Acoustic emission standards and technology update ASTM special technical publication 1353

Sach tiếng Anh: Acoustic Emission: Standards and Technology Update, Acoustic Emission (AE) has been commercially available for more than thirty (30) years. Has any progress been made? The purpose of the Symposium held in January 1998 in Plantation, Florida was to discuss the evolution of the technology of AE over the years in instrumentation, applications, standards and codes and its overall worldwide acceptance. Authors have made comparisons between AE and other Nondestructive Testing (NDT) technologies as to their suitability in solving practical industrial problems worldwide.

S T P 1353 Acoustic Emission: Standards and Technology Update Sotirios J Vahaviolos, editor ASTM Stock #: STP1353 ASTM 100 Barr Harbor Drive West Conshohocken, PA 19428-2959 Printed in the U.S.A Library of Congress Cataloging-in-Publication Data Acoustic emission : standards and technology update / Sotirios J Vahaviolos, editor p c m - (STP : 1353) Includes bibliographical references "ASTM Stock #: STP1353." ISBN 0-8031-2498-8 Acoustic emission testing I Vahaviolos, Sotirios J II Series: ASTM special technical publication : 1353 TA418.84 A263 1999 620.1 '27 dc21 99-38512 CIP Copyright 1999 AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA All rights reserved This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher Photocopy Rights Authorization to photocopy Items for internal, personal, or educational classroom use, or the Internal, personal, or educational classroom use of specific clients, Is granted by the American Society for Testing and Materials (ASTM) provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923; Tel: 508-750-8400; online: http //www.copyrig ht.com/ Peer Review Policy Each paper published in this volume was evaluated by two peer reviewers and at least one editor The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM Committee on Publications To make technical information available as quickly as possible, the peer-reviewed papers in this publication were prepared "camera-ready" as submitted by the authors The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of the peer reviewers In keeping with long standing publication practices, ASTM maintains the anonymity of the peer reviewers The ASTM Committee on Publications acknowledges with appreciation their dedication and contribution of time and effort on behalf of ASTM Printed in Philadelphia,PA October 1999 Foreword This publication, Acoustic Emission: Standards and Technology Update, contains papers presented at the symposium of the same name held in Plantation, Florida, on 22-23 January 1998 The symposium was sponsored by ASTM Committee E7 on Nondestructive Testing The symposium chairman was Sotirios J Vahaviolos, Physical Acoustics Corporation Contents Overview vii AE SOURCES: CHARACTERIZATION Use of Acoustic Emission to Characterize Focal and Diffuse Microdamage in BonemR M RAJACHAR, D L CHOW, C E CURTIS, N A WEISSMAN, AND D H KOHN CONCRETE APPLICATIONS A Proposed Standard for Evaluating Structural Integrity of Reinforced Concrete Beams by Acoustic E m i s s l o n - - s , YUYAMA,T OKAMOTO,M SHIGEISH],M OHTSU, AND T KISI-H 25 On the Necessity of a New Standard for the Acoustic Emission Characterization of Concrete and Reinforced Concrete Structures E o NESWJSKI 41 AE Evaluation of Fatigue Damage in Traffic Signal Poles H R HAMILTON,HI, T J FOWLER, AND J A PUCKETI" INTmGRrrY AND LEAK 50 DETECTION/LOCATION METHODS The Development of Acoustic Emission for Leak Detection and Location in LiqnidFilled, Buried Pipelines R ~ MILLER, A A POLLOCK, P FINKEL, D J WATI'S, J M CARLYLE, A N TAFURI, AND J J y1~7.71 JR 67 Acoustic Emission and Ultrasonic Testing for Mechanical Integrity s J TERNOWCHEK, T J GANDY, M V CALVA, AND T S PATIT~SON 79 AE SENSORS, STANDAm)S, AND QUANTITATIVEAE Calibration of Acoustic Emission Transducers by a Reciprocity Method H HATANO 93 DIVERSE INDUS1RIAL APPLICATIONS Acoustic Emission Applied to Detect Workpiece Burn During G r i n d i n g - 107 P R DE AGUIAR, P WILLETI', AND J WEBSTER Analysis of Fracture Scale and Material Quality Monitoring with the Help of Acoustic Emission Measurementsms A NIKULIN,M A SHTREMEL,V G KnANZH~, 125 E Y KURIANOVA, AND A P MARKELOV Characterization of Micro and Macro Cracks in Rocks by Acoustic Emission-G M NAGARAJA RAO, C R L MURTHY, AND N M RAJU Prediction of Slope Failure Based on AE Activity T SHIOTANIANDM OHTSU 141 156 A E SOURCES: RESEARCH T o P I c S Identification of AE Sources by Using SiGMA-2D Moment Tensor Analysism 175 M SHIGEISHI AND M OHTSU TRANSPORTATION APPLICATIONS, STANDARDS, AND METHODOLOGy Practical AE Methodology for Use on AircraftmJ M CARLYLE, H L BODINE, S S HFa'qLEY, R L DAWES, R DEMESKI, AND E v K HILL 191 COMPRESSED GAS APPLICATIONS AND STANDARDS Periodic AE Re-Tests of Seamless