FIELD OF THE INVENTION:
The present invention relates to theMagnetic Particle Inspection (MPI) method applicable for identifying surface & sub-surface cracks in valve bodies manufactured for high pressure boilers applications. The invention is particularly related to the method of changeover of supply of high current to different portion of the valve bodies without any material handling activities. In the proposed invention the method of “Electro–Pneumatic changeover mechanism for High current port in MPI equipment” and the mode ofhigh current cables connections in the valve body are improved. By this invention the MPI inspection time gets reduced and as the manual handling is reduced the safety for the inspection person is improved.
BACKGROUND AND PRIOR ART OF THE INVENTION:
In high pressure industrial& power boilers, valves are the critical components in various process controls and safety applications. During manufacturing process the valve bodies are subjected to non-destructive testing using Magnetic particle inspection (MPI) method in order to identify the surface and subsurface cracks.
The Magnetic particle Inspection (MPI) is a process for detecting surface and slightly subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. It is classified into two categories.
Direct magnetization:In this method, the MPI test current is passed directly through the test object and the magnetic field produced is used to detect the subsurface discontinuities.
Indirect magnetization: In this method, no electric current is directly passed through the test object, but a magnetic field is applied from an outside source.

In the existing MPI equipment the fo lowing problems exists:-1) The high current cables of the MPI equipment connected to the valve body are to be changed manually by the NDT inspection personnel to different parts test body, which results to delay in testing time and also has possibilities for injuries for the inspection persons. For every inspection, 4 nos. of clamping & 4 nos. of de-clamping activities (depending upon the size & shape of valve body) have to be carried out which is tedious in nature. The corroded nature of the test bed as a result of itsexposure to corrosive chemicals over a long period of time makes the process still more difficult. 2) For completing themagnetic particle inspectionof a valve body the NDT inspection persons need to manually change the high current cable connections on the test job to many different locations depending upon the size & shape of the valve body.
To overcome the above drawbacks a method has been developed using the electro pneumatic change over mechanism builtinside the MPI equipment by which the current direction in the valve body can be selected by the NDT persons.
US9349516B2 relates tonon-contact type multidirectional magnetic particle inspection testing method butnot relevant to our specific requirement of testing of valve bodies.
OBJECTS OF THE INVENTION:
It is therefore the objective of the invention is to propose a device having Electro-Pneumatic changeover of high current port connections between the MPI test equipment and the valve bodywork piece.
The further object of the invention is to reduce the time taken for MPI testing of valve body and also to avoid the human interference during testing.

SUMMARY OF THE INVENTION:
The invention“Electro-Magnetic Changeover Mechanism for the High Current output port inthe MPI equipment” provides an efficient way for NDT inspection of High pressure valve