Using MFL Corrosion Signals to Determine Biaxial Stress in Operating Pipelines

2000 ◽  
Author(s):  
Alfred E. Crouch
Keyword(s):  
Magnetic Flux ◽  
Internal Pressure ◽  
Pipe Wall ◽  
Axial Stress ◽  
Wall Stress ◽  
Biaxial Stress ◽  
Metal Loss ◽  
Pipe Surface ◽  
The Difference ◽  
Hoop Stresses

Previous work has shown that a corrosion assessment more accurate than B31.G or RSTRENG can be made if pipeline stresses are considered. A shell analysis can be carried out if both the corrosion profile and local pipe wall stresses are known. The corrosion profile can be approximated from analysis of magnetic flux leakage (MFL) signals acquired by an inline inspection tool (smart pig), but a measure of pipe wall stress has not been available. Approximations have been made based on pipe curvature, but a more direct measurement is desirable. Recent work has produced data that show a correlation between multi-level MFL signals from metal-loss defects and the stress in the pipe wall at the defect location. This paper presents the results of MFL scans of simulated corrosion defects in pipe specimens subjected to simultaneous internal pressure and four-point bending. MFL data were acquired at two different magnetic excitations using an internal scanner. The scanner’s sensor array measured axial, radial and circumferential magnetic flux components on the inner pipe surface adjacent to the defect. Comparison of the signals at high and low magnetization yields an estimate of the difference between axial and hoop stresses. If internal pressure is known, the hoop component can be determined, leaving data proportional to axial stress.

Ultimate Elastic Wall Stress (UEWS) Test under Biaxial Loading for Glass-Fibre Reinforced Epoxy (GRE) Pipes

2014 ◽  
Vol 974 ◽  
pp. 188-194 ◽  
Author(s):  
Tarak A. Assaleh ◽  
Lutfeya A. Almagguz
Keyword(s):  
Biaxial Loading ◽  
Pipe Wall ◽  
Axial Stress ◽  
Wall Stress ◽  
Current Method ◽  
Raw Material ◽  
Attractive Alternative ◽  
Filament Wound ◽  
Elastic Wall ◽  
Filament Wound Composite

This paper presents the results of an experimental investigation into the Ultimate Elastic Wall Stress (UEWS) of ±55° filament wound composite pipes. The UEWS test appears to provide an attractive alternative to the current method, and has proved to be one of the most effective in term of accuracy and speed. Moreover, it has been found to be sensitive to changes in key manufacturing and raw material parameters. The pipes were subjected to biaxial loading, which was achieved by combinations of hoop and axial stress. Loads were applied as groups of cycles which, were gradually increased until the UEWS had been determined. Various ratios of hoop to axial stress were applied to the pipes, ranging from pure axial to pure hoop loading at room temperature and at 65°C. These ratios were investigated by applying different pressures in both the main and small chambers built inside the pipe, and therefore it was unnecessary to add any external loads to the pipe wall. Tests were also conducted to observe leakage through the pipe wall. The main failure mode observed was weepage through the pipe wall, which was due to intensive matrix microcracking. The results from the UEWS tests are presented in the form of failure envelopes showing the effects of testing at an elevated temperature. Finally, degradation in the elastic properties of the pipe wall is also discussed and plotted against wall stress.

Effect of Biaxial Stress on Crack Driving Force

2006 ◽  
Author(s):  
G. Shen ◽  
W. R. Tyson
Keyword(s):  
Internal Pressure ◽  
Driving Force ◽  
Axial Stress ◽  
Axial Strain ◽  
Biaxial Stress ◽  
J Integral ◽  
Longitudinal Stress ◽  
Secondary Stress ◽  
Stress Strain ◽  
Strain Equation

A stress-strain equation of Ramberg-Osgood type is proposed to correlate the longitudinal stress with longitudinal strain of a thin plate when a constant stress is applied transversely. The same approach can be used to correlate the axial stress with axial strain for a thin-walled pipe in axial tension with internal pressure. The proposed stress-strain equation relating the longitudinal stress and strain closely approximates that of deformation theory. The effect of a secondary stress (hoop stress) on the J-integral for a circumferential crack in a pipe under axial load and internal pressure is evaluated by finite element analysis (FEA). The results show that the J-integral decreases with internal pressure at a given axial stress but increases with internal pressure at a given axial strain. It is concluded that while a secondary stress may be safely neglected in a stress-based format because it decreases the driving force at a given applied stress, it should not be neglected in a strain-based format because it significantly increases the driving force at a given applied strain.

