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1、 CGA C-202005 METHODS FOR ULTRASONIC EXAMINATION OF METALLIC, DOT AND TC 3-SERIES GAS CYLINDERS AND TUBES FIRST EDITION COMPRESSED GAS ASSOCIATION, INC. 4221 Walney Road, 5th Floor Chantilly, VA 20151 Phone: 703-788-2700 Fax: 703-961-1831 E-mail: PAGE ii COMPRESSED GAS ASSOCIATION, INC. CGA C-20200
2、5 PLEASE NOTE: The information contained in this document was obtained from sources believed to be reliable and is based on technical information and experience currently available from members of the Compressed Gas Association, Inc. and others. However, the Association or its members, jointly or se
3、verally, make no guarantee of the results and assume no liability or responsibility in connection with the information or suggestions herein contained. Moreover, it should not be assumed that every acceptable commodity grade, test or safety procedure or method, precaution, equipment or device is con
4、tained within, or that abnormal or unusual circumstances may not warrant or suggest further requirements or additional procedure. This document is subject to periodic review, and users are cautioned to obtain the latest edition. The Associa- tion invites comments and suggestions for consideration. I
5、n connection with such review, any such comments or suggestions will be fully reviewed by the Association after giving the party, upon request, a reasonable op- portunity to be heard. Proposed changes may be submitted via the Internet at our web site, . This document should not be confused with fede
6、ral, state, provincial, or municipal specifications or regulations; insurance requirements; or national safety codes. While the Association recommends reference to or use of this document by government agencies and others, this document is purely voluntary and not binding. A listing of all publicati
7、ons, audiovisual programs, safety and technical bulletins, and safety posters is available via the Internet at our website at . For more information contact CGA at Phone: 703-788-2700, ext. 799. E-mail: Docket 98-61 Cylinder Specifications Committee NOTEAppendix C (Normative) is a requirement. NOTE
8、Appendices A and B (Informative) are for information only. FIRST EDITION: 2005 2005 BY THE COMPRESSED GAS ASSOCIATION, INC. ALL RIGHTS RESERVED. 4221 WALNEY ROAD, 5TH FLOOR, CHANTILLY, VA 20151 Printed in U.S.A. CGA C-202005 COMPRESSED GAS ASSOCIATION, INC. PAGE iii Contents Page 1 Introduction.1 2
9、Scope .1 3 Definitions.1 4 Operational description 3 4.1 Objective3 4.2 Ultrasonic examination equipment 3 4.3 Monitoring of acoustic coupling.4 4.4 Flaw detection .4 4.5 Maximum flaw limits 4 5 Equipment and material .4 5.1 Power supply.4 5.2 Transducer 4 5.3 Pulser/receiver.4 5.4 Display device .6
10、 5.5 Coaxial cable.6 5.6 Oscilloscope display controls 6 5.7 Data storage6 5.8 C-scan.6 6 Calibration 8 6.1 Cylinder calibration procedure.9 6.2 Gain control accuracy10 6.3 Calibration cylinder requirements10 6.4 Reference features in the calibration cylinder (standard reference)10 6.5 Verification
11、of equipment calibration11 7 Cylinder and tube examination procedures11 8 Documentation.12 8.1 Report12 8.2 Record requirements.12 8.3 Records maintenance13 9 Rejection criteria.13 10 Operator qualifications .13 11 References.13 12 Additional references13 Figures Figure 1Typical pulse-echo unit, blo
12、ck diagram 5 Figure 2A-scan display7 Figure 3B-scan display7 Figure 4C-scan display8 Figure 5Sidewall-to-base transition (SBT) notch diagram.10 -,-,- PAGE iv COMPRESSED GAS ASSOCIATION, INC. CGA C-202005 Appendices Appendix ADOT exemptions/special permits and TC permits for equivalent level of safet
13、y (Informative)15 Appendix BTypes of flaws (Informative).16 Appendix CCalibration standards for changes in nominal diameter or design minimum wall thickness of a cylinder (Normative)17 -,-,- CGA C-202005 COMPRESSED GAS ASSOCIATION, INC. PAGE 1 1 Introduction The U.S. Department of Transportation (DO
14、T) has issued exemptions/special permits and Transport Canada (TC) has issued permits for equivalent level of safety that authorize ultrasonic examination (UE) to be per- formed in place of internal visual inspection and hydrostatic requalification of certain compressed gas cylinders and tubes. See
15、Appendix A for a list of DOT exemptions and TC permits. Modern UE automates the inspection of cylinders and the measurement of wall thickness. UE also automates the detection of both internal and external pits, cracks, and other flaws that might or might not be detected by visual inspection methods.
