Assessment of Local Decreases in Wall Thickness at the Connection Straight-Pipe to Bend

2002 ◽  
Author(s):  
Robert Kauer ◽  
Wieland Holzer
Keyword(s):  
Wall Thickness ◽  
Maximum Stress ◽  
Straight Pipe ◽  
Material Loss ◽  
Pipe Bend ◽  
Stress Indices ◽  
Service Testing ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Bend Angles

Welds are ground during manufacturing to free them from offset edges and notches and thus to obtain a more favorable stress distribution. Apart from the above, welds are also ground to prepare them for and improve the conditions of in-service testing and inspection. The grinding of welds may result in a local decrease in wall thickness, so that there may be local deviations from the required minimum wall thickness. In order to fulfill the task of evaluating the strength of such material-loss regions, we have determined appropriate stress concentration factors for typical wall-thickness deviations and various wall-thickness/diameter ratios, which enable us to assess quickly and, if necessary, directly after the on-site measurement of wall thickness, whether a detected deviation from the minimum value is permissible. To be able to evaluate deviations from minimum wall thickness, especially in welds that form a connection to bends, we have determined stress indices for the beginning and the end of bends for common pipe bend dimensions and various bend angles. Compared with the maximum stress indices commonly used in piping calculations for the crown of the bend, the stress indices at the end of the bend are lower than those at the crown and can help to reduce unnecessary conservatism. In the paper, stress indices for various grinding geometries and for the beginning and the end of common bend shapes will be presented, as well as the method used to evaluate strength and the criteria pertaining to the tolerability of decreases in wall thickness.

Assessment of Local Decreases in Wall Thickness at the Connection Straight-Pipe to 0°–90°-Bends

2004 ◽  
Author(s):  
Robert Kauer ◽  
Wieland Holzer
Keyword(s):  
Wall Thickness ◽  
Beam Theory ◽  
Original Design ◽  
Straight Pipe ◽  
Material Loss ◽  
Pipe Bend ◽  
Transverse Beam ◽  
Stress Indices ◽  
Stress Curve ◽  
Weld Area

Welds are ground during manufacturing to free them from offset edges and notches and thus to obtain a more favorable stress curve. Apart from the above, welds are also ground to prepare them for periodic testing and inspection by improving the conditions for these in-service inspection measures. The latter is one reason for a local decrease in wall thickness in the weld area at the connection between straight pipe and bend, so that there may be local deviations from the original design-based minimum required wall thickness. In order to fulfill the task of evaluating the strength of such material-loss regions, this paper determines appropriate stress indices for typical wall-thickness deviations and various wall-thickness/diameter ratios. For the beginning and the end of the bends, the factors B* and C* for common pipe bend dimensions have been determined. In [1], the factors B* and C* for 90°-bends are compared to the stress indices B and C given in the literature for the crown of the bend. These factors B and C are commonly used in piping calculations, which are based on the transverse beam theory. In this paper the factors B* and C* are presented for both ends of the bends with bend angles in the range of 0° to 90° degree. These factors for the beginning and the end of 0°–90°-bends will also be compared with factors given in the literature. The correct combination of both factors — wall-thickness reduction and B* or C* — allows to decide, whether a detected deviation from the minimum value is permissible.

The Stress Concentration Factors in Cylindrical Tubes with Transverse Circular Holes

1959 ◽  
Vol 10 (4) ◽  
pp. 326-344 ◽  
Author(s):  
H. T. Jessop ◽  
C. Snell ◽  
I. M. Allison
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
Stress System ◽  
Complete Knowledge ◽  
Geometrical Shapes ◽  
Cylindrical Tubes ◽  
Circular Holes ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Better Than

The “frozen stress” techniques of photoelasticity can give a complete knowledge of the stress, system in a solid body, but the examination of the stresses requires more time and care than in corresponding flat plate tests. In tests on tubes with transverse circular holes, sponsored by The Royal Aeronautical Society, all practicable geometrical shapes are examined and the maximum stress is measured in tension, bending and torsion. The results are comprehensive and show the inadequacy of previous results. In all cases the maximum stress occurs inside the bore of the hole. The accuracy of all the graphs of stress concentration factors is better than five per cent.

