1. ME367 NON-DESTRUCTIVE TESTING MODULE-3 M.P.I. Sukesh O P, AP-ME, JECC 10/16/2018 SUKESH O P/ APME/JECC 1

2. ME357 Non-Destructive Testing 10/16/2018 SUKESH O P/ APME/JECC 2 Introduction to NDT- Visual Inspection- Liquid Penetrant Inspection- Magnetic Particle Inspection - Ultrasonic Testing- Radiography Testing- Eddy Current Testing.

3. MODULE-3 10/16/2018 SUKESH O P/ APME/JECC 3  Magnetic Particle Inspection (MPI)- Principles of MPI, basic physics of magnetism, permeability, flux density, cohesive force, magnetizing force, rentivity, residual magnetism, Methods of magnetization, magnetization techniques such as head shot technique, cold shot technique, central conductor testing, magnetization using products using yokes, direct and indirect method of magnetization, continuous testing of MPI, residual technique of MPI, system sensitivity, checking devices in MPI- Interpretation of MPI, indications, advantage and limitation of MPI.

4. INTRODUCTION 10/16/2018 SUKESH O P/ APME/JECC 4  MPI  MPI is governed by the laws of magnetism and is therefore restricted to the inspection of materials that can support magnetic flux lines, metals can be classified as ferromagnetic, paramagnetic, or diamagnetic.  Ferromagnetic metals are those that are strongly attracted to a magnet and can become easily magnetized. Ex: iron, nickel, cobalt.  Paramagnetic metals such as austenitic stainless steel are very weakly attracted by magnetic forces of attraction and cannot be magnetized. Ex: Aluminum  Diamagnetic metals which have a weak, negative susceptibility to magnetic fields. Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Ex: copper, silver, gold MPI- it is not applicable to non-magnetic materials

5. INTRODUCTION 10/16/2018 SUKESH O P/ APME/JECC 5  The only requirement For the inspection through this technique is that the components being inspected must be made of a ferromagnetic material (a materials that can be magnetized) such as iron, nickel, cobalt, or some of their alloys.  The method is used to inspect a variety of product forms including castings, forgings, and weldments.  Many different industries use MPI such as structural steel, automotive, petrochemical, power generation, and aerospace industries. offshore structures and underwater pipelines.  Underwater inspection is another area where magnetic particle inspection may be used to test items such as offshore structures and underwater pipelines.

6. Introduction to Magnetism 10/16/2018 SUKESH O P/ APME/JECC 6 Magnetism is the ability of matter to attract other matter to itself. Objects that possess the property of magnetism are said to be magnetic or magnetized and magnetic lines of force can be found in and around the objects. A magnetic pole is a point where the a magnetic line of force exits or enters a material. Magnetic field lines: Form complete loops. Do not cross. Follow the path of least resistance. All have the same strength. Have a direction such that they cause poles to attract or repel. Magnetic lines of force around a bar magnet Opposite poles attracting Similar poles repelling

7. Ferromagnetic Materials 10/16/2018 SUKESH O P/ APME/JECC 7  A material is considered ferromagnetic if it can be magnetized. Materials with a significant Iron, nickel or cobalt content are generally ferromagnetic.  Ferromagnetic materials are made up of many regions in which the magnetic fields of atoms are aligned. These regions are call magnetic domains.  Magnetic domains point randomly in demagnetized material, but can be aligned using electrical current or an external magnetic field to magnetize the material. Demagnetized Magnetized

8. How Does Magnetic Particle Inspection Work? A ferromagnetic test specimen is magnetized with a strong magnetic field created by a magnet or special equipment. If the specimen has a discontinuity, the discontinuity will interrupt the magnetic field flowing through the specimen and a leakage field will occur.

9. How Does Magnetic Particle Inspection Work? (Cont.) Finely milled iron particles coated with a dye pigment are applied to the test specimen. These particles are attracted to leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.

