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Title: Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes

Abstract

Prior finite element modeling (FEM) has shown how creep damage reduces the voltage signal in a secondary coil wrapped around a C-core electromagnet positioned above a seam weld in a steel pipe. Prior hysteresis modeling has also demonstrated the reduction of magnetoacoustic emission (MAE) due to uniform creep damage in a steel specimen. In this article, it is shown how to evaluate the MAE due to a nonuniform distribution of creep damage at a seam weld using FEM. Also, FEM is used to evaluate the C-core secondary emf due to a nonuniform stress distribution, which is developed at a seam weld due to the internal pressure of hot steam passing through the pipe. In this latter case, use is made of the stress distribution computed at the seam weld by Stevick. It is found that nonuniform creep damage also reduces the MAE signal, as is found experimentally. The stresses due to internal pressure in the pipe are shown by FEM to increase the C-core secondary emf, which is opposite to the effect of creep damage. A comparison is made between stressed and unstressed cases, with and without creep damage. {copyright} 2001 American Institute of Physics.

Authors:
; ;
Publication Date:
Sponsoring Org.:
(US)
OSTI Identifier:
40203854
Alternate Identifier(s):
OSTI ID: 40203854
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 89; Journal Issue: 11; Other Information: DOI: 10.1063/1.1355325; Othernumber: JAPIAU000089000011006731000001; 176111MMM; PBD: 1 Jun 2001
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CREEP; DISTRIBUTION; ELECTROMAGNETS; HYSTERESIS; MAGNETOACOUSTICS; PHYSICS; STEAM; STEELS; STRESSES

Citation Formats

Sablik, M. J., Weidner, C., and Augustyniak, B. Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes. United States: N. p., 2001. Web. doi:10.1063/1.1355325.
Sablik, M. J., Weidner, C., & Augustyniak, B. Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes. United States. doi:10.1063/1.1355325.
Sablik, M. J., Weidner, C., and Augustyniak, B. Fri . "Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes". United States. doi:10.1063/1.1355325.
@article{osti_40203854,
title = {Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes},
author = {Sablik, M. J. and Weidner, C. and Augustyniak, B.},
abstractNote = {Prior finite element modeling (FEM) has shown how creep damage reduces the voltage signal in a secondary coil wrapped around a C-core electromagnet positioned above a seam weld in a steel pipe. Prior hysteresis modeling has also demonstrated the reduction of magnetoacoustic emission (MAE) due to uniform creep damage in a steel specimen. In this article, it is shown how to evaluate the MAE due to a nonuniform distribution of creep damage at a seam weld using FEM. Also, FEM is used to evaluate the C-core secondary emf due to a nonuniform stress distribution, which is developed at a seam weld due to the internal pressure of hot steam passing through the pipe. In this latter case, use is made of the stress distribution computed at the seam weld by Stevick. It is found that nonuniform creep damage also reduces the MAE signal, as is found experimentally. The stresses due to internal pressure in the pipe are shown by FEM to increase the C-core secondary emf, which is opposite to the effect of creep damage. A comparison is made between stressed and unstressed cases, with and without creep damage. {copyright} 2001 American Institute of Physics.},
doi = {10.1063/1.1355325},
journal = {Journal of Applied Physics},
number = 11,
volume = 89,
place = {United States},
year = {Fri Jun 01 00:00:00 EDT 2001},
month = {Fri Jun 01 00:00:00 EDT 2001}
}
  • Creep damage in steel causes a reduction of magnetic properties. A mathematical model, previously formulated, accounts for this. Recently, this model was used in finite element modeling (FEM) of a magnetic C-core signal due to creep damage at a seam weld in Cr-Mo steam pipe. The FEM assumed unrealistically that in the absence of creep damage, the weld material and heat-affected zone (HAZ) and base metal all had the same magnetic properties. In this paper, new finite element simulations are presented for worst case relative permeabilities of 1271, 784 and 571 for base metal, HAZ, and weld material. Reduced permeabilitymore » at the weld results in a considerably reduced emf at low probe magnetic fields. However, creep damage does produce an additional emf reduction that is large enough to be detected, even when the creep damage does not extend to the pipe wall surface. A method is suggested for calibrating the magnetic signal for weld, HAZ, and base metal effects.« less
  • Using appropriately modified magnetization curves for each element of creep-damaged material, a finite element calculation has been carried out to simulate magnetic detection of non-uniform creep damage around a seam weld in a 2.25 Cr 1 Mo steam pipe. The magnetization curves for the creep-damaged elements were obtained from an earlier model for the magnetic effect of a uniformly creep-damaged material as given by Chen, et al. In the finite element calculation, a magnetic C-core with primary and secondary coils was placed with its pole pieces flush against the specimen in the vicinity of the weld. The secondary emf wasmore » shown to be reduced when creep damage was present inside the pipe wall at the cusp of weld and in the vicinity of the cusp. The C-core detected the creep damage best if it completely spanned the weld seam width. Also, the current in the primary needed to be such that the C-core was not magnetically saturated.« less
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  • The paper discusses modeling of a multi-layer coal seam under hydrodynamic action based on the coupled equations of poroelasticity and filtration with the nonlinear relationship of permeability and porous pressure. The calculations by the finite element method use correspondence between the poroelasticity and thermoelasticity equations. The influence of input data on the size of a degassing hole area is analyzed for the couple problem and pure filtration problem.