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Wilmington,. Delaware, December, 1965 Accession No. 12152
COMPARATIVE EVALUATION OF
GASKET MATERIAL IN ACID SERVICE
Prepared by: J._ E. Preiser
ABSTRACT
Nine types of gasket material were tested under controlled
conditions in 60$ HNO3 and 9S$
acid service at 210F
to investigate their chemical resistance and mechanical
characteristics. The report is intended as an aid in the
selection of gasket material for this service.
DUP 0827062
UNDER NO CIRCUMSTANCES SHOULD THIS PUBLICATION BE DISTRIBUTED, REPRODUCED
OR USED OUTSIDE THE DU PONT COMPANY.
290
Engineering Test Center Wilmington, Delaware, December, 1965
Accession No. 12152
COMPARATIVE EVALUATION
OF
GASKET MATERIAL IN ACID SERVICE
I. SUMMARY
PURPOSE
To obtain comparative performance data on various gasket materials in sulfuric and nitric acid service at elevated temperatures. This information will be used as a guide in gasket selection for process applications.
SCOPE
Nine types of gasket material were tested in 9&% sulfuric
and 60% nitric acids at 210F and 45 psig operating pressure. Periodic inspections were made during the tests for leaks. Comparative evaluation of performance was made in an engineering workshop following the test program. G. F. Hickey, E.S.D. Maintenance Engineering Consultant, assisted in the gasket selection, test design and comparative evaluation phases.
RESULTS AND CONCLUSIONS
1. A summary of comparative performance data is shown in Table I.
2. Virgin Teflon and glass-filled "Teflon" showed some evidence of creep under test operating conditions. Creep is aggravated with increased temperature and pressure and may lead to failure when temperatures exceed 300F.
FOR DU PONT COMPANY USE ONLY
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3 . The Duriron ''Task Line" gasket (Teflon-stainless steel) showed no noticeable evidence of creep under temperatures and pressures encountered in the test. Company operating experience has shown this material to be suitable in temperatures up to 400F.
4. The envelope gasket made of "Teflon" with compressed asbestos insert (Garlock #547) showed no evidence of creep in either of the test programs. Field installations in other services as high as 550F have given satisfactory service,
5. The blue asbestos impregnated with "Teflon" (Johns Manville Chempac 92) was outstanding in its performance. Field experience has demonstrated successful applications of this material in high temperature, high pressure ser vice (440F-500 psi).
6. Test results show the Mosite Rubber Co. envelope gasket of Viton fluoroelastomer to be satisfactory in 98$ sulfuric acid service. However, severe degradation occurred in 60$ HNO3 after 800 hours* exposure.
7. The Klinger Acidit material became brittle after exposure to the test acids. System mechanical stresses could lead to ultimate failure.
8. Armalon PDX7700 gasket material performed well in both services. The recommended 15 foot-lb. bolts torque makes it an excellent candidate for use in glass-lined or plastic pipe systems. Retorquing of flange bolts due to gasket relaxation will be necessary to maintain a leak-free system.
9. Satisfactory leak-free gaskets can be formed using the Crane "Zip Joint" material; however, installation difficulty between vertical flange faces will restrict its use.
RECOMMENDATIONS
1. Use test results and other data sources as a guide in selecting gasket material for specific process application.
2. Consider temperature limitations and related creep problems in the application of products made of "Teflon" as gaskets.
FOR DU PONT COMPANY USE ONLY
DUP 0827064
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3. Consider gasket face loading requirements in glass lined or plastic pipe systems as stress induced from flange bolts could cause pipe failure.
4. Compare cost and performance of various gasket materials in selecting the most suitable material for process systems.
Noted by:
(1 F. Hickey Engineering Service Division
Engineering Test Center
Submitted by:
"/.P.
u/izt
L. R. Millett
Engineering Service Division Engineering Test Center
Approved by:
E. M. Homan
Engineering Service Division Engineering Test Center
DUP 0827065
FOR DU PONT COMPANY USE ONLY
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II. DISCUSSION
TEST DESCRIPTION
A flow loop operating at 210F and pressure of 45 psig was used for the testing of gasket materials in acid service. Gaskets were installed using torques recommended for the specific material. Two sets of similar materials were tested.
