- Email: [email protected]
Steps for developing a fugitive emission packing for valves
Feature S a m m i s Plant, USA, said that at his plant's seven coal fired u n i t s the plant's pipe crew spent 38% of its time repacking valves. On average, motor operated valves were forcing a unit off-line or delaying a start u p once every 15 months. This statement illustrates the lack of progress being m a d e in valve sealing technology. The Environmental Protection Agency (EPA) further confirmed the state of sealing technology i n its emission model of six refineries. This s t u d y disclosed that the most excessive pollution was associated with the leakage from valves, as opposed to p u m p s a n d flanges. The typical distribution of fugitive emission sources is a s follows:
S t e p s for d e v e l o p i n g a fugitive e m i s s i o n p a c k i n g for valves by J a m e s 8 u g g s , RM E n g i n e e r e d P r o d u c t s Inc. (Member o f FSA a n d Materials S t a n d a r d s Society} Over t h e p a s t 15 y e a r s , t h e e l i n d n a t i o n o f t r a d i t i o n a l s e a l / n g m a t e r i a l s a n d c l e a n air l e g i s l a t i o n h a v e c r e a t e d t h e n e e d for a f u g i t i v e e m i s s i o n s packing for v a l v e s . T h / s a r t i c l e d e s c r i b e s v a r / o u s criteria t h a t a f f e c t s e a l i n g p e r f o r m a n c e a s it r e l a t e s t o s e r v i c e c o n d i t i o n s , t h e q u a l i t y o f t h e v a l v e s t e m p a c k i n g , a n d d o c u m e n t a t i o n by t e s t i n g . T e s t r e s u l t s m p r e s e n t e d o n t o r q u e r e t e n t i o n , s e a l a b i l i t y v e r s u s applied t o r q u e , e f f e c t s o f live l o a d i n g , e f f e c t s o f s t e m f i n i s h o n s e a l s h i l i t y , e n d t h e e f f e c t s o f t r a v e l s p e e d o n sealabflity. T h e s e are s o m e o f t h e t e s t f a c t o r s required for d e v e l o p i n g f u g i t i v e e m i s s i o n p a c k i n g . The m a n u f a c t u r e of fluid sealing p r o d u c t s h a s c h a n g e d more in the last fifteen years t h a n in the previous eighty years of the 20th century. About forty years ago approximately 90% of all new p u m p s came packed, only 10% came with mechanical seals. Now the percentages are more t h a n reversed in favour of seals. Even the primary sealing material, asbestos fibre, h a s been p h a s e d out. Until the mid-eighties, asbestos was the primary material employed in the braided packing a n d gasket m a r k e t s as a m e a n s to seal media being p u m p e d or piped. I n d u s t r y studies indicated that a high percentage of the material shipped b y packing m a n u f a c t u r e r s was asbestos-based. When health related problems associated with a s b e s t o s surfaced, the search began to find a suitable replacement. Some p r o d u c t s that were evaluated a n d f o u n d their position in the m a r k e t included: • fibreglass • • •
acrylics aramids carbon
• graphite • thermoplastics • elastomers • perfluoroelastomers • synthetic materials The Electric Power Research Institute (EPRI) took a leading role
Sealing Technology No. 20
Class
in evaluating replacement materials. In 1982 EPRI, in conjunction with Stone a n d Webster, published a report (NP2560) which outlined some real Improvements in the area of sealing valves. The s t u d y included input from packing manufacturers, utilities, a n d valve manufacturers. There were three main conclusions: • graphite is the best replacement for asbestos • m a x i m u m sealing efficiency is accomplished with a m a x i m u m of five packing rings • live loading is beneficial to critical valves At EPRI's F o u r t h Valve Technology S y m p o s i u m held, ten years later, in A u g u s t of 1992, Thomas B Smyth, a n engineer with Ohio Edison's
