1、ASME PTB-6-2013Guidelines for Strain Gaging of Pressure Vessels Subjected to External Pressure Loading in the PVHO-1 StandardPTB-6-2013 GUIDELINES FOR STRAIN GAGING OF PRESSURE VESSELS SUBJECTED TO EXTERNAL PRESSURE LOADING IN THE PVHO-1 STANDARD Lawrence J. Goland Southwest Research Institute PTB-6
2、-2013 Date of Issuance: June 21, 2013 This document was supported by ASME Pressure Technology Codes and Standards (PTCS) through the ASME Standards Technology, LLC (ASME ST-LLC). Neither ASME, the author, nor others involved in the preparation or review of this document, nor any of their respective
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9、l system or otherwise, without the prior written permission of the publisher. The American Society of Mechanical Engineers Two Park Avenue, New York, NY 10016-5990 Copyright 2013 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All rights reserved Printed in the U.S.A. PTB-6-2013 iii TABLE OF CONTENT
10、S Foreword . v Abstract vi Acknowledgements . vii 1 PURPOSES OF STRAIN GAGING PRESSURE HULL 1 1.1 General . 1 1.2 Monitoring For Behavior . 1 1.3 Monitoring For Stability. 2 2 STRAIN GAGE ROSETTE TYPES AND RECOMMENDED USES . 3 2.1 General . 3 2.2 Use of Uniaxial Strain Gages . 4 2.3 Use of Biaxial (
11、Tee) Strain Gage Rosettes. 4 2.4 Use of Triaxial Strain Gage Rosettes . 5 3 NOMENCLATURE FOR PRESSURE HULLS 6 4 GENERAL GUIDELINES FOR LOCATIONS OF STRAIN GAGES AND ROSETTES . 9 5 EXAMPLE OF BASIC STRAIN GAGE LOCATIONS 10 6 EXAMPLE OF COMPLEX STRAIN GAGE LOCATIONS 12 6.1 General . 12 6.2 Locations o
12、n Ring-Stiffened Cylindrical Hull . 17 6.3 Locations on Hemispherical Heads 17 LIST OF FIGURES Figure 2.1 Examples of Uniaxial and Typical Strain Gage Rosettes . 3 Figure 3.1 Illustrative Hull Components . 6 Figure 3.2 End Bay Region in Typical Ring Stiffened Hull (and Exaggerated Displaced Shape un
13、der External Pressure Load) 7 Figure 3.3 Out-of-Circularity (OOC) of Cylindrical Pressure Hull . 7 Figure 3.4 Out-of-Fairness (OOF) of Cylindrical Pressure Hull . 8 Figure 3.5 Out-of-Sphericity (OOS) of Spherical/Hemispherical Pressure Hull 8 Figure 5.1 Basic Strain Gage Location on Pressure Hull 10
14、 Figure 6.1 Complex Strain Gage Locations on Pressure Hull . 13 PTB-6-2013 iv Figure 6.2 Complex Strain Gage Locations on Pressure Hull . 14 Figure 6.3 Complex Strain Gage Locations on Pressure Hull . 15 Figure 6.4 Complex Strain Gage Locations on Pressure Hull . 18 Figure 6.5 Complex Strain Gage Lo
15、cations on Pressure Hull . 19 Figure 6.6 Complex Strain Gage Locations on Pressure Hull . 20 Figure 6.7 Complex Strain Gage Locations on Pressure Hull . 21 Figure 6.8 Complex Strain Gage Locations on Pressure Hull . 22 Figure 6.9 Complex Strain Gage Locations on Pressure Hull . 23 Figure 6.10 Comple
16、x Strain Gage Locations on Pressure Hull . 24 Figure 6.11 Complex Strain Gage Locations on Pressure Hull . 25 Figure 6.12 Complex Strain Gage Locations on Pressure Hull . 26 Figure 6.13 Complex Strain Gage Locations on Pressure Hull . 27 PTB-6-2013 v FOREWORD Strain gaging of pressure vessels (also
17、known as pressure hulls) subjected to the external hydrostatic test pressure loading serves to monitor the structural behavior and response of the pressure vessel under external pressure load conditions. Monitoring the gages during the hydrostatic test can allow the hydrostatic test to be halted pri
18、or to causing significant damage and/or collapse of the hull. Therefore the use of strain gaging is recommended to help observe any deviation from the predicted strains (stresses) vs. external pressure in order to avoid unexpected deformation of the hull and possible collapse during the hydrostatic
19、test. Established in 1880, the American Society of Mechanical Engineers (ASME) is a professional not for-profit organization with more than 127,000 members promoting the art, science and practice of mechanical and multidisciplinary engineering and allied sciences. ASME develops codes and standards t
20、hat enhance public safety, and provides lifelong learning and technical exchange opportunities benefiting the engineering and technology community. Visit www.asme.org for more information. The ASME Standards Technology, LLC (ASME ST-LLC) is a not-for-profit Limited Liability Company, with ASME as th