One set was subjected to 9$% H2SO4 for 1500 hours. A second set was subjected to 60% HNO3 for 800 hours. Observations
were made during the test for leaks, extrusion and other external evidence of failure. Qualitative evaluation of performance was determined in an engineering workshop at the conclusion of physical testing.
ENGINEERING EVALUATION
Task Line (The Duriron Co.)
This gasket is made of molded virgin Teflon with a perforated stainless steel core. Performance in both the HNO3 and H2SO4 tests was excellent. Inspection following testing showed no^ deformation or tendency to creep at the temperatures and pressures encountered.
Garlock Co. 8547
Construction of this gasket (Du Pont Code G58} consists of an envelope made of "Teflon" molded over a Grey SBR Bonded com pressed white asbestos core. Performance under conditions of both tests was excellent. No creep or deformation was evident in the inspection which followed the test program.-
Pore Inc. - Glass-Filled "Teflon"
A glass-filled sheet of "Teflon" was used to cut gaskets of the appropriate size for the tests. Performance in both acids was excellent and no problems were encountered. Inspection following the tests revealed some evidence of creep on the inner circumference of the gasket. This should not become a problem, based on plant experience, tinless temperatures in excess of 300F are encountered.
FOR DU PONT COMPANY USE ONLY
DUP 0827066
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Virgin Teflon
Material was purchased in 1/16" sheet form and gaskets of the appropriate size were cut for the tests. The material re mained both leak- and maintenance-free for the duration of each test. Inspection at the conclusion of the tests revealed more extensive creep of "Teflon" than that encountered with the glass-filled material. Operation at higher temperatures would have required retorquing of flange bolts.
Armalon PDX7700 - Du Pont - Fabrics & Finishes Department
Armalon is a felt made of "Teflon" impregnated with "Teflon". The material is available in sheet form and gaskets are cut to the required size. This material offers the advantage of low seating stress and should be considered for use with glasslined or plastic pipe. While slight leakage occurred after 20 hours in the nitric acid test and 216 hours in the sulfuric acid test, leaks were easily stopped by retorquing bolts to the original 15 foot-lb. loading. Inspection following testing revealed some signs of porosity. Seating stress imposed was low and porosity would have been much less with a higher load ing. Porosity noted, however, was not judged harmful to the material's overall performance.
Zip Joint - John Crane Packing Co.
This material is string made of virgin "Teflon" 3/32" in diameter. The appropriate length of material is pulled from a can dispenser for installation. The manufacturer suggests that a single strand, with ends overlapped, is sufficient for sealing the joint. Leaks resulted when the recommended in stallation procedure was followed. Leak-free operation was achieved using several strands of the material and a bolt torque of 130 ft.-lbs. Installation of the material between flanges in the vertical position was difficult. For this reason, testing was limited to the nitric acid service. Leakfree joints- can be obtained with this material. Its use as an emergency gasket, rather than a standard gasket, is recommended.
FOR DU PONT COMPANY USE ONLY
DUP 0827067
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Chempac 92 - Johns Manvilie
Basic material for this sheet gasket is woven blue asbestos cloth impregnated with "Teflon". Processing includes a press compaction and resintering operation. Performance in the nitric and sulfuric acid services was excellent. Inspection following the tests showed no deformation, porosity, embrittlement or other evidence which would indicate the possibility of future failure.
Klinger Acidit - Richard Klinger. Inc.
This gasket is compressed white asbestos with a polyvinyl chloride binder. Performance during both tests was excellent with no external signs of failure. Inspection following testing revealed that exposure to each acid had caused material embrittlement. The material cracked when subjected to a slight bending stress and flakes of material could be chipped off easily with the fingernail. Its use in a system subjected to rapid heating and cooling or .vibration could result in mechanical failure.
Envelope of Viton - Mosites Rubber Co.
Gasket construction consisted of an envelope of "Viton" molded
over a 316 stainless steel core. Performance of this gasket
in sulfuric acid service for 1500 hours was excellent. In
spection following this test revealed no degradation or swelling
of "Viton". Exposure of the material to BOO hours* nitric acid
service, however, produced unsatisfactory results. While leaks
did not occur during the test period, relatively few additional
test hours would have resulted in failure. Inspection revealed
severe degradation of "Viton" and erosion with scarcely
of
unattached material on the circumference of the gasket maintain
ing a seal.
DUP 0827068
FOR DU PONT COMPANY USE ONLY
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