16、 CAUTION: UE has benefits, but it also creates hazards for the operators by potential exposure to compressed gas. The examination methods in this publication permit inspection of the cylinders without removal of the valve and gaseous product contained in the cylinder. Consequently, UE can subject th
17、e personnel performing examina- tions to certain hazards such as exposure to high pressure conditions and flammable and poisonous gases. 2 Scope This publication identifies and describes the various acceptable ultrasonic examination (UE) methods (also known as ultrasonic testing UT methods) that can
18、 be used in place of internal visual inspection and hydro- static requalification methods used to examine certain metallic, TC/DOT 3-series gas cylinders and tubes as mandated by Title 49 of the U.S. Code of Federal Regulations (49 CFR) and TCs Transportation of Dangerous Goods Regulations, and cyli
19、nders manufactured under certain DOT exemptions/special permits or TC permits 1, 2.1 This publication does not address all of the safety and health considerations associated with UE. It is the re- sponsibility of the person(s) performing UE to ensure that appropriate safety precautions are used and
20、that ap- propriate safety regulations and publications are followed. See additional references in Section 12 for informa- tion on safety regulations and publications. NOTEThe UE methods described in this publication apply to both cylinders and tubes unless specifically noted. 3 Definitions For the p
21、urpose of this publication, the following definitions apply. 3.1 A-scan Method of data presentation using a horizontal base line that indicates distance or time and a vertical deflection from the base line that indicates amplitude. 3.2 Acoustic coupling Use of couplant to ensure continuous transmiss
22、ion of high frequency sound waves (ultrasonic energy) between the search unit or transducer and the wall of the cylinder or calibration cylinder. 3.3 Amplitude Vertical pulse height of a signal, usually base to peak, when indicated by an A-scan presentation. 3.4 B-scan Means of ultrasonic data prese
23、ntation that displays a cross section of the specimen, indicating the approximate length (as detected by scan) of reflectors and their relative positions. 3.5 C-scan Ultrasonic data presentation that provides a plan view of the specimen and discontinuities therein. 1 References are shown by brackete
24、d numbers and are listed in order of appearance in the reference section. -,-,- PAGE 2 COMPRESSED GAS ASSOCIATION, INC. CGA C-202005 3.6 Calibration cylinder Typically a section of an actual cylinder that is used as a means of providing ultrasonic reflections of known characteristics; used for calib
25、ration of the UE system. NOTEAlso termed a standard reference. 3.7 Couplant Substance used between the search unit and test surface to permit or improve transmission of ultrasonic en- ergy. 3.8 Cylinder Seamless pressure vessel designed for pressures higher than 40 psia and having a circular cross s
26、ection. NOTEAlso described by TCs Transportation of Dangerous Goods Regulations as a container with a water capacity not greater than 450 L, in a cylindrical or spherical shape, and capable of withstanding an internal absolute pressure greater than 275 kPa 2. 3.9 Design minimum wall thickness (td) M
27、inimum thickness required by the specification under which the cylinder was designed. 3.10 Flaw Imperfection or discontinuity detectable by visual or other nondestructive examination. 3.11 Gain Electronic magnification or diminution of an electronic signal. 3.12 Guided wave Wave that propagates alon
28、g the entire thickness of the cylinder wall. 3.13 Indication That which marks or denotes the presence of a reflector. 3.14 Longitudinal wave Wave in which the particle motion of the material is essentially in the same direction as the wave propagation. 3.15 Minimum allowable in-service wall thicknes
29、s (tis) Minimum wall thickness permitted for cylinders while in service as established by a relevant authority. 3.16 Mode Type of ultrasonic wave propagating in the materials as characterized by the particle motion (for example, lon- gitudinal, transverse, guided, etc.). 3.17 Nondestructive testing
30、(NDT) Test methodologies that detect flaws in materials without destroying the materials or altering their serviceability. 3.18 Pip Short, high-pitched, electronic signal displayed as vertical pulses on the A-scan of a cathode ray tube (CRT). 3.19 Pulse-echo method Inspection method in which the pre
31、sence and position of a reflector are indicated by the echo amplitude and time. 3.20 Search unit Electro-acoustic device used to transmit or receive ultrasonic energy, or both. 3.21 Shear wave Wave motion in which the particle motion is perpendicular to the direction of propagation. CGA C-202005 COM
32、PRESSED GAS ASSOCIATION, INC. PAGE 3 3.22 Sidewall-to-base transition (SBT) area Point where the wall of the cylinder begins to thicken and/or where the inside wall of the cylinder departs from the parallel relation with the outside wall of the cylinder as the cylinder side wall starts to form the b