% of total fugitive missions
pipeline valves relief valves pump seals flanges compressors others
75% 11% 5% 4% 2% 3%
In response, the Od a n d Gas
Journal reports that of the 204 US refineries, 109 have implemented corrective programs. Is there a problem with complying with the Clean Air Act's environmental s t a n d a r d s of controlling leakage in valves to 500 p a r t s per million (ppm)? Virtually every valve a n d packing m a n u f a c t u r e r asserts that its p r o d u c t s easily meet the 500 p p m threshold. Many even insisted that s t a n d a r d p r o d u c t s designed 20 or more years ago
Torque loss after 5 cycles, 5/6" packing
_o ~r
50%
190
228
286
304
% of recommended torque Figure 1. T o r q u e r e t e n t i o n after s e a t i n g a n d s t r o k i n g
5
Feature
Sealability vs. percent of recommended torque 1500 F 450 ~400
• Sample #l
o Sample #2
@ Sample #3
O Sample #4
• Sample #5
~ Sample #6
• Sample #7
o Sample #8
300 250 ~ 200er !00
50 o
% % of recommended torque
F i g u r e 2. T h e e f f e c t o f u n d e r / o v e r c o m p r e s s i o n EFFECT OF LWELOADINGON LEAKAGE 1600
WITHOUT UVE LOADING
SET: F L . E ~ ( ~ A P H I ~ JACV~WTH I~IOED ~
1260 1000
'n:~VEL ~ E D : 14 I I 1 ~
v m
CORE(5 RINGS}
--"WITH
LIVE LOADING
FRIEfll Y r E
700 000 200
\
0 600
1000
1100
2000
2800
3000
3800
4000
CYCLES
comply. But, if compliance'is so easy, w h y did the EPA find so m a n y leaking valves in its s t u d y of operating plants? Why does the chemlcal i n d u s t r y see valve monitoring a n d repair as a potentially expensive program? Why have so m a n y plants installed leak-free bellows sealed valves to a s s u r e low leakage? Why do valve companies aggressively m a r k e t solutions to this problem? There is little controversy a b o u t new valves. They will be virtually leak free. The real question is for how long? How m a n y thermal cycles and how m a n y mechanical strokes at plant conditions? Difficult applications involving high temperatures, high pressure, or frequent stem movement (for example control valves) will require a modern, more sophisticated system to meet the 500 ppm for a long period of time. Is there a new awareness of valves leaking today? Is what was considered adequate sealing In the 700 and 800 considered non-acceptable in the 90s? The Synthetic Organic Chemical Manufacturer's Institute (SOCMI) h a s b e e n proactive in attacking the valve leaking statistics published by the Environmental Protection Agency.
Figure 3. Live l o a d i n g
Figure 4. Effect of stem finish on sealability 2 RMS Stem finish Cycle
Leakage
16 RMS Stem finish Stem friction closing stroke
Cycle
Parts per million Pounds
Leakage
Stem friction closing stroke
32 RMS Stem finish Cycle
Parts per million Pounds
229
0
612
272
0
345
518
0
745
536
0
339
Leakage
Stem friction closing stroke
Parts per million Pounds 364
22
470
575
85
669
175
655
470
661
812
0
725
768
8
629
875
1001
0
729
959
34
629
1040
Test Conditions Set: Flexible graphite jacket with braided carbon/graphite core (5 rings) Gas: 300PSI Methane Travel speed: 14 inches per minute
Conclusion For effective sealing on frequently stroked valves, ie air or motor operated valves, the smoother finishes are absolutely essential
to obtain best sealing. For static valves, that are essentially either open or closed, the rougher stem finish is not as great a factor in sealing performance.