10. Basic Procedure- MPI Basic steps involved: 1.Component pre-cleaning 2.Introduction of magnetic field 3.Application of magnetic media 4.Interpretation of magnetic particle indications

11. 1. Pre-cleaning  When inspecting a test part with the magnetic particle method it is essential for the particles to have an unimpeded path for migration to both strong and weak leakage fields alike. The part’s surface should be clean and dry before inspection.  Contaminants such as oil, grease, or scale may not only prevent particles from being attracted to leakage fields, they may also interfere with interpretation of indications.

12. 2. Introduction of the Magnetic Field The required magnetic field can be introduced into a component in a number of different ways. 1.Using a permanent magnet or an electromagnet that contacts the test piece 2.Flowing an electrical current through the specimen 3.Flowing an electrical current through a coil of wire around the part or through a central conductor running near the part.

13. 3. Application of Magnetic Media (Wet Versus Dry) With the dry method, the particles are lightly dusted on to the surface. MPI can be performed using either dry particles, or particles suspended in a liquid. With the dry method, the particles are lightly dusted on to the surface. With the wet method, the part is flooded with a solution carrying the particles. The dry method is more portable. The wet method is generally more sensitive since the liquid carrier gives the magnetic particles additional mobility.

14. 4. Interpretation of Indications After applying the magnetic field, indications that form must interpreted. This process requires that the inspector distinguish between relevant and non-relevant indications.

15. Crane Hook with Service Induced Crack Fluorescent, Wet Particle Method

16. Gear with Service Induced Crack Fluorescent, Wet Particle Method

17. Drive Shaft with Heat Treatment Induced Cracks Fluorescent, Wet Particle Method

18. Splined Shaft with Service Induced Cracks Fluorescent, Wet Particle Method

19. Threaded Shaft with Service Induced Crack Fluorescent, Wet Particle Method

20. Large Bolt with Service Induced Crack Fluorescent, Wet Particle Method

21. Crank Shaft with Service Induced Crack Near Lube Hole Fluorescent, Wet Particle Method

22. Lack of Fusion in SMAW Weld Visible, Dry Powder Method Indication

23. Toe Crack in SMAW Weld Visible, Dry Powder Method

24. Throat and Toe Cracks in Partially Ground Weld Visible, Dry Powder Method

25. Magnetic Particles/ media The particles used in magnetic particle testing are made of ferromagnetic materials, usually combinations of iron and iron oxides, having a high permeability and low retentivity. Particles having high permeability are easily attracted to and magnetized by the low- level leakage fields at discontinuities. combinations Low retentivity is required to prevent the particles from being permanently magnetized. Strongly retentive particles will cling together and to any magnetic surface, resulting in reduced particle mobility and increased background accumulation. A common particle used to detect cracks is iron oxide, for both dry and wet system/ styleiron oxide

26. Dry Magnetic Particles Magnetic particles come in a variety of colors. A color that produces a high level of contrast against the background should be used.

27. Wet Magnetic Particles Wet particles are typically supplied as visible or fluorescent. Visible particles are viewed under normal white light and fluorescent particles are viewed under black light.

28. 10/16/2018 SUKESH O P/ APME/JECC 28 Dry ● Common, relatively cheap ● Generally applied to rougher surfaces ● Particle types ○ Elongated - align well with magnetic fields ○ Rounded - move freely across a surface Wet ● More expensive, accurate ● Painted or sprayed onto surfaces ● Wet dye classifications ○ Light (UV or fluorescent) ○ Removal type (water, solvent, or emulsifier)

29. Types of Magnetization types of magnetic fields Two general types of magnetic fields (longitudinal and circular) may be established within the specimen. The type of magnetic field established is determined by the method used to magnetize the specimen. longitudinal magnetic field A longitudinal magnetic field has magnetic lines of force that run parallel to the long axis of the part. circular magnetic field A circular magnetic field has magnetic lines of force that run circumferentially around the perimeter of a part.

30. Importance of Magnetic Field Direction Being able to magnetize the part in two directions is important because the best detection of defects occurs when the lines of magnetic force are established at right angles to the longest dimension of the defect. This orientation creates the largest disruption of the magnetic field within the part and the greatest flux leakage at the surface of the part. An orientation of 45 to 90 degrees between the magnetic field and the defect is necessary to form an indication. Since defects may occur in various and unknown directions, each part is normally magnetized in two directions at right angles to each other. Flux Leakage No Flux Leakage

31. Methods of magnetization 10/16/2018 SUKESH O P/ APME/JECC 31  There are a variety of methods that can be used to establish a magnetic field in a component for evaluation using magnetic particle inspection. It is common to classify the magnetizing methods as either direct or indirect.

