Magnetic Particle Method of Non-Destructive Testing

Transcription

1 Magnetic Particle Method of Non-Destructive Testing PURPOSE The purpose of this course is to provide basic instruction in the theory of magnetization, magnetic particle test methods, applications and magnetic particle test equipment. INTRODUCTION The magnetic particle method of non-destructive testing is recognized by many industries as an invaluable tool for detecting surface and slightly sub-surface discontinuities/cracks. Non-destructive testing is just as the name implies; the testing of materials without damage or destruction. The magnetic particle method of non-destructive testing is also self-descriptive. This method utilizes small iron particles and a magnetic source to locate discontinuities and/or cracks on the surface and slightly sub-surface of the test material. Due to the fact that some metals are able to be magnetized, it is possible to detect some discontinuities by utilizing a medium with magnetic attractive abilities such as small iron particles. A magnetic field can be introduced to the test piece and the medium applied to highlight the discontinuity. This type of testing is called Magnetic Particle Testing. Magnetic Particle Testing (commonly abbreviated MT) is a simple test method that is relatively easy to perform, provides a visual indication of discontinuities and does not permanently impair the material being tested. This process can be performed at various stages of manufacture and processing of materials. Copyright 2003 US Technical Training Center Page 1 of 22

2 THEORY OF MAGNETIZATION In order for a material to be magnetized it must contain inherent magnetic domains (indicated in Sketch a). When the magnetic domains are aligned (as depicted in Sketch b) the material is magnetized. Materials with aligned domains are known as magnets and have the ability to attract iron particles. Sketch a Sketch b When all of the magnetic domains are aligned the material develops a total magnetic force equal to the sum of all the aligned magnetic domains. The sum of the aligned domains is referred to as the Magnetic Field. The magnetic field is delineated by Magnetic Flux which form a circuit or pathway within the material and complete the circuit by flowing outside the material from the North to the South pole (refer to Sketch c). The strongest area of attraction and repulsion on a magnet is at the North and South poles Sketch c Copyright 2003 US Technical Training Center Page 2 of 22

3 MATERIAL PROPERTIES Every material reacts differently when a magnetic field is exerted upon it. However, metals can be generally classified in one of the following three categories; Diamagnetic Metals Have a small and negative susceptibility to magnetization. These metals are slightly repelled by magnetic fields. Examples of diamagnetic metals are: copper, silver and gold. Paramagnetic Metals Have, at a minimum, a small and positive susceptibility to magnetization. They are slightly attracted to magnets. Examples of paramagnetic metals are: magnesium, molybdenum, lithium and tantalum. Ferromagnetic Metals Have a large and positive susceptibility to magnetization i.e. their magnetic domains are easily aligned. They are strongly attracted by magnets and have the ability to retain magnetization after the magnetizing field has been removed. Examples of ferromagnetic metals are: iron, nickel and cobalt. (Ferromagnetic metals are actually a subset of the paramagnetic metal group) The following inherent material properties are important in determining if a metal is suitable for magnetic particle testing: Permeability - is the ease with which a magnetic flux field can be established in the metal. Reluctance - is the opposite of permeability and is the opposition to the establishment of a magnetic flux field in a metal. Metals with inherently high permeability will have low reluctance and those with low permeability will have high reluctance. Residual Magnetism is the total magnetism remaining in a material after the magnetizing force has been removed. Retentivity - is the ability of the metal to retain some Residual Magnetism after the magnetizing force is removed. Metals with high retentivity will require a high Coercive Force to remove the residual magnetism from the part. Coercive force is the reverse magnetizing force necessary to remove the residual magnetism. Copyright 2003 US Technical Training Center Page 3 of 22

