Title of Invention

METHOD OF EVALUATION OF HEAT TREATMENT EFFECTIVENESS THROUGH MEASUREMENT OF COERCIVE FORCE IN FERRO MAGNETIC MATERIALS

Abstract

A method for determination of effectiveness of Post weld stress relieving heat treatment in ferromagnetic materials through measurement of coercive force, comprising steps magnetizing the area of the job selected by the probe demagnetizing the selected area; measuring the coercive force; comparing with standard coercive force values for that material recorded in the laboratory for the given stress relieving heat treatment parameters, determining the effectiveness of Post weld stress relieving heat treatment; Characterized in that the determination of said effectiveness is done through coercive force measurement in a non destructive way and with portable equipment.

Full Text

TITLE: A METHOD FOR DETERMINATION OF EFFECTIVENESS OF POST WELD STRESS RELIEVING HEAT TREATMENT IN FERROMAGNETIC MATERIALS THROUGH MEASUREMENT OF COERCIVE FORCE FIELD OF INVENTION The present invention relates to a Non destructive examination method for evaluating the effectiveness of Post weld stress relieving Heat treatments of Pipe joint welds say at Boiler erection sites in general and to a method for determination of effectiveness of post weld stress relieving heat treatment in ferromagnetic material through measurement of coercive force in particular. This method is based on the difference in measurements of coercive force before and after Post weld stress relieving heat treatment. BACKGROUND OF INVENTION Stress relieving Heat treatment is a very important process employed to improve the mechanical properties of Heat Affected Zone & weld and to relieve the residual stresses in parts fabricated / erected by welding. This process is carried out by using either an oil/gas fired or electrical furnace in production shops where the entire weldment is kept under uniform temperature condition throughout the heat treatment operation. However at erection sites, local post weld heat treatment is often applied by wrapping heating coils around the circumference of weld joints covering the weld and certain region close to the weld joint. In this context the effectiveness of heat treatment becomes a matter of interest, especially in temper sensitive materials. At present there are many methods for determining the effectiveness of Heat treatment such as Hardness measurements and Microstructure evaluation in weld and HAZ (Heat Affected Zone) of weld joints. In addition residual stress measurements using X ray diffraction method or Hole drilling strain gage method are also carried out as a laboratory tool, to establish the Heat treatment procedure. Hardness measurements require surface preparation; Microstructure evaluation can be done only in labs. X ray diffraction method requires more space and heavier equipments not much suitable for erection sites. Hole drilling strain gauge method is a destructive method, requiring drilling equipment, surface preparation and time consuming. A new non-destructive evaluation method, using measurement of magnetic coercive force values, before and after Post weld stress relieving is illustrated in this presentation. This non-destructive testing method is based on the change in coercive force values due to changes in submicroscopic imperfections in the material. As high temperature heat treatment process brings about changes in the micro and submicroscopic level*; due to creep and plastic deformation, the application of the coercive force to evaluate the change in structure becomes a possibility. Patent no.: JP2001252785 (A) provides a device and a method for non destruction evaluation about the adequacy of a heat treatment after welding, which is applied for a ferromagnetic weldment. This method uses an AC magnetizing waveform. By detecting a phase difference between an exciting waveform and a detected waveform, the heat treatment is evaluated. This is a complicated method and evaluation is difficult, Patent no.: JP59155743 (A) describes a method for measuring hardness of heat- treated steel by x-ray diffraction using gaussian curve. This method involves X ray source and is not suitable for erection sites. Patent no.: US4129033 (A) describes a System for determining the level of heat treatment. This method employs strain gauges for determining the heat treatment level. This method is applicable only to a particular product process line. OBJECTS OF INVENTION It is therefore an object of the invention to propose a non-destructive method for evaluating the effectiveness of Post weld stress relieving Heat treatment of welded parts at erection sites Another object of the invention is to propose a method using standard portable coercive force measuring equipment for evaluating the effectiveness of Post weld stress relieving Heat treatment of welded parts at erection sites A further object of the invention is that no surface preparation is required for taking coercive force measurements for evaluating the effectiveness of Post weld stress relieving Heat treatment of welded parts at erection sites A further object of the invention is to devise a simple and reliable method for evaluating the effectiveness of Post weld stress relieving Heat treatment of welded parts at erection sites SUMMARY OF THE INVENTION A standard portable Coercimeter [Magnetic structurescope) is used for the proposed method. The coercive force measurements are taken before and after the Post weld stress relieving Heat treatment around the pipe circumference in weld & HAZ. The substantial changes in the readings show the effectiveness of the Post weld stress relieving Heat treatment process. By conducting laboratory experiments for stress relieving heat treatment, the coercive values before and after stress relieving can be recorded for welds of different material combinations as per requirement. The coercive values obtained at actual jobs can be compared with standard values, to evaluate the effectiveness of