6
Sealing Technology No. 20
Feature
R g u r e 5. Effect of travel speed on smooth stems and seslabllity 14 Inch minute on 2 RMS stem Cycle
28 Inch per minute on 2 RMS stem
Leakage
Stem friction closing stroke
Cycle
Leakage
Stem friction closing stroke
Parts per million
Pounds
Parts per million
Pounds
229
0
612
238
0
510
518
0
745
338
0
550
812
0
725
552
580
595
1001
0
729
Test conditions Gas: 300PSI Methane Conclusion Extreme stem speed drastically affects sealability. S o m e of t h e a r e a s a d d r e s s e d b y SOCMI m e m b e r s a r e : • c a r e f u l m o n i t o r i n g for l e a k a g e and repair or replacement of leaking components on start up •
extensive monitoring practices by some plants
improved valve packings nature of valve and process conditions W h a t c a n m a n u f a c t u r e r s o f valve s t e m p a c k i n g , b e i n g m a r k e t e d for v o l a t i l e o r g a n i c c h e m i c a l service, d o to b e o f a s s i s t a n c e to b o t h valve makers and users who have a tremendous investment in installed valves? A practical approach would a p p e a r to be:
•
identify those service conditions t h a t affect s e a l i n g r e q u i r e m e n t s
•
identify those factors of the v a l v e s t h a t will h a v e a p h y s i c a l effect o n t h e l e a k a g e performance r a t e t h e s t e m p a c k i n g s offered in t h e i r a b i l i t y to s a t i s f y t h e service conditions encountered and the contingencies that need to b e c o n s i d e r e d
•
• •
•
r e v i e w t h e d o c u m e n t a t i o n of t h e s t e m s e a l s b e i n g offered to s e a l under demanding conditions S e r v i c e c o n d i t i o n s t h a t affect sealing requirements include: •
process variables (temperature,
pressure, chemical a g g r e s s i v e n e s s , specific gravity, a b s o l u t e viscosity)
•
operation (throttling or on/off service)
• installation • system maintenance F a c t o r s o f t h e valve t h a t w o u l d h a v e a p h y s i c a l effect o n l e a k a g e performance include: • valve type (rotary or linear stem movement, quarter turn versus rising stem) • sealing design (packing system, b e l l o w seals} •
m a t e r i a l s of c o n s t r u c t i o n
•
q u a l i t y of m a n u f a c t u r i n g
Figure 6. Effect of stem travel • )eed on sealabllity and friction 7 inch per minute on 16 RMS stem Cycle
Leakage
Stem friction closing stroke
Parts per million
Pounds
14 inch per minute on 16 RMS stem Cycle
Leakage
Stem friction dosing stroke
Parts per million
Pounds
196
0
375
195
22
715
504
10
425
844
95
880
897
110
400
931
105
892
998
100
395
1093
105
884
Test conditions Set: Flexible graphite jacket with braided carbon/graphite core (5 rings) Gas: 300PSI Methane Conclusion Slower speeds on slightly rougher stem finishes do not produce great amounts of leakage but do generate more stem fiction.
Sealing Technology No. 20
7
Feature There are also certain m i n i m u m valve conditions that m u s t be met in order for conventional packing systems to have a c h a n c e to perform satisfactorily. Surface finishes, concentriclties, a n d stuffing box clearances m u s t be within certain standards. Generally accepted s t a n d a r d s are as follows:
stem finish
32 rms maximum for hand valves 16 maximum for control valves
bore finish
64-132 rms
stem diameter deviation 0.003 inches maximum stuffing box
0.025 inches maximum radial clearance
New valves are generally well within these standards. In rating the valve stem packing's ability to satisfy service conditions, a n u m b e r of the qualities of the packing m u s t be evaluated. These will ultimately dictate its sealabfltty a n d how well it performs in a d e m a n d i n g applications. These qualities include the following: • chemlcal compatibility resistance to aggressive chemical attack • heat resistance • radial expansion - ability to transfer axial forces to radt~l forces • retained flexibility - ability to retain shape a n d recover u n d e r pressure • torque requirements - packing gland force required to seal • fire safe - passing API 589 a n d API 607 • stem friction - c a n the p r o d u c t be u s e d in frequently stroking valves without increasing actuator force? • corrosive inhibitor Other considerations include ease of installation, form available a n d acquisition cost. To d o c u m e n t the performance of stem seals, testing is obviously required. Since the demise of asbestos as a sealing material, there have been no established industry testing procedures agreed
8
upon. Some individual users, valve makers, a n d packing m a n u f a c t u r e r s have established their own, b u t there are no industry wide s t a n d a r d s established to date. Thls is a cause of both confusion a n d concern to all involved in compliance sealing. There are ongoing programs trying to establish testing parameters by the Manufacturers Standardization Society Committee 308, the Valve Manufacturers Association, Pressure Vessel Manufacturers, a n d the I n s t r u m e n t Society of America. The Petroleum Environmental Research Forum, a n association of refineries, performed testing in 1990-91. The results will remain confidential for a while longer. In the absence of industry sealing tests, it is still wise to ask for a n y documentation on sealing products being offered for compliance applications, as well as user referrals. The testing data published here have been generated in the RM lab a n d are offered for the purpose of illustrating the effect different variables can have on sealing results obtained. In conclusion, it is believed that the reason s u c h widely differing views are expressed on how serious the problem of valve sealing is, is in direct proportion to the strength of the valve monitoring program in place. Is the media being sealed a m o n g the easiest or hardest? Are the valves in excellent condition or not so good? Do the service requirements m a n d a t e the valve be
stroked frequently or are they opened a n d / o r closed? Is the valve sealing p r o d u c t evaluated carefully before being p u r c h a s e d a n d is it designed for the "extra mile" sometimes encountered; or is valve packing given very low priority? Is the packing installed according to the m a n u f a c t u r e r ' s installation instructions? Are the valves monitored regularly? D e m a n d the best for your sealing dollar, a n d everyone wlll benefit from s o u n d sealing.