4 MAGNETIC FIELDS A magnetic field surrounds all magnets. Magnetic fields can be magnetically induced with another permanent or temporary magnet. Magnetic fields can also be electrically induced surrounding conductors which carry electric current. The main difference between the two types of magnetic fields is that the magnetic field surrounding the magnet has polarity (a North and South pole) and the magnetic field surrounding the current carrying conductor does not. The Magnetic Flux in the magnetic field travels from the North to the South pole outside of the magnet and from the South to the North pole inside the magnet (as depicted in Sketch d). Outside of the magnetized material the magnetic flux is also referred to as Lines of Force. Lines of force are defined as the magnetic flux lines that attract magnetizable materials to the magnetic poles. All of the magnetic flux and lines of force seek the path of least resistance, enter/exit the magnet at the poles and never cross each other. Sketch d A typical magnet is a straight piece of magnetized material and is commonly referred to as a Bar Magnet. A bar magnet has an opposite pole at each end (as depicted in Sketch e). Sketch e If the bar magnet is bent into a curve it becomes a Horseshoe Magnet (as depicted in Sketch f). Copyright 2003 US Technical Training Center Page 4 of 22

5 Sketch f If the magnet is bent into a complete loop a Circular Magnet is formed (as depicted in Sketch g). The lines of force/magnetic field are contained entirely within the circular magnet. Sketch g If the magnetized material is disrupted by a crack, break or other discontinuity a set of localized North and South poles are established on either side of the break. The lines of force/magnetic field will flow through the air (outside of the material) across the discontinuity from the pole to pole. This is known as a Flux Leakage Field (as depicted in Sketch h). The flux leakage field is comprised of the lines of force that are forced to travel outside of the magnetized material due to a crack, break or other discontinuity. Copyright 2003 US Technical Training Center Page 5 of 22

6 Sketch h Because of the locally created poles the flux leakage field attracts other magnetizable material including small iron particles. It is the attraction of visible iron particles to the flux leakage field at a crack, break or other discontinuity in a magnetized material that forms the basis for magnetic particle testing. The magnitude of magnetic flux is measured as Flux Density or flux-per-unit area at a given point 90 degrees (perpendicular) to the lines of force. The flux density unit of measure is in Gauss. A common method of determining the direction the magnetic lines of force are flowing in an electrically induced magnetic field is by the use of the Right Hand Rule. Curl your fingers and point your right thumb in the direction of the current flow (from positive to negative) in the electrical conductor, your curled fingers will then point in the direction the lines of force are flowing (as depicted in Sketch i). The magnetic lines of force always flow perpendicular (at right angles) to the current flow. Sketch i Copyright 2003 US Technical Training Center Page 6 of 22

7 There are two types of magnetization utilized for magnetic particle testing, Circular and Longitudinal. The names of the two types of magnetism refer to the direction of flow of the lines of flux within the magnetic field. Circular magnetism flows in a continuous loop around the object and longitudinal magnetism flows from point to point, usually from the pole of the magnet, linearly through the test piece, and then back into the opposite pole of the applied magnet. CIRCULAR MAGNETIZATION A circular magnetic field can be created within the test material by two methods, Direct Induction and Indirect Induction. These two methods utilize electric current flow directly though the test material (direct induction) or by utilizing a central conductor which is not part of the test material to conduct the electric current (indirect induction). An example of direct induction is illustrated in Sketch j where current is flowing directly through the test material and creating a circular field. You can use the right hand rule in this Sketch to verify the direction of flow of the circular magnetic field. If the test material is uniform in all respects (shape, density, etc.) the circular magnetic field will also be uniform. Sketch j An example of indirect induction is illustrated in Sketch k where current is flowing through a separate current carrying conductor placed within the test material. This method is sometimes referred to as the Central Conductor Technique. Again, you can use the right hand rule in this Sketch to verify the direction of flow of the circular magnetic field. Indirect induction of the magnetic field is utilized on hollow test pieces and eliminates the possibility of the test piece being burned/damaged by arcing at the contact points which is possible during direct induction. Copyright 2003 US Technical Training Center Page 7 of 22