Steel Gas Cylindersmp R BLACKBURN 209 Field Data on Testing of Natural Gas Vehicle (NGV) Containers Using Proposed ASTM Standard Test Method for Examination of Gas-Filled Filament-Wound Pressure Vessels Using Acoustic Emission (ASTM E070403-95/1)-R D FULTINEER, JR AND J R MITCHELL 224 Acoustic Emission Testing of Steel-Lined FRP Hoop-Wrapped NGV Cylinders-A AKHTAR AND D KUNG 236 Author Index 257 Subject Index 259 Overview Acoustic Emission (AE) has been commercially available for more than thirty (30) years Has any progress been made? The purpose of the Symposium held in January 1998 in Plantation, Florida was to discuss the evolution of the technology of AE over the years in instrumentation, applications, standards and codes and its overall worldwide acceptance Authors have made comparisons between AE and other Nondestructive Testing (NDT) technologies as to their suitability in solving practical industrial problems worldwide As the newcomer in the Nondestructive Evaluation (NDE) industry, AE was first tried on applications where other NDT technologies had previously failed or was used where wild financial cost savings were promised The issue of suitability of AE for an application was never considered until the very late 70's and early 80's, when a new breed of industrial and university researchers entered the field in USA, Europe and Japan AE "noise counting" was replaced with basic work on source characterization, wave propagation, mode conversion, the study of the inverse problem using a number of Green's functions, pattern recognition and, most importantly, they considered AE as a science, using all available tools at their disposal While the university academics worked hard to identify certain AE waveform features with source and failure mechanisms, a number of industrial researchers explored a myriad of "Pseudo-sources" of AE and their statistical nature Instead of absolute one-on-one correlations and exact location of defects, practitioners developed zonal location and data bases based on case studies that enabled them to relate AE to fracture mechanics, corrosion phenomena, and overall part integrity assessment, especially in composite structures first and then in pressurized systems and individual components The introduction of artificial intelligence, coupled with existent data bases, led to the development of ready-to-use knowledge-based systems based on very complex structures that are found in power utilities, refineries, chemical plants, complex pipelines, wind tunnels, aircraft structures, etc The hard work of the late 70's and early 80's by CARP (Committee on AE for Reinforced Plastics) and the wide application of AE in testing of Fiberglass (FRP/GRP) vessels and pipes rejuvenated the technology! Eventually they became ASTM Standards now widely in use The well-publicized early failures of AE in several metal vessels tests, especially in Europe by INEXPERIENCED personnel, were now reconsidered Unknown to most AE Researchers/ Practitioners a behind the scenes branch of CARP known as CAM (Committee for Acoustic Emission for Metal) start looking carefully utilizing vast experience in Fracture Mechanics, Civil Engineering, NDT and, most importantly, vessel construction maintenance and use, realized early on that the same inexperience that prevented the use of AE in FRP in the early 70's has prevented users to Metal Vessel Testing by AE With the help of t h e ' 'core members" of CARP, metal vessel testing was reconsidered, especially after the successes of MONPAC ~ (a commercially available knowledge-based expert system that formed the basis of acceptance of AE by American Society of Mechanical Engineers (ASME) and Department of Transportation (DOT) and, thus, gave credence to the newcomer NDE technology) In addition, the more than ten AE ASTM Standards and AE's acceptance by American Society for Nondestructive Testing (ASNT) as another major NDT technique and the establishment of Level III in AE were major steps forward for the technology worldwide vii viii ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY In this Symposium basic important work is being presented that constitutes the basis for Natural Gas Vehicle (NGV) Cylinder Testing with AE, no matter how controversially some people might view their work When properly applied, AE can save NGV assets for customers as the ASTM FRP vessel has done for the past 10-plus years It is interesting to note that infrastructure and slope stability applications worldwide and especially in Japan are now to the point of standardization of existing working procedures We were very much encouraged by the continuing success of the Reciprocity Method for Calibrating AE Sensors and hope that it eventually will become another ASTM Standard As for the other applications, I can only comment on their existing uniqueness from micro damage in bones