References I. Valve Reliability: I n d u s t r y Challenge for the 90's Steven E Kuehn, Power Engineering M a g a z i n e / J a n u a r y , 1993 2. Fugitive Emissions Regulations S p a r k Low Leak Claims J e r o m e A Baechotti, Ph.D., CPI P u r c h a s i n g / F e b r u a r y , 1992 3. Fugitive Emission Control in Packed Valves, Sydney Lipton, Chemical Engineering Progress/August, 1990
Contact: J a m e s W. 8ugga. Bales Manager of Sealing Products, 104 Engineered Products Inc. 4 8 5 4 O'Hear Avenue. North Charleston 8C 2 9 4 0 5 . 4 9 7 2 . USA. Tel: +1 803 7 4 4 6261; Fax: +1 8 0 3 7 4 4 0461; Or Nick Hathaway, Product ~ d e s Manager. Hydraul/c Equipment Supermarkets Ltd, I n n s w o r t h T e c h n o l o g y Park. I n n s w o r t h Lane. Gloucester GL3 1DL. UIL
Factors tested that impact sealing seating
five strokes 35% loss of torque
stem finish
2, 16, 32, 64 rms
stroke travel
7, 14, 28 inch/minute
packing - lube/dry
does lubrication effect sealing?
pressure
100 - 300 psi
temperature
ambient vs. 350°F
live loading
how much effect for how long?
number of rings
2, 5, 7
bushing location
top versus bottom
sealability
various brands and compositions
torque
manufacturers recommendation vs. 25% compression
end rings
effect on sealing stroked valves
Sealing Technology No. 20
S t e p s for d e v e l o p i n g a fugitive e m i s s i o n p a c k i n g for valves by J a m e s 8 u g g s , RM E n g i n e e r e d P r o d u c t s Inc. (Member o f FSA a n d Materials S t a n d a r d s Society} Over t h e p a s t 15 y e a r s , t h e e l i n d n a t i o n o f t r a d i t i o n a l s e a l / n g m a t e r i a l s a n d c l e a n air l e g i s l a t i o n h a v e c r e a t e d t h e n e e d for a f u g i t i v e e m i s s i o n s packing for v a l v e s . T h / s a r t i c l e d e s c r i b e s v a r / o u s criteria t h a t a f f e c t s e a l i n g p e r f o r m a n c e a s it r e l a t e s t o s e r v i c e c o n d i t i o n s , t h e q u a l i t y o f t h e v a l v e s t e m p a c k i n g , a n d d o c u m e n t a t i o n by t e s t i n g . T e s t r e s u l t s m p r e s e n t e d o n t o r q u e r e t e n t i o n , s e a l a b i l i t y v e r s u s applied t o r q u e , e f f e c t s o f live l o a d i n g , e f f e c t s o f s t e m f i n i s h o n s e a l s h i l i t y , e n d t h e e f f e c t s o f t r a v e l s p e e d o n sealabflity. T h e s e are s o m e o f t h e t e s t f a c t o r s required for d e v e l o p i n g f u g i t i v e e m i s s i o n p a c k i n g . The m a n u f a c t u r e of fluid sealing p r o d u c t s h a s c h a n g e d more in the last fifteen years t h a n in the previous eighty years of the 20th century. About forty years ago approximately 90% of all new p u m p s came packed, only 10% came with mechanical seals. Now the percentages are more t h a n reversed in favour of seals. Even the primary sealing material, asbestos fibre, h a s been p h a s e d out. Until the mid-eighties, asbestos was the primary material employed in the braided packing a n d gasket m a r k e t s as a m e a n s to seal media being p u m p e d or piped. I n d u s t r y studies indicated that a high percentage of the material shipped b y packing m a n u f a c t u r e r s was asbestos-based. When health related problems associated with a s b e s t o s surfaced, the search began to find a suitable replacement. Some p r o d u c t s that were evaluated a n d f o u n d their position in the m a r k e t included: • fibreglass • • •
