FIELD OF THE INVENTION
The present invention generally relates to a non destructive method for
identifying different ferrous materials including different electrodes used in
fabrication of the ferrous materials and to evaluate residual mechanical
properties of ferrous materials through measurement of coercive force In Ferro
magnetic materials. More particularly, the invention relates to a method of
measuring coercive force for different materials, different electrodes and residual
mechanical properties before and after service.
BACKGROUND OF THE INVENTION
Different varieties of materials are used in engineering industries for various
applications in shop floor and at site erections. Similarly, different electrodes are
used in fabrication where these different materials are to be handled. Mixing up
of these base materials and electrodes causes rejection of manufactured
component.
At the erection sites, mixing up of base materials such as tubes, pipes and
electrodes are common issues and lead to many undesirable consequences in the
fabrication. In this context, a proper identification of the base material becomes
more important. Similarly the electrode material grade used for the welding has
to be identified correctly. This ensures that the fabrication is carried out as per
the original fabrication requirement.
The serviced condition of the material after its long term usage has to be
checked based on the material mechanical properties in case of ferrous
materials. This gives an idea about remaining life of the component in ferrous
materials.
Prior art methods exist for determining base materials and electrodes used for
the fabrication such as spectrometry, PMI (Positive metal identifier), TEM
(Transition Electron microscope), SEM (Scanning Electron microscope), EDAX, X
ray diffraction. Except PMI all other techniques are laboratory oriented testing
methods. PMI is widely used for material identification in shop floor which is
however, a costly equipment. To identify the remaining life of the component,
the prior art use destructive and semi destructive methods.
US 7948247 describes a metal identifying device which identifies a metal material
in a metal member having a plurality of through-hole portions penetrating
through the metal member. The metal identifying device includes a
measurement unit that obtains a measurement value by measuring an electrical
property and/or optical property of a test object, a threshold value determination
unit that determines a threshold value with use of a reference value obtained by
measuring the property of a metal member having a metal composition to be
identified and information indicating a ratio of the through-hole portions to a
measurement area in the test object and/or information indicating a
configuration of the through-hole portion, and a comparison/identification unit
that identifies a metal composition of the test object by comparing the
measurement value and the threshold value. This method is suitable to the
condition where plurality of holes is available and this identifies the composition
of material. This equipment is costly.
US 4692875 describes a method to identify the composition of a metal alloy in
which sparks generated from the alloy are optically observed and
spectrographically analyzed. The spectrographs data, in the form of a full-
spectrum plot of intensity versus wavelength, provide the signature of the metal
alloy. This signature can be compared with similar plots for alloys of known
composition to establish the unknown composition by a positive match with a
known alloy. An alternative method is to form intensity ratios for pairs of
predetermined wavelengths within the observed spectrum and to then compare
the values of such ratios with similar values for known alloy compositions,
thereby to positively identify the unknown alloy composition. This method is
however, costly and requires expertise to read and analyse the signatures.
US 4709383 discloses a method for evaluating a residual fatigue life of
mechanical parts, comprising the steps of grinding a surface layer of a
mechanical part to be inspected by a minute amount to form an inspection
surface, measuring half-width data of an X-ray diffraction intensity curve on the
inspection surface, calculating a depth (do) of a fatigue damaged region from a
graph of a half-width ratio (H/Ho) versus a depth (d) below the surface layer,
and determining a fraction of fatigue life N/Nf on the basis of data of the depth
(do) of the defective region versus the fraction of fatigue life N/Nf which were
separately obtained from a test piece. This method requires high level expertise
and is having lengthy procedures.
US 4907457 teaches a method of evaluating residual life of a heat-resistant steel
member after and during service at high temperature and stress. The method
uses a residual life evaluation diagram which is obtained beforehand on a
plurality of samples of the heat-resistant steel and which represents a
relationship between the life consumption and a parameter which indicates the
life consumed. The parameter may be data concerning the density of an alloy
element such as molybdenum and chromium, or the state of degradation in the
metallurgical structure and/or state of precipitation of carbides. This method
requires a set of practical data for each and every material, and hence time
consuming.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a non-destructive testing
method for selecting different grade of ferrous materials, different ferrous grade
weid metals and residual (mechanical properties) of the ferrous materials based
on measured coercive force values.
