1、STP-PT-050AN INVESTIGATION OF THREE RADIOGRAPHIC ACCESS PORT PLUG GEOMETRIES AND THE SURROUNDING PIPE WALL UNDERGOING CREEPSTP-PT-050 AN INVESTIGATION OF THREE RADIOGRAPHIC ACCESS PORT PLUG GEOMETRIES AND THE SURROUNDING PIPE WALL UNDERGOING CREEP Prepared by: Chris Tipple, Quest Integrity Group, LL
2、C Date of Issuance: June 15, 2012 This report was prepared as an account of work sponsored by ASME Pressure Technology Codes & Standards and the ASME Standards Technology, LLC (ASME ST-LLC).). Neither ASME, ASME ST-LLC, the author, nor others involved in the preparation or review of this report, nor
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9、the publisher. ASME Standards Technology, LLC Three Park Avenue, New York, NY 10016-5990 ISBN No. 978-0-7918-3427-5 Copyright 2012 by ASME Standards Technology, LLC All Rights Reserved Radiographic Access Port Plug STP-PT-050 iii TABLE OF CONTENTS Foreword . vi Executive Summary . vii 1 INTRODUCTION
10、 . 1 2 FINITE ELEMENT MODELS 2 2.1 Geometry . 2 2.2 Loading and Constraints 4 2.3 Material Properties and Creep Behavior . 6 3 FINITE ELEMENT RESULTS FOR THE THREE ORIGINAL GEOMETRIES . 7 3.1 Maximum Principal Stress 17 3.1.1 Maximum Value . 17 3.1.2 Average Value 19 3.2 Von Mises Stress . 21 3.2.1
11、Maximum Value . 21 3.2.2 Average Value 23 3.3 Hoop Stress . 24 3.3.1 Maximum Value . 24 3.3.2 Average Value 26 3.4 Radial Stress 27 3.4.1 Maximum Value . 27 3.4.2 Average Value 29 4 BORE DEPTH . 31 5 INCREASED INTERNAL PRESSURE . 35 6 CONCLUSION 37 References 38 Acknowledgments 39 LIST OF TABLES Tab
12、le 1 - Model Sizes for Each of the Three Geometries 2 Table 2 - Symmetry Boundary Conditions . 4 Table 3 - Elastic Material Properties 6 Table 4 - Strain Hardening Creep Law Material Properties . 6 Table 5 - Maximum Stress Values Observed in WeldSolid Plug . 8 Table 6 - Maximum Stress Values Observe
13、d in Weld3/8“ Plug 8 Table 7 - Maximum Stress Values Observed in Weld1/4“ Plug 9 Table 8 - Average Stress Value Observed in WeldSolid Plug . 9 Table 9 - Average Stress Values Observed in Weld3/8“ Plug . 10 Table 10 - Average Stress Values Observed in Weld1/4“ Plug . 10 STP-PT-050 Radiographic Access
14、 Port Plug iv LIST OF FIGURES Figure 1 - ES-16 Compliant Plug for Pipe Wall Thickness from 3 in. (76 mm) through 5 in. (127 mm) 1 . 1 Figure 2 - Meshed Solid, 3/8“ and 1/4“ Geometries . 2 Figure 3 - Spatial Relationship between the Plug, Pipe and Weld 3 Figure 4 - Tied Contact between Weld Metal Bui
15、ldup and Circumferentially Uniform 3/8“ Weld (Highlighted In Red) . 3 Figure 5 - Meshed Solid Plug Model Including Plug, Pipe and Weld 4 Figure 6 - Symmetry Boundary Conditions Applied To the Models 5 Figure 7 - Internal Pressure and Axial Thrust Applied To Models . 5 Figure 8 - Angular Locations of
16、 Stress Reporting Positions in Weld . 7 Figure 9 - Weld Plane (Highlighted) for Stress Extraction . 7 Figure 10 - Maximum Principal Stress (MPa), Time = 106hrs, 1000x Deformation (Top - Solid Plug, Middle - 3/8“ Plug, Bottom - 1/4“ Plug) 11 Figure 11 - Von Mises Stress (MPa), Time = 106hrs, 1000x De
17、formation (Top - Solid Plug, Middle - 3/8“ Plug, Bottom - 1/4“ Plug) . 12 Figure 12 - Hoop Stress (MPa), Time = 106hrs, 1000x Deformation (Top - Solid Plug, Middle - 3/8“ Plug, Bottom - 1/4“ Plug) 13 Figure 13 - Radial Stress (MPa), Time = 106hrs, 1000x Deformation (Top - Solid Plug, Middle - 3/8“ P
18、lug, Bottom - 1/4“ Plug) 14 Figure 14 - Von Mises Stress Creep Evolution for the Solid Plug, 1000x Deformation 15 Figure 15 - Von Mises Stress Creep Evolution for the 3/8” Plug, 1000x Deformation 16 Figure 16 - Von Mises Stress Creep Evolution for the 1/4” Plug, 1000x Deformation 17 Figure 17 - Maxi
19、mum Max Principal Stress at Theta=0 . 18 Figure 18 - Maximum Max Principal Stress at Theta=90 . 18 Figure 19 - Average Max Principal Stress at Theta=0 20 Figure 20 - Average Max Principal Stress at Theta=90 20 Figure 21 - Maximum Von Mises Stress at Theta=0 21 Figure 22 - Maximum Von Mises Stress at
20、 Theta=90 22 Figure 23 - Average Von Mises Stress at Theta=0 . 23 Figure 24 - Average Von Mises Stress at Theta=90 . 24 Figure 25 - Maximum Hoop Stress at Theta=0 . 25 Figure 26 - Maximum Hoop Stress at Theta=90 . 25 Figure 27 - Average Hoop Stress at Theta=0 26 Figure 28 - Average Hoop Stress at Th