to burning of grinding tools in high speed manufacturing We hope this publication will prove interesting to a wide spectrum of readers, especailly those who look for new AE Standards and are interested to explore the future directions for the application of the Acoustic Emission Technology Sotirios J Vahavidos, Ph.D Physical Acoustics Corporation Princeton Junction,NJ 08550 SymposiumChairmanand Editor AE Sources: Characterization Rupak M Rajachar, Dann L Chow, l Christopher E Curtis, Neil A Weissman, and David H Kohn USE O F A C O U S T I C E M I S S I O N T O C H A R A C T E R I Z E F O C A L AND D I F F U S E M I C R O D A M A G E IN BONE REFERENCE: Rajachar, R M., Chow, D L., Curtis, C E., Weissman, N A., and Kolm, D H., "Use of Acoustic Emission to Characterize Focal and Diffuse Microdamage in Bone," Acoustic Emission: Standards and Technology Update, ASTM STP 1353, S J Vahaviolos, Ed., American Society for Testing and Materials, West Conshohocken, PA, 1999 A B S T R A C T : Fatigue of cortical bone results in the initiation, accumulation, and propagation of microdamage AE techniques were adopted to monitor damage generated during ex-vivo tension-tension fatigue testing of cortical bone The primary objectives were to determine the sensitivity of AE in detecting microdamage in cortical bone and to elucidate mechanisms guiding the onset of microdamage Fatigue cycle data and histological data show that AE techniques are more sensitive than modulus reduction techniques in detecting incipient damage in cortical bone Confocal microscopy revealed the ability of AE to detect crack lengths and damage zone dimensions as small as 25 gm Furthermore, measured signal parameters such as AE events, event amplitude, duration, and energy suggest that AE techniques can detect and distinguish microdamage mechanisms spatially and temporally in bone As fatigue processes continue, AE increases in terms of number of events, event intensities and spatial distribution Diffuse damage appears to be a precursor to the development of linear microcracks The spatial and temporal sequence of AE events enables differentiation between linear microcracks and more diffuse damage K E Y W O R D S : acoustic emission, bone, microdamage, confocal microscopy l Graduate Student, Department of Biomedical Engineering, College of Engineering, University of Michigan, Ann Arbor, MI 48109-2125 Undergraduate Student, Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078 Associate Professor, Departments of Biologic and Materials Sciences, School of Dentistry and Biomedical Engineering, College of Engineering, University of Michigan, Ann Arbor, MI 48109-1078 Copyright9 by ASTM International www.astm.org AKHTAR AND KUNG ON NGV CYLINDERS ~ i L079-10/90 II j L1131-4/91 i I I ! i I i-"Damage ' ~5~ FIG -Orientation of liner flaws in relation to FRP abrasion damage This illustration is a two dimensional representation of the curved cylinder surface obtained through making an imaginary axial cut and flattening Acoustic Emission Testing Acoustic emission remains an attractive option because of its potential for in-situ testing, i.e without removing the cylinder from the vehicle However, that potential may be realized only through demonstrated correlation between acoustic emission and structural integrity of the vessel The total number of hits measured in the present work during the first test cycle (Table 1) are not helpful in that regard The as-received cylinders subjected to burst tests (Table 3) gave values in the range of 61.9 • 2.6 MPa (8975 • 375 psi) This scatter in the measured values of burst pressure is small being • yet the associated acoustic emission hits ranged from 2212 (L0529) to 65 174 (L1132) More importantly, this wide range of hits did not show a systematic variation with burst pressure within the narrow span of burst pressures measured This lack of correlation between burst pressure and total acoustic emission noted above, is also observed if one uses loading, hold and unloading segments for the analysis of hits or counts as seen from Table An analysis of "knee pressure" has been proposed by Mitchell and Newhouse [2] based on their work with one type of all composite NGV cylinders These last mentioned authors have claimed that a lower "knee pressure" implies a lower burst pressure Some of the data obtained in the present work are shown in Fig as a plot of cumulative acoustic hits vs pressure during the first test cycle A 247 248 ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY cursory examination of Fig shows that for a given criterion to define "knee pressure" (such as 1000 hits) one obtains a wide range of knee pressures even though the cylinders have a narrow range of scatter in their burst pressure One arrives at similar conclusions as regards felicity ratio and emissions during pressure hold at 27.6 MPa (4000 psi) The