Another object of the invention is to propose a non-destructive testing method
for selecting different grade ferrous materials, different ferrous grade weld
metals and residual (mechanical properties) of the ferrous materials based on
measured coercive force values, which adopts a standard portable coercive force
measuring meter providing coercive force values of welded parts at shop floor
and at erection sites.
Yet another object of the invention is to propose,a non-destructive testing
method for selecting different grade ferrous materials, different ferrous grade
weid metals and residual (mechanical properties) of the ferrous materials based
on measured coercive force values, in which surface preparation is not required
for measurement of coercive force values.
A further object of the invention is to propose a non-destructive testing method
for selecting different grade ferrous materials, different ferrous grade weld
metals and residual (mechanical properties) of the ferrous materials based on
measured coercive force values, which is simple and reliable.
SUMMARY OF THE INVENTION
Thus, the present invention provides a non-destructive evaluation method, using
measurement of magnetic coercive force values, classification of different base
materials and different electrodes used for fabrication including determining
residual life of ferrous materials. This non-destructive testing method is based on
the change in coercive force values due to changes in sub microscopic
imperfections in the material. As different materials and weld metafs are having
different microstructures, inclusions, magnetic properties and domain walls
having different coercive force values hence the application of the coercive force
to evaluate the material becomes a possibility. Similarly the serviced materials
undergo changes in mechanical properties and dislocation densities which results
in change in coercive force values thus the application of coercive force to
evaluate the serviced condition of ferrous material becomes possible.
According to the invention, a standard portable coercimeter (magnetic structure
scope) is adopted for measurement of the coercive force values. The coercive
force measurements are taken different grade ferrous materials. The changes in
the readings segregate different ferrous materials. By conducting a laboratory
experiments for different grade ferrous materials, the coercive force values are
established for different materials. The coercive force values obtained in actual
jobs can be compared with the standard values, to evaluate different grade
ferrous materials.
The coercive force measurements are taken from different grade ferrous weld
metals. The changes in the readings segregate different ferrous weld metals. By
conducting laboratory experiments for different grade ferrous weld materials, the
coercive values are established for different weld materials. The coercive values
obtained at actual jobs can be compared with standard values, to evaluate the
different grade weld materials. By this the electrode used for the fabrication can
be identified.
The coercive force measurements are taken from different serviced ferrous
materials (used for different periods. The changes in the readings segregate
different service levels of the ferrous materials. By conducting laboratory
experiments for different grade ferrous materials with different service cycles
(fatigue) and load levels, the coercive force values are established for different
service levels. The coercive values obtained at actual jobs can be compared with
standard values, to identify the serviced condition of the material.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The proposed invention will be better understood by the following description
with reference to the accompanying drawings:
Figure 1 - shows Hysteresis loop representing magnetic properties of
ferromagnetic materials.
Figure 2 - shows a known coercive force-measuring meter used for
implementing the inventive method.
DETAILED DESCRIPTION OF A PREFEREP EMBODIMENT IOF THE
INVENTION
The invention will now be described with reference to the accompanying drawing
which depict exemplary embodiments of the invention. However there can be
several other embodiments, all of which are deemed to be covered by the
disclosure and claims appended below. The feature coercive force (or coercivity)
is a magnetic characteristic, which may be measured for any ferromagnetic
material. The most common representation of magnetic properties of
ferromagnetic material is its hysteresis loop, represented graphically In Flgure-1.
In this graph H(magnetizing force), and B (flux density) are the coordinates in X
and Y axes respectively. On a hysteresis loop, the "coercivity (HC) is the loop
width on H axes. To understand the term coercive force, the hysteresis loop is of
great help. Measuring the magnetic flux of a ferromagnetic material while the
magnetizing force is changed, generates a hysteresis loop. A magnetic material,
which has not been magnetized previously or not gone through complete
demagnetization, will follow a dashed line as shown in Fig 1, as the magnetizing
force is increased. Higher the applied current for magnetizing force (H), the
higher is the magnetic field (B). Beyond a saturation point, even if the
magnetizing force is increased, there will be a little increase in the magnetic flux.