Stress concentration factors in compression—fit couplings

2010 ◽  
Vol 224 (6) ◽  
pp. 1143-1152 ◽  
Author(s):  
D Croccolo ◽  
N Vincenzi
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
External Pressure ◽  
Geometrical Parameters ◽  
Boundary Zone ◽  
Finite Element Analyses ◽  
Axially Symmetric ◽  
Numerical Investigations ◽  
Concentration Factors ◽  
Stress Concentration Factors

The aim of the present work is to define the maximum stress generated by the coupling of axially symmetric and continuous shafts press-fitted into axially symmetric hubs. The theoretical stresses given by the well-known formulae of the thick-walled cylinders theory are constant on the whole coupling surface, but if the shaft extends beyond the hub there is a stress concentration factor on the boundary zone. This occurrence is confirmed by finite element analyses performed by the authors on several different shaft—hub couplings. The analysed couplings have the shaft extended beyond the hub, the shafts press-fitted into the hubs, and both shafts and hubs loaded by an external pressure and an internal pressure. The stress concentration factors have been calculated in this work and their expressions have been derived as a function of some tensile and geometrical parameters. By combining the thick-walled cylinders theory with the proposed formulae, it is possible to evaluate the maximum stress located at the end of the hub without performing any numerical investigations.

Stress Concentration Factors in Shouldered Shafts Subjected to Combinations of Flexure and Torsion

1968 ◽  
Vol 90 (2) ◽  
pp. 301-307 ◽  
Author(s):  
H. G. Rylander ◽  
P. M. A. daRocha ◽  
L. F. Kreisle ◽  
G. J. Vaughn
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
Small Diameter ◽  
Bending Moment ◽  
Pure Bending ◽  
Principal Stresses ◽  
Torsional Loads ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Experimental Values

Geometric stress concentration factors were determined experimentally for shouldered aluminum shafts subjected to combinations of flexural and torsional loads. Diameter ratios were varied from 0.42 to 0.83, and fillet radius to small diameter ratios were varied from 0.1 to 0.7 with bending moment to torque ratios varying over a range from 1:4 to 4:1. Experimental values for the stress concentration factors were obtained by using birefringent coatings and a reflection polariscope. Strain gage measurements and torsional relaxation solutions were used to verify some of the polariscope data. For the cases considered, the static geometric stress concentration factor was between 1.11 and 1:50 for pure torsion, between 1.08 and 1.46 for pure bending, and between 1.09 and 1.50 for combined torsion and bending. The directions of the principal stresses on the surface of the shouldered shafts do not change due to the presence of the discontinuity for a particular specimen and type of loading. Also, the location of the maximum stress in the fillet of a particular specimen under a certain type of loading does not change as the magnitude of the load is varied, but it does vary with the type of loading.

scholarly journals The research of the stress-strain state with local thinning in pipelines and determination of allowable values of concentration stress and strain

2019 ◽  
Vol 15 (5) ◽  
pp. 384-391
Author(s):  
Dmitry A. Kuzmin ◽  
Anastasia V. Andreenkova
Keyword(s):  
Stress Concentration ◽  
Internal Pressure ◽  
Wall Thickness ◽  
Strain State ◽  
Stress Strain ◽  
Flow Acceleration ◽  
Stress Strain State ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Equipment And Pipelines

