HYDROSTATIC PRESSURE EFFECTS ON 1/4 INCH POLYPROPYLENE LINE Ronald Erwin Harder NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS HYDROSTATIC PRESSURE EFFECTS ON 1/4 INCH POLYPROPYLENE LINE by Ronald Erv/in Harder Thesis Advisor : E. B. Thornton Co-Advisor : S. P. Tucker March 1972 Apptiovzd faon. puhtic ^eXeaie; du>tnAJbution unLimlt2.d. Hydrostatic Pressure Effects on 1/4 Inch Polypropylene Line by Ronald Erwin Harder Lieutenant, United States Navy B.S., United States Naval Academy, 1964 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY March 1972 ABSTRACT The effects of hydrostatic pressure on the mechanical properties of 1/4 inch polypropylene line were investigated. The line was exposed to hydrostatic pressures of 5,000 and 10,000 psi for periods of 6, 12, and 24 hours, respectively. Upon completion of the pressurization period, the line was removed from the pressure vessel and its ultimate tensile strength recorded and compared to that of the line before pressurization. There was an increase in the tensile strength of the line as pressure increased and time progressed, with a maximum increase of 3.1 percent occurring after pressurization at 10,000 psi for 12 hours and at 5,000 psi for 24 hours. Secondly, there was no measurable difference in the relative elongation of the line after pressurization as compared to that before pressurization. The mode of failure was investigated by testing individual line fibers. Microscopic observation after failure showed no discernible difference between the mode of failure before and after pressurization. In each case, the fibers presented a somewhat jagged edge and the outer portions of the fiber appeared to have peeled back. TABLE OF CONTENTS I. INTRODUCTION 6 II. PRESSURE VESSEL DESCRIPTION 8 I A. PROOF TESTING 11 B. COMPONENT DESCRIPTION , 12 1 . Hydraulic Power Source 12 2 . Air Compressor 17 3. Fluid Media 17 4 . Fittings , Valves and Tubing 18 5. Electrical Entry .... 18 III. TESTING PROCEDURE 20 A. DATA COLLECTION 20 B. DISCUSSION OF DATA 22 C. MODE OF FAILURE 28 IV. CONCLUSIONS 30 V. RECOMMENDED FUTURE RESEARCH 31 BIBLIOGRAPHY 32 INITIAL DISTRIBUTION LIST 33 FORM DD 1473 34 LIST OF FIGURES 1. Basic Dimensions of the Mk 13, Mod 2, High Capacity, 16 Inch Naval Projectile 9 2. Internal Dimensions of the Naval Postgraduate School Pressure Vessel 10 3. Schematic Diagram of Naval Postgraduate School Pressure Facility 13 4 . Naval Postgraduate School Pressure Testing Facility 14 5. Side View of Naval Postgraduate School Pressure Testing Facility, Showing Position of Pressure Vessel 15 6 . Sprague Model S-440 Hydraulic Power Unit 16 7. Typical Connection Between High Pressure Tubing and Female Fitting 19 8 . Instron Tensile Testing Machine 21 9 . Plot of Ultimate Tensile Strength vs . Time 24 10 . Plot of Ultimate Tensile Strength vs . Pressure 25 11. Microscopic Photographs of Individual Line Fibers After Failure 29 TABLE OF SYMBOLS AND ABBREVIATIONS STU Submersible Test Unit NCEL Naval Civil Engineering Laboratory NWC Naval Weapons Center MTT Massachusetts Institute of Technology WHOI Woods Hole Oceanographic Institution circ Circumferential Stress acial Axial Stress I. PRODUCTION Synthetic materials have received extensive use in the ocean environ- ment since their introduction in about 1950 [7] . They have been used in manners ranging from the use of nylon for the lifting of heavy loads, as in the recovery of the submersible Alvin, to the plexiglass construction of the underwater observatory NEMO. The advantages of the synthetic materials over their metal counterparts are that they are lighter, giving a greater strength to weight ratio, and they are more flexible. Poly- propylene, the lightest of the synthetics, is positively buoyant in sea water and has been used for anchor and buoy lines as well as providing an inverted catenary recovery line [6] . Muroaka, at NCEL, has done extensive work in the field of the bio- deterioration of materials in the deep ocean. In one particular test, nylon and polypropylene lines were attached to a Submersible Test Unit (STU) which was left at a depth of 6800 feet for a period of 13 months. The tensile strength of these lines was recorded before and after sub- mergence with the result that the tensile strength had increased by approximately 8 percent after exposure to the ocean environment [6] . Considerable effort has also been applied to solving the problem of line dynamics; that is, the determination of the dynamic response of a synthetic line with one end attached to a platform with six degrees of freedom, and the other end attached to a heavy weight suspended in the ocean. The mathematical models developed to date have