processes involve new facilities and introduction of new materials in the process, a more lengthy qualification was necessary. The environmental trailer was ac- cepted as being similar to the clean, dry conditions of the manufacturing area and was easier to qualify.
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Methyl Chloroform Use Reduction In RSRM Manufacture
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I
1988 1989 1990 1
1w1
Space Operations TCA use. Thiokol's TCA use had remained nearly con- stant in the years before the TCA elimination program. In 1991 the effort to eliminate TCA really began in earnest. By 1992 there was a significant reduction from previous years. Consumption of TCA contin- ues to decline in 1993 and 1994. It is expected that in 1995 and 1996 there will be other significant drops as the large degreasers are shut down.
1992 1993 1994 EsflmatEd Although the TCA use will drop off
the scale of this chart by 1996, there are some significant small-quantity uses of TCA which must be elimi- nated. Some of the smaller uses of TCA have been disappearing as the need to eliminate TCA was under- stood by everyone on plant. As the work is completed on elimination of the largest users of TCA, more effort will be dedicated to the smaller uses. An essential-use waiver will be presented to the United Nations on October 25 to allow continued pro- cessing until the last uses of TCA are eliminated.
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Chemlok 205/Chemlok 236Msilica- filled EPDM tensile strength. Every bondline which would be affected by a change in the metal bond surface preparation was tested. Test samples were bonded immediately after refur- bishment and after six to nine months storage as bare metal. Some panels which were bonded after refurbish- ment were held for six months before they were tested to ensure that there were no long-term effects on the bondlines. In addition, panels were bonded and tested periodically during the six-month aging period. The fol- lowing charts illustrate that all of the test bondlines fall within the capabili- ty limits of the original process:
The EPDM rubber is used as an external insulation for the case joints all tests showed that the elimination of preservative grease, vapor degreasing and hand-wiping of the case did not affect the tensile strength of the EPDM bondline.
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Methyl Chloroform Use Reduction in RSRM Manufacture
140
120 9 b
5 g 80
2 a 4 0 -
Averages +I- 3 standard-denallan and produnion capability limns
Chemlok 205/Chemlok 236Msilica- fiied EPDM peel strength. Similar results were found for the peel strength of the EPDM bondline. All test samples bonded with EPDM failed cohesively in the rubber which means that the bond to the surface was stronger than the insulation.
Chemlok 205Ehemlok 233kilica- fiied NBR tensile strength. Silica- filled NBR is used as the insulation between the solid propellant and the steel case. It is critical that a good insulation-to-case bond be provided with each motor. As before, the bond specimen averages were all within the capability limits for the original pro- cess and failed cohesively in the rubber.
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Merhyl Chloroform Use Reducrlon In RSRM Manufacture
NO vapor dqrease bond and led lHe16monlhs .torag and le¶
33 34 51 52
No vapor dqmse bond alters monlhr
Chemlok 205/Chemlok 236A/silica- filled NBR peel strength. The peel strength of the NBR bonds also were stronger than the insulation. The data point which lies above the upper capa- bility limit demonstrates, due to the cohesive failure, that the lot-to-lot variation of the rubber was the reason for the higher-than-normal peel strength.
SteeYRustoleum paint/Hysol EA913- NA tensile strength. The paint for the outside of the rocket motors was also tested. Although process capability limits were not available at the time of the test, the paint specimens averaged over 5,000 psi tensile strength and exhibited cohesive failure in the paint or primer. Paint samples were tested with and without vapor degreasing and it was found that there was no difference in the bond strength.
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Merhyl Chloroform Use Reduction In RSRM Manufacture
Steel/Hysol EA913NNsteel tensile strength. Hysol EA913NA adhesive is a structural epoxy adhesive used in the manufacture of the RSRM nozzle. All sample averages were well within the process capability limits for the original process.
SteellHysol EA934NNsteel tensile strength. Hysol EA934N.4, a slightly more flexible adhesive, is used to bond the systems tunnel to the outside of the case. These bond specimens also showed satisfactory perform- ance.
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Merhyl Chloroform Use Reducllon , In RSRM Manufacture
SteeYHysol EA946Lsteel tensile strength. Bonds with Hysol EA946, a very flexible epoxy adhesive, which is used in the RSRM nozzle, were at or above the process capability limits. The bonds were all satisfactory. The higher-than-normal bond strength is a subject for another discussion.
AluminumlHysol EA9 13NA/steel ten- sile strength. All of the bond data presented to this point has been for steel. The RSRM nozzle does use some aluminum components and alu- minum bondlines were tested exten- sively. This chart presents a number of panels which were bonded and tested with Hysol EA913NA at various interval. All of the bondlines were satisfactory.
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Melhyl Chloroform Use Reduclion in RSRM Manufacfure
Averages +I- 3 standard deviations and process capability limits
AluminumIHysol EA946Isteel tensile strength. As with the steel bondlines, the EA946-to-aluminum bonds were at or above the process capability lim- its, even though the test specimens were bonded by different people on different dates.
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Mefhyl Chloroform Use Reduction In RSRM Manufacfure "
The Future: Cleaners to eliminate all degreasing In summary the tests I have described here were an initial step directed at reduction of TCA use as much as possible without significant facility costs. The 36,000 psi water blast and aqueous cleaner projects to replace ozone depleting chemicals are new processes and will involve significant facility costs.
The facilities are under construc-
tion for the high-pressure water blast to replace vapor degreasing and some grit blasting in the refurbishment process. Several aqueous cleaners have been investigated and Thiokol is close to accepting the cleaner which will provide cleaning for the largest uses of TCA. The facilities and equipment for the aqueous cleaner to replace vapor degreasing in the manufacturing process are well along in the process and will be ready for production in 1996.