21、eta=90 27 Radiographic Access Port Plug STP-PT-050 v Figure 29 - Maximum Radial Stress at Theta=0. 28 Figure 30 - Maximum Radial Stress at Theta=90. 28 Figure 31 - Average Radial Stress at Theta=0 29 Figure 32 - Average Radial Stress at Theta=90 30 Figure 33 - Deep Bore Plug Compared with Original G
22、eometry . 31 Figure 34 - Max Principal Stress Creep Evolution for the Deep Bore 3/8” Plug, 1000x Deformation 32 Figure 35 - Max Principal Stress Creep Evolution for the Deep Bore 3/8” Plug . 32 Figure 36 - Max Principal Stress Creep Evolution for the Deep Bore 3/8” Plug . 33 Figure 37 - Max Principa
23、l Stress Creep Evolution for the Deep Bore 3/8” Plug . 33 Figure 38 - Max Principal Stress Creep Evolution for the Deep Bore 3/8” Plug . 34 Figure 39 - Vohn Mises Stresses for All Geometries at Theta=0 for Internal Pressures 2 MPa and 10 MPa . 35 Figure 40 - Von Mises Stresses for All Geometries at
24、Theta=90 for Internal Pressures 2 MPa and 10 MPa . 36 STP-PT-050 Radiographic Access Port Plug vi FOREWORD This report evaluates the effects of various plug geometries on stresses that evolve during creep. A quantitative investigation of creep-compliant plugs was conducted. This work identifies the
25、stresses, as a function of plug geometry, in the weld between the plug and the pipe wall. 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 mu
26、ltidisciplinary engineering and allied sciences. ASME develops codes and standards that 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 Technolo
27、gy, LLC (ASME ST-LLC) is a not-for-profit Limited Liability Company, with ASME as the 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 an
28、d services, which advance the application of emerging and newly commercialized science 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. Radiographic Acc
29、ess Port Plug STP-PT-050 vii EXECUTIVE SUMMARY When heavy-wall pipe field welds are radiographed, common practice is to route the radiation source through a hole in a pipe near a weld, and locate it on the centerline using a J-shaped tube. The J-shaped tube is then removed and a plug is screwed into
30、 the hole. The plug is then welded to the pipe around the plugs circumference. Initially, the stresses are carried by the plugs threads. However, after prolonged service, stresses are increasingly carried by the circumferential plug welds. In addition to thread corrosion, creep stretches the hole in
31、 which the plug is located, possibly increasing stress on the circumferential plug weld. Creep failures of radiographic access port plugs have been observed. The objective addressed in the report is to evaluate the effects of various plug geometries on stresses that evolve during creep. This was don
32、e by examining stresses using finite element creep simulation on three different plug geometries. No threads were considered in any of the geometries. The forces due to internal pressure were only resisted by the plug fillet weld. The following geometries were considered. 1) A solid plug with no thr
33、eads. 2) A bored out plug (3/8” wall thickness) ceteris paribus. (1/2” bore) 3) A bored out plug (1/4” wall thickness) ceteris paribus. (5/8” bore) The weld geometry considered was a 3/8” circumferential fillet weld between the plug and the pipe. Three identically-loaded finite-element models were a
34、ssessed. To assess the plug geometries, maximum and average stress values were compared at two locations in each weld. Principal, Von Mises, hoop and radial stresses were examined (where hoop and radial stress were defined as local to the plug). Both maximum and average principal stress (largest ten
35、sile stress) in the weld increased with plug bore diameter, as did hoop stress values. The analysis results also seemed to show that the use hollowed-out plugs had a detrimental effect on both the maximum and average hoop stress around the plug. Von Mises stress showed no significant dependence or a
36、 slight increase with increasing bore diameter. The hollowed-out plugs were slightly more compliant during the initial phases of creep, as shown by more rapid stress changes and a quicker time to reach steady-state. However, the relevant stresses, both initially and after creep evolution to steady s