8 Sketch k When a magnetic field is directly induced into a diamagnetic material with extremely high reluctance such as copper, the magnetic lines of force DO NOT stay within the material. The magnetic lines of force and magnetic field are established around the material. Conversely, when a magnetic field is directly induced into a ferromagnetic material with extremely high permeability such as iron the lines of force are conducted within the material. The magnetic lines of force and magnetic field flow completely within the material and only exit at points where flux leakage exists. No matter what the material, the lines of force always travel perpendicular (at right angles) to the current flow as illustrated by the right hand rule. In ferromagnetic metals, the lines of force will stay within the material except where flux leakage exists. The test medium (iron particles) will only be attracted to the material where the lines of force travel through the air (flux leakage). Flux leakage (and the formation of localized poles) can occur at cracks, breaks or other discontinuities in the test material. Circular magnetization will detect cracks, breaks and discontinuities that are between 45 and 90 degrees to the lines of force. A crack that is parallel to the lines of force will not exhibit flux leakage and will NOT attract the test medium. Refer to Sketch l. Copyright 2003 US Technical Training Center Page 8 of 22

9 Sketch l LONGITUDINAL MAGNETIZATION A longitudinal magnetic field can be created within the test material by two methods, Indirect Induction and Direct Magnetization. Indirect induction is created by encircling the test material with a coil of current carrying conductor such as copper wire. The current flowing through the coiled conductors creates a circular magnetic field around the conductors and indirectly imparts a longitudinal magnetic field on test metal placed lengthwise inside the coil as depicted in Sketch m. When the copper wire is wound into a coil, the lines of flux around each turn combine and therefore increase the flux density in the longitudinal direction.. Sketch m The second method is known as direct magnetization. Direct magnetization utilizes a magnet or magnets, temporary or permanent, to allow the lines of magnetic force to flow through the test piece. The most common form of temporary magnet utilized for magnetic particle test purposes is a temporary horseshoe magnet created by a curved piece of soft, permeable iron and an electric coil. This temporary magnet is often referred to as a Yoke. The curved iron core is temporarily magnetized which creates a horseshoe magnet by the indirect induction method described above. Copyright 2003 US Technical Training Center Page 9 of 22

10 The induced magnetic field is then applied to the test piece and forced to flow through the metal via direct magnetization as depicted in Sketch n. Sketch n Another method of direct magnetization is to impart a magnetic field through the test material with a permanent magnet or pair of magnets. The magnets can be placed on the test material so that the lines of force travel through the test material from magnet to magnet or pole to pole. As with all other methods, disruptions or discontinuities in the test material will cause flux leakage and attract the test medium (depicted in Sketch o). Copyright 2003 US Technical Training Center Page 10 of 22

11 Sketch o CURRENT FLOW VS. FLUX DENSITY When using induced current to create a magnetic field, there is a corresponding relationship between the amount of current used and the strength of the resulting magnetic field. The relationship is relatively simple, the higher the current, the stronger the magnetic field/flux density. Typically when a test article is several times longer than its diameter (L/D Ratio) it may be magnetized by a coil or wrapping the part with loops of current carrying conductor. Since we already learned that the magnetic fields generated by each conductor wrap are cumulative, we know that more wraps of the conductor equates to a greater field strength given the same current flow. As an example; 100 coil wraps with 2 amperes of current (200 amp-turns) will create the same approximate magnetic field strength as 50 coil wraps with 4 amperes of current which is also 200 amp-turns (100x2 = 50x4). Another method of induced current magnetization passes current directly through the part with hand held prods or on a stationary bench from end to end (known as a Head Shot). In this method no coils are used so the only way to increase or decrease the magnetic field strength is to vary the current. Copyright 2003 US Technical Training Center Page 11 of 22