32. Magnetization Using Direct Induction (Direct Magnetization) 10/16/2018 SUKESH O P/ APME/JECC 32  With direct magnetization, current is passed directly through the component. The flow of current causes a circular magnetic field to form in and around the conductor.  When using the direct magnetization method, care must be taken to ensure that good electrical contact is established and maintained between the test equipment and the test component to avoid damage of the component (due to arcing or overheating at high resistance points).

33. (HEAD SHOT Method) Clamping the component between two electrical contacts(HEAD SHOT Method) 10/16/2018 SUKESH O P/ APME/JECC 33  Current is passed through the component and a circular magnetic field is established in and around the component. When the magnetizing current is stopped, a residual magnetic field will remain within the component.  The strength of the induced magnetic field is proportional to the amount of current passed through the component.

34. Using clamps or prods 10/16/2018 SUKESH O P/ APME/JECC 34  which are attached or placed in contact with the component. Electrical current flows through the component from contact to contact.  The current sets up a circular magnetic field around the path of the current.

35. Magnetization Using Indirect Induction (Indirect Magnetization) 10/16/2018 SUKESH O P/ APME/JECC 35  Indirect magnetization is accomplished by using a strong external magnetic field to establish a magnetic field within the component. As with direct magnetization, there are several ways that indirect magnetization can be accomplished.

36. Use of permanent magnets 10/16/2018 SUKESH O P/ APME/JECC 36  The use of permanent magnets is a low cost method of establishing a magnetic field. However, their use is limited due to lack of control of the field strength and the difficulty of placing and removing strong permanent magnets from the component.

37. Electromagnets(using yokes) 10/16/2018 SUKESH O P/ APME/JECC 37  Electromagnets in the form of an adjustable horseshoe magnet (called a yoke) eliminate the problems associated with permanent magnets and are used extensively in industry.  Electromagnets only exhibit a magnetic flux when electric current is flowing around the soft iron core. When the magnet is placed on the component, a magnetic field is established between the north and south poles of the magnet.

38. Central conductor magnetization 10/16/2018 SUKESH O P/ APME/JECC 38  Another way of indirectly inducting a magnetic field in a material is by using the magnetic field of a current carrying conductor. A circular magnetic field can be established in cylindrical components by using a central conductor.  Typically, one or more cylindrical components are hung from a solid copper bar running through the inside diameter. Current is passed through the copper bar and the resulting circular magnetic field establishes a magnetic field within the test components.

39. Use of coils and solenoids 10/16/2018 SUKESH O P/ APME/JECC 39  When the length of a component is several times larger than its diameter, a longitudinal magnetic field can be established in the component.  The component is placed longitudinally in the concentrated magnetic field that fills the center of a coil or solenoid. This magnetization technique is often referred to as a "coil shot".

40. Longitudinal &Circular Magnetic Fields Longitudinal 1. Permanent magnets 2. Electromagnetic yokes 3. Using a Coil(COIL SHOT) Circular 1.Clamping the component between two electrical contacts(HEAD SHOT) 2.Using clamps or prods 3.Central conductor magnetization

41. Types of Magnetizing Current 10/16/2018 SUKESH O P/ APME/JECC 41  As mentioned previously, electric current is often used to establish the magnetic field in components during magnetic particle inspection. Alternating current (AC) and direct current (DC) are the two basic types of current commonly used.

42. 1. Direct Current 10/16/2018 SUKESH O P/ APME/JECC 42 flows continuously in one direction at a constant voltage.  Direct current (DC) flows continuously in one direction at a constant voltage. A battery is the most common source of direct current.  The current is said to flow from the positive to the negative terminal, though electrons flow in the opposite direction.  DC is very desirable when inspecting for subsurface defects because DC generates a magnetic field that penetrates deeper into the material.  In ferromagnetic materials, the magnetic field produced by DC generally penetrates the entire cross-section of the component.