Sources of Acoustic Emission Reasons for emissions at low pressures (Fig 8) and the variability in the quantity of emission from vessels having similar structural integrity may be considered It is noteworthy that the steel liner and the FRP both produce AE in hoop-wrapped cylinders Moreover, emissions may occur at their interface due to the cracking of the coating applied sometimes on the liner for corrosion protection prior to the application of the FRP Remnants of such a coating are seen in Fig 7c The AE sources in the FRP are: matrix cracking which may occur in varying degrees in NGV service due to ultraviolet exposure, etc., delaminations which occur in the transverse plane resulting from the axial expansion of the vessel (Fig 4) and fiber breakage Of these, the first two have no direct bearing on structural integrity Although fiber breakage occurs when the structural integrity of the vessel has been compromised (Fig 7), the occurrence of fiber breakage is not necessarily an indication of structural integrity loss In an idealized hoop-wrapped cylinder, the fiber axis will lie along the circumference of a circle However, in practice the roving of fibers used for the fabrication of cylinders contains many misaligned and twisted fibers Such fibers will fracture at relatively low pressures or even in the absence of cylinder pressurization with time, since the FRP remains under tension due to the autofrettage treatment An attempt has been made with some success by Walker et al [3] through neural networks and amplitude distribution of acoustic events to predict the burst pressure of all composite cylinders in their as fabricated state Matrix cracking and fiber breakage were considered relevant sources by those authors, while debonding was considered not relevant However, the situation appears to be different with hoop-wrapped cylinders removed from NGV service As shown in Fig 5, the amplitude distribution remains similar for vessels with and without gross fiber damage The explanation for that similarity possibly lies in the varibility of transverse delamination (Fig 4) observed with NGV cylinders removed from service Amplitude distribution is therefore unlikely to be of value when applied to cylinders removed from NGV service Another source of emission is the oxide scale left on the interior surface of the steel due to fabrication heat treatment In their search for a correlation between the quantity of emission and structural integrity of all-steel NGV cylinders, Akhtar et al [4] eliminated the oxide scale associated emissions and established a quantitative relationship between crack depth and AE In hoop-wrapped vessels, the autofrettage treatment forces the steel liner into compression while the vessel remains at low pressures The cracked and debonded oxide scale interfaces will produce AE as a result even at low pressures AKHTAR AND KUNG ON NGV CYLINDERS FIG Cylinder L1131-4/91 after 29 230 simulated fuelling cycles, AE tests, and pressurization to 45.5 MPa (6600 psi) (a) Fracture face of the liner flaw (b) Schematic transverse section of the cylinder through the liner flaw (c) Underside of FRP showing the crack and two delaminations (vertical) (d) Transverse section shows FRP crack originated from the FRP inner surface 249 250 ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY Those sources in the liner, the FRP and their interface may explain emissions at low pressures (Fig 8) and the variability in the quantity of emission observed in the present work with vessels having similar burst pressures (Tables 1, and 5) An approach to overcome those difficulties in the AE testing of hoop-wrapped cylinders may be to examine relative emissions during two consecutive test cycles (Tables and 3) The ratio of high amplitude hits (>_60 dB) shows a trend towards higher values when the vessel undergoes degradation through simulated fueling (Table 3) A similar approach is recommended in ASTM E 1888-97, "Standard Test Method for Acoustic Emission Testing of Pressurized Containers Made of Fiberglass Reinforced Plastic with Balsa Wood Cores" Pressure (psi) 12 000 1000 20O0 3000 L 4000 t-i - 10000 8000 Cylinder Burst MPa (psi) # L0531 D 8000J "r" 64.5 (9 350) ; L0529 63.8 (9 250) Ll132 60.7 (8 800) L1126 59.3(8600) Ll122 FiberDarnaged 0oo j I 10 20 30 Pressure ( M P a ) FIG Cumulative hits vs pressure for as-received cylinders during the first cycle AKHTAR AND KUNG ON NGV CYLINDERS Conclusion Visual inspection has shortcomings; it is not capable of detecting certain types of flaws in the FRP and it rejects cylinders which are fit for service with a wide margin of safety as observed in the present study Hence, there exists a need for other nondestructive test methods for the periodic inspection of NGV cylinders in service Acoustic emission data obtained through incremental pressurization to 27.6 MPa (4000 psi) holding