12 Although not covered in this module, there are several formulas used to determine the correct number of coil wraps, current, and L/D ratio when performing magnetic particle testing. While these formulas are more advanced than this basic lesson, the important point to remember is: When performing testing, only the minimum satisfactory amount of current should be utilized to prevent over-magnetizing, arcing, burning or damaging the part. AC AND DC FIELD DISTRIBUTION Alternating Current (AC) is the most common power source for performing magnetic particle testing. Alternating current is readily available, easily converted to low voltages with transformers and can be rectified to create Direct Current (DC). Alternating current flow continuously reverses direction (refer to Sketch p). A Cycle is a complete set of values through which an alternating current repeatedly passes. In typical household current in the North America the AC current reverses direction and completes 60 cycles per second. Hence, in North America, the current is referred to as 60 cycle. In some countries the current completes 50 cycles per second and is referred to as 50 cycle. Since the alternating current is continually reversing direction, the iron particles in the test medium are pulled back and forth. This back and forth movement vibrates/agitates the particles which greatly increases the particle mobility and enhances their ability to travel toward areas of flux leakage (cracks or discontinuities). It should be noted that alternating current tends to flow near the surface of a conductor, this is known as the Skin Effect. Because of the surface flow of AC it has little penetrating power and is best utilized for the detection of surface discontinuities. Typically, AC is ineffective for detecting subsurface discontinuities. Sketch p Direct Current is most commonly utilized in magnetic particle testing for detecting slightly sub-surface discontinuities in the test material. There are two common types of DC current utilized, Straight DC and Half Wave Direct Current (HWDC). Straight DC is the type of current produced by a battery with a positive and negative terminal. Current flows from positive to negative. Half Wave DC is produced by rectifying alternating current with a half bridge. The rectification basically truncates the negative portion of the AC sine wave (illustrated in Sketch q) and creates pulses of DC. Because of this phenomena (periods of current flow and no current flow) half wave DC is also referred to as Pulsed DC. Copyright 2003 US Technical Training Center Page 12 of 22

13 Sketch q When direct current is passed through a solid conductor, the magnetic field strength is greatest at the surface and diminishes with the distance from the conductor s center. The magnetic field strength (flux density) increases evenly from the center of the conductor to the outer edge. When alternating current is passed through a solid conductor, the current tends to flow near the surface of the conductor due to the skin effect. As with DC, the magnetic field strength is greatest at the surface however, because the current is more concentrated at the surface, the magnetic field strength/flux density is more concentrated near the surface. This differs from DC because with AC the magnetic field strength is NOT evenly distributed to the center of the conductor. Each type of current is useful in magnetic particle testing, however, each has its limitations. To summarize; AC Is most suited for detecting surface discontinuities Provides better magnetic particle medium mobility DC Is better suited for detecting surface and slightly sub-surface discontinuities Produces a stronger (continuous) magnetic field Copyright 2003 US Technical Training Center Page 13 of 22

14 MAGNETIC PARTICLE TEST MEDIUMS A magnetic particle test medium is a particulate powder with magnetic attractive abilities such as small iron particles (usually small enough to pass through a 100 mesh screen). The particles are generally spherical in shape to provide good mobility but still maintain good attractive power. Completely round particles offer the best mobility but have low attractive power while long, jagged, slender particles have good attractive power but impaired mobility. The best compromise is an oblong shaped particle which is not too rough to detrimentally impair mobility (refer to Sketch r). Sketch r The most important properties of the magnetic particles are they have high permeability and low retentivity. It is important for the particles not to remain magnetized when the magnetic field is removed as this can mask discontinuities or cause false indications on the test specimen. Mobility is extremely important in magnetic particle testing to allow the particles to move toward the area of flux leakage (crack or discontinuity) and form a visual pattern around the field. Mobility is aided by the use of AC current since the bi-directional current flow causes the particles to vibrate. Mobility can also be enhanced by blowing or externally vibrating the particles during the testing process. Another important quality of the particles is visibility. Visibility of the particles is enhanced by several methods. The particles are colored to provide a contrast against the test specimen. Common colors include grey, red, black and yellow. Visibility of the particles can also be enhanced by the use of fluorescently treated particles. These particles fluoresce (glow) under a black light to further enhance visibility. Magnetic particle test mediums can be classified into four basic groups: Dry particles, non-fluorescent - usually dyed a solid color for contrast. Dry particles, fluorescent - requires a UV black light to cause the particles to glow/fluoresce. Wet particles, non-fluorescent - particles are suspended in a liquid which allows great mobility due to the lubricating qualities of the suspension fluid. Copyright 2003 US Technical Training Center Page 14 of 22