Relevance. The nuclear power plant contains a large number of equipment and pipelines subject to flow acceleration corrosion. As a result of a combination of various parameters - sizes (diameters, wall thickness), operational parameters (internal pressure, temperature), steels and elements types - the number of design cases is tens of thousands, without counting the possible forms of thinning. The process of maintenance and repair at the stations are doing an assessment of the accordance of actual and allowable values of wall thicknesses. The ensuring safe operations of equipment and pipelines have been introduced correction functions for regulatory functions, taking into account the forms of thinning, to determine the permissible thinning. The aim of the work. The task is to determine the influence of the forms and types of thinning on the stress-strain state and to determine the most critical thinning for straight sections of pipelines subject to flow acceleration corrosion taking into account emergency conditions. Methods. The allowable values of stress concentration factors (deformations) of pipelines subject without flow acceleration corrosion was determined taking into account allowable values, the requirements of the federal norms and rules for emergency operating conditions. For researches of the stress concentration coefficients were used the finite element method and analytical methods for various shapes, sizes and depths of thinning. Results. A method has been developed, that allows getting the maximum allowable values of stress concentration factors (deformations) for emergency operation, which afford to determine the maximum allowable depth of thinning in emergency conditions - an above criterion. The researches have been carried out definition of the stress concentration factors for local thinning with various types of these thinning. The functions of concentration coefficients depending on the geometric parameters of local thinning wall thickness were determined for a straight section of the pipeline. As a result of the research, the dependences of the sizes of thinning on the concentration coefficients for straight pipelines were created and a master-curve was obtained. The researches were carried out take into account the load from internal pressure and bending moment.

Theoretical Stresses Near a Circular Opening in a Flat Plate, Reinforced With a Cylindrical Outlet

1959 ◽  
Vol 81 (2) ◽  
pp. 189-200 ◽  
Author(s):  
Everett O. Waters
Keyword(s):  
Stress Concentration ◽  
Flat Plate ◽  
Circular Hole ◽  
Wall Thickness ◽  
Plate Thickness ◽  
Pressure Vessels ◽  
Circular Opening ◽  
Concentration Factors ◽  
Stress Concentration Factors

Formulas are derived for stresses in the neighborhood of a circular hole in a flat plate, when the opening is reinforced with a cylindrical outlet such as a pipe or nozzle. The plate is loaded in tension, either uniformly in all directions, or with transverse and longitudinal tensions in the ratio of 2:1 as is the case in cylindrical pressure vessels. Consideration is given to the possibility of “balanced reinforcement” by adding material on both sides of the plate. Tables and graphs are included for the use of designers who wish to find the stress-concentration factors for different combinations of plate thickness, outlet-wall thickness, and outlet diameter.

Stress-Concentration Factors in Shafts With Transverse Holes as Found by the Electroplating Method

1955 ◽  
Vol 22 (2) ◽  
pp. 193-196
Author(s):  
H. Ōkubo ◽  
S. Satō
Keyword(s):  
Stress Concentration ◽  
Outer Surface ◽  
Maximum Stress ◽  
Accurate Determination ◽  
Slicing Method ◽  
Concentration Factors ◽  
Mathematical Difficulties ◽  
Stress Concentration Factors ◽  
Maximum Stresses

Abstract In this paper the torsion of shafts with transverse holes has been investigated experimentally. Usual methods for stress measurements, such as the method of brittle coatings and the use of sensitive extensometers, are not applied effectively to the present problem because the maximum stress occurs in the bore and does not occur on the outer surface of the shaft. The stress may be measured by the stress-freezing and slicing method but we cannot expect too much from this method for the accurate determination of the stress when the diameter of the hole is comparatively small. In treating the problem theoretically, considerable mathematical difficulties are encountered on account of its axially nonsymmetrical nature. The electroplating method recently developed by one of the authors (1), however, has been proved to be useful in this case, so the maximum stresses in shafts are measured by this method and the stress-concentration factors are found for various diameters of the hole.