acrylics aramids carbon
• graphite • thermoplastics • elastomers • perfluoroelastomers • synthetic materials The Electric Power Research Institute (EPRI) took a leading role
Sealing Technology No. 20
Class
in evaluating replacement materials. In 1982 EPRI, in conjunction with Stone a n d Webster, published a report (NP2560) which outlined some real Improvements in the area of sealing valves. The s t u d y included input from packing manufacturers, utilities, a n d valve manufacturers. There were three main conclusions: • graphite is the best replacement for asbestos • m a x i m u m sealing efficiency is accomplished with a m a x i m u m of five packing rings • live loading is beneficial to critical valves At EPRI's F o u r t h Valve Technology S y m p o s i u m held, ten years later, in A u g u s t of 1992, Thomas B Smyth, a n engineer with Ohio Edison's
% of total fugitive missions
pipeline valves relief valves pump seals flanges compressors others
75% 11% 5% 4% 2% 3%
In response, the Od a n d Gas
Journal reports that of the 204 US refineries, 109 have implemented corrective programs. Is there a problem with complying with the Clean Air Act's environmental s t a n d a r d s of controlling leakage in valves to 500 p a r t s per million (ppm)? Virtually every valve a n d packing m a n u f a c t u r e r asserts that its p r o d u c t s easily meet the 500 p p m threshold. Many even insisted that s t a n d a r d p r o d u c t s designed 20 or more years ago
Torque loss after 5 cycles, 5/6" packing
_o ~r
50%
190
228
286
304
% of recommended torque Figure 1. T o r q u e r e t e n t i o n after s e a t i n g a n d s t r o k i n g
5
Feature
Sealability vs. percent of recommended torque 1500 F 450 ~400
• Sample #l
o Sample #2
@ Sample #3
O Sample #4
• Sample #5
~ Sample #6
• Sample #7
o Sample #8
300 250 ~ 200er !00
50 o
% % of recommended torque
F i g u r e 2. T h e e f f e c t o f u n d e r / o v e r c o m p r e s s i o n EFFECT OF LWELOADINGON LEAKAGE 1600
WITHOUT UVE LOADING
SET: F L . E ~ ( ~ A P H I ~ JACV~WTH I~IOED ~
1260 1000
'n:~VEL ~ E D : 14 I I 1 ~
v m
CORE(5 RINGS}
--"WITH
LIVE LOADING
FRIEfll Y r E
700 000 200
\
0 600
1000
1100
2000
2800
3000
3800
4000
CYCLES
comply. But, if compliance'is so easy, w h y did the EPA find so m a n y leaking valves in its s t u d y of operating plants? Why does the chemlcal i n d u s t r y see valve monitoring a n d repair as a potentially expensive program? Why have so m a n y plants installed leak-free bellows sealed valves to a s s u r e low leakage? Why do valve companies aggressively m a r k e t solutions to this problem? There is little controversy a b o u t new valves. They will be virtually leak free. The real question is for how long? How m a n y thermal cycles and how m a n y mechanical strokes at plant conditions? Difficult applications involving high temperatures, high pressure, or frequent stem movement (for example control valves) will require a modern, more sophisticated system to meet the 500 ppm for a long period of time. Is there a new awareness of valves leaking today? Is what was considered adequate sealing In the 700 and 800 considered non-acceptable in the 90s? The Synthetic Organic Chemical Manufacturer's Institute (SOCMI) h a s b e e n proactive in attacking the valve leaking statistics published by the Environmental Protection Agency.
