Fatigue Strength Reduction Factors for Welds Based on Nondestructive Examination

1999 ◽  
Vol 121 (1) ◽  
pp. 6-10 ◽  
Author(s):  
J. L. Hechmer ◽  
E. J. Kuhn
Keyword(s):  
Fatigue Strength ◽  
Weld Metal ◽  
Base Metal ◽  
Pressure Vessels ◽  
Strength Reduction ◽  
Initial Development ◽  
Nondestructive Examination ◽  
Additional Information ◽  
Visual Testing ◽  
Reduction Factors

Based on the author’s hypothesis that nondestructive examination (NDE) has a major role in predicting the fatigue life of pressure vessels, a project was initiated to develop a defined relationship between NDE and fatigue strength reduction factors (FSRF). Even though a relationship should apply to both base metal and weld metal, the project was limited to weld metal because NDE for base metal is reasonably well established, whereas NDE for weld metal is more variable, depending on application. A matrix of FSRF was developed based on weld type (full penetration, partial penetration, and fillet weld) versus the NDE that is applied. The NDE methods that are included are radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT), dye penetrant testing (PT), and visual testing (VT). The first two methods (RT and UT) are volumetric examinations, and the remaining three are surface examinations. Seven combinations of volumetric and surface examinations were defined; thus, seven levels of FSRF are defined. Following the initial development of the project, a PVRC (Pressure Vessel Research Council) grant was obtained for the purpose of having a broad review. The report (Hechmer, 1998) has been accepted by PVRC. This paper presents the final matrix, the basis for the FSRF, and key definitions for accurate application of the FSRF matrix. A substantial amount of additional information is presented in the PVRC report (Hechmer, 1998).

Fatigue-Strength-Reduction Factors for Welds in Pressure Vessels and Piping

2000 ◽  
Vol 122 (3) ◽  
pp. 297-304 ◽  
Author(s):  
Carl E. Jaske
Keyword(s):  
Fatigue Strength ◽  
Weld Joint ◽  
Pressure Vessels ◽  
Strength Reduction ◽  
Current Status ◽  
Published Data ◽  
Weld Joints ◽  
Class 1 ◽  
Asme Code ◽  
Reduction Factors

Fatigue-strength-reduction factors (FSRFs) are used in the design of pressure vessels and piping subjected to cyclic loading. This paper reviews the background and basis of FSRFs that are used in the ASME Boiler and Pressure Vessel Code, focusing on weld joints in Class 1 nuclear pressure vessels and piping. The ASME Code definition of FSRF is presented. Use of the stress concentration factor (SCF) and stress indices are discussed. The types of welds used in ASME Code construction are reviewed. The effects of joint configuration, welding process, cyclic plasticity, dissimilar metal joints, residual stress, post-weld heat treatment, the nondestructive inspection performed, and metallurgical factors are discussed. The current status of weld FSRFs, including their development and application, are presented. Typical fatigue data for weldments are presented and compared with the ASME Code fatigue curves and used to illustrate the development of FSRF values from experimental information. Finally, a generic procedure for determining FSRFs is proposed and future work is recommended. The five objectives of this study were as follows: 1) to clarify the current procedures for determining values of fatigue-strength-reduction factors (FSRFs); 2) to collect relevant published data on weld-joint FSRFs; 3) to interpret existing data on weld-joint FSRFs; 4) to facilitate the development of a future database of FSRFs for weld joints; and 5) to facilitate the development of a standard procedure for determining the values of FSRFs for weld joints. The main focus is on weld joints in Class 1 nuclear pressure vessels and piping. [S0094-9930(00)02703-7]

Low-Cycle Fatigue of Large-Diameter Bolts

1967 ◽  
Vol 89 (1) ◽  
pp. 53-60 ◽  
Author(s):  
A. L. Snow ◽  
B. F. Langer
Keyword(s):  
Fatigue Strength ◽  
Yield Strength ◽  
Low Cycle Fatigue ◽  
Large Diameter ◽  
Fatigue Curve ◽  
Fatigue Tests ◽  
Strength Reduction ◽  
Additional Information ◽  
Thread Root ◽  
Reduction Factors

New constant-deflection amplitude fatigue data on bolting materials are presented. The relationship of cyclic yield strength to static yield strength is examined. Several series of full-size stud fatigue tests are analyzed and compared to the basic failure curve to obtain experimental fatigue strength reduction factors for bolts and studs. The variation of fatigue strength reduction factors with thread root radius, stud size, thread taper, and other variables is noted. A new design fatigue curve for bolts is proposed which reflects the additional information available at the present time.

Design of Pressure Vessels for Low-Cycle Fatigue

1962 ◽  
Vol 84 (3) ◽  
pp. 389-399 ◽  
Author(s):  
B. F. Langer
Keyword(s):  
Fatigue Strength ◽  
Pressure Vessel ◽  
Low Cycle Fatigue ◽  
Fatigue Curve ◽  
Pressure Vessels ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
The Mean ◽  
Fatigue Evaluation

Methods are described for constructing a fatigue curve based on strain-fatigue data for use in pressure vessel design. When this curve is used, the same fatigue strength-reduction factor should be used for low-cycle as for high-cycle conditions. When evaluating the effects of combined mean and alternating stress, the fatigue strength-reduction factor should be applied to both the mean and the alternating component, but then account must be taken of the reduction in mean stress which can be produced by yielding. The complete fatigue evaluation of a pressure vessel can be a major task for the designer, but it can be omitted, or at least drastically reduced, if certain requirements can be met regarding design details, inspection, and magnitude of transients. Although the emphasis in this paper is on pressure vessel design, the same principles could be applied to any structure made of ductile metal and subjected to limited numbers of load cycles.