33、ase of the cylinder. 3.23 Straight beam Vibrating pulse wave train traveling perpendicular to the test surface. 3.24 Transducer Electro-acoustic device for converting electrical energy into acoustical energy and vice versa. 3.25 Tube Seamless container of cylindrical shape with openings at both ends
34、, an outside diameter of 9 in or greater, and designed to withstand pressures greater than 40 psia. NOTEAlso described by TCs Transportation of Dangerous Goods Regulations as a container with a water capacity greater than 450 L, in a seamless cylindrical form, and capable of withstanding an internal
35、 service pressure of at least 3450 kPa 2. 3.26 Ultrasonic examination (UE) Nondestructive method that uses high frequency sound waves to examine material. NOTEAlso known as ultrasonic testing (UT). 3.27 Ultrasonic examination system System that includes UE apparatus, electronic hardware and software
36、, transducers, and interconnecting ca- bles. 4 Operational description 4.1 Objective The objective of UE of compressed gas cylinders and tubes is to ensure product safety and reliability by provid- ing a means of: obtaining a visual recorded image of flaw(s) in the cylinder or tube; identifying the
37、nature of the flaw(s) without impairing the material; and separating acceptable and unacceptable cylinders and tubes in accordance with predetermined rejection criteria. UE can be used to measure the thickness of a material or to examine the internal structure of a material for possible discontinuit
38、ies such as voids and/or cracks. 4.2 Ultrasonic examination equipment The UE equipment shall be capable of detecting the appropriate flaws and wall thickness as required by the limits set in 4.5. The equipment demonstrates this capability by repeatedly detecting the reference features and measuring
39、the proper thickness of the machined thin areas on the calibration cylinder that is produced from limitations set forth by a relevant authority. The equipment shall be capable of performing UE of 100% of the cylinders sidewall-to-base transition (SBT) area. The UE equipment can consist of multiple s
40、ensors or a single sensor (also known as transducer). However, if a single sensor is used, the UE equipment shall be designed so the angle of the sensor can be varied during in- spection, the required areas on the cylinder or tube can be scanned, and the data analysis can be adjusted for different s
41、ensor alignments. -,-,- PAGE 4 COMPRESSED GAS ASSOCIATION, INC. CGA C-202005 4.3 Monitoring of acoustic coupling Acoustic coupling shall be monitored throughout the examination. The technique used to ensure ultrasonic coupling shall be designed and controlled consistent with the test apparatus and i
42、ts potential failure modes. The monitoring shall be continuous and integrated into the control systems. If there is a loss of signal during any part of the examination, the operator has the option of repeating the examination or re-examining the areas where the signal was lost. A lack-of-expected-re
43、sponse (LER), also known as loss-of-back-wall-echo, indication of the wall thickness channel in the SBT area does not invalidate the test, provided a minimum of two shear wave channels are transmitting the ultrasonic signals into the SBT area. If automated UE of a cylinder or tube cannot be performe
44、d due to LER indications, then the UE operator may use manual UE to examine the area where the LER is found so the operator can determine if there is a hidden defect in the LER zone. 4.4 Flaw detection All relevant flaws such as isolated pits, sidewall defects (for example, fatigue cracks, laps, fol
45、ds), and line cor- rosion on the internal and external walls of the cylinder and within the cylinder wall material shall be detected and measured by UE. Rejected cylinders shall be further inspected (for example, by visual or mechanical means) to check if the flaw size exceeds maximum allowable flaw
46、 limits. Cylinders without relevant, detectable flaws may be returned to service after examination results are documented in accordance with Section 8. 4.5 Maximum flaw limits Maximum allowable flaw sizes are based upon the specified design minimum wall thickness (td) of the cylinder undergoing requ
47、alification. Cylinders shall be deemed to have failed requalification and be rejected from ser- vice if the depth and size of the flaw exceeds the limitations set forth by a relevant authority or the cylinder has internal or external defects that affect the cylinders suitability for continued servic
48、e. See Appendix B for a summary of common types of flaws found in cylinders or tubes, which can result in rejection of the cylinder or tube from continued service. 5 Equipment and material Essential features of the equipment required for UE are provided in this section and in Figure 1. 5.1 Power supply Circuits for supplying electrical current for all basic functions of the UE equipment constitute the power supply. 5.2 Transducer A UE system using the pulse-echo method emits short, evenly timed pulses of ultrasonic waves that are trans- mitted into the material being tested to locate discon