1、 PPI PENT Test Investigation TN-21/2013 105 Decker Court, Suite 825, Irving, TX 75062 P: 469-499-1044 F: 469-499-1063 www.plasticpipe.org Foreword This report was developed and published with the technical help and financial support of the members of the PPI (Plastics Pipe Institute, Inc.). The memb
2、ers have shown their interest in quality products by assisting independent standards-making and user organizations in the development of standards, and also by developing reports on an industry-wide basis to help engineers, code officials, specifying groups, and users. The purpose of this technical
3、note is to provide general information on use of the PENT test (ASTM F1473) when conducted on samples molded from PE pellets and also when conducted on extruded solid wall pipe with the samples cut in the axial direction. This report has been prepared by PPI as a service of the industry. The informa
4、tion in this report is offered in good faith and believed to be accurate at the time of its preparation, but is offered “as is” without any express or implied warranty, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Any reference to or testing of a particular proprieta
5、ry product should not be construed as an endorsement by PPI, which does not endorse the proprietary products or processes of any manufacturer. The information in this report is offered for consideration by industry members in fulfilling their own compliance responsibilities. PPI assumes no responsib
6、ility for compliance with applicable laws and regulations. PPI intends to revise this report from time to time, in response to comments and suggestions from users of the report. Please send suggestions of improvements to PPI. Information on other publications can be obtained by contacting PPI direct
7、ly or visiting the web site. The Plastics Pipe Institute, Inc. http:/www.plasticpipe.org This Technical Note, TN-21, was first issued in 2000 and was revised in January 2013. 105 Decker Court, Suite 825, Irving, TX 75062 P: 469-499-1044 F: 469-499-1063 www.plasticpipe.orgPENT Test Investigation 1. S
8、cope The purpose of this project was to evaluate applicability of the PENT test (ASTM F 1473 “Standard Test Method for Notch Tensile Test to Measure the Resistance to Slow Crack Growth of Polyethylene Pipes and Resins”) for slow crack growth determination of polyethylene (PE) resins and extruded sol
9、id wall pipe. The PENT method was also evaluated as a quality control (QC) indicator for extruded pipe. PENT has been identified as a potential test protocol to supplement 80C hydrostatic testing of PE pipe resins. The evaluation included the compression molded plaques under slow cooled condition th
10、at were further prepared by machining and band sawing, and longitudinal samples cut directly from the wall of extruded pipe along the pipe direction. Testing included numerous laboratories and several commercially available medium density gas pipe resins. The resins chosen were 1st generation resins
11、 with significant long-term field experience. A number of extrusion conditions were also evaluated to determine if the PENT test has applicability as an extrusion quality monitor. 2. Results As shown in Attachment #1, molded plaque specimens that were further prepared by machining produced the most
12、consistent and reproducible results. Molded plaques prepared by band sawing yielded similar average test times but produced significant data scatter and a standard deviation of results about twice that for machined samples. Attachment #2 summarizes testing of samples cut longitudinally (axial direct
13、ion) from the wall of pipe, which yielded widely scattered and non-reproducible results. Sample preparation and direction of sample loading for pipe samples, compared to polymer orientation, appears to handicap PENT applicability to pipe. PPI also conducted PENT and 80 C sustained pressure testing (
14、ASTM D1598) on pipe samples prepared with several changes in extrusion variables (see attachment #4). These tests showed there is no apparent correlation between the PENT results (cut from axial direction) and those of traditional 80C hydrostatic testing of pipe (see attachment #3). No significant d
15、ifference between samples loaded with level-arm type or air-cylinder type test apparatuses was indicated. 3. Summary Based on the results of this evaluation, it appears that the PENT test as performed on molded plaques of PE further prepared by machining yields results that are correlatable to 80C h
16、ydrostatic testing of PE pipe. However, post preparation of molded plaque samples by band sawing produced a considerable increase in data scatter. Results of samples cut from extruded pipe (axial direction) indicate that there is no correlation between the PENT results and those of 80C hydrostatic t