Figure 3. Live l o a d i n g
Figure 4. Effect of stem finish on sealability 2 RMS Stem finish Cycle
Leakage
16 RMS Stem finish Stem friction closing stroke
Cycle
Parts per million Pounds
Leakage
Stem friction closing stroke
32 RMS Stem finish Cycle
Parts per million Pounds
229
0
612
272
0
345
518
0
745
536
0
339
Leakage
Stem friction closing stroke
Parts per million Pounds 364
22
470
575
85
669
175
655
470
661
812
0
725
768
8
629
875
1001
0
729
959
34
629
1040
Test Conditions Set: Flexible graphite jacket with braided carbon/graphite core (5 rings) Gas: 300PSI Methane Travel speed: 14 inches per minute
Conclusion For effective sealing on frequently stroked valves, ie air or motor operated valves, the smoother finishes are absolutely essential
to obtain best sealing. For static valves, that are essentially either open or closed, the rougher stem finish is not as great a factor in sealing performance.
6
Sealing Technology No. 20
Feature
R g u r e 5. Effect of travel speed on smooth stems and seslabllity 14 Inch minute on 2 RMS stem Cycle
28 Inch per minute on 2 RMS stem
Leakage
Stem friction closing stroke
Cycle
Leakage
Stem friction closing stroke
Parts per million
Pounds
Parts per million
Pounds
229
0
612
238
0
510
518
0
745
338
0
550
812
0
725
552
580
595
1001
0
729
Test conditions Gas: 300PSI Methane Conclusion Extreme stem speed drastically affects sealability. S o m e of t h e a r e a s a d d r e s s e d b y SOCMI m e m b e r s a r e : • c a r e f u l m o n i t o r i n g for l e a k a g e and repair or replacement of leaking components on start up •
extensive monitoring practices by some plants
improved valve packings nature of valve and process conditions W h a t c a n m a n u f a c t u r e r s o f valve s t e m p a c k i n g , b e i n g m a r k e t e d for v o l a t i l e o r g a n i c c h e m i c a l service, d o to b e o f a s s i s t a n c e to b o t h valve makers and users who have a tremendous investment in installed valves? A practical approach would a p p e a r to be:
•
identify those service conditions t h a t affect s e a l i n g r e q u i r e m e n t s
•
identify those factors of the v a l v e s t h a t will h a v e a p h y s i c a l effect o n t h e l e a k a g e performance r a t e t h e s t e m p a c k i n g s offered in t h e i r a b i l i t y to s a t i s f y t h e service conditions encountered and the contingencies that need to b e c o n s i d e r e d
•
• •
•
r e v i e w t h e d o c u m e n t a t i o n of t h e s t e m s e a l s b e i n g offered to s e a l under demanding conditions S e r v i c e c o n d i t i o n s t h a t affect sealing requirements include: •
process variables (temperature,
pressure, chemical a g g r e s s i v e n e s s , specific gravity, a b s o l u t e viscosity)
•
operation (throttling or on/off service)
• installation • system maintenance F a c t o r s o f t h e valve t h a t w o u l d h a v e a p h y s i c a l effect o n l e a k a g e performance include: • valve type (rotary or linear stem movement, quarter turn versus rising stem) • sealing design (packing system, b e l l o w seals} •
m a t e r i a l s of c o n s t r u c t i o n
•
q u a l i t y of m a n u f a c t u r i n g
Figure 6. Effect of stem travel • )eed on sealabllity and friction 7 inch per minute on 16 RMS stem Cycle
Leakage
Stem friction closing stroke
Parts per million
Pounds
14 inch per minute on 16 RMS stem Cycle
Leakage
Stem friction dosing stroke
Parts per million
Pounds
196
0
375
195
22
715
504
10
425
844
95
880
897
110
400
931
105
892
998
100
395
1093
105
884
Test conditions Set: Flexible graphite jacket with braided carbon/graphite core (5 rings) Gas: 300PSI Methane Conclusion Slower speeds on slightly rougher stem finishes do not produce great amounts of leakage but do generate more stem fiction.
