The Effect of Hoop Stress on the Burnthrough Susceptibility During In-Service Welding of Thin-Walled Pipelines

2008 ◽  
Author(s):  
Matthew A. Boring ◽  
William A. Bruce
Keyword(s):  
Failure Mechanism ◽  
Wall Thickness ◽  
Hoop Stress ◽  
Pipe Diameter ◽  
Welding Parameters ◽  
Minor Effect ◽  
Circumferential Welds ◽  
Welding Arc ◽  
Thin Walled ◽  
Longitudinal Welds

Most companies control the risk of burnthrough by prohibiting welding on pipelines with wall thicknesses below a specified thickness. This is a safe approach but the risk of burnthrough depends not only on the wall thickness, but also on the welding parameters and the operating parameters of the pipeline which include pressure. It is generally acknowledged that the hoop stress caused by pressurizing the pipeline has a relatively minor effect on the risk of burnthrough since the size of the area heated by the welding arc is small. While this has certainly been shown to be true for thicker materials, previous research has shown that the pressure can have a dramatic effect on burnthrough risk for thinner materials. The objective of this project was to further investigate the effects pressure and hoop stress has on the burnthrough risk of welding onto thin-walled pipelines in service. For circumferential welds, pressure and wall thickness determine the burnthrough risk and pipe diameter appears to have no effect. The failure mechanism for circumferential welds is consistently a burnthrough. For longitudinal welds, pipe diameter does appear to affect burnthrough risk even though the effect appears to be secondary to pressure and wall thickness. The pipe diameter is believed to be more influential for longitudinal welds because of the larger area of heated material that is exposed to the hoop stress. Also, the results indicate that the magnitude of the hoop stress has a direct effect on the failure mechanism for longitudinal welds (i.e., burnthrough or weld centerline cracks). For longitudinal welds, the failure mechanism is commonly burnthrough for welds made onto pipes with a hoop stress below 30% specified minimum yield stress (SMYS) which indicates that the internal pressure of the pipe is the main driving force for failure. Longitudinal welds made on pipes which are experiencing hoop stress above 30% SMYS commonly fail by weld cracking. It is important to note that even though pressure does have an effect on the burnthrough susceptibility of welds made on thin-walled pipelines, pressure only becomes a factor for welds made at heat input levels in excess of what is predicted safe by thermal analysis modeling.

Validation of an Ultrasonic-Phased Array Method for Testing of Circumferential Welds at Thin-Walled Pipes

NDT World ◽  
2016 ◽  
Vol 19 (3) ◽  
pp. 30-33
Author(s):  
Бросиус ◽  
David Brosius ◽  
Шуберт ◽  
Frank Schubert ◽  
Хильманн ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Power Plants ◽  
Phased Array ◽  
Practical Method ◽  
Probability Of Detection ◽  
Circumferential Welds ◽  
Ultrasonic Methods ◽  
Ultrasonic Phased Array ◽  
Thin Walled ◽  
The Moment

Introduction. For testing of circumferential welds at thin-walled pipes with wall thickness lower than 6 mm using ultrasonic methods no standardization is available at the moment. Nevertheless, there are newest technologies available such as ultrasonic-phased-array technique and semi-automated handheld-scanner for pipes, with which it is possible to achieve promising and reliable results in that area. In order to bring the technique in operation in the field of coal-fired power plants or petrochemical industry a validation is needed, which will be approved by the inspecting authorities. Method. In that article we will present a successful validation of an ultrasonic-phased- array method for testing circumferential welds at thin-walled pipes with a wall thickness lower than 6 mm. Therefore, the complete geometry area was divided into several clusters, and single elements of that matrix were validated. The procedure conforms to the guideline VGB R-516 and other established standards. Besides theoretical analysis including simulations of the sound paths and reflections, extensive practical tests were performed. For this purpose six typical types of defects were analyzed by using a large number of test samples and the probability of detection was determined using this practical method. Result. The result of this work is a report for validation for each geometry cluster of the pipes including an inspection instruction and a qualification instruction for the testing equipment and the calibration samples. Conclusion. Based on that validations the ultrasonic-phased-array method was accepted by the inspecting authorities and thereby allowed to use in the regulated area of coal-fired power plants by a NDT-service provider and was applied very successful at several thousand welds.