17、esting. A number of causal factors are hypothesized including difficulty in sample preparation and direction of notching relative to polymer orientation; however, no further work is planned to evaluate potential factors for reductions in data scatter. Slow crack growth resistance is significantly in
18、creased when the notch is perpendicular to the polymer orientation direction, while decreased when the notch is parallel to the polymer orientation direction. PENT evaluation of pipe produced with various changes in extrusion variables produced nearly the opposite results of 80C hydrostatic tests. N
19、ote that hydrostatic tests measure the pipe strength in the hoop direction, while PENT tests using longitudinally cut specimens measure the slow crack growth resistance in the pipe direction under axial loading. PPI did not conduct PENT testing on the same pipe samples cut in the circumferential dir
20、ection. 4. Recommendations Based on the results of this evaluation, the task group concluded that the PENT test (ASTM F1473) may be used to compare the relative slow crack growth resistance of PE materials when samples are prepared from molded plaques. The task group further concluded that the PENT
21、test could not be used as a QC test for PE pipe when samples are cut in the axial direction. Due to the difference in measured slow crack growth property relative to polymer orientation directions, there appears to be an inverse correlation between PENT values obtained from PE pipe samples cut in th
22、e axial direction with long-term 80 C sustained pressure testing (ASTM D1598) performed on the same pipe samples. Attachment 1 Phase I. PENT Test Investigation Scope Testwork was initiated to evaluate newly issued Tech Team PENT Testers. Sample was provided as compounded black resin. Nominal resin p
23、roperties are 0.09 melt flow (190/2.16), 9.4 (190/21.6) and 0.954 density. Data evaluation included comparison of specimen measurement, specimen molding, and notching. Equipment operators for each lab were not varied for the course of the study. Pent Tester Load Type Lab A Tech Team Air Cylinder Lab
24、 B Tech Team Lever Arm Lab B Tech Team Lever Arm No. of Stations 12 20 20 Temp Verified Yes Yes Yes Notcher Conditions Dr. Brown Mfg ASTM F1473 Dr. Brown Mfg ASTM F1473 Dr. Brown Mfg ASTM F1473 Exceptions None None None Sample Prep Mold & Machined Mold & Band Saw Mold & Machined No. of Specimens 68
25、47 38 PENT, hrs 20.6 34.2 26.9 Std Dev, hrs 1.9 7.3 3.4 Std Dev, % 9.2% 21.3% 12.6% Between Lab Variability STD Dev, hrs 4.4 (Machined Specimens) STD Dev, % 19.0% Conclusions 1. Machining Improved accuracy of sample measurement thereby improving data. 2. Minimal difference noted between air cylinder
26、 and lever arm testing. 3. Noted that dimensions varied with time. A tt a c hme nt 2Phase II - PE NT T estin gS cop e: P i pe S am pl es w ere produc ed f r om th e s am e c om po un de d res i n i n P ha s e I f or ev al ua ti on of proc es s i ng c on di ti on s .T he pi pe s am pl es w ere 2” IP
27、S DR11 produc ed by a s ing le m an uf ac turer an d s up pl ied to al l pa r ti c ipa ti ng te s t l ab oratorie s .T he te s t s pe c i m en s w ere c ut ax i al l y f r om th e p i pe to m ee t g eo m etry c r i teri a. T he no tc h w as trans v ers e t o t he ax i al .T he proc es s c on di ti o
28、n s v arie d d r aw do w n a nd c oo l i ng te m pe r atu r e.L A B C L A B D L A B A L A B E L A B B L A B F L A B G A v er ageP E NT T es ter T ec h T ea m T ec h T ea m T ec h T ea m Dr . B r ow n M f g T ec h T ea m Dr B r ow n M f g T ec h T ea mLo ad T y pe Le v er Arm A i r Cy l i nd er A i r
29、 Cy l i nd er Le v er Ai r Le v er Arm Le v er ArmNo. o f S tat i on s 12 12 12 12 20 12 12T em p V erif i ed Y es No Y es Y es Y es Y esNotc he r Dr B r ow n M f g T ec h T ea m Dr . B r ow n M f g Dr . B r ow n M f g Dr . B r ow n M f g Dr . B r ow n M f gCond i ti on s A S T M F147 3 A S T M F147
30、 3 A S T M F147 3 A S T M F147 3 A S T M F147 3 A S T M F147 3 A S T M F147 3E x c ep ti on s No No No No F l at S pe c B ac k F i x tured t o No tc hS am pl e S pe c i m en 2” DR 11 2” DR 11 2” DR 11 2” DR 11 2” DR 11 2” DR 11 2” DR 11S amp leA No.o f S pe c i m es 6 11 2 12 1 2 6P E NT , h r s 137
31、.5 118.7 327.5 195.4 232.0 162.0 203.5 196.6S td Dev , h r s 15.6 43.3 275.1 76.2 22.6 30.5 69.8S td Dev , % 11.4% 36.5% 84.0% 39.0% 14.0% 15.0% 35.5%B No. o f S pe c i m en s 6 11 2 12 1 2 3P E NT , h r s 93.6 98.9 155.0 83.7 192.0 105.1 118.0 121.6S td Dev , h r s 10.1 36.6 94.8 35.6 20.4 35.2 40.