pressure for minutes and unloading, not provide useful information for structural integrity assessment Relative emissions during two consecutive test cycles hold promise for the periodic inspection of hoop-wrapped NGV cylinders Acknowledgment A portion of the work reported here was carried out under Gas Research Institute (GRI-Chicago) sponsorship The authors are grateful to Steve Takagishi and Marco Liem, formerly of GRI, for their patience and support The opinions expressed in this paper are those of the authors and not of Powertech Labs References [1] Akhtar, A and Kung, D., "An Assessment of All-Steel Cylinders Currently in NGV Service for the Storage of Compressed Natural Gas Fuels on Vehicles," Report NGV200-3.19, Gas Technology Canada, Toronto, Ontario, 1996 [21 Mitchell, J.R and Newhouse, N., "Techniques for Using Acoustic Emission to Produce Smart Tanks for Natural Gas Vehicles." Paper presented at the Fifth International Symposium on Acoustic Emission from Composite Materials (AECM 5), Sundvall, Sweden, 1995 [3] Walker, J.L., Russell, S.S., Workman, G.L., and Hill, E.V.K., "Neural Network/ Acoustic Emission Burst Pressure Prediction for Impact Damaged Composite Pressure Vessels," Materials Evaluation, Vol 55, No 8, August 1997, pp 903907 [41 Akhtar, A., Wong, J.Y., Bhuyan, G.S., Webster, C.T., Kung, D., Gambone, L., Neufeld, N., and Brezden, W.J., "Acoustic Emission Testing of Steel Cylinders for the Storage of Natural Gas on Vehicles," Nondestructive Testing and Evaluation International, Vol 25, No 3, March 1992, pp 115-125 251 252 ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY DISCUSSION L.R Gambonel Comment The conclusion that "Visual inspection has some shortcomings; it is not capable of detecting certain types of flaws in the FRP " is misleading and without basis given the data provided in the paper The authors have failed to include pertinent design information regarding the intended service life of natural gas vehicle (NGV) cylinders Specifically, the ANSI/NGV2-1992 standard for NGV cylinders requires the designs to provide 13 000 pressure cycles to service pressure and 000 pressure cycles to 1.25 times service pressure The July 1997 draft revision to the ANSI/NGV2 standard requires that cylinders intended for a 15 year design life provide only 11 250 pressure cycles to 1.25 times service pressure These performance test requirements are based on actual pressure cycling service conditions experienced by cylinders in NGV service The cracks in the composite wrap of the three hoop-wrapped cylinders were artificially created in the laboratory by applying test conditions that imposed an excessive number of pressure cycles (fatigue), and overpressurization cycles, several of which far exceeded the allowable design stress for the glass fibers For example, the cylinders L1122 and L1131 were subjected to the following: (i) First used in NGV service for years (possibly some 000 pressure cycles incurred) (ii) Pressure cycled in the laboratory up to 29 230 cycles to 500 psi (equivalent to an additional 39 years of NGV service) (iii) Overpressurized in the laboratory cycles to 000 psi for AE measurements (not done in NGV service) (iv) Overpressurized in the laboratory to 000 psi for a hydrostatic test (not done in NGV service - there is no requirement for periodic retesting) (v) Overpressurized in the laboratory to some 500 psi in an attempt to predict the eventual burst pressure (certainly not done in NGV service) As a result, the damage observed in the FRP wrap would have been caused by stress rupture Neither the fatigue conditions (excessive pressure cycles), nor the stress rupture damage could occur to the FRP wrap in service Tens of thousands of hoop-wrapped cylinders have been used in NGV service since 1982 Since that time there has never been an incident or failure associated with "hidden" damage A review by Powertech Labs in 1997 of the condition of hoopwrapped cylinders removed from NGV service ["Condition Assessment of Glass Fiber Hoop-Wrapped Cylinders Used in NGV Service" - Gas Research Institute Report i Engineer, Materials TechnologiesUnit, PowertechLabs Inc 12388- 88th Avenue, Surrey, B.C Canada V3W 7R7 AKHTAR AND KUNG ON NGV CYLINDERS GRI-97/0052] did not provide any evidence of "hidden" damage in the FRP wrap There has never been any reported instance of any metal or metal-lined composite NGV cylinder falling by fatigue associated with pressure cycling in service Of the only Type (hoop-wrapped) cylinders that have failed in service, both were associated with extensive external damage to the composite wrap that would have been readily detected by visual inspection ["Cylinder Safety Revisited" by W Liss - Gas Research Institute Natural Gas Fuels, November 1996] Comment The authors claim in their discussion that the visually apparent damage on cylinders L1122 and L1131 