15 Wet particles, fluorescent is the preferred method for sensitive testing due to enhanced mobility AND enhanced visibility. When describing magnetic particle testing the Dry Method refers to the use of dry particles (either fluorescent or non-fluorescent). The particles are sprinkled, dusted or blown on to the test specimen and allowed to crawl towards the flux leakage fields. The Wet Method refers to the use of wet particles (suspended in a fluid) either fluorescent or nonfluorescent. The particles are sprayed or poured onto the test specimen and allowed to swim towards the flux leakage fields. MAGNETIC PARTICLE TEST METHODS There are two basic types of magnetic particle test methods; The Continuous Method refers to the method in which the magnetic particle medium is applied to the test specimen WHILE the magnetizing field is applied. The Residual Method refers to the method in which the magnetic particle medium is applied AFTER the magnetizing field is applied or the magnetizing current is discontinued. As mentioned in the previous section, there are four basic types of magnetic particle mediums. These mediums, when multiplied by the two methods (continuous or residual), result in 8 basic types of test method applications: Dry Continuous Method, Non-fluorescent This is the most commonly utilized field inspection method. This process is quicker to perform, inexpensive, requires less clean-up and a minimal amount of equipment. For these reasons, it is the preferred process for most NDT field technicians. Dry Continuous Method, Fluorescent This is one of the least common processes encountered. This process is typically only used where a wet fluorescent bath or liquid would be detrimental to the test specimen. Dry Residual Method, Non-fluorescent This process is sometimes utilized in difficult to access areas where a magnetic field is applied, the magnetic field generating equipment is removed and then the dry particle medium is applied. This method is usually avoided on test specimens with low retentivity and is typically a last resort for testing due to low particle mobility, inconsistent residual fields and variations in retentivity. Dry Residual Method, Fluorescent As with non-fluorescent residual methods this process is sometimes utilized in difficult to access areas. A magnetic field is applied, the magnetic field generating equipment is removed and then the dry particle medium is applied. This method is usually avoided on test specimens with low retentivity and is typically a last resort for testing due to low particle mobility. Wet Continuous Method, Non-fluorescent This method is utilized in areas where lighting is sufficient to visually ascertain the suspended particulates in the suspension fluid. A contrasting color is essential for this type of particle. Typically, this method is commonly Copyright 2003 US Technical Training Center Page 15 of 22

16 applied in the field as a mixture of dry powder and water or kerosene to enhance the particle mobility and provide easier clean-up. Wet Continuous Method, Fluorescent This method is the most desirable and hence widely utilized due to the positive characteristics of high visibility (under UV black light ) and high particle mobility. Generally, the wet fluorescent method utilizes the residual method but on test specimens with low retentivity, this continuous method may be specified. Wet Residual Method, Non-fluorescent This method is utilized in areas where lighting is sufficient to visually ascertain the suspended particulates in the suspension fluid. A contrasting color is essential for this type of particle. Typically this method is reserved for bench test equipment in a controlled environment. This method is used on test specimens with high retentivity and is utilized to prevent over-magnetization of the component. Wet Residual Method, Fluorescent This method is utilized in areas where lighting is insufficient or undesirable to visually ascertain the suspended particulates in the suspension fluid. The particles in this method have high visibility under UV black light and high particle mobility. This method is used on test specimens with high retentivity and is utilized to prevent over-magnetization of the component. This is one of the most common methods utilized in testing labs for shafts, spindles, etc. DEMAGNETIZATION Demagnetization is the removal of residual magnetism left in a metal, usually when testing is completed. Residual magnetism is always in the same direction as the applied magnetic field and residual magnetism is usually weaker than the original applied magnetic field. As discussed earlier, Retentivity is the ability of the metal to retain some Residual Magnetism after the magnetizing force is removed. Residual magnetism left remaining in some test specimens is undesirable and may be detrimental to the part or component. Residual magnetism left in rotating parts such as shafts or bearing races can attract metal particles and cause premature wear or damage. Residual magnetic fields can also affect magnetic compasses and cause welding problems during DC welding. For these reasons the residual magnetism must be removed after testing is completed. In order for residual magnetism to be measured there MUST be some flux leakage. There is NO easy way to measure a circular magnetic field which is contained within a part unless some type of flux leakage exists. To measure flux leakage (which by default indicates residual magnetism) a Magnetic Leakage Field Indicator is used. The indicator compares the external magnetic field (at leakage points) with an internal comparator field within the indicator. The comparison results are indicated on a meter with strength and direction. As you have learned in the preceding sections there are two types of magnetism, circular and longitudinal. Because the lines of flux generally do not leave a part that has been circularly magnetized it is usually difficult to determine if residual magnetism exists. Because of this characteristic most shafts, rods, axles, spindles, etc. that have been circularly magnetized are usually re-magnetized longitudinally prior to removing residual magnetism. In a longitudinally magnetized metal such as a bar magnet, the lines of force enter and exit at the ends or poles of the magnet which make it very easy to determine if residual magnetism exists. Copyright 2003 US Technical Training Center Page 16 of 22