not accurately predicted measured results [5] . Muraoka's work and the line dynamics problem provided the impetus for this study. It was hoped that a thorough investigation of the effects of hydrostatic pressure on the mechanical properties of synthetic materials would provide an input to the line dynamics problem such that a better mathematical model could be developed. The first step was to obtain a pressure vessel so that the hydrostatic pressures encountered in the deep ocean environment could be simulated in the laboratory. This was accomplished by using a 16-inch Naval projectile in the construction of a pressure testing facility. A description of the Naval Postgraduate School pressure testing facility follows this introduction . Primarily due to the availability of material, 1/4 inch polypropylene line was chosen as the test material. The effects of hydrostatic pressure on the mechanical properties of the polypropylene line were determined by exposing the line to various hydrostatic pressures for different periods of time and comparing the mean ultimate tensile strength of the line before and after exposure. An attempt was also made to determine the mode of failure by considering individual fibers of the line and examining them microscopically after failure. II. PRESSURE VESSEL DESCRIPTION In the past decade, considerable effort has been expended in the exploration and utilization of the deep ocean for such purposes as Naval operations, canrercial enterprises and scientific research. Hydrostatic pressure, in addition to corrosion, presents one of the most serious problems in the effective utilization of the deep ocean environment; pressure increases at a rate of about 0.44 psi per foot of depth with 16,000 psi approximately representing the deepest points in the ocean. The Naval Postgraduate School pressure testing facility utilizes an MK13, Mod 2, 16-inch high capacity Naval projectile as the pressure vessel; the basic installation was received by the Naval Postgraduate School in 1968 from NWC China Lake. It is believed that this method was first used by Maurice Ewing, Allan Vine and Joe Vforzel at Lehigh University [1] , and subsequently at MIT, WHOI, NCEL and NW2 China Lake. Of the various types of projectiles available, the 16-inch high capacity type was originally chosen because it offered the largest internal volume. Figure 1 shows the basic dimensions of this projectile and Figure 2 the internal dimensions of the Naval Postgraduate School pressure vessel. The exact composition of the steel used in the produc- tion of these projectiles is not known; however, the alloy is generally described as a special high-capacity projectile Chromium-Nickel- Molybdenum alloy steel with a nunimum tensile yield strength of 78,000 psi, an ultimate tensile strength of 105,000 psi and an elongation of 18 percent [4] . <- CO IS W -11.00"- 9.75"- P"l S O iw hi o ■g.& Is ■a •& Id fe o- TOP PLUG 3.250"- CAST IN PLACE EPOXY SEAL LOCKING RING 9.47' .ELECTRICAL FITTING < 3.250" BOTTOM Pl^UG 7- HIGH PRESSURE FITTING FIGURE 2. Internal Dimensions of the Naval Postgraduate School Pressure Vessel. 10 A. PROOF TESTING The pressure vessel is a typical thick walled cylinder, and as shown by NOEL [4] , the Lame solution is applicable to the calculation of stresses in such a vessel. Lame's solution for the circumferential stresses on the interior of the vessel can be expressed as circ P(0D2 - id2) -L-uo^ and the circumferential stresses on the exterior of the vessel as a . = 2p SU = 2.089p CirC (CD2 - ID2) The axial stresses in the thick walled vessel are assumed to be uniform across the thickness of the wall, and their magnitude can be calculated by a . , = p 0(ID ) „ = 0.545p axial ^(0D2 - ID2) A series of proof tests were run on the 16-inch projectile at NCEL [4] and the following conclusions and recommendations were made: 1. Pressure vessels fabricated from Mk 13, Mod 2, 16-inch Naval projectiles are useful up to 20,000 psi internal pressure. With proper precautions to prevent corrosion of the vessel body, they may be used with sea water. 2. It was recommended that the converted 16-inch Naval gun shells not be subjected to pressure cycling service at 20,000 psi until experi- mental data has been generated on which reliable and safe cycling pressure limits can be based. 11 B. COMPONENT DESCRIPTION A schematic diagram of the pressure testing facility as installed at the Naval Postgraduate School is shown in Figure 3. Front and side view photographs of the installation are illustrated in Figures 4 and 5 respectively. A discussion of the various components of the system follows . 