would be sufficient to warrant their removal from NGV service in accordance with CGA C-6.4; however, both cylinders still had considerable pressure cycle life remaining As a result, the authors concluded " there exists a need for other nondestructive test methods for the periodic inspection of NGV cylinders " The fact that the visual inspection criteria in CGA C-6.4 is conservative for this particular hoop-wrapped cylinder design does not provide evidence that some other inspection method is required It is a result that must be expected of inspection criteria erring on the side of conservatism For other cylinder designs the inspection criteria will be less conservative The purpose of the inspection criteria in the CGA C-6.4 document is as follows: (i) To prevent essentially any damage to the composite wrap (other than scratches from routine handling) from remaining in service (ii) To have a single set of inspection criteria applicable to all cylinder types, and not confuse inspection staff by trying to establish different criteria for each different cylinder design and cylinder size Comment -The conclusion that AE emissions generated during two consecutive pressure cycles " holds promise for the periodic inspection of hoop-wrapped NGV cylinders" cannot be justified since the data has been generated from cylinders subjected to excessive pressure cycling and overpressurization conditions that would not occur in service A Akhtar and D Kung (authors' closure) The authors appreciate this opportunity to clarify issues surrounding visual inspection Mr Gambone has made two assumptions of which one is false and the other speculative at best His translation of 29 230 laboratory hydraulic pressure cycles into 39 years of NGV service presumably means that a vehicle cylinder may be fueled to a maximum of 750 times a year While the authors agree that 750 cycles is a reasonable assumption, the implication of the critic that a fueling cycle in NGV service is equivalent to a hydraulic pressure cycle is incorrect The synergistic action of the dynamic stresses between refuelings and the corrosive contaminants present in natural gas, principally H2S, CO2 and H20, causes accelerated degradation of the cylinder in NGV service which is only beginning to be documented For example, in a recent study (Ref I of the paper) approximately 350 all-steel cylinders were removed for ultrasonic scanning after they had been in NGV service for up to 13 years Fifteen among them were pressure cycled in the laboratory for their remaining life assessment It was concluded that the incubation period (the fatigue regime leading to the nucleation but prior to the growth of cracks) is reduced by a factor of in NGV service when compared 253 254 ACOUSTIC EMISSION: STANDARDSAND TECHNOLOGY with that obtained through hydraulic pressure cycling Such information is still lacking for the crack growth regime However, if one applies that equivalence of laboratory hydraulic pressure cycles to one NGV service pressure cycle, the 29 230 laboratory hydraulic pressure cycles reported in the paper (Table 3) would not translate into 39 years as done by the critic but to a further service life of 5.8 years, placing the cylinder well within its intended service life of 15 years The statements concerning ANSI/NGV2 document (comment 1) would have one believe that 11 250 cycles were applied over a period of 15 years using natural gas for fueling to a peak pressure of 1.25 times the service pressure through each cycle Neither a reference to this effect is provided in the said ANSI/NGV2 document nor is it likely that such precise information has been or would be generated What is certain is that the figures used in the ANSI/NGV2 document (and in other standards as well), which are set with the state of the knowledge at the time of formulation of the standard, will undergo revision as new information (such as that contained in Ref I of the paper) becomes available In his systematic enumeration of the cylinder treatment used to create the FRP flaw, Mr Gambone has overlooked the important fact that Type cylinders made from fiber rovings (all the cylinders examined in the paper were made in this manner) are subjected to an autofrettage pressure of approximately 40 MPa (5 800 psi) as apart of the fabrication process However, the evidence suggests that neither the autofrettage treatment nor the laboratory pressure cycling (including the subsequent overpressurization) caused stress rupture damage Had there been stress rupture damage, it would be widespread The damage seen to the underside of the FRP (Fig in the paper) was confined to the region immediately above the flaw in the steel (which was only part way through the metallic liner) The authors believe that this FRP flaw, which cannot be detected through visual inspection, to have been a result of the liner flaw The final