17 To remove residual magnetism two steps must occur. The magnetic field must be reversed to negate the residual field and the Coercive Force (reverse magnetizing force) must be reduced to less than the original magnetizing force. Metals with high retentivity will require a high Coercive Force to remove the residual magnetism from the part. In longitudinally magnetized parts, the magnetic field can be reversed by: Reversing the part in the magnetic field (swapping the part end for end) Reversing the magnetizing coil (turn the coil around 180 degrees, front to back) Reverse the current through the coil (swap positive for negative, DC coil ONLY) The magnetic field can be reduced by: Reducing the magnetizing current Moving the magnetizing coil away from the part Moving the part away from the magnetizing coil AC coils are commonly used for demagnetization of parts since in an AC coil the current automatically reverses direction times per second. When using AC, only the second step of reducing the magnetic field must be performed in the demagnetization process. A rheostat is sometimes used to reduce the current in the AC coil, thereby reducing the magnetic field OR the distance between the part and coil can be increased, which also decreases the strength of the magnetic field. Since DC current does not automatically reverse additional steps must be performed when demagnetizing with a DC coil. The DC current polarity must be manually switched back and forth between positive and negative. Experience has shown that the best degree of demagnetization occurs if the DC current is reversed at a rate of one reversal per second. For materials with high permeability and low retentivity, such as iron, at least 10 reversals are required to facilitate proper demagnetization. Normally, when demagnetizing with DC, the magnetizing field should be first reduced, then reversed. MAGNETIC PARTICLE TEST EQUIPMENT Magnetic particle test equipment is primarily comprised of the magnetizing unit, particle medium applicator, visibility enhancers (lights, magnifiers, etc.) and calibration devices. For field applications, the most common type of equipment used for magnetic field generation is known as a yoke. Most yokes are portable, lightweight, can use AC or DC input power, have switchable field current AC/DC, can be used with wet or dry methods and are relatively inexpensive. The yoke produces longitudinal magnetization by the use of an electric coil wrapped around a curved iron horseshoe. When current is flowing a temporary horseshoe magnet is created with longitudinal magnetism created between the two adjustable legs known as poles (refer to Sketch s). The current flow can be AC, DC or half-wave DC depending upon the test requirements. Copyright 2003 US Technical Training Center Page 17 of 22

18 Sketch s For in-lab testing of shafts or spindles, the most common type of test equipment is the wet horizontal bench (refer to Sketch t). The wet horizontal bench uses a wet bath (usually incorporated into the bench) and induced current to produce a magnetic field. Both circular and longitudinal magnetization can be created at the bench. By inducing current from end to end (known as a head shot) the test specimen can be circular magnetized and by using a coil or wraps of conductor the test specimen can be longitudinally magnetized. Because of the flexibility of producing both types of magnetic fields and the enhanced mobility of the wet particle method, the wet bench is the best choice for most in-lab work. Copyright 2003 US Technical Training Center Page 18 of 22

19 Sketch t Other types of magnetic field generating equipment include: Permanent Magnets are used for longitudinal magnetization where inaccessible locations, weight considerations or lack of AC/DC power preclude other equipment (refer to Sketch u). Copyright 2003 US Technical Training Center Page 19 of 22