1. Hydraulic Power Source The Sprague Model S-440 Power Unit, shown in Figure 6, provides a compact, high pressure, low volume hydraulic power source which is used to obtain internal pressures in the pressure vessel ranging from 0 to 20,000 psi. The S-440 Power Unit operates from a compressed air supply and consists of a Sprague Model S-216C-100 Air-Opera ted Pump, muffler, Lubro-Control Unit, driving air shutoff valve, output pressure gage, pressure outlet, bleed valve and baseplate. The S-216C-100 pump is a piston- type, air-operated, boost pump incorporating an automatically operated, snap action, air selector valve. This pump develops high pressures through application of the principle of differential areas. The pump employs a large area piston, air-driven at low pressure, to drive a small piston that displaces a small volume of fluid at high pressure. The output pressure developed by the small area piston is determined by the ratio between the area of the driving piston, the area of the driven piston and the operating air pressure applied. The 20,000 psi pump used in the Naval Postgraduate School installation has a 1:200 pumping ratio; i.e., an input air pressure of 100 psi will enable the pump to produce a fluid pressure of 20,000 psi. This same ratio applies to all but the lowest pressure ranges, where the efficiency of the pump decreases due to the increasing effect of friction in the 12 H P4 13 FIGURE 4. Naval Postgraduate School Pressure Testing Facility. 14 FIGURE 5. Side View of the Naval Postgraduate School Pressure Testing Facility Showing Position of Pressure Vessel. 15 »♦ r < . UALtir. <>*,♦<*. <>r ltr( iX-inm/t'M* FIGURE 6. Sprague Model S-440 Hydraulic Bower Unit. 16 pump at lew air pressures. The advantage of this type of pump is that when the input air pressure is regulated to a certain pressure, it is possible to leave the pump unattended while the prescribed output pressure is being built up in the pressure vessel. When the pressure in the vessel reaches the preset output pressure (200 times the input air pressure) the pump stalls and automatically shuts down. It will only resume pumping (again automatically) if the pressure on the output side drops, or the input air pressure increases. The Lubro-Control Unit, located in the driving air supply line, provides filtration, regulation and lubrication of the air supply. The air shutoff valve is positioned in the driving air supply line between the Lubro-Control Unit and the high pressure pump and is used to control the operation of the pump. 2. Air Compressor An Inger soil-Rand Type 30, Model 7 IT air compressor provides low pressure air at 100 psi to the Strague Hydraulic Power Unit described above; it is a 10 horsepower, two-stage, single acting, air-cooled com- pressor. It is equipped with a water-cooled aftercooler which reduces the discharge temperature of the compressed air and facilitates removal of water vapor and oil vapor, and is also equipped with dual speed regulation which permits a manual selection between constant speed con- trol (compressor is unloaded at a predetermined pressure while the motor continues to operate) and automatic start and stop control (makes or breaks electrical contact to the motor at predetermined pressures) . 3. Fluid Medium The fluid medium used in the Naval Postgraduate School instal- lation is ethylene glycol, a non-corrosive fluid. The sea water environment (Salinity 33.4 parts per thousand) was obtained by filling a cylindrical 17 tube, approximately 2 feet in length, 6.5 inches in diameter and closed on one end, with sea water and sealing the open end with a flexible diaphragm and hose clamp; the flexible diaphragm served to transmit the hydrostatic pressure of the pressure vessel to the sea water environment. 4. Fittings, Valves and Tubing The high pressure fittings and valves are rated for 60,000 psi use and the high pressure tubing for 30,000 psi use; all are fabricated from type 316 stainless steel. The tubing is 1/4 inch O.D. by .083 inch I.D. and connections are of the union type. The male tube has a 59 degree conical seating surface that fits into a corresponding 60 degree female conical seat in the body. The male tube and inner sleeve have left hand threads; the gland nut and opening in the body have right hand threads. When the gland nut is slipped over the sleeve and screwed into the opening in the body, the sleeve is tightened on the tubing at the same time that the conical seating surfaces are being sealed. Figure 7 shows the make-up of a typical connection between high pressure tubing and a female fitting. Piping on the low pressure side of the pump and all air piping is 3/4 inch galvanized pipe; standard 3/4 inch gate valves are used throughout the low pressure piping. 