Minimum Weight of Tapered Round Thin-Walled Columns

1952 ◽  
Vol 19 (3) ◽  
pp. 375-380
Author(s):  
Morris Feigen
Keyword(s):  
Wall Thickness ◽  
Minimum Weight ◽  
Weight Ratio ◽  
Optimum Shape ◽  
Bending Stress ◽  
Round Tube ◽  
Cylindrical Column ◽  
Truncated Cone ◽  
Thin Walled ◽  
Tapered Column

Abstract It is shown that the optimum wall thickness of a cylindrical round tube column is a function of load only and is independent of diameter. The optimum wall thickness of a tapered round thin-walled column is found to be constant along its length. The optimum shape of a tapered round thin-walled column is derived, being that column whose bending stress in the buckled state is constant along its length. The weight ratio of the optimum tapered column to an equal-strength optimum cylindrical column is found to be 0.8924. It is shown that a double truncated cone whose diameter ratio is in the range 0.35 ⩽ D1/D2 ⩽ 0.50 closely approaches the optimum column. If it is specified that no portion of the double truncated cone shall yield, then the weight advantage of the cone over the cylindrical column is rapidly lost as the stress in the cylindrical column approaches the yield stress. In the inelastic range the weight advantage of the tapered column will be less than in the elastic range.

An Elementary Theory of the Bourdon Gage

1946 ◽  
Vol 13 (3) ◽  
pp. A207-A210
Author(s):  
Alfred Wolf
Keyword(s):  
Wall Thickness ◽  
Maximum Stress ◽  
Transverse Section ◽  
Elementary Theory ◽  
Thin Walled ◽  
Longitudinal Extension

Abstract A theory of the Bourdon gage is presented based upon two elements of strain, namely, the bending of the walls in a transverse section through the gage tubing, and a longitudinal extension parallel to the axis of the tubing. Practical formulas are derived for the calculation of the sensitivity and the torque of the Bourdon gage. An estimate is made of the maximum stress. The sensitivity of a very thin-walled gage is shown to be proportional to the inverse first power of the wall thickness. Results of a few measurements show agreement with the theory.

scholarly journals Comparison of Hot Cracking Susceptibility of TIG and Laser Beam Welded Alloy 718 by Varestraint Testing

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 985 ◽  
Author(s):  
Pedro Alvarez ◽  
Lexuri Vázquez ◽  
Noelia Ruiz ◽  
Pedro Rodríguez ◽  
Ana Magaña ◽  
...  
Keyword(s):  
Grain Size ◽  
Laser Beam ◽  
Laser Beam Welding ◽  
Hot Cracking ◽  
Welding Parameters ◽  
Minor Effect ◽  
Alloy 718 ◽  
Material Source ◽  
Cross Sectional ◽  
Varestraint Test

Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 is usually welded in a solution annealed state. However, even with this thermal treatment, cracks can be induced during standard industrial manufacturing conditions, leading to costly and time-consuming reworking. In this work, the cracking susceptibility of wrought and investment casting alloy 718 is studied by the Varestraint test. The test is performed while applying different welding conditions, i.e., continuous tungsten inert gas (TIG), low frequency pulsed TIG, continuous laser beam welding (LBW) and pulsed LBW. Welding parameters are selected for each welding technology in order to meet the welding quality criteria requested for targeted aeronautical applications, that is, full penetration, minimum cross-sectional welding width and reduced overhang and underfill. Results show that the hot cracking susceptibility of LBW samples determined by the Varestraint test is enhanced due to extended center line hot cracking, resulting in a fish-bone like cracking pattern. On the contrary, the minor effect of material source (wrought or casting), grain size and pulsation is observed. In fact, casting samples with a 30 times coarser grain size have shown better performance than wrought material.

Axial Force Reduction in Friction Stir Welding of AA6061-T6 at Right Angle

2014 ◽  
Author(s):  
Yousef Imani ◽  
Michel Guillot
Keyword(s):  
Friction Stir Welding ◽  
Solid State ◽  
Axial Force ◽  
Tool Design ◽  
Industrial Robots ◽  
Welding Parameters ◽  
Minor Effect ◽  
Friction Stir ◽  
Force Reduction ◽  
Solid State Joining

Invented in 1991, friction stir welding (FSW) is a new solid state joining technique. This process has many advantages over fusion welding techniques including absence of filler material, shielding gas, fumes and intensive light, solid state joining, better microstructure, better strength and fatigue life, and etc. The difficulty with FSW is in the high forces involved especially in axial direction which requires use of robust fixturing and very stiff FSW machines. Reduction of FSW force would simplify implementation of the process on less stiff CNC machines and industrial robots. In this paper axial welding force reduction is investigated by use of tool design and welding parameters in FSW of 3.07 mm thick AA6061-T6 sheets at right angle. Attempt is made to reduce the required axial force while having acceptable ultimate tensile strength (UTS). It is found that shoulder working diameter and shoulder angle are the most important parameters in the axial force determination yet pin angle has minor effect. According to the developed artificial neural network (ANN) model, proper selection of shoulder diameter and angle can lead to approximately 40% force reduction with acceptable UTS. Regions of tool design and welding parameters are found which result in reduced axial force along with acceptable UTS.