The Effect of Multiaxiality on the Evaluation of Weldment Strength Reduction Factors in High-Temperature Creep

1994 ◽  
Vol 116 (1) ◽  
pp. 76-80 ◽  
Author(s):  
R. Sandstro¨m ◽  
S.-T. Tu
Keyword(s):  
Transfer Function ◽  
Weld Metal ◽  
Creep Strength ◽  
Rupture Strength ◽  
Reduction Factor ◽  
Strength Reduction ◽  
Strength Reduction Factor ◽  
Welded Tube ◽  
Metal Creep ◽  
Reduction Factors

The conventional way to define the weldment creep strength reduction factor is usually based on uniaxial creep data of weld metals and parent metals. In order to take the multiaxial effect into consideration, this paper has defined a structural transfer function which can be evaluated from general creep stress analysis. An analytical model is then proposed in the light of the function. Two numerical examples of typical weld properties show that the transfer function has a load-independent feature, which allows one to obtain multiaxial stress components in a weldment through minimal computation effort. Fairly good estimation of the stress level in the weld metal is achieved. On the basis of the present semi-analytical procedure, the weldment creep strength reduction factors are evaluated. For a 0.5Cr0.5Mo0.25V butt-welded tube under internal pressure, which has a higher weld metal creep-rupture strength, and lower weld metal creep strain rate, the reduction factors range from 0.9 to 0.95. For the AISI 316 butt-welded tube of cold-worked parent metal and creep soft weld metal, lower strength reduction factors are found, but they may still be nonconservative due to stress enhancement in the heat-affected zone.

PWSCC of Bottom Mounted Instrument Nozzles at South Texas Project

2004 ◽  
Author(s):  
Steven Thomas
Keyword(s):  
Base Metal ◽  
Weld Interface ◽  
South Texas ◽  
The Other ◽  
Bottom Surface ◽  
Nondestructive Examination ◽  
Additional Information ◽  
Welding Defects ◽  
Primary Water ◽  
Axial Crack

Primary water stress corrosion cracking (PWSCC) susceptibility of bottom mounted instrument (BMI) nozzles in the South Texas Project reactor vessels was considered low due to the Tcold temperature of the bottom head. During a routine bare metal visual inspection of the Unit 1 bottom head in April 2003 small boric acid deposits were identified at the location where two of the BMI nozzles penetrated the bottom surface of the vessel head. Subsequent nondestructive examination showed three cracks in one of the nozzles two crack in the second nozzle and no cracks in the other 56 nozzles. The nondestructive examinations showed that both leaking nozzles had an axial crack in the nozzle base metal extending from above the J-weld to below the J-weld. One of these cracks extended nearly through-wall while the other did not extend through wall. A boat sample removed from one of the leaking nozzles confirmed the presence of a PWSCC crack in the nozzle base metal and the presence of welding defects at the tube to J-weld interface which could be responsible for initiating the cracks. This paper summarizes the field inspections and laboratory investigations and briefly descries the repair method. See References 1 and 2 for additional information.

Study on Skirt-to-Shell Attachment of Coke Drum by Evaluation of Fatigue Strength of Weld Metal

2011 ◽  
Author(s):  
Yasuhiko Sasaki ◽  
Shinta Niimoto
Keyword(s):  
Fatigue Strength ◽  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Inner Radius ◽  
Section Viii

A skirt-to-shell attachment of a coke drum experience severe thermal cyclic stresses, which cause failures due to low cycle fatigue. Various skirt attachment designs, therefore, have been proposed and implemented. A design where the skirt is attached by a weld build-up is most commonly used. A design where the skirt is attached to the drum shell by utilizing an integral machined plate or forging has been utilized in several projects. One of the advantages of the integral skirt attachment is that a large inner radius can be formed which allows reducing stress concentration compared with the weld build-up design. This advantage can be confirmed easily by FE-analysis in recent years [1] [2] [3]. Another major advantage of the integral skirt attachment is that the area of highest stress intensity is located at the base metal section, not at the weld metal or the heat affected zone which are generally thought to have lower fatigue strength. The fatigue design curve from ASME Section VIII Division 2 [9] is based on fatigue tests for the base metal. It is necessary to reveal differences of fatigue strength among these metals. This paper describes a comparison of fatigue strength of three metals: i) base metal ii) weld metal iii) heat affected zone provided by the low cycle fatigue test for 1 1/4Cr-1/2Mo materials. Our results indicate that the fatigue life of the base metal is about twice as long as that of the weld metal and about three times as long as the heat affected zone. Accordingly, the integral skirt attachment is more resistant to cracking than its welded counterpart from a fatigue strength viewpoint.

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