5. Electrical Entry Electrical entry is gained to the interior of the pressure vessel via a 7 conductor plug; location of the electrical plug is illustrated in Figures 2 and 3. 18 Assembled (Connection If 8 Body FIGURE 7. Typical Connection Between High Pressure Tubing and Female Fittings. 19 III. TESTING PROCEDURE A. DATA COLLECTION The purpose of the experiments was to compare the mechanical proper- ties, namely tensile strength and elongation, of 1/4 inch polypropylene line before pressurization to those after pressurization at various pressures and for varying durations. Because no method had been developed for tensile testing inside the pressure vessel, i.e., in situ, and due to limitations on the time available to devise such a method, testing of the line samples was commenced within approximately 15 minutes after removal from the pressure vessel. All testing was done on the Instron testing machine illustrated in Figure 8. The tensile testing device used for holding the polypropylene line is also illustrated in Figure 8 (arrow) . The line was reeved around the inside of the device so that the line would not slip when tension was applied. The tensile testing device was designed in such a way that the line was tangent at top and bottom to pieces of round stock so that when tension was applied failure occurred between the two points of tangency, not at the points of contact with the device. This method of testing the line proved satisfactory with the exception that it was not possible to precisely measure the absolute elongation of each sample since some elongation did occur inside of the device; a typical elongation of approximately 60 percent was recorded. There was no measurable difference in the relative elongation of the line after pressurization compared to that before pressurization. 20 FIGURE 8. Instron Tensile Testing Machine. 21 B. DISCUSSION OF DATA Table 1 presents a summary of the data collected. A plot of mean ultimate tensile strength versus time (pressure held constant) is shown in Figure 9, and Figure 10 shows a plot of mean ultimate tensile strength versus pressure (time held constant) . In all cases the tensile strength of the line increased after pressurization. However/ the fact that the increase in the tensile strength of the line after pressurization at 10,000 psi for 12 hours was not further increased after pressurization at 10,000 psi for 24 hours was unexpected. A confidence interval for the true mean of the population having the degree of confidence (1 - a) was calculated for each set of data. It is assumed that the sample population has a normal distribution. The statistic, t-*ZJL s/Ax is the value of a random variable having the Student t_distribution with n-1 degrees of freedom, where y is the mean of the normal population from which the sample is taken, thus, C s-w4<^< x + tr4< = l-~ 2 ^ V^\ - i ^ ^ where, x = population mean t = t-statistic s = standard deviation of the population n = number of samples in the population 1 - a = confidence interval li = true population mean 22 I b B ITJ •H > to co o •^ in co CT> rH ■^ • • • • • • • r* co o co o in CN ^ VD 00 <^> vo in 00 r> r* r» r> r- r- r- V V V V V V V 3 3 3 n. 3. 3. 3. V V V V V V V CN •^ r- ro CO r^ r^ r>- r- r^ rH 00 m vo r- £> *3" <^D CO VT> m 1-* • • • • • • • O ID rH 00 O VD O ■** LO r- in in •^ r^ Is- r-» co co r>- r~ r- | co 1 N 0 1 co CO CO 1 -U o w 0 O fO K o K a Q r» r>- t^ r^ •H 'w +J m o 04 H En Ultimate Tensile Strength (Lbs) 24 o o o CD o % rH CO w o o o in 0) •H to B 0 -P 0a o E>4 Ultimate Tensile Strength (lbs) 25 This inequality provides an exact 1 - a confidence interval for \x provided the assumption of normal population is true. A confidence interval of 90 percent (a = .10) was calculated for the data collected and is tabulated in Table 1. These confidence intervals are also indi- cated as dotted lines on the plots of ultimate tensile strength versus time and pressure in Figures 9 and 10 respectively. Inconsistencies in the data could exist due to the fact that the temperature of the sea water environment to which the line samples were exposed was uncontrollable. Synthetic materials are sensitive to temperature variations [2] , and the temperature of the sea water environment did vary during some of the tests. In initial attempts to collect the data presented above, inconsis- tencies were encountered as progression was made through a coil of line. It was generally found that the mechanical properties of the line changed as the coil of line was used. Insufficient data was collected to state this as a fact; however, it is felt that due to the compaction of the outer layers of line on