Stress concentration caused by an oblique round hole in a flat plate under uniaxial tension

1968 ◽  
Vol 3 (2) ◽  
pp. 98-102 ◽  
Author(s):  
H W McKenzie ◽  
D J White
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
Elliptical Hole ◽  
Round Hole ◽  
Flat Plates ◽  
Reasonable Estimate ◽  
Load Carrying ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Plate Width

Stress-concentration factors have been determined for oblique holes in flat plates by a method using frozen-stress photoelasticity. The ellipses formed at the intersection of the hole and the plate surfaces had their major axes perpendicular to the direction of application of the load. The maximum stress-concentration factor was found to increase with increasing angle of obliquity with respect to the normal to the plate but the experimental factors were found to be considerably lower than those predicted from a theory of Ellyin et al. Graphs are given which enable maximum stress-concentration factors to be obtained for oblique holes having a ratio of hole diameter to plate width of 0.1. It was found that, for the models tested, elliptical hole data gave a reasonable estimate of the maximum stress-concentration factors based on net area. Removing the feather edge of the hole, by applying various edge radii, did not alter the stress concentration appreciably except in so far as load-carrying area was reduced.

Stress Concentration Factors for a Drilling Riser Containing Corrosion Pits

2007 ◽  
Author(s):  
Adilson C. Benjamin ◽  
Divino J. S. Cunha ◽  
Rita C. C. Silva ◽  
Joa˜o N. C. Guerreiro ◽  
George C. Campello ◽  
...  
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Wall Thickness ◽  
External Surface ◽  
Corrosion Defects ◽  
Concentration Factors ◽  
Residual Fatigue ◽  
Stress Concentration Factors ◽  
Corrosion Pits ◽  
Outside Diameter

The residual fatigue life of a corroded riser joint can be evaluated by means of a fatigue analysis based on S-N data. In this case nominal stresses are determined through a global riser analysis in which the drilling riser is modeled as a tensioned beam subjected to loads throughout its length and with boundary conditions at each end. The effect of the corrosion defects is taken into account multiplying the nominal stresses by stress concentration factors (SCFs) derived by local Finite Element (FE) analyses of the riser joints containing corrosion defects. In this paper stress concentration factors for a drilling riser containing corrosion pits are calculated using solid FE models. These pits are situated on the external surface of the riser joints. Three shapes of corrosion pits are considered: semi spherical, cylindrical wide and cylindrical narrow. Five depths of corrosion pits are considered: 12.6%, 20.1%, 30.2%, 40.3% and 50.3% of the riser wall thickness. The riser outside diameter and the riser wall thickness are 533.4 mm (21 in) and 15.9 mm (0.625 in), respectively.

Derivation of Stress Intensification Factors for a Special, Contoured, Integrally Reinforced Branch Connection

1973 ◽  
Vol 95 (1) ◽  
pp. 106-112
Author(s):  
R. W. Schneider ◽  
E. C. Rodabaugh
Keyword(s):  
Three Dimensional ◽  
Fatigue Tests ◽  
Stress Indices ◽  
Cylindrical Pressure Vessel ◽  
Out Of Plane ◽  
Stress Intensification Factor ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Fitting In ◽  
Standard Weight

The results of an extensive experimental investigation of a contoured, integrally reinforced branch connection in a cylindrical pressure vessel (or run pipe) have been reported [1]. One size model, specifically a 12 in. (0.375) × 6 in. (0.280) standard weight header was studied by three-dimensional photoelasticity using the stress-freezing and slicing technique. Loads applied were internal pressure, plus in-plane and out-of-plane bending moments on the branch; one model was used for each mode of loading. In addition, carbon steel headers were fatigue tested by longitudinal and transverse moments cyclically applied to the branch pipes. A model was required for each mode of loading for each level of amplitude of applied nominal stress. Stress concentration factors (stress indices) were derived from the photoelastic tests, whereas, the fatigue tests produced stress intensification factors. The stress indices and stress intensification factors derived from the tests apply only to 12 × 6 standard weight headers, or geometrically identical headers, with the particular type of branch connection. This paper describes how generalized stress intensification factor equations were derived to cover a broad range of sizes and thicknesses of headers incorporating the same type of branch fitting. In this paper the term “header” applies to a single branch connection in a pipe remote from all other discontinuities.

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