20 Sketch u Another type of apparatus used in generating magnetic fields is Induced Current Equipment. Induced current equipment is for use with current carrying coils or prods to induce current around or through the test specimen. The equipment looks very similar to a welder with a transformer and variable current output. The cables on this equipment can be anywhere from 15 to 100 feet in length depending upon necessary current output. One of the disadvantages of this equipment is that it usually takes a minimum of two technicians to manipulate the prods and apply the particle medium. This type of equipment has been largely replaced by the yoke due to potential damage to the test specimen (heat, arcing, etc.) caused by the induced current the equipment weight, portability issues and man-power requirements with the equipment. However, this type of equipment is still utilized occasionally in the field where circular magnetization is required. Copyright 2003 US Technical Training Center Page 20 of 22

21 SAFETY Personal safety and the safety of others should always be your number one priority. Certain precautions must be taken when performing or closely observing testing utilizing the Magnetic Particle Method. Recommended Personal Protective Equipment (PPE): Safety glasses/goggles Ultra-violet light filtering glasses/goggles Gloves Dust respirator Protective clothing such as an apron, long pants, long sleeve shirt, etc. Some Common Safety Hazards Associated with Magnetic Particle Testing: Burns The electrical resistance encountered when using the direct current method can cause heating in the part or electrodes causing burns to the skin. Care should be exercised in handling hot components immediately after testing. Another source for burns can be the UV black light. The bulb and housing can get very hot after extended usage. Electrical Arcing Excessive current, electrode slippage and poor contact can cause electrical arcing on the test material. Electrical arcing is a hazard that causes sparks which may cause injury or fire. Every effort should be made to minimize electrical arcing during the testing process to prevent injury, fire and damage to the component being tested. Fumes The wet magnetic medium (particles) aerosols contain a propellant. Although this propellant is generally non-toxic excessive amounts should not be inhaled. Always use aerosol mediums in a well ventilated area to reduce personal contact/inhalation. The Material Safety Data Sheets (MSDS) for the aerosol test mediums should ALWAYS be reviewed prior to testing to insure all safety precautions have been addressed. Dust The dry magnetic medium (particles) contain an inherent dust. Although this dust is generally non-toxic, excessive amounts should not be inhaled. A dust respirator can be used to reduce personal contact/inhalation. The Material Safety Data Sheets (MSDS) for the dry test mediums should ALWAYS be reviewed prior to testing to insure all safety precautions have been addressed. Fire Open flames, sparks or smoking should not be permitted near the wet method or wet bath processes. Some wet baths and aerosol mediums are extremely flammable. UV Light/Black Light The typical black lights used in the fluorescent magnetic particle methods will not damage the skin or eyes AS LONG AS THE FILTER IS ON THE LIGHT. NEVER use the black light without the protective filter in place! Always wear protective UV glasses when using the black light. If the black light is directed towards the eyes during testing it is possible to experience a clouding of vision even with the filter in place. This temporary phenomena occurs because the fluid in the human eye fluoresces under black light. Copyright 2003 US Technical Training Center Page 21 of 22

22 The following documents, websites and professional organizations are recommended for additional information and reference on this topic outside the scope of this module: DOCUMENTS Recommended Practice No. SNT-TC-1A (2001) 2001 The American Society for Nondestructive Testing, Inc. ISBN Annual Book of Standards Volume Nondestructive Testing 2003 ASTM International ISBN (Stock # S030303) Classroom Training Handbook (CT-6-3) Nondestructive Testing, Magnetic Particle 1977 General Dynamics, Convair Division Principles of Magnetic Particle Testing 1985 Betz, Carl E. MAGNAFLUX Corporation Nondestructive Testing, Second Edition 1975 McGonnagle, Warren J. Nondestructive testing Handbook 1959 McMaster, Robert C American Society for Nondestructive Testing Introduction to Nondestructive Testing 1987 Mix, Paul E WEBSITES PROFESSIONAL ORGANIZATIONS ASNT The American Society for Nondestructive Testing, Inc Arlingate Lane Columbus, OH Tel: (800) ASTM International The American Society for Testing and Materials 100 Barr Harbor Drive PO Box C700 West Conshohocken, PA , Tel: (610) Fax: (610) BINDT The British Institute of Non-Destructive Testing 1 Spencer Parade, Northampton NN1 5AA, England Tel: +44 (0) Fax: +44 (0) Copyright 2003 US Technical Training Center Page 22 of 22