the coil, the line nearer the center of the coil is stronger. The line samples that were used to collect the data pre- sented above were removed from the outer portions of a large diameter coil of line in order to avoid the possibility just described. A statistical Student t-test for comparing two sample means [3] was run on the data collected in order to make an unbiased decision about the relative values of the mean ultimate tensile strength before and after pressurization. The statistical test was based on the null hypothesis : H : x - x =1 percent of x = 7.406 o p u r u 26 where, x = mean ultimate tensile strength after pressurization x = mean ultimate tensile strength before pressurization The alternate hypothesis is stated as: H_: x - x >7.406 1 p u If the null hypothesis can be rejected, then the alternate hypothesis can be unbiasedly accepted at some level of significance. It is necessary to assume that the sample populations have a normal distribution in using the Student t-distribution; this appears to be a reasonable assumption for the data collected. The t-statistic was calculated using the formula: where, x and x are as indicated above p u n = n = number of samples in each population = 10 6=1 percent of x = 7.406 s = population variance The result of comparing the mean ultimate tensile strength of the line after pressurization to that before pressurization via the Student-t test described above was that the null hypothesis could be rejected and the alternate hypothesis accepted at a 97.5 percent level of significance for the cases where the line samples were exposed to hydrostatic pressures of 10,000 psi for 12 and 24 hours and 5,000 psi for 24 hours; this implies that in these cases the tensile strength of the line increased by at least 1 percent of x after exposure. A level of significance less than 90 percent was calculated for pressurization at 5,000 psi for 6 and 12 hours and 10,000 psi for 6 hours. Hence, the effect of hydrostatic pres- sure on the breaking strength of 1/4 inch polypropylene line is dependent on the duration and degree of pressurization. 27 C. MDDE OF FAILURE An attempt was also made to determine the mode of failure of the polypropylene line. This was accomplished by testing individual fibers of the line and observing them under a microscope after failure. Figure 11 shows the microscopic photographs of individual line fibers that were broken before pressurization and after pressurization at 10,000 psi for 6 hours. In the upper portion of each photograph, a sample of fiber before testing is shown to demonstrate the degree of necking down at failure; the blunted end of the samples is due to cutting the fiber. There is no discernible difference between the mode of failure before pressurization compared to that after pressurization. In each case there appears to be a somewhat jagged edge, and in each case the outer portions of the fiber seem to have peeled back, as in the removal of a banana peel. This is observable only in the lower right-hand photograph, but did occur in every case. In the photographs in which this is not visible, the outer fibers had peeled back beyond the field of view of the microscope. 28 Before Pressurization After Pressurization : 10,000 PSI for 6 Hours FIGURE 11. Microscopic Photographs (40X) of Individual Line Fibers After Failure. 29 IV. CONCLUSIONS a. There was an increase in the tensile strength of the line for all cases as pressure increased and time progressed with a maximum increase of 3.1 percent occurring after pressurization at 10,000 psi for 12 hours or at 5,000 psi for 24 hours. b. There was no measurable difference in the relative elongation of the line after pressurization compared to that before pressurization. c. There is no discernible difference between the mode of failure before and after pressurization. d. The hydrostatic pressures encountered in the deep ocean environ- ment have no deleterious effects on the mechanical properties of 1/4 inch polypropylene line which has been exposed for 24 hours or less. 30 V. RECOMMENDED FUTURE RESEARCH It is not possible, with the limited amount of data collected, to make any contribution which would directly solve the line dynamics prob- lem as was originally hoped. The following areas are reconmended for future research. a. Devise a method whereby tensile testing could be accomplished in situ, i.e., inside the pressure vessel. b. Conduct an in situ analysis of the creep characteristics of synthetic materials. c. Develop a method of absolute temperature control for the Naval Postgraduate School pressure vessel so that more meaningful data could be collected and so that the deep ocean environment could be better simulated. A means of doing this has been described by NCEL [4] . 