Sealing Technology No. 20
7
Feature There are also certain m i n i m u m valve conditions that m u s t be met in order for conventional packing systems to have a c h a n c e to perform satisfactorily. Surface finishes, concentriclties, a n d stuffing box clearances m u s t be within certain standards. Generally accepted s t a n d a r d s are as follows:
stem finish
32 rms maximum for hand valves 16 maximum for control valves
bore finish
64-132 rms
stem diameter deviation 0.003 inches maximum stuffing box
0.025 inches maximum radial clearance
New valves are generally well within these standards. In rating the valve stem packing's ability to satisfy service conditions, a n u m b e r of the qualities of the packing m u s t be evaluated. These will ultimately dictate its sealabfltty a n d how well it performs in a d e m a n d i n g applications. These qualities include the following: • chemlcal compatibility resistance to aggressive chemical attack • heat resistance • radial expansion - ability to transfer axial forces to radt~l forces • retained flexibility - ability to retain shape a n d recover u n d e r pressure • torque requirements - packing gland force required to seal • fire safe - passing API 589 a n d API 607 • stem friction - c a n the p r o d u c t be u s e d in frequently stroking valves without increasing actuator force? • corrosive inhibitor Other considerations include ease of installation, form available a n d acquisition cost. To d o c u m e n t the performance of stem seals, testing is obviously required. Since the demise of asbestos as a sealing material, there have been no established industry testing procedures agreed
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upon. Some individual users, valve makers, a n d packing m a n u f a c t u r e r s have established their own, b u t there are no industry wide s t a n d a r d s established to date. Thls is a cause of both confusion a n d concern to all involved in compliance sealing. There are ongoing programs trying to establish testing parameters by the Manufacturers Standardization Society Committee 308, the Valve Manufacturers Association, Pressure Vessel Manufacturers, a n d the I n s t r u m e n t Society of America. The Petroleum Environmental Research Forum, a n association of refineries, performed testing in 1990-91. The results will remain confidential for a while longer. In the absence of industry sealing tests, it is still wise to ask for a n y documentation on sealing products being offered for compliance applications, as well as user referrals. The testing data published here have been generated in the RM lab a n d are offered for the purpose of illustrating the effect different variables can have on sealing results obtained. In conclusion, it is believed that the reason s u c h widely differing views are expressed on how serious the problem of valve sealing is, is in direct proportion to the strength of the valve monitoring program in place. Is the media being sealed a m o n g the easiest or hardest? Are the valves in excellent condition or not so good? Do the service requirements m a n d a t e the valve be
stroked frequently or are they opened a n d / o r closed? Is the valve sealing p r o d u c t evaluated carefully before being p u r c h a s e d a n d is it designed for the "extra mile" sometimes encountered; or is valve packing given very low priority? Is the packing installed according to the m a n u f a c t u r e r ' s installation instructions? Are the valves monitored regularly? D e m a n d the best for your sealing dollar, a n d everyone wlll benefit from s o u n d sealing.
References I. Valve Reliability: I n d u s t r y Challenge for the 90's Steven E Kuehn, Power Engineering M a g a z i n e / J a n u a r y , 1993 2. Fugitive Emissions Regulations S p a r k Low Leak Claims J e r o m e A Baechotti, Ph.D., CPI P u r c h a s i n g / F e b r u a r y , 1992 3. Fugitive Emission Control in Packed Valves, Sydney Lipton, Chemical Engineering Progress/August, 1990
Contact: J a m e s W. 8ugga. Bales Manager of Sealing Products, 104 Engineered Products Inc. 4 8 5 4 O'Hear Avenue. North Charleston 8C 2 9 4 0 5 . 4 9 7 2 . USA. Tel: +1 803 7 4 4 6261; Fax: +1 8 0 3 7 4 4 0461; Or Nick Hathaway, Product ~ d e s Manager. Hydraul/c Equipment Supermarkets Ltd, I n n s w o r t h T e c h n o l o g y Park. I n n s w o r t h Lane. Gloucester GL3 1DL. UIL
Factors tested that impact sealing seating
five strokes 35% loss of torque
stem finish
2, 16, 32, 64 rms
stroke travel
7, 14, 28 inch/minute
packing - lube/dry
does lubrication effect sealing?
pressure
100 - 300 psi
temperature
ambient vs. 350°F
live loading
how much effect for how long?
number of rings
2, 5, 7
bushing location
top versus bottom
sealability
various brands and compositions
torque
manufacturers recommendation vs. 25% compression
end rings
effect on sealing stroked valves
Sealing Technology No. 20