21、e sole member, formed in 2004 to carry out work related to newly commercialized technology. The ASME ST-LLC mission includes meeting the needs of industry and government by providing new standards-related products and services, which advance the application of emerging and newly commercialized scien
22、ce and technology and providing the research and technology development needed to establish and maintain the technical relevance of codes and standards. Visit www.stllc.asme.org for more information. PTB-6-2013 vi ABSTRACT This document provides information and guidance regarding the use of strain g
23、aging of pressure hulls subjected to external hydrostatic test pressure loading. The document presents two examples of strain gaging a pressure vessel subjected to external pressure loading. The first example shows a basic strain gaging plan useful for validating strain and stress analyses, which re
24、quires a minimal number of strain gages located at general positions on the hull, and the second example shows a strain gage layout plan which is useful for not only validating strain and stress analyses, but also for monitoring the behavior of the hull during the hydrostatic test, which requires th
25、e most number of strain gages since gages are placed at both general locations and regions of concern due to hull as-built geometries that might initiate collapse. These two strain gaging examples are provided as illustrative examples only. These examples in no way establish actual strain gaging req
26、uirements per any code, design rules, or jurisdictional body. They do not establish required placement gage locations, gage types to be used, or number of gages. For each hull, the actual strain gaging plan implemented is a function of many factors, such as the chambers configuration, number and siz
27、e of openings, attachments, actual as-built geometry, weld details, and whether just validating an analysis and/or monitoring hull behavior to preclude collapse. PTB-6-2013 vii ACKNOWLEDGEMENTS The authors wish to acknowledge the review performed by the following members of the PVHO Standards Commit
28、tee: Michael Allen, William Crowley, William Davison, Michael Frey, Thomas Galloway, Gary Jacob, Barton Kemper III, James Lawrence, Peter Lewis, Jack Maison, Guy Richards, Thomas Schmidt, John Selby, James Sheffield, Robert Smith, Kenneth Smith, Deepak Talati, Roy Thomas, Matthew Walters, George Wol
29、fe, Eric Fink, Harald Pauli, Todd Marohl, Stephen Reimers and John Witney. PTB-6-2013 viii INTENTIONALLY LEFT BLANK PTB-6-2013 1 1 PURPOSES OF STRAIN GAGING PRESSURE HULL 1.1 General The strain gaging of pressure vessels (also known as pressure hulls) subjected to the external hydrostatic test press
30、ure loading serves two purposes. First and foremost, the gaging is to monitor the structural behavior and response of the pressure vessel under external pressure load conditions. The resulting strains and stresses can then be compared to those obtained from the design analyses performed. Secondly, p
31、roper strain gaging can indicate the onset of collapse of the pressure hull under the external hydrostatic pressure test. Theoretically, using the design rules of the latest ASME PVHO-1 “Safety Standard for Pressure Vessels for Human Occupancy,” standard, the pressure hull will not collapse during t
32、he external hydrostatic pressure test and serves as the proof test. However, given an unknown circumstance such as an undetected out-of-tolerance fabrication issue, onset of the collapse of the pressure hull can be detected by monitoring the strain gages. Deviation from the predicted strains (stress
33、es) vs. external pressure is an indicator that the hull is behaving unexpectedly, deforming more than expected, and possibly be near collapse. Monitoring the gages during the hydrostatic test can allow the test to be halted prior to causing significant damage and/or collapse of the hull. Two example
34、s of strain gaging a pressure vessel subjected to external pressure loading are presented herein. The first example, presented in Section 5.0, shows a basic strain gaging plan useful for validating strain and stress analyses. This level of gaging requires a minimal number of strain gages located at
35、general positions on the hull. The second example, presented in Section 6.0, shows a strain gage layout plan which is useful for not only validating strain and stress analyses, but also for monitoring the behavior of the hull during the hydrostatic test. This level of strain gaging requires the most