31 BIBLIOGRAPHY 1. Edgerton, H. E. and I.D. Hoadley, "Pressure Testing Facility," Underwater Engineering, v. 2, no. 2, p. 29-30, March/April 1961. 2. Imperial Chemical Industries Limited, Plastics Division, Engineering Properties of Thermoplastics , Wiley-Interscience , 1970. 3. Miller, I. and J. E. Freund, Probability and Statistics for Engineers, Prentice-Hall, Inc., 1965. 4. Naval Civil Engineering Laboratory Technical Note N-755, The Conversion of 16-Inch Projectiles to Pressure Vessels , by K. 0. Gray and J. D. Stachiw, June 1965. 5. Naval Civil Engineering laboratory Technical Report R-703, Dynamic Response of Lifting Lines for Oceanic Operations , by C. L. Liu, November 1970. 6. Naval Civil Engineering Laboratory Technical report R-456, Deep Ocean Biodeterioration of Materials - Part IV. One Year at 6,800 Feet, by James S. Muraoka, June 1966. 7 . North American Rockwell Corporation , Handbook of Ocean and Underwater Engineering , p. 4-42, McGraw-Hill, 1969. 32 INITIAL DISTRIBUTION LIST No. Copies 1. Defense Documentation Center 2 Cameron Station Alexandria, Virginia 22314 2. Library, Code 0212 2 Naval Postgraduate School Monterey, California 93940 3. Professor E. B. Thornton, Code 58Tm 5 Department of Oceanography Naval Postgraduate School Monterey, 1 alif ornia 93940 4. LT Ronald E. Harder, USN 1 589-C Sampson Lane Monterey, California 93940 5. Senior Oceanographer S. P. Tucker, Code 58Tu 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 6. Dr. James S. Muraoka 1 Naval Civil Engineering Laboratory Port Hueneme, California 93041 7. Dr. C. L. Liu 1 Naval Civil Engineering Laboratory Port Hueneme, California 93041 8. Mr. Jack Mellor 1 Department of Oceanography Naval Postgraduate School Monterey, California 93940 9. Oceanographer of the Navy *■ The Madison Building 732 N. Washington Street Alexandria, Virginia 22314 10. Dr. Ned A. Ostenso 1 Office of Naval Research, Code 480D Arlington, Virginia 22217 11. Department of Oceanography, Code 58 3 Naval Postgraduate School Monterey, California 93940 33 UNCLASSIFIED Secuntv Classification DOCUMENT CONTROL DATA -R&D r Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified) i ORiCina ting ACTIVITY (Corporate author) Naval Postgraduate School Monterey, California 93940 2a. REPORT SECURITY CLASSIFICATION Unclassified 26. GROUP 3 REPORT TITLE Hydrostatic Pressure Effects on 1/4 Inch Polypropylene Line 4 DESCRIPTIVE NOTES (Type of report and, inclusive dales) Master's Thesis; March 1972 5 autmORiSi (First name, middle initial, last name) Ronald Erwin Harder 6 REPOR T D A TE March 1972 7a. TOTAL NO. OF PACES 35 7b. NO. OF RE FS 7 (a. CONTRACT OR GRANT NO b. PROJ EC T NO 9a. ORIGINATOR"* REPORT NUMBER(S) 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned this report) 10 DISTRIBUTION STATEMENT Approved for public release; distribution unlimited, ii supplementary notes 12. sponsoring military activity Naval Postgraduate School Monterey, California 93940 13 ABSTRACT The effects of hydrostatic pressure on the mechanical properties of 1/4 inch polypropylene line were investigated. The line was exposed to hydrostatic pressures of 5,000 and 10,000 psi for periods of 6, 12, and 24 hours, respectively. Upon completion of the pressurization period, the line was removed from the pressure vessel and its ultimate tensile strength recorded and compared to that of the line before pressurization. There was an increase in the tensile strength of the line as pressure increased and time progressed, with a maximum increase of 3.1 percent occurring after pressurization at 10,000 psi for' 12 hours and at 5,000 psi for 24 hours. Secondly, there was no measurable difference in the relative elongation of the line after pressurization as compared to that before pressurization. The mode of failure was investigated by testing individual line fibers. Microscopic observation after failure snowed no discernible difference between the mode of failure before and after pressurization. In each case, the fibers presented a somewhat jagged edge and the outer portions of the fiber appeared to have peeled back. DD ,F.T.,1473 S/N 0101 -807-681 1 (PAGE 1) 34 UNCLASSIFIED Security Classification A-9140S UNCLASSIFIED Security Classification KEV WORDS Polypropylene Line Hydrostatic Pressure Strength Elongation Failure )D,Fr\,1473 '"OK) /*« ^101-907-69?! UNCLASSIFIED 35 Security Classification A- 3 1 404 Thesis H2065 Harder Cl 134487 Polypropylene Hne. Thesis H2065 Harder c.l Hydrostatic pressure effects on 1/4 inch polypropylene line. 134487 thesH2065 Hydrostatic pressure effects on 1/4 inch 3 2768 002 08155 6 DUDLEY KNOX LIBRARY