ASTM E2191/E2191M-16

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2191/E2191M − 10 E2191/E2191M − 16
Standard Practice for
Examination of Gas-Filled Filament-Wound Composite
Pressure Vessels Using Acoustic Emission
This standard is issued under the fixed designation E2191/E2191M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This practice provides guidelines for acoustic emission (AE) examination of filament-wound composite pressure vessels, for
example, the type used for fuel tanks in vehicles which use natural gas fuel.
1.2 This practice requires pressurization to a level equal to or greater than what is encountered in normal use. The tanks’
pressurization history must be known in order to use this practice. Pressurization medium may be gas or liquid.
1.3 This practice is limited to vessels designed for less than 690275 bar [10,000[4,000 psi] maximum allowable working
3 3
pressure and water volume less than 1 m or 1000 L [35.4 ft ].
1.4 AE measurements are used to detect emission sources. Other nondestructive examination (NDE) methods may be used to
gain additional insight into the emission source. Procedures for other NDE methods are beyond the scope of this practice.
1.5 This practice applies to examination of new and in-service in-service, Type II, filament-wound composite pressure vessels.
1.6 This practice applies to examinations conducted at ambient temperatures above 20°C [70°F]. This practice may be used at
ambient temperatures below 20°C [70°F] if provision has been made to fill to the tank’s rated pressure at 20°C [70°F]. Also that
the test temperature must not exceed the glass transition temperature of the matrix material.
1.7 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated
in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values
from the two systems may result in non-conformance with the standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. Specific precautionary statements are given in Section 8.
2. Referenced Documents
2.1 ASTM Standards:
E543 Specification for Agencies Performing Nondestructive Testing
E650 Guide for Mounting Piezoelectric Acoustic Emission Sensors
E976 Guide for Determining the Reproducibility of Acoustic Emission Sensor Response
E1316 Terminology for Nondestructive Examinations
E2374 Guide for Acoustic Emission System Performance Verification
2.2 Natural Gas Vehicle Standard:
American National Standard for Basic Requirements for Compressed Natural Gas Vehicle (NGV) Fuel Containers ANSI/AGA/
NGV2
2.3 Compressed Gas Association Standard:
Pamphlet C-6.4, Methods for Visual Inspection of AGA NGV2 Containers
This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.04 on Acoustic Emission
Method.
Current edition approved June 1, 2010Feb. 1, 2016. Published July 2010February 2016. Originally approved in 2002. Last previous edition approved in 20082010 as
E2191 - 08.E2191 - 10. DOI: 10.1520/E2191_E2191M-10.10.1520/E2191_E2191M-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2191/E2191M − 16
2.4 U.S. Department of Transportation Reference:
NHTSA Federal Motor Vehicle Safety Standard No. 304, March 27, 1995
2.5 ASNT Standards:
ANSI/ASNT CP-189, Standard for Qualification and Certification of Nondestructive Testing Personnel
SNT-TC-1A, Recommended Practice for Nondestructive Testing Personnel Qualification and Certification
2.6 International Standards Organization (ISO) Standards:
ISO 9712 Nondestructive Testing—Qualification and Certification of NDT Personnel
3. Terminology
3.1 Definitions—See Terminology E1316 for general terminology applicable to this practice.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 AE test pressure, n—110 % of the greatest pressure that the examination article contains during previous service. Usually
125 % of the filling pressure is an acceptable AE examination pressure. (Normally, gas is heated when compressed during the
filling process; hence, tanks are filled to more than rated service pressure). After filling, pressure should settle to rated service
pressure as gas temperature within the tank becomes equal to ambient temperature.
3.2.2 detectability distance, n—the maximum distance from a sensor at which a defined simulated AE source can be detected
by the instrumentation with defined settings and using appropriate pressurization medium.
4. Summary of Practice
4.1 AE sensors are mounted on a vessel and emission is monitored while the vessel is pressurized to the “AE examination
pressure.”