43. 2. Alternating Current 10/16/2018 SUKESH O P/ APME/JECC 43  Alternating current (AC) reverses in direction at a rate of 50 or 60 cycles per second. Since AC is readily available in most facilities, it is convenient to make use of it for magnetic particle inspection.  However, when AC is used to induce a magnetic field in ferromagnetic materials, the magnetic field will be limited to a thin layer at the surface of the component. This phenomenon is known as the "skin effect" and occurs because the changing magnetic field generates eddy currents in the test object.  The eddy currents produce a magnetic field that opposes the primary field, thus reducing the net magnetic flux below the surface. Therefore, it is recommended that AC be used only when the inspection is limited to surface defects.

44. 3. Rectified Alternating Current 10/16/2018 SUKESH O P/ APME/JECC 44  Clearly, the skin effect limits the use of AC since many inspection applications call for the detection of subsurface defects.  Luckily, AC can be converted to current that is very much like DC through the process of rectification. With the use of rectifiers, the reversing AC can be converted to a one directional current.

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46. Half Wave Rectified Alternating Current (HWAC) 10/16/2018 SUKESH O P/ APME/JECC 46  When single phase alternating current is passed through a rectifier, current is allowed to flow in only one direction.  The reverse half of each cycle is blocked out so that a one directional, pulsating current is produced.  The current rises from zero to a maximum and then returns to zero. No current flows during the time when the reverse cycle is blocked out.  The HWAC repeats at same rate as the unrectified current (50 or 60 Hz). Since half of the current is blocked out, the amperage is half of the unaltered AC. This type of current is often referred to as half wave DC or pulsating DC. The pulsation of the HWAC helps magnetic particle indications form by vibrating the particles and giving them added mobility where that is especially important when using dry particles. HWAC is most often used to power electromagnetic yokes.

47. Full Wave Rectified Alternating Current (FWAC) (Single Phase) 10/16/2018 SUKESH O P/ APME/JECC 47  Full wave rectification inverts the negative current to positive current rather than blocking it out. This produces a pulsating DC with no interval between the pulses. Filtering is usually performed to soften the sharp polarity switching in the rectified current.  While particle mobility is not as good as half-wave AC due to the reduction in pulsation, the depth of the subsurface magnetic field is improved.

48. Three Phase Full Wave Rectified Alternating Current 10/16/2018 SUKESH O P/ APME/JECC 48  Three phase current is often used to power industrial equipment because it has more favorable power transmission and line loading characteristics.  This type of electrical current is also highly desirable for magnetic particle testing because when it is rectified and filtered, the resulting current very closely resembles direct current.  Stationary magnetic particle equipment wired with three phase AC will usually have the ability to magnetize with AC or DC (three phase full wave rectified), providing the inspector with the advantages of each current form.

49. Equipment's used for MPI 10/16/2018 SUKESH O P/ APME/JECC 49  MPI equipment serves the following purposes, it provides  Sufficient power of right type  Suitable contact and coils  Convenient means for accomplishing proper magnetization with respect to field strength and direction.  Means of applying the magnetic particles  Well lighted space for careful examination of the part of indication.

50. 10/16/2018 SUKESH O P/ APME/JECC 50 1. Simple equipment: 1. Simple equipment: for occasional testing of small casting or machine parts for detection of surface cracks, small and easily portable equipment is most convenient.

51. Permanent Magnets 10/16/2018 SUKESH O P/ APME/JECC 51  The use of industrial magnets is not popular because they are very strong (they require significant strength to remove them from the surface, about 250 N for some magnets) and thus they are difficult and sometimes dangerous to handle. inspection in underwater environments or other areas, such as explosive environments, where electromagnets cannot be used.  However, permanent magnets are sometimes used by divers for inspection in underwater environments or other areas, such as explosive environments, where electromagnets cannot be used.  Permanent magnets can also be made small enough to fit into tight areas where electromagnets might not fit.