Biaxial Cyclic Deformation and Creep-Fatigue Behavior of Materials for Solar Thermal Systems

1982 ◽  
Vol 104 (2) ◽  
pp. 88-95 ◽  
Author(s):  
S. Majumdar
Keyword(s):  
Stainless Steel ◽  
Internal Pressure ◽  
Cyclic Deformation ◽  
Fatigue Behavior ◽  
Axial Stress ◽  
Thermal Systems ◽  
Creep Fatigue ◽  
Incoloy 800 ◽  
The Difference ◽  
Tubular Specimens

Biaxial cyclic deformation and creep-fatigue data for Incoloy 800 and Type 316H stainless steel at elevated temperature are presented. Tubular specimens were subjected to constant internal pressure and strain-controlled axial cycling with and without hold times in tension as well as in compression. The results show that the internal pressure affects diametral ratchetting and axial stress range significantly. However, the effect of a relatively small and steady hoop stress on the cyclic life of the materials is minimal. A 1-min compressive hold per cycle does not seriously reduce the fatigue life of either material; a tensile hold of equal duration causes a significant reduction in life for Type 316H stainless steel, but none for Incoloy 800. Fracture surfaces of specimens made of both materials were studied by scanning electron microscopy to determine the reason for the difference in behavior.

Stress Redistribution During Local Annealing of a Multi-Pass Butt-Welded Pipe

1986 ◽  
Vol 108 (2) ◽  
pp. 125-130
Author(s):  
B. L. Josefson
Keyword(s):  
Pipe Wall ◽  
Rotational Symmetry ◽  
Stress Fields ◽  
Pipe Material ◽  
Pipe Surface ◽  
Pipe Wall Thickness ◽  
Final Stress ◽  
Welded Pipe ◽  
Hoop Stresses ◽  
Mn Steel

Stress redistributions during local Post Weld Heat Treatments (PWHT) are numerically studied for a multi-pass butt-welded pipe with mechanically unrestrained ends. The pipe material is a micro-alloyed C-Mn steel. Temperature and stress fields developed during welding and PWHT are determined from a FE-analysis where rotational symmetry is assumed. Use of heaters with a total axial width less than four times the pipe wall thickness is found to result in substantially different final stress fields than those obtained after a uniform (furnace) heat treatment. The tensile axial and hoop stresses on the inner pipe surface near the centre section of the weldment are considerably higher after a local PWHT. The differences were found to arise mainly during the cooling periods of the PWHTs.

Understanding Magnetic Flux Leakage Signals From Gouges

2010 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar ◽  
Jian Dien Chen ◽  
Chris Alexander
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Mechanical Damage ◽  
Internal Surface ◽  
Magnetic Flux Leakage ◽  
Wall Surface ◽  
Pipe Surface ◽  
Early Results ◽  
Flux Leakage ◽  
Wall Geometry

The Magnetic Flux Leakage (MFL) technique is sensitive both to pipe wall geometry and pipe wall strain, therefore MFL inspection tools have the potential to locate and characterize mechanical damage in pipelines. The present work is the first stage of a study focused on developing an understanding of how MFL signals arise from pipeline gouges. A defect set of 10 gouges were introduced into sections of 12″diameter, 5m long, end capped and pressurized X60 grade pipe sections. The gouging tool displacement ranged (before tool removal) between 2.5 to 12.5mm. Gouges were approximately 50mm in length. The shallowest indentation created only a very slight scratch on the pipe surface, the deepest created a very significant gouge. All gouges were axially oriented. Experimental MFL measurements were made on the external pipe wall surface (pressurized) as well as the internal surface (unpressurized). The early results of the experimental MFL studies, and a hypothesis for the origin of the MFLaxial signal “dipole” are discussed in this paper.

scholarly journals High-temperature creep rupture of low alloy ferritic steel butt-welded pipes subjected to combined internal pressure and end loadings

2005 ◽  
Vol 363 (1836) ◽  
pp. 2629-2661 ◽  
Author(s):  
F Vakili-Tahami ◽  
D.R Hayhurst ◽  
M.T Wong
Keyword(s):  
Internal Pressure ◽  
Constitutive Equations ◽  
Ferritic Steel ◽  
Loading Condition ◽  
Damage Mechanics ◽  
Axial Stress ◽  
Biaxial Stress ◽  
Type Iv ◽  
Modes Of Failure ◽  
Wide Range

Constitutive equations are reviewed and presented for low alloy ferritic steels which undergo creep deformation and damage at high temperatures; and, a thermodynamic framework is provided for the deformation rate potentials used in the equations. Finite element continuum damage mechanics studies have been carried out using these constitutive equations on butt-welded low alloy ferritic steel pipes subjected to combined internal pressure and axial loads at 590 and 620 °C. Two dominant modes of failure have been identified: firstly, fusion boundary failure at high stresses; and, secondly, Type IV failure at low stresses. The stress level at which the switch in failure mechanism takes place has been found to be associated with the relative creep resistance and lifetimes, over a wide range of uniaxial stresses, for parent, heat affected zone, Type IV and weld materials. The equi-biaxial stress loading condition (mean diameter stress equal to the axial stress) has been confirmed to be the worst loading condition. For this condition, simple design formulae are proposed for both 590 and 620 °C.