4.2 This practice provides guidelines for the detection of AE from structural flaws in the composite overwrap in gas-filled,
filament-wound composite pressure vessels. Damage mechanisms which produce AE include: resin cracking, fiber debonding, fiber
pullout, fiber breakage, delamination and bond failure. Flaws in liner portions of a vessel may not be detected.
4.3 This practice and others found in ASTM, ASME, ASNT, SPI relate Acoustic Emission to applied load on the composite
material. At relatively low load (safe operating conditions) the acoustic emission from the composite material is low. At higher
loads (unsafe operating conditions) the slope of the AE versus load curve changes drastically. In some cases this phenomenon can
be identified and quantified by a single AE parameter (that is, AE counts).
4.4 Structurally insignificant flaws or processes (for example, leaks) may produce emission.
4.5 This practice is convenient for periodic examination of vessels in-service.
4.6 Gas-filled filament-wound pressure vessels which exhibit unacceptable levels of AE should be examined by other methods;
for example, visual, ultrasound, dye penetrant, etc., and may be repaired and re-examined in accordance with government
regulations and manufacturers guidelines. Repair and repair examination procedures are outside the scope of this practice.
4.7 Any number of pressure vessels may be examined simultaneously as long as the appropriate number of sensors and
instrumentation channels are used.
5. Significance and Use
5.1 Due to safety considerations, the Compressed Gas Association (CGA) and others have produced guidelines which address
in-service inspection of NGV fuel containers (see 2.2 – 2.4). AE examination is listed as an alternative to the minimum three-year
visual examination which generally requires that the container be removed from the vehicle to expose the entire container surface.
The AE method allows “in-situ” examination of the container.
5.1.1 Slow-fill pressurization must proceed at flow rates that do not produce background noise from flow of the pressurizing
medium. Acoustic emission data are recorded throughout a pressurization range (that is, 50 % to 100 % of AE examination
pressure).
5.1.2 Fast-fill pressurization can be used if hold periods are provided. Acoustic emission data are recorded only during the hold
periods.
NOTE 1—Fast-fill pressurization is less appropriate for carbon (or graphite) composites due to the lower sensitivity of carbon fibers to stress rupture
compared to other fibers.
5.1.3 Background noise above the threshold will contaminate the AE data and render them useless. Users must be aware of the
following common causes of background noise: high fill rate (measurable flow noise); mechanical contact with the vessel by
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://www.dodssp.daps.mil.
Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
E2191/E2191M − 16
objects; electromagnetic interference (EMI) and radio frequency interference (RFI) from nearby broadcasting facilities and from
other sources; leaks at pipe or hose connections and airborne particles, insects, rain and snow. This practice should not be used
if background noise cannot be eliminated or controlled.
5.2 Sensitivity is influenced by factors that affect elastic wave propagation, sensor coupling and signal processor settings.
5.3 It is possible to measure AE from AE sources that cannot be verified by other NDE methods.
6. Basis of Application
6.1 The following items are subject to contractual agreement between the parties using or referencing this practice.
6.2 Personnel Qualification—If specified in the contractual agreement, personnel performing examinations to this practice shall
be qualified in accordance with a nationally or internationally recognized NDT personnel qualification practice or standard such
as ANSI/ASNT-CP-189, SNT-TC-1A, ISO 9712, or a similar document and certified by the employer or certifying agency, as
applicable. The practice or standard used and its applicable revision shall be identified in the contractual agreement between the
using parties.
6.3 Qualification of Nondestructive Test Agencies—If specified in the contractual agreement, NDT agencies shall be qualified
and evaluated as described in Practice E543. The applicable edition of Practice E543 shall be specified in the contractual
agreement.
6.4 Extent of Examination—The extent of examination shall be in accordance with 4.2 unless otherwise specified.
6.5 Reporting Criteria/Acceptance Criteria—Reporting criteria for the examination results shall be in accordance with Section
11 unless otherwise specified.
6.6 Personnel Training/Test Requirements—NDE personnel (examiner) shall be familiar with CGA Pamphlet C6 and shall have
attended a training course and passed a written test which cover the following topics.