Heat treatment BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING Figl - Hysterisys Loop Fig2 - Equipment and Job setup DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The invention will now be described with help of accompanying drawings which depict an exemplary embodiments of the invention. However there can be several other embodiments, all of which are deemed covered by the description Coercive force (or Coercivity) is a magnetic characteristic, which may be measured for any ferromagnetic material. The most common representation of magnetic properties of a ferromagnetic material is its hysteresis loop. H (magnetizing force) B (Flux density) are the coordinates. On a hysteresis loop, the Coercivity (He) is the loop width on H axes. To understand the term coercive force, 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 ferromagnetic material, which has not been magnetized previously or not gone through complete demagnetization, will follow a dashed line as in the Fig 1, as the magnetizing force is increased. Higher the applied current for magnetizing force (H), higher is the magnetic field (B). Beyond the Saturation point , however 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 exists 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 centimeter is very sensitive to microscopic structural changes in the material. Hence by measuring this value with a portable equipment we can evaluate the effectiveness of Post weld stress relieving Heat treatment 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 reduction in the coercive force value indicates the Post weld stress relieving Heat treatment effectiveness. We can compare the coercive force values with already recorded standard values for various stress relieving parameters taken during lab tests for the same material and conditions of the stress relieving process. This coercive force value is different for different materials. This value is very sensitive to submicroscopic changes in the atomic structure of the materials. Hence stress relieving heat treatment of welded components effects a 50% change in the value before and after the heat treatment. These values when compared with standard values already measured in lab and recorded for the same material under the predefined process conditions, results in the evaluation of the effectiveness of Post weld stress relieving Heat treatment. The method can be applied to ferrc(magnetic materials even with 2mm coating on its surface. The method for determination of effectiveness of Post weld stress relieving heat treatment in ferromagnetic materials through measurement of coercive force comprises of a number of steps described herein. The area of the job selected by the probe is magnetized. The selected area is then demagnetized and the coercive force is measured. The measured values are then compared with standard coercive force values for that material recorded in the laboratory for the given stress relieving heat treatment parameters. The effectiveness of Post weld stress relieving heat treatment is then determined or evaluated. The determination or evaluation of said effectiveness is done through coercive force measurement in a non destructive way and with portable equipment WE CLAIM 1. A method for determination of effectiveness of Post weld stress relieving heat treatment in ferromagnetic materials through measurement of coercive force, comprising steps of - magnetizing the area of the job selected by the probe; - demagnetizing the selected area; - measuring the coercive' force; - comparing with standard coercive force values for that material recorded in the laboratory for the given stress relieving heat treatment parameters, - determining the effectiveness of Post weld stress relieving heat treatment; characterized in that the determination of said effectiveness is done through coercive force measurement in a non destructive way and with portable equipment. 2. The method as claimed in claim 1, wherein the coercive force measuring equipment is battery operated and standard one. 3. The method as claimed in claim 1, wherein the job can be carried out on the selected area without special preparation of the surface. 4. The method as claimed in claim 1, wherein said effectiveness can be determined if the surface is covered w»th even upto 2m m of coating. 5. The method as claimed in claim 1, wherein said equipment being portable is suitable for boiler erection sites. 6. The method as claimed in claim 1, wherein said stress relieving heat treatment of welded component effects a change in the range 45 to 55 percent, preferably 50 % in value before and after the heat treatment. A method for determination of effectiveness of Post weld stress relieving heat treatment in ferromagnetic materials through measurement of coercive force, comprising steps magnetizing the area of the job selected by the probe demagnetizing the selected area; measuring the coercive force; comparing with standard coercive force values for that material recorded in the laboratory for the given stress relieving heat treatment parameters, determining the effectiveness of Post weld stress relieving heat treatment; Characterized in that the determination of said effectiveness is done through coercive force measurement in a non destructive way and with portable equipment.

Documents:

2154-KOL-2008-(24-09-2014)-ABSTRACT.pdf

2154-KOL-2008-(24-09-2014)-CLAIMS.pdf

2154-KOL-2008-(24-09-2014)-CORRESPONDENCE.pdf

2154-KOL-2008-(24-09-2014)-DESCRIPTION (COMPLETE).pdf

2154-KOL-2008-(24-09-2014)-DRAWINGS.pdf

2154-KOL-2008-(24-09-2014)-FORM-1.pdf

2154-KOL-2008-(24-09-2014)-FORM-2.pdf

2154-KOL-2008-(24-09-2014)-OTHERS.pdf

2154-kol-2008-abstract.pdf

2154-kol-2008-claims.pdf

2154-kol-2008-correspondence.pdf

2154-kol-2008-description (complete).pdf

2154-kol-2008-form 1.pdf

2154-kol-2008-form 18.pdf

2154-kol-2008-form 2.pdf

2154-kol-2008-form 3.pdf

2154-kol-2008-gpa.pdf

2154-kol-2008-specification.pdf

abstract-2154-kol-2008.jpg