Non-Destructive Measurement of Residual Stresses in U-0.8 WT% Ti by Neutron Diffraction

1989 ◽  
Vol 166 ◽  
Author(s):  
A. Salinas-Rodriguez ◽  
J.H. Root ◽  
T.M. Holden ◽  
S.R. Macewen ◽  
G.M. Ludtka
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Wall Thickness ◽  
Radial Stress ◽  
Biaxial Stress ◽  
Axial Residual Stress ◽  
Residual Strains ◽  
The Difference ◽  
Hoop Stresses

ABSTRACTThe macroscopic residual stress distribution in γ-quenched and stress levelled U-0.8wt% Ti alloy tubes was studied using neutron diffraction techniques. Residual strains were evaluated from the difference in d-spacings measured in the tubes and in small reference samples machined from each tube. Residual stresses were calculated with the isotropic bulk values of the elastic constants for polycrystalline α-U. Quenching from the γ field resulted in a nearly equi-biaxial stress state at every point across the wall thickness of the tube. The magnitude of the radial stress was very small compared with that of the axial and hoop stresses which were compressive at the surfaces and tensile in the interior. Stress levelling relieved almost completely the hoop residual stress without affecting the radial stress. The axial residual stress becomes tensile through the wall thickness and remains constant at about 20% of its magnitude in the as-quenched condition.

Computational and experimental studies of the strength of full-scale samples of pipes with defects "metal loss" and "dent with groove"

2020 ◽  
Vol 10 (3) ◽  
pp. 226-233
Author(s):  
Dmitry A. Neganov ◽  
◽  
Victor M. Varshitsky ◽  
Andrey A. Belkin ◽  
◽  
...  
Keyword(s):  
Internal Pressure ◽  
Experimental Studies ◽  
Full Scale ◽  
The Other ◽  
Metal Loss ◽  
Calculation Methods ◽  
Reliable Operation ◽  
Sufficient Stability ◽  
Comparative Results ◽  
The Moment

The article contains the comparative results of the experimental and calculated research of the strength of a pipeline with such defects as “metal loss” and “dent with groove”. Two coils with diameter of 820 mm and the thickness of 9 mm of 19G steel were used for full-scale pipe sample production. One of the coils was intentionally damaged by machining, which resulted in “metal loss” defect, the other one was dented (by press machine) and got groove mark (by chisel). The testing of pipe samples was performed by applying static internal pressure to the moment of collapse. The calculation of deterioration pressure was carried out with the use of national and foreign methodical approaches. The calculated values of collapsing pressure for the pipe with loss of metal mainly coincided with the calculation experiment results based on Russian method and ASME B31G. In case of pipe with dent and groove the calculated value of collapsing pressure demonstrated greater coincidence with Russian method and to a lesser extent with API 579/ASME FFS-1. In whole, all calculation methods demonstrate sufficient stability of results, which provides reliable operation of pipelines with defects.

On Thick-Walled Cylinder Under Internal Pressure

2003 ◽  
Vol 125 (3) ◽  
pp. 267-273 ◽  
Author(s):  
W. Zhao ◽  
R. Seshadri ◽  
R. N. Dubey
Keyword(s):  
Internal Pressure ◽  
Strain Curve ◽  
Stress Strain ◽  
Piecewise Linearization ◽  
Elastic Plastic ◽  
Plastic Cylinder ◽  
Parametric Functions ◽  
The Difference ◽  
New Formulation ◽  
Walled Cylinder

A technique for elastic-plastic analysis of a thick-walled elastic-plastic cylinder under internal pressure is proposed. It involves two parametric functions and piecewise linearization of the stress-strain curve. A deformation type of relationship is combined with Hooke’s law in such a way that stress-strain law has the same form in all linear segments, but each segment involves different material parameters. Elastic values are used to describe elastic part of deformation during loading and also during unloading. The technique involves the use of deformed geometry to satisfy the boundary and other relevant conditions. The value of strain energy required for deformation is found to depend on whether initial or final geometry is used to satisfy the boundary conditions. In the case of low work-hardening solid, the difference is significant and cannot be ignored. As well, it is shown that the new formulation is appropriate for elastic-plastic fracture calculations.

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