6.6.1 Basic technology of acoustic emission.
6.6.2 Failure mechanisms of reinforced plastics.
6.6.3 Acoustic emission instrumentation.
6.6.4 Instrumentation verification.
6.6.5 Vessel filling requirements.
6.6.6 Data collection and interpretation.
6.6.7 Examination report generation.
7. Apparatus
7.1 Essential features of the apparatus required for this standard are shown in Fig. 1. Specifications are provided in Annex A1.
7.2 Couplant must be used to acoustically couple sensors to the vessel surface. Adhesives that have acceptable acoustic
properties and traditional couplants are acceptable.
7.3 Sensors may be held in place with elastic straps, adhesive tape, or other mechanical means.
3 3
7.4 On small vessels (that is, where less than 1.3 yd [1 m ] (where 100 % coverage can be achieved with two sensors) the
sensor locations on the vessel wall will be determined by accessibility. Ideally they should be placed 180° apart at opposite ends
of the container on the shoulders.
7.5 On larger vessels (that is, where two sensors cannot provide 100 % coverage) sensors are positioned on the vessel wall so
as to provide complete coverage. Sensor spacings are governed by the attenuation of the material. If attenuation characteristics are
not available from previous examinations of similar vessels follow the directions found below.
FIG. 1 Essential Features of the Apparatus
E2191/E2191M − 16
7.5.1 Attenuation Characterization—Typical signal propagation losses shall be determined in accordance with the following
procedure. This procedure provides a relative measure of the attenuation but may not be representative of a genuine AE source.
It should be noted that peak amplitude caused by a mechanical pencil lead break may vary with surface hardness, resin condition
and cure. Select a representative region of the vessel with clear access along the cylindrical section. Mount an AE sensor and mark
off 15-cm [6-in.] intervals from the center of the sensor along a line parallel to the principal direction of the surface fiber. Select
additional points on the surface of the vessel at 15-cm [6-in.] intervals along lines angled 45° and 90°, respectively, to the principal
direction of the surface fiber. Break pencil leads (see Guide E976) and record peak amplitude. All lead breaks shall be done at an
angle of approximately 30° to the surface with a 2.5-mm [0.1-in.] lead extension. The attenuation data shall be retained as part of
the test report.
7.5.2 Record the distances from the center of the sensor to the points where hits are no longer detected. Repeat this procedure
along lines angled 45° and 90° to the direction of the original line. The data shall be retained as part of the test report. The minimum
distance from the sensor at which the pencil lead break can no longer be detected is known as the detectability distance; this
distance shall be recorded. Use the same threshold during testing that was used to determine the detectability distance.
NOTE 2—Detectability distance may be reduced to achieve greater sensitivity to sources at farther distance.
7.5.3 Sensor spacing (distance between adjacent sensors) shall not be greater than 1.5 times the detectability distance.
7.6 AE sensors are used to detect stress waves produced by flaws. Sensors must be held in contact with the vessel wall to ensure
adequate acoustic coupling.
7.7 A preamplifier may be enclosed in the sensor housing or in a separate enclosure. If a separate preamplifier is used, cable
length, between sensor and preamplifier, must not result in a signal loss of greater than 3 dB (typically 2 m [6 ft] is acceptable).
7.8 Power/signal cable length (that is, cable between preamplifier and signal processor) shall not result in a signal loss of greater
than 3 dB (typically 150 m [500 ft] is acceptable).
7.9 Signal processorsAE systems are computerized instruments with independent channels that filter, measure and convert
analog information into digital form for display and permanent storage. A signal processorAn AE system must have sufficient speed
and capacity to independently process data from all sensors simultaneously. The signal processorAE system should provide
capability to filter data for replay.
7.10 A video monitor display is used to display visually present processed data in various formats. Display format may be
selected by the examiner.
7.11 A data storage device, such as a magnetic disk, device is used to store data for replay or for archives.archive purposes.
7.12 Hard-copy capability should be available from a graphics/line printer or equivalent device.printer.
8. Safety Precautions
8.1 Ambient temperature should not be below the d
...