52. Electromagnetic Yokes 10/16/2018 SUKESH O P/ APME/JECC 52  An electromagnetic yoke is a very common piece of equipment that is used to establish a magnetic field. A switch is included in the electrical circuit so that the current and, therefore, the magnetic field can be turned on and off.  They can be powered with AC from a wall socket or by DC from a battery pack. This type of magnet generates a very strong magnetic field in a local area where the poles of the magnet touch the part being inspected.

53. 10/16/2018 SUKESH O P/ APME/JECC 53 2. Large portable equipment: it is used where higher power is required or heavier duty cycles make the small kits inadequate. One of the smallest of this series operates at 120V AC and delivers up to 700amperes, either AC or half wave DC

54. Prods 10/16/2018 SUKESH O P/ APME/JECC 54  Prods are handheld electrodes that are pressed against the surface of the component being inspected to make contact for passing electrical current (AC or DC) through the metal.  Prods are typically made from copper and have an insulated handle to help protect the operator. One of the prods has a trigger switch so that the current can be quickly and easily turned on and off. Sometimes the two prods are connected by any insulator, to facilitate one hand operation. This is referred to as a dual prod and is commonly used for weld inspections.

55. Portable Coils and Conductive Cables 10/16/2018 SUKESH O P/ APME/JECC 55  Coils and conductive cables are used to establish a longitudinal magnetic field within a component. When a preformed coil is used, the component is placed against the inside surface on the coil. Coils typically have three or five turns of a copper cable within the molded frame. A foot switch is often used to energize the coil.  Also, flexible conductive cables can be wrapped around a component to form a coil. The number of wraps is determined by the magnetizing force needed and of course, the length of the cable. Normally, the wraps are kept as close together as possible. When using a coil or cable wrapped into a coil, amperage is usually expressed in ampere-turns. Ampere-turns is the amperage shown on the amp meter times the number of turns in the coil.

56. Portable Power Supplies 10/16/2018 SUKESH O P/ APME/JECC 56  Portable power supplies are used to provide the necessary electricity to the prods, coils or cables. Power supplies are commercially available in a variety of sizes. Small power supplies generally provide up to 1,500A of half-wave DC or AC. They are small and light enough to be carried and operate on either 120V or 240V electrical service.  When more power is necessary, mobile power supplies can be used. These units come with wheels so that they can be rolled where needed. These units also operate on 120V or 240V electrical service and can provide up to 6,000A of AC or half-wave DC.

57. 10/16/2018 SUKESH O P/ APME/JECC 57 3. Stationary magnetizing equipment: A large variety of stationary, bench-type units is available, with various characteristics to fit different testing requirements. The smaller size equipment is used for small parts that can be easily transported and handled by hand. The larger ones are used for heavy parts such as long diesel engine crankshafts, where handling must be crane.

58. Stationary Equipment 10/16/2018 SUKESH O P/ APME/JECC 58  Stationary magnetic particle inspection equipment is designed for use in laboratory or production environment. The most common stationary system is the wet horizontal (bench) unit. Wet horizontal units are designed to allow for batch inspections of a variety of components. The units have head and tail stocks (similar to a lathe) with electrical contact that the part can be clamped between. A circular magnetic field is produced with direct magnetization.  Most units also have a movable coil that can be moved into place so the indirect magnetization can be used to produce a longitudinal magnetic field. Most coils have five turns and can be obtained in a variety of sizes. The wet magnetic particle solution is collected and held in a tank. A pump and hose system is used to apply the particle solution to the components being inspected. Some of the systems offer a variety of options in electrical current used for magnetizing the component (AC, half wave DC, or full wave DC). In some units, a demagnetization feature is built in, which uses the coil and decaying AC.

59. 10/16/2018 SUKESH O P/ APME/JECC 59 4. Large heavy duty DC equipment: very versatile types of heavy duty stationary equipment are those DC units designed for application of the “overall” method of magnetizing, for the inspection of very large and complicated castings. Rectified three-phase AC is delivered with current values running as high as 20,000 amperes.