36、 number of strain gages since gages are placed at both general locations and regions of concern due to hull as-built geometries that might initiate collapse. These two strain gaging examples are provided as illustrative examples only. These examples in no way establish actual strain gaging requireme
37、nts per any code, design rules, or jurisdictional body. They do not establish required placement gage locations, gage types to be used, or number of gages. For each hull, the actual strain gaging plan implemented is a function of many factors, such as the chambers configuration, number and size of o
38、penings, attachments, actual as-built geometry, weld details, and whether just validating an analysis and/or monitoring hull behavior to preclude collapse. Other factors not mentioned here might also dictate the placement of strain gages. 1.2 Monitoring For Behavior The primary purpose of strain gag
39、ing a pressure hull subjected to external pressure loading is to monitor its structural behavior under load. Monitoring the behavior consists of measuring the resulting strains, and then typically calculating the corresponding stresses. Traditionally, the desired type of strains and stresses are the
40、 maximum and minimum principal strains and stresses. Given these principal stresses, the von Mises stress (also known as the equivalent stress) and stress intensity can then calculated if desired. Given these strains and stresses, they then can be compared to the predicted strains and stresses calcu
41、lated by classical formulations and/or finite element analysis, thereby validating the analyses performed. The key to obtaining the correct principal strains at a particular location is knowing the principal strain directions on the structure at the location in question. Whether or not these princip
42、al strain directions are known is a deciding factor in choosing the proper type of strain gage or strain gage rosette to use. (A strain gage rosette consists of two or PTB-6-2013 2 three uniaxial gages combined together in a predefined orientation relative to one another as a single unit.) The three
43、 types of strain gages and rosettes are: (a) The uniaxial strain gage, (b) The biaxial strain gage rosette, and (c) The triaxial strain gage rosette. A discussion of these types of gages and their use for monitoring hull response during test conditions is discussed in Section 2.0 of this document. I
44、t is noted that a strain gage rosette provides strain data only in the plane on which the rosette is attached. In many cases, the structure is 3 dimensional in nature with loads resulting in 3 orthogonally oriented principal strains and stresses. See Section 2.1 for a discussion of the use of planar
45、 (2D) strain gage rosettes and three dimensional (3D) structures. 1.3 Monitoring For Stability The secondary purpose of strain gaging a pressure hull subjected to the external hydrostatic pressure test loading is to indicate the possible onset of hull collapse. Theoretically, using the design rules
46、of the latest ASME PVHO-1 “Safety Standard for Pressure Vessels for Human Occupancy,” standard, the external hydrostatic pressure test serves as a proof test, and the pressure hull should not collapse during the test. However, given an unknown circumstance such as an undetected out-of-tolerance fabr
47、ication issue or test equipment malfunction, onset of the collapse of the pressure hull can be detected by real-time monitoring of the strain gages. Unexplained deviation from predicted strains (stresses) vs. external pressure is a possible indicator that the hull is deforming more than expected and
48、 possibly near collapse. This can allow the test to be halted prior to complete hull collapse. The hull can then possibly be repaired, strengthened, or rerated to a shallower depth if acceptable, and retested. Just as for monitoring the hull for structural behavior, uniaxial strain gages and biaxial
49、/triaxial strain gage rosettes are utilized for this purpose. Although not a requirement of the PVHO-1 rules, for the hydrostatic tests of some pressure hulls, the internal volume of the hull is filled with water and vented through an orifice and piped to the atmosphere. As the external pressure on the hull is increased, the water in the hulls internal volume is expelled. The internal volume change as a function of increasing external pressure, determined by measuring the amount of water expelled from the internal volume, is another set of data tha