Optimal Design of an Elastic Column of Thin-Walled Cross Section

1968 ◽  
Vol 35 (2) ◽  
pp. 285-288 ◽  
Author(s):  
N. C. Huang ◽  
C. Y. Sheu
Keyword(s):  
Optimal Design ◽  
Cross Section ◽  
Wall Thickness ◽  
Cross Sections ◽  
Unit Length ◽  
Compressive Load ◽  
Median Line ◽  
Vertical Column ◽  
Thin Walled ◽  
Allowable Compressive Stress

This paper treats the optimal design of a vertical column that is built-in at the lower end. In addition to its own weight, the column is to carry an axial compressive load at its unsupported upper end. The column is to be designed as a thin-walled tube. The median line is to be the same for all cross sections; the wall thickness, though constant along the median line of any cross section, is allowed to vary along the length of the tube. Accordingly, the weight per unit length of the tube is proportional to the bending stiffness. For given length and total weight, the variation of the wall thickness along the column is to be determined to maximize the critical value of the compressive load at the upper end. The influence of a maximum allowable compressive stress on the design is also investigated.

scholarly journals Investigation of an inverse thermal injection mould design methodology in dependence of the part geometry

2021 ◽  
Author(s):  
C. Hopmann ◽  
J. Gerads ◽  
T. Hohlweck
Keyword(s):  
Wall Thickness ◽  
Injection Moulding ◽  
Thermal Design ◽  
Internal Stresses ◽  
Cooling Channel ◽  
Injection Mould ◽  
Compression Moulding ◽  
Compression Pressure ◽  
Injection Moulding Process ◽  
Thin Walled

AbstractThe production of injection moulded components with low shrinkage and warpage is a constant challenge for manufacturers. The thermal design of the injection mould plays an important role for the achievable quality, especially the placement of the cooling channels. This design is usually based on empirical knowledge of the mould designers. The construction is supported iteratively by injection moulding simulations. In the case of thick-walled plastic optics with big wall thickness jumps, the shrinkage is compensated by injection compression moulding. In this process, the thin-walled areas freeze earlier and the necessary compression pressure introduces stresses into these areas which reduces the optical performance. An adapted cooling channel design can reduce these problems. At the IKV, Institute for Plastics Processing in Industry and Crafts at the RWTH Aachen University, a methodology was developed which inversely calculates the cooling requirement of the moulded part A demand-oriented cooling channel system is derived based on the computed results. The aim of the research projects is to minimise displacement and internal stresses by temperature control of the moulded parts according to the demand. In this paper, the methodology is applied to three different geometries, representing three classical parts for the injection moulding process. Three different quality areas in the mould for the inverse optimisation are defined and investigated. For each geometry the cooling channel designs are then validated in injection moulding simulations based on the results from the thermal optimisation. It can be shown that for different component geometries and thicknesses, different quality areas are advantageous and decrease the maximum warpage of the parts. For thin-walled ribbed components, a 2D approach leads to a 15% smaller displacement, for components with wall thickness jumps, all investigated quality ranges show no differences in displacement, but a surface in the middle of the part is preferred due to a 3 °C lower standard deviation of the temperature distribution.

Compositional Aspects of Cellulosic Electrodes Used for Welding Pipelines

2008 ◽  
Author(s):  
Frank J. Barbaro ◽  
Valerie M. Linton ◽  
Erwin Gamboa ◽  
Leigh Fletcher
Keyword(s):  
Weld Metal ◽  
User Involvement ◽  
Charpy Impact ◽  
Carbon Equivalent ◽  
Welding Parameters ◽  
Line Pipe ◽  
User Input ◽  
Welding Arc ◽  
Simulated Field ◽  
And Performance

The mechanical properties and compositional limits of line pipe for all major pipeline projects are subject to stringent project specific specifications and have substantial user input. The standards for welding electrodes do not have the same level of user involvement and permit significant latitude in terms of alloy design despite the fact that it is known the original electrode design can be markedly altered by elemental transfer as a result of changes in welding parameters and also the condition of the electrodes prior to welding. Several commercially available E8010 consumables have been evaluated under simulated field welding conditions. In addition, the influence of welding arc length and electrode conditioning were investigated. Significant variations in microstructure, hardness and Charpy impact toughness were noted and appear to be primarily related to the final chemical composition of the deposited weld metal. The weld metal carbon equivalent values ranged from 0.20 to 0.42 and all consumables contained additions of Ti and B in the flux coating which resulted in significant levels of B in the final deposited weld metal. It is recommended that the appropriate standards relating to the production and performance of cellulosic consumables be addressed to ensure complete disclosure of consumable formulations to the end user.

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