This point is called as the magnetic saturation point. When the magnetizing force
(H) is made zero, still there exits some magnetism in'the material. This is called
as the point of retention (residual magnetism). This gives a measure of the
residual magnetism present in the material. Coercive force is the magnetizing
force required to be applied in the opposite direction to bring the residual
magnetism to zero value.
The coercive force value He measured in (A/cm) Ampere per centimetre is very
sensitive to microscopic structural changes in the material. Hence by measuring
this value with portable instrument, different ferrous grade materials, different
electrodes used for fabrication and the residual mechanical can be evaluated
properties of the ferrous materials at erection sites also.
This method as shown in fig 2 uses a portable battery operated standard
coercive force - measuring meter (1). By magnetizing and demagnetizing the
material (2) it measures the coercive force in the material. The change in the
coercive force values indicates the change in the microstructure of materials,
weld metal and residual (fatigue) life condition of serviced material. The coercive
force value can be compared with already recorded standard values under
various conditions established during lab tests the same material and conditions
of the actual job.
This can be applied to ferromagnetic material even with 2mm coating on its
surface. The method for determination of the different ferrous materials,
different weld metal used for welding, and service condition of ferromagnetic
materials through measurement of coercive force comprises of a number of steps
described herein. The area of the component which is in contact with the probe
is magnetized. The selected area is then demagnetized and the coercive force is
measured. The measured values are then compared with known coercive force
values that were obtained through a laboratory calibration process. The
determination or evaluation of said embodiments is done through coercive force
measurement in a non destructive way and with portable equipment.
WE CLAIM
1. A method for identifying different grade ferromagnetic materials through
measurement of coercive force, comprising the steps of
- magnetizing an area of a sample piece selected by a probe;
- demagnetizing the selected area;
- measuring the coercive force;
- comparing the measured value with standard coercive force value for
that material recorded in the laboratory;
- determining the coercive force values on the actual job and comparing
with the laboratory results,
- Characterized in that the Identification of said material is done through
standardization and polarization of data representing coercive force in a
non destructive way and in a portable measuring meter.
2. A method for identifying different grade weld ferromagnetic materials
through measurement of coercive force, the steps of:
- magnetizing by using a probe an area of a sample weld metal made of
ferromagnetic materials;
- demagnetizing the selected area of the weld metal sample;
- measuring the coercive force on the weld metal sample;
- comparing the measured value with standard coercive values established
for that weld metal in the laboratory;
- determining the corrective force values on the actual metal weld and
comparing with known laboratory data;
characterized in that the identification of said weld metal is done
through standardization and polarization of data representing coercive
force in a non-destructive way in a portable measuring meter.
3. A method for identifying different service(fatigue) life condition and
mechanical properties of ferromagnetic materials through measurement of
coercive force, comprising the steps of:
- magnetizing an area of a serviced component-made of ferromagnetic
materials;
- demagnetizing the selected area;
- measuring the coercive force;
- comparing the measured value with standard coercive force value for
that material recorded in the laboratory for different service levels;
- determining the coercive force values on the actual job and comparing
with known laboratory data;
- characterized in that the identification of said material life is done
through standardization and polarization of data relating to coercive
force measurement in a non destructive way and with a portable
measuring meter.
4. The method as claimed in claim 1,2 and 3, where in the coercive force
measuring meter is a battery operated and portable device,
5. The method as claimed in claim 1,2 and 3, where in the measurement is
carried out on the selected area without special preparation of the surface.
6. The method as claimed in claim 1,2 and 3, wherein said difference in
coercive force can be determined if the surface is covered with even up
to 2mm of coating.

ABSTRACT

The invention relates to a method for identifying different grade ferromagnetic
materials through measurement of coercive force, comprising the steps of
magnetizing an area of a sample piece selected by a probe; demagnetizing the
selected area; measuring the coercive force; comparing the measured value with
standard coercive force value for that material recorded in the laboratory;
determining the coercive force values on the actual job and comparing with the
laboratory results, the identification of said material is done through
standardization and polarization of data representing coercive force in a non
destructive way and in a portable measuring meter.