60. SENSITIVITY 10/16/2018 SUKESH O P/ APME/JECC 60  MPI Methods are sensitive means of locating small and shallow surface cracks in ferromagnetic components. Many incipient fatigue cracks and fine grinding cracks having size less than 0.02mm deep and surface openings of one tenth of that or less can be located using MPI.  Detectability generally involves a relation b/w surface opening and depth.  If defects sought are usual cracks, comparatively low level of magnetic force will give sufficient build-up.

61. 10/16/2018 SUKESH O P/ APME/JECC 61  However, to find minute cracks or subsurface flaws, the flux level should be high. Theoretically, a level just below saturation would give the most sensitive results. But this is impractical owing to the non- regular shapes of the components encountered.  Sensitivity also depends on the type of current used.

62. 10/16/2018 SUKESH O P/ APME/JECC 62  Various tests have conclusively proved the following information:  AC magnetization is most effective for surface defects.  AC magnetization is not effective for subsurface defects.  DC( straight or half wave) must be used for subsurface defects.  Half wave DC gives superior penetration as compared to straight DC  Half wave DC dry method gives the greatest penetration.

63.  fast, simple and inexpensive  direct, visible indication on surface  unaffected by possible deposits, e.g. oil, grease or other metals chips, in the cracks  can be used on painted objects  results readily documented with photo or tape impression  Post-cleaning generally not necessary.  A relatively safe technique; materials generally not combustible or hazardous.  Indications can show relative size and shape of the discontinuity.  Easy to use and requires minimal amount of training. Advantages of MPI

64. Limitations of MPI  Non-ferrous materials, such as aluminum, magnesium, or most stainless steels, cannot be inspected.  Examination of large parts may require use of equipment with special power requirements.  May require removal of coating or plating to achieve desired sensitivity.  Limited subsurface discontinuity detection capabilities.  Post-demagnetization is often necessary.  Alignment between magnetic flux and indications is important.  Each part needs to be examined in two different directions.  Only small sections or small parts can be examined at one time.

65. Testing techniques 10/16/2018 SUKESH O P/ APME/JECC 65  In MPI, various methodologies for inspections are used some are:  Dry particle inspection  Wet suspension inspection  Magnetic rubber inspection  Residual and continuous magnetization technique.

66. Steps for performing dry particles inspection: 10/16/2018 SUKESH O P/ APME/JECC 66  Surface preparation  Applying the magnetizing force  Applying dry magnetic particles  Blowing off excess powder  Terminating the magnetizing force  Inspection for indications

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68. Steps for performing wet particle inspection: 10/16/2018 SUKESH O P/ APME/JECC 68  Surface preparation  Applying suspended magnetic particles  Applying the magnetizing force  Inspection for indications

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70. Residual magnetization technique 10/16/2018 SUKESH O P/ APME/JECC 70  In this technique, component to be inspected is magnetized first, then before application of magnetic particle magnetizing force is stopped. Thus indication is produced by magnetic particle attracted due to residual field of magnetized component. This technique is insensitive to components or material with high permeability and for low permeable material special care taken to ensure the sufficient strength of residual field so that indications may be produced.

71. Continuous magnetization technique 10/16/2018 SUKESH O P/ APME/JECC 71  This technique is used when great level of sensitivity is required. In this technique, component to be inspected is magnetized and magnetization is continued while the magnetic particles are applied on the surface of component.  The technique provides an advantage of strong leakage field(strong magnetic field). Thus a strong magnetic flux is produced, which forces more particles to vibrate and slide down towards the crack surface or leakage surface.  Only limitation with this method is that, it produces heat which may sometime damages the test component when direct magnetization is used.

72. TASK -3 (MODULE-3) ME367 NDT TASK -3 (MODULE-3) 10/16/2018 SUKESH O P/ APME/JECC 72  Explain about the Interpretation and indications of MPI.  Write short notes on Magnetic field indicators / Equipments 09/10/17 Submit on or before : 09/10/17 (in class note)

73. ME367 NDT 10/16/2018 SUKESH O P/ APME/JECC 73 END OF MODULE -3 Write a review…..

74. 10/16/2018 SUKESH O P/ APME/JECC 74 Quality & Process Control Magnetic rubber inspection