32、5S td Dev , % 10.8% 37.0% 61.1% 42.5% 19.4% 29.8% 33.3%C No. o f S pe c i m en s 7 11 2 12 1 2P E NT , h r s 79.6 92.8 92.5 74.2 102.0 122.6 93.9S td Dev , h r s 37.0 36.3 13.4 24.1 9.1 17.2S td. Dev , % 46.5% 39.2% 14.5% 32.5% 7.4% 18.3%C No. o f S pe c i m en s 6 11 2 12 1 2P E NT , h r s 103.3 12
33、8.0 143.0 89.3 105.0 122.8 115.2S td Dev , h r s 16.2 54.5 5.7 23.6 9.1 19.6S td Dev , % 15.7% 42.6% 4.0% 26.5% 7.4% 17.0%E No. o f S pe c i m en s 6 11 2 12 1 2 3P E NT , h r s 96.9 104.7 111.0 89.3 105.0 98.0 131.3 100.8S td Dev , h r s 16.7 42.1 15.6 23.6 11.7 27.7 7.7S td Dev , % 17.3% 40.2% 14.
34、0% 26.5% 11.9% 21.1% 7.6%H No. o f S pe c i m en s 6 11 2 12 1P E NT , h r s 130.2 205.8 158.5 119.6 58.0 112S td Dev , h r s 10.1 77.6 17.7 24.7 73.2S td Dev , % 7.7% 37.7% 11.2% 20.6% 66.4%I No. o f S pe c i m en s 6 11 2 12 1P E NT , h r s 149.1 211.3 153.0 146.5 78 167.6S td Dev , h r s 14.8 110
35、.8 14.1 31.7 27.5S td Dev , % 9.9% 52.4% 9.2% 21.6% 16.4%Co n clusion s 1. Data v aria bi l i ty i nc r ea s ed f or m os t l ab oratorie s .2. A l arge s ou r c e o f th e v aria bi l i ty i s be l i ev ed to be th e d i f f i c ul ty i n p r ec i s el y no tc hi ng a c urv ed s pe c i m en w i tho
36、 ut a f i x ture.3. A po ten ti al s ou r c e o f v aria bi l i ty m ay be th e s am pl e m ea s urem en t o f a c urv ed s pe c i m en .A tt a c hme nt 3Ph ase I I I - Pi p e Pr o cessing - 80C H o o p Str en g thS amp le S p ec 1 S p ec 2 S p ec 3 L A B A L A B BA No.o f S pe c i m en s 3 180 C HS
37、 , h r s 841 879 1075 926 1543S td Dev , h r s 126S td Dev , % 14%B No. o f S pe c i m en s 3 180 C HS , h r s 460 1349 2111 1094 926S td Dev , h r s 826S td Dev , % 76%C No. o f S pe c i m en s 3 180 C HS , h r s 978 1388 1868 1364 1246S td Dev , h r s 445S td. Dev , % 33%C No. o f S pe c i m en s
38、3 180 C HS , h r s 770 1201 1319 1068 1297S td Dev , h r s 289S td Dev , % 27%E No. o f S pe c i m en s 3 180 C HS , h r s 1635 2834 2636 2303 1487S td Dev , h r s 643S td Dev , % 28%H No. o f S pe c i m en s 3 180 C HS , h r s 279 790 1593 705 1628S td Dev , h r s 662S td Dev , % 94%I No. o f S pe
39、c i m en s 3 180 C HS , h r s 886 1019 1306 1056 1802S td Dev , h r s 215S td Dev , % 20%A t t a c h m e n t 4P h a s e I I I - P i p e P r o c e s s i n g v e r s u s P E N T a n d H o o p S t r e n g t hS c o p e P i p e S a m p l e s w e r e p r o d u c e d f r o m t h e s a m e c o m p o u n d e