overpressurization cycle to 44.9 MPa (6 500 psi) did not produce a detectable change in the liner flaw depth There was only a slight increase in the axial length of the flaw as seen in Fig 7a It is conceivable that a smaller FRP flaw would have resulted had there been no overpressurization The salient point conveyed in the paper, however, is that the creation of a liner flaw over the next 5.8 years of NGV service would produce FRP damage that cannot be detected through visual inspection The second assumption made by Mr Gambone that there has never been any incident of failure associated with "hidden" damage is speculative at best With reference to the two Type (hoop-wrapped) cylinder failures in NGV service, he has stated that both were associated with extensive external damage to the composite wrap that would have been readily detected by visual inspection When a Type cylinder ruptures in a catastrophic manner under gas pressure as opposed to hydraulic pressure (the former being the case with the two incidents under discussion), the composite material is obliterated adjacent to the region of the FRP flaw which might have caused the failure Thus the relevant material not being available, post failure analysis is carried out on the adjacent regions of the FRP which have not been obliterated Hence, the existence of FRP surface flaws at these adjacent regions, revealed through post failure analysis, does not preclude the possibility that the failure occurred as a result of FRP flaws that were not on the surface The evidence from materials examined in the adjacent regions being AKHTAR AND KUNG ON NGV CYLINDERS circumstantial, the conclusion regarding the nature of the FRP flaw that caused the failure may at best be considered speculative A reference has been made by Mr Gambone to the project carried out at Powertech Labs on behalf of Gas Research Institute (GRI Chicago) for the evaluation of Type cylinders removed after they had been in NGV service That work was done by the present authors (A Akhtar and D Kung) A conclusion of that investigation, transmitted to GRI, was that visual inspection has shortcomings The GRI did not wish to see such a conclusion in its report Upon request from GRI, an alternative interpretation was provided by L.R Gambone, C.T Webster and J.Y Wong of Powertech Labs Inc who concluded that visual inspection is an acceptable periodic inspection method The latter interpretation was accepted by GRI The statement made by Mr Gambone that the review by Powertech Labs of hoop-wrapped cylinders removed from NGV service did not provide any evidence of "hidden" damage in the FRP is correct to the extent that the draft report submitted by the present authors to the GRI and to Mr Gambone et al for their reinterpretation did not contain the evidence shown in Figure of this paper That information was gathered later A single rationally based acceptance criterion when applied to a number of cylinder designs may reject cylinders of one of those designs with a wider margin than that dictated by fitness for purpose for that specific design However, this is not the case with the visual inspection of NGV cylinders That so called "margin" is such that out of cylinders shown in Figure of the paper (L079-10/90 and L1133-4/91) would have life limitation occurring at locations far removed from the band which the visual inspection has identified as being FRP flawed In other words, not only is the acceptance criterion not rationally based, the visual inspection method itself is not rationally based as far as the NGV cylinders are concerned If one adds to the shortcomings of visual inspection identified in the present work the fact that certain types of significant impact damage on carbon fiber wrapped vessels can not be detected visually2'3, visual inspection becomes unsuitable indeed for the inspection of NGV cylinders Christoforou, A.P., and Swanson, S.R., "Strength Loss in Composite Cylinders Under Impact", Trans ASME, JEMT, Vol 110, April 1988, pp 180-184 Kaczmarek, H., and Maison, S., "Comparative Ultrasonic Analysis of Damage in CFRP Under Static Indentation and Low Velocity Impact", Composites ,Scienceand Technology, Vol 51, 1994, pp 11-26 255 STP 1353-EB/Oct 1999 Auihor Index A M Akhtar, A., 236 Markelov, A P., 125 Miller, R K., 67 Mitchell, J R., 224 Murthy, C R L., 141 B Blackburn, P R., 209 Bodine, H L., 191 C N Calva, M V., 79 Carlyle, J M., 67, 191 Chow, D L., Curtis, C E., Nagaraja Rao, G M., 141 Nesvijski, E G., 41 Nikulin, S A., 125 D O Dawes, R L., 191 De Aguiar, P R., 107 Demeski, R., 191 Ohtsu, M., 25, 156, 175 Okamoto, T., 25 Finkel, P., 67 Fowler, T J., 50 Fultineer, R D., Jr., 224 P Patterson, T S., 79 Pollock, A A., 67 Puckett, J A., 50 G Gandy, T J., 79 H R Hamilton, H R., lIl, 50 Hatano, H., 93 Henley, S S., 191 Hill, E v K., 191 Rajachar, R M., Raju, N M., 141 K Khanzhin, V G., 