Evolution of Residual Stress in Tensile Armour Wires of Flexible Pipes During Pipe Manufacture

2017 ◽  
Author(s):  
Upul S. Fernando ◽  
Michelle Davidson ◽  
Kun Yan ◽  
Matthew J. Roy ◽  
Thilo Pirling ◽  
...  
Keyword(s):  
Residual Stress ◽  
Manufacturing Process ◽  
Relaxation Method ◽  
High Energy ◽  
Contour Method ◽  
Fe Model ◽  
Flexible Pipes ◽  
The Wire ◽  
Unbonded Flexible Pipes ◽  
Pipe Manufacturing

Tensile armour layers in unbonded flexible pipes are constructed by the parallel helical wrapping of several rectangular wires. Pairs of layers, wound in opposite directions and with different helical shapes are used to provide the necessary axial strength, water depth capacity and torsion balance. The forming of armour wires as supplied by the vendor into a helix shape on the pipe involves significant plastic straining; twisting and repeated bending of the wires in different planes. The wires that are wrapped on the pipe are not unloaded. Therefore the armour wires in flexible pipes are considered to contain residual stress (RS). Knowledge of RS in the wires of the manufactured pipe is essential in making appropriate design decisions with high confidence to meet material utilization requirements and subsequently predict the integrity and fatigue durability of the pipe. This paper describes an investigation performed to examine the evolution of RS in the tensile wires during various stages of the pipe manufacturing process. To this end, different methods including a relatively simple and inexpensive stress relaxation method termed the contour method, as well as diffraction methods were used to evaluate RS in the wire. A finite element (FE) model has been developed to simulate the wire deformation involved in the pipe manufacturing process. The procedure was used to predict the evolution of RS in a tensile wire and change in material response during the pipe manufacturing process. A comparison of FE model predictions and measured data is given. The results show that the RS measured by the contour method give comparable values to those obtained from more advanced methods such as high energy synchrotron X-ray and neutron diffraction. The need for using representative material properties and deformation boundary conditions in FE models to predict RS accurately is highlighted.

End Fitting Effect on Stress Evaluation of Tensile Armor Tendons in Unbonded Flexible Pipes Under Axial Tension

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Leilei Dong ◽  
Qi Zhang ◽  
Yi Huang ◽  
Gang Liu ◽  
Zhiyuan Li
Keyword(s):  
Lateral Displacement ◽  
Axial Strain ◽  
Supplementary Condition ◽  
Bending Stress ◽  
Stress Evaluation ◽  
Axial Tension ◽  
Flexible Pipes ◽  
Helical Angle ◽  
The Wire ◽  
Unbonded Flexible Pipes

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives the lateral displacement of the wire, which is determined by minimizing the energy functional that consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is verified with a finite element (FE) simulation. Comparisons between the model predictions and the FE results in terms of the change in helical angle and transverse bending stress show good correlations. The verified model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear, and friction could significantly increase the stress at the end fitting compared with the frictionless case.

Measurement of Residual Stress Shakedown in Pressure/Tensile Armour Wires of Flexible Pipes by Neutron Diffraction

2015 ◽  
Author(s):  
Upul S. Fernando ◽  
Michelle Davidson ◽  
Christopher Simpson ◽  
Thilo Pirling ◽  
Kun Yan ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Metal Layer ◽  
Diffraction Method ◽  
Acceptance Test ◽  
Flexible Pipes ◽  
Before And After ◽  
Unbonded Flexible Pipes ◽  
Hoop Stresses