37、tate, were higher for the hollowed-out plugs. The comparative behavior of the various plug geometries did not change as the internal pressure was increased, even though the initial stress and creep rates increase. This suggests that hollowed-out plugs offer no significant advantage even at higher in
38、ternal pressures. Further examination of a plug design using a 3/8” wall thickness plug (1/2” bore), but with a deeper flat bottom bore hole showed no significant benefit as compared to the original bore geometry. There was no significant stress reduction or improvement in creep compliance, and the
39、resulting stresses initially, and after creep, were still higher than the solid plug geometry. As failure of the plug weld will be governed predominately by hoop or principal stresses, these results indicate there are no substantial benefits, and possibly detrimental impact, to the use of hollowed-o
40、ut plugs. STP-PT-050 Radiographic Access Port Plug viii INTENTIONALLY LEFT BLANKRadiographic Access Port Plug STP-PT-050 1 1 INTRODUCTION When heavy-wall pipe field welds are radiographed, common practice is to route the radiation source through a hole in a pipe near a weld, and locate it on the cen
41、terline using a J-shaped tube. The J-shaped tube is then removed and a plug is screwed into the hole. The plug is then welded to the pipe around the plugs circumference. Initially, the stresses are carried by the plugs threads. However after prolonged service, stresses are increasingly carried by th
42、e circumferential plug welds. In addition to thread corrosion, creep stretches the hole in which the plug is located, possibly increasing stress on the circumferential plug weld. Creep failures of radiographic access port plugs have been observed. Historically, Pipe Fabrication Institute standard ES
43、-16 1 offered guidance for the design of these plugs. An example of an ES-16 compliant plug geometry is shown in Figure 1. ES-16 plugs are solid, however some high temperature component manufacturers use bored out or thimble-shaped plugs with the intent of offering more compliance with creep. Figure
44、 1 - ES-16 Compliant Plug for Pipe Wall Thickness from 3 in. (76 mm) through 5 in. (127 mm) 1 A quantitative investigation of creep-compliant plugs is here conducted. This work identifies the stresses, as a function of plug geometry, in the weld between the plug and the pipe wall. The objective addr
45、essed in the report is to evaluate the effects of various geometries on stresses that evolve during creep. This is done by examining stresses using finite element creep simulation on three different plug geometries. No threads are considered in any of the geometries. The forces due to internal press
46、ure are only resisted by the plug fillet weld. The following geometries are considered. 1) A solid plug with no threads. 2) A bored out plug (3/8” wall thickness) ceteris paribus. (1/2” bore) 3) A bored out plug (1/4” wall thickness) ceteris paribus. (5/8” bore) The weld geometry considered is a 3/8
47、” circumferential fillet weld between the plug and the pipe. Additional plug geometries as specified by ASME may be considered as an extension to this work. STP-PT-050 Radiographic Access Port Plug2 2 FINITE ELEMENT MODELS Finite element analysis (FEA) is used to quantify the stresses in the plug fi
48、llet weld and to determine how these stresses evolve as the pipe undergoes creep. The behavior of these stresses can be used to help determine if a hollowed-out plug design is beneficial to help prevent creep related failures. 2.1 Geometry Three distinct finite element models are created, correspond
49、ing to the three plug geometries as provided by ASME. Figure 2 shows an image of the three plug geometries. Each finite element model utilizes a reduced integration quadratic hexahedral element mesh (identified by ABAQUS as C3D20R elements) 2. Table 1 outlines the model size for each of the three geometries. The high degree of mesh refinement allows any significant stress variations to be captured. Figure 2 - Meshed Solid, 3/8“ and 1/4“ Geometries Table 1 - Model Sizes for Each of the Three Geometries Model Number of Elem