40、 d r e s i n i n P h a s e I f o r e v a l u a t i o n o f p r o c e s s i n g c o n d i t i o n s .T h e p i p e s a m p l e s w e r e p r o d u c e d b y a s i n g l e m a n u f a c t u r e r a n d s u b m i t t e d t o a l l p a r t i c i p a t i n g t e s t l a b o r a t o r i e s .P e n t d a t
41、 a f r o m L a b C w a s u s e d a s a b a s i s a s i t i s m o s t c o m p l e t e w i t h m i n i m u m v a r i a b i l i t y .L a b A 8 0 C d a t a w a s u s e d a s a b a s i s a s i t h a d t h e m i n i m u m v a r i a b i l i t y .T h e p r o c e s s c o n d i t i o n s a r e s h o w n b e l
42、 o w .D e s i g n o f E x p e r i m e n t s w a s t h r e e f a c t o r , f u l l f a c t o r i a l w i t h i n i t i a l p o i n t r e p l i c a t i o n .T w o d a t a p o i n t s c o u l d n o t b e g e n e r a t e d d u e t o p r o c e s s l i m i t a t i o n .W a l l D r a w D o w n D i a D r a
43、w D o w n C o o l i n g R a t eLow 24% 15% 62FH i g h 24% 54% 83FC o n d i t i o n W a l l D r a w D o w n O D D r a w D o w n N u m b e r P E N T , h S t d D e v , % N u m b e r 8 0 C H S , h S t d D e v , %A H i g h H i g h H i g h 6 1 3 7 . 5 1 1 . 4 % 3 926 14%B Low Low Low 6 9 3 . 6 1 0 . 8 % 3
44、 1094 76%C Low Low H i g h 6 7 9 . 6 4 6 . 5 % 3 1364 33%D H i g h Low Low 6 1 0 3 . 3 1 5 . 7 % 3 1068 27%E H i g h Low H i g h 6 9 6 . 9 1 7 . 3 % 3 2303 28%F Low H i g h Low U n a b l e t o P r o d u c e P i p e a t T h i s C o n d i t i o nG Low H i g h H i g h U n a b l e t o P r o d u c e P i
45、p e a t T h i s C o n d i t i o nH H i g h H i g h Low 6 1 3 0 . 2 7 . 7 % 3 705 94%I H i g h H i g h H i g h 6 1 4 9 . 1 9 . 9 % 3 1056 20%S t a t i s t i c s A v e r a g e 1 1 2 . 9 1 7 . 0 % 1217 42%S t d D e v , % 23% 43%R e p l i c a t i o n 108% 114%A f f e c t R e d u c e d O D D r a w D o w
46、n I n v e r t e d M a j o r M a j o rR e d u c e d O D & W a l l D r a w D o w n I n v e r t e d M a j o r M a j o rR e d u c e d C o o l i n g R a t e N e g l i g i b l e M i n o rC o n c l u s i o n s 1 . G o o d R e p l i c a t i o n o f I n i t i a l C o n d i t i o n s2 . N o t c h i n g o f P
47、i p e S p e c i m e n s t r a n s v e r s e t o a x i a l r e v e r s e d t h e e x p e c t e d r e l a t i o n s t o d r a w d o w n a n d c o o l i n g r a t e .3 . D r a w d o w n p r o v i d e d a m o j o r a f f e c t u n d e r b o t h m e a s u r e s .4 . U n a b l e t o i n d i v i d u a l l y q u a n t i f y w a l l d r a w d o w n a f f e c t o r m e a s u r e i n t e r a c t i o n t o d i a m e t e r d r a w d o w n .5 . C o o l i n g a f f e c t n o t s i g n i f i c a n t f o r t h e s e p r o d u c t i o n r u n s .