The manufacture of unbonded flexible pipes (flowlines and risers) involves wrapping steel wires to create pressure and tensile armour layers. The forming of armour wires from vendor supply conditions to a helix shape on the pipe involves significant plastic straining and the wires that are wrapped onto the pipe are not unloaded. Therefore the armour wires in flexible pipes are expected to contain significant residual stress (RS) as a result of the plastic straining and loading during manufacture and placement. This may lead to detrimental effects on the strength, durability and the service integrity of the pipe. It is postulated that the unfavorable RS introduced during pipe manufacture reduces due to stress shakedown during the factory acceptance test (FAT) where the pipe is subjected to a high internal pressure. This paper describes the first attempts to measure RS in the armour wires in unbonded flexible pipes. The key development is the use of a neutron diffraction method which allows the measurement of RS in-situ on the manufactured pipe through the whole wire sections. Pipe samples were prepared exposing the relevant metal layer and the measurements were performed on pipe samples taken before and after performing the pressurized FAT. The effect of the FAT on the shakedown of residual stress in pressure armour wires is discussed. As shown by the measurements, the elastic strains and stresses in the pressure armour wires are much larger in the hoop direction of the pipe (i.e. along the length of the wire) than radial or axial to the pipe. In pre-FAT pipe the hoop stresses are essentially tensile on the extrados and compressive on the intrados. The results have shown that the FAT reduces the hoop strains and stresses to approximately 1/3 of their as manufactured level.

Characterization of a Plate Specimen From Phase I of the NRC/EPRI Weld Residual Stress Program

2011 ◽  
Author(s):  
Matthew Kerr ◽  
David L. Rudland ◽  
Michael B. Prime ◽  
Hunter Swenson ◽  
Miles A. Buechler ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Phase I ◽  
Nuclear Regulatory Commission ◽  
Contour Method ◽  
304L Stainless Steel ◽  
Fe Model ◽  
Stress Measurements ◽  
Weld Residual Stress ◽  
Plate Specimen

Time-of-flight neutron diffraction and contour method residual stress measurements were conducted at Los Alamos National Lab (LANL) on a lab sized plate specimen (P4) from Phase I of the joint U.S. Nuclear Regulatory Commission and Electric Power Research Institute Weld Residual Stress (NRC/EPRI WRS) program. The specimen was fabricated from a 304L stainless steel plate containing a seven pass Alloy 82 groove weld, restrained during welding and removed from the restraint for residual stress characterization. This paper presents neutron diffraction and contour method results, and compares these experimental stress measurements to a WRS Finite Element (FE) model. Finally details are provided on the procedure used to calculate the residual stress distribution in the restrained or as welded condition in order to allow comparison to other residual stress data collected as part of the EPRI lead Phase I WRS program.

Residual Stress Characterization in a Dissimilar Metal Weld Nuclear Reactor Piping System Mock Up

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Matthew Kerr ◽  
Michael B. Prime ◽  
Hunter Swenson ◽  
Miles A. Buechler ◽  
Michael Steinzig ◽  
...  
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Phase 1 ◽  
Nuclear Regulatory Commission ◽  
Contour Method ◽  
Hole Drilling ◽  
Piping System ◽  
304L Stainless Steel ◽  
Fe Model ◽  
Stress Measurements

Time-of-flight neutron diffraction, contour method, and surface hole drilling residual stress measurements were conducted at Los Alamos National Lab (LANL) on a lab sized plate specimen (P4) from phase 1 of the joint U.S. Nuclear Regulatory Commission and Electric Power Research Institute Weld Residual Stress (NRC/EPRI WRS) program. The specimen was fabricated from a 304L stainless steel plate containing a seven pass alloy 82 groove weld, restrained during welding and removed from the restraint for residual stress characterization. This paper presents neutron diffraction and contour method results, and compares these experimental stress measurements to a WRS finite element (FE) model. Finally, details are provided on the procedure used to calculate the residual stress distribution in the restrained or as welded condition in order to allow comparison to other residual stress data collected as part of phase 1 of the WRS program.

End Fitting Effect on Stress Evaluation of Tensile Armors in Unbonded Flexible Pipes Under Axial Tension

2017 ◽  
Author(s):  
Leilei Dong ◽  
Qi Zhang ◽  
Yi Huang ◽  
Gang Liu ◽  
Zhiyuan Li
Keyword(s):  
Finite Element ◽  
Lateral Displacement ◽  
Supplementary Condition ◽  
Bending Stress ◽  
Stress Evaluation ◽  
Axial Tension ◽  
Flexible Pipes ◽  
Helical Angle ◽  
The Wire ◽  
Unbonded Flexible Pipes