125 Kishi, T., 25 Kohn, D H., Kung, D., 236 Kurianova, E Y., 125 Copyright9 by ASTM International Shigeishi, M., 25, 175 Shiotani, T., 156 Shtremel, M A., 125 257 www.astm.org 258 ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY T Weissman, N A., Willett, P., 107 Tafuri, A N., 67 Ternowchek, S J., 79 Y W Watts, D J., 67 Webster, J., 107 Yezzi, J J., Jr., 67 Yuyama, S., 25 STP 1353-EB/Oct 1999 Subject Index A Defect detection, 191 Deformation, 125 Aging dock, 25 Aircraft, aging, 191 Amplitude, E Eigenvalue analysis, 175 Embrittlement, 79 B F Bone, microdamage, Burn, workpiece, 107 Burst testing, 224, 236 B-value, 156 C Calibration procedure standard, 93 Cold proof testing, 191 Composite wrapped pressure vessels, 224, 236 Concrete beams, structural integrity, 25 Concrete, reinforced beams, structural integrity, 25 structures, characterization, 41 Corrosion, 79 reinforced concrete beams, 25 Cortical bone, fatigue, Crack characterization, rocks, 141 Crack determination, 79 Crack lengths, Crack measurement, 125 Crack mechanisms, twodimensional model, 175 Crack resistance, 41 Crack, shear, 25 Crack volume estimation, 175 Curve-fitting techniques, 156 Cyclic loading test, 25 Fatigue, aging aircraft, 191 Fatigue damage, traffic signal poles, 50 Fatigue testing, bone, Flaw depth, 209 Fracture, 125 brittle, traffic signal structures, 50 rock, 141 G Gas containers, natural, 224, 236 Gas cylinders, seamless steel, 209 Graphical analysis, 156 Green's function, simplified, for moment tensor analysis, 175 Grinding, 107 lnconel, workpiece burn detection, 107 Iron alloys, material quality monitoring, 125 K Kaiser effect, 25 Japanese Societ~r for NonDestructive Inspection calibration procedure standard, 93 D Damage zone dimensions, Davies-bar technique, 175 259 260 ACOUSTIC EMISSION: STANDARDS AND TECHNOLOGY Laser opto-interferometer, bar end oscillation measurement, 175 Leak detection, buried pipelines, 67 Linear location mode, 209 Loading unloading, 25 l_x)cation methods, buried pipelines, 67 la)ngitudinal wave, 93 M Material quality monitoring, 125 Mechanical integrity testing, 79 Metals gas cylinders, seamless steel, inspection, 209 material quality monitoring, 125 steel-lined hoop wrapped, 236 workpiece burn detection, 107 Microscopy, confocal, Mineralogy, rock fault formation, 141 Moment tensor analysis, 175 N Natural gas vehicle, 224, 236 Niobium, material quality monitoring, 125 P Parametric plot, 141 Peak-amplitude distributions, 156 Pipelines, buried, leak detection, 67 Plastic, continuous fiberreinforced, 236 Pneumatic proof pressurization, 191 Pressure processing, 125 Pressure vessels gas distribution, seamless steel, testing, 209 inspection, ultrasonics, 79 natural gas, filament wound, 224 natural gas, hoop wrapped, steel lined, 236 Process safety management, 79 Proof testing, 191 R Rate process analysis, 156 Rayleigh wave, 93 Reciprocity method, 93 Reference standards, laboratory, pipeline leaks, 67 Rocks, crack characterization, 141 S Screening, in-service, traffic signal poles, 50 Sensor calibration, 175 Shear cracking, 25 Shear wave analysis, 79 SiGMA-two-dimensional procedure, 175 Signal difference location technique, 67 Signal enhancement, 67 Signalprocessing, 41, 107, 191 Slope failure prediction, 156 Standards characterization, concrete structures, 41 laboratory reference, 67 proposed, gas-filled filament-wound pressure vessels, 224 proposed, reinforced concrete structural integrity, 25 transducer calibration, reciprocity method, 93 Steels alloy, pressure vessel testing, 209 bearing, workpiece burn detection, 107 INDEX 261 dual phase, material quality monitoring, 125 gas cylinders, steel-lined, 236 Stiffness, 41 Storage tank, mechanical integrity, 79 Strength, concrete structures, 41 Stress effects, rock, 141 Superconductors, 125 V Volumetric strain, 141 Volumetric testing technique, 224 W T Tin alloys, material quality monitoring, 125 Titanium alloy superconductors, 125 Traffic signal poles, 50 Transducer calibration, 93 Wave attenuation, 156 Waveforms analysis, 141, 175 b-value, 156 digital, 191 Welds, 50 Wind-induced vibrations, 50 Workpiece burn, 107 U Ultrasonic imaging, 141 Ultrasonic testmg, 79 U.S Department of Transportation, seamless pressure vessel inspection, 209 Z Zirconium-tin-niobium-iron alloys, 125 O~ ! rU ! ILl D ! Z ... T., " A Proposed Standard for Evaluating Structural Integrity of Reinforced Concrete Beams by Acoustic Emission, " Acoustic Emission: Standards and Technology Update, ASTM STP 1353, S J Vahaviolos,... Cataloging-in -Publication Data Acoustic emission : standards and technology update / Sotirios J Vahaviolos, editor p c m - (STP : 1353) Includes bibliographical references "ASTM Stock #: STP1353."...S T P 1353 Acoustic Emission: Standards and Technology Update Sotirios J Vahaviolos, editor ASTM Stock #: STP1353 ASTM 100 Barr Harbor Drive West Conshohocken,