This paper deals with the effect of termination restraint due to end fitting on the stress evaluation of tensile armors in unbonded flexible pipes under axial tension. The problem is characterized by one single armoring tendon helically wound on a cylindrical supporting surface subjected to traction. The deviation from the initial helical angle is taken to describe the armor wire path as the pipe is stretched. The integral of this angle change gives lateral displacement of the wire, which is determined by minimization of the energy functional consists of the strain energy due to axial strain, local bending and torsion, and the energy dissipated by friction, leading to a variational problem with a variable endpoint. The governing differential equation of the wire lateral displacement, together with the supplementary condition, is derived using the variational method and solved analytically. The developed model is validated with a finite element simulation. Comparisons between the model predictions and the finite element results in terms of the change in helical angle and transverse bending stress show good correlations. The validated model is then applied to study the effects of imposed tension and friction coefficient on the maximum bending stress. The results show that the response to tension is linear and friction could significantly increase the stress at the end fitting compared with the frictionless case.

FEM and Contour Method Study of Quenching Residual Stress of 7050 Aluminum Alloy Cross-Shaped Component

2017 ◽  
Vol 887 ◽  
pp. 89-95 ◽  
Author(s):  
Yang Li ◽  
Yun Xin Wu ◽  
Hai Gong ◽  
Feng Xiao
Keyword(s):  
Residual Stress ◽  
Aluminum Alloy ◽  
Stress Distribution ◽  
Stress Reduction ◽  
Residual Stress Distribution ◽  
Contour Method ◽  
Fe Model ◽  
Residual Stress Field ◽  
Heat Transfer Theory ◽  
7050 Aluminum Alloy

In order to study the quenching residual stress of typical aluminum alloy component used in aerospace, the finite element (FE) model of quenching process of 7050 aluminum alloy cross-shaped component was established based on heat transfer theory and elastic-plastic mechanics theory, the distribution regularities of quenching residual stress field of cross-shaped component was analyzed. The results indicate that the residual stress distribution of web of cross-shaped component is similar to the residual stress distribution of thick plate, the large tensile stress concentration is exist in web plate and the connection part of the stiffener with a certain influence area. The error data of the component contour deformation were processed and the component deformation contour was fitted, which makes the test result of the contour method and FE simulation result have good consistency. The results of the study provides guidance for quenching residual stress reduction of aviation aluminum alloy components and provides the basis for calculating of machining deformation of monolithic component.

A FE Model to Predict the Stress Concentration Factors in the Tensile Armor Wires of Flexible Pipes Inside End Fittings

2013 ◽  
Author(s):  
José Renato M. de Sousa ◽  
George C. Campello ◽  
Fabiano Bertoni ◽  
Gilberto B. Ellwanger
Keyword(s):  
Stress Concentration ◽  
High Stress ◽  
Axial Stiffness ◽  
Fe Model ◽  
Acceptance Test ◽  
Stress Distributions ◽  
High Stress Concentration ◽  
Flexible Pipes ◽  
The Wire ◽  
Stress Concentration Factors

In this work, a bidimensional finite element (FE) approach is proposed to estimate the stresses induced in the tensile armor wires inside end fittings (EF) of flexible pipes. This approach accounts for the residual stresses caused by the mounting procedure and the deformed configuration of the wire. The resin and its interaction with the wires are also addressed. A parametric study was performed aiming at investigating the influence of three parameters on the stress state along the wire, i. e., the contact conditions between the resin and the wire inside the EF, the stress levels induced during the factory acceptance test (FAT) or the offshore leak test (OLT) and the resin elastic properties. The study pointed that high stress concentration is induced in the transition between the flexible pipe’s body and the EF and the stress distribution along the wire may be significantly affected by these parameters. Moreover, the apparent axial stiffness of the wire is also modified by its anchoring conditions, which may lead to non-uniform stress distributions among the wires of the tensile armor layers.

Manufacture, Residual Stress Measurement and Analysis of a VVER-440 Nozzle Mockup

2013 ◽  
Author(s):  
Levente Tatár ◽  
Gyula Török ◽  
David J. Smith ◽  
Son Do ◽  
Carsten Ohms ◽  
...  
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Stress Measurement ◽  
Welding Process ◽  
Full Scale ◽  
Residual Stress Measurement ◽  
Contour Method ◽  
Scale Model ◽  
Fe Model

As part of the STYLE EU FP7 project a modified 1:5 scale replica of a VVER-440 type reactor pressure vessel inlet nozzle was manufactured. The nozzle included a dissimilar metal weld of the type found in full-scale nozzles. This scale model was developed to permit accurate measurements to be made and detailed finite element (FE) models to be developed without recourse to using a full scale mock-up. It was also found that a full-scale mock-up would not permit the application of certain residual stress measurement methods. Temperatures and displacements were recorded during welding of the dissimilar metals, with measurements used to guide simulation of the welding process using finite element models. Through thickness residual stress profiles were measured using a comprehensive range of different techniques, such as deep hole drilling, neutron diffraction, magnetic Barkhausen noise. Usage of contour method had been planned too, but it but could not be accomplished in due time. The measured residual stresses obtained by the different methods are presented and compared. Measured residual stresses, temperatures and displacements were then used to validate the results derived from the FE model.

Residual Stress Measurements Using the Contour, Deep-Hole Drilling and Neutron Diffraction Methods in T-Section Specimens

2016 ◽  
Author(s):  
Karim Serasli ◽  
Douglas Cave ◽  
Ed Kingston
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Complex Geometry ◽  
Contour Method ◽  
Hole Drilling ◽  
Deep Hole ◽  
Premature Failure ◽  
Deep Hole Drilling ◽  
The Wire

The presence of high magnitude residual stresses in welded components causes material degradation, local yielding and plastic deformation. Their presence provides the potential for premature failure and compromises the integrity of a structure. This paper presents a review of work carried out to ascertain the residual stresses present within T-section specimens, made from ferritic steel, in their as-welded condition. The standard and incremental deep hole drilling (DHD and iDHD) techniques, the neutron diffraction (ND) and the contour method were applied to characterise the residual stresses in the regions in and around the two fillet welds of the specimens and the surrounding parent material within which the balancing residual stresses needed to be measured. The results of these measurements are presented and compared to highlight agreements and discrepancies in the measured residual stress distributions using these different techniques. A compendium of measurements at a similar location in various T-sections and their comparison with the BS7910 standard show that the measured longitudinal distributions are similar despite the observed scatter. Finally, this paper briefly attempts to investigate and discuss the technical challenges identified when applying the contour method to complex geometry components. The constraint of the specimen during the wire electro-discharge machining (EDM) process, the quality of the wire EDM cut made and the analysis of the raw data for the conversion into residual stresses directly affect the accuracy of the contour method results. The identification and investigation of these challenges lead to continuous improvements of the contour method procedure and reduce uncertainties of the measurement.

Assessment of the Influence of Plasticity and Constraint on Measured Residual Stresses Using the Contour Method

2008 ◽  
Author(s):  
R. J. Dennis ◽  
D. P. Bray ◽  
N. A. Leggatt ◽  
M. Turski
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Stress Measurement ◽  
General Procedure ◽  
Relaxation Method ◽  
Cutting Process ◽  
Contour Method ◽  
Hole Drilling ◽  
Residual Stress Field ◽  
Rigid Constraint

The contour method is a relatively new relaxation method for residual stress measurement and may be seen as an evolution of established methods such as hole drilling. The general procedure when applying the contour method is cutting, measurement and calculation of residual stress normal to the cut plane using Bueckner’s principle of elastic superposition. That is the residual stresses are determined from the measured profile of a cut surface. While the contour method is simple in concept there are certain underlying issues relating to the cutting process that may lead to uncertainties in the measured results. Principally the issues are that of constraint and plasticity during cutting and the influence they have on the measured residual stresses. In this paper both issues are investigated in detail by simulating the entire contour method process using finite element techniques for two welded specimens. Constraint has been a recognised concern for the contour method with the general requirement being to hold the specimen as rigidly as possible. Both clamping and fixing bolts are routinely used however in reality these methods do not provide a fully rigid constraint. In this work a range of constraints have been examined to determine the influence on the measured residual stresses. Plasticity, as a consequence of the cutting process, has also been recognised as a factor which may affect the measured residual stresses. In this work the extent of plasticity is predicted by simulation of the cutting process. With a known initial residual stress field the effects of plasticity are directly quantifiable. This work therefore provides an extremely useful insight into some of the key issues that affect the measurement performance of the contour method.

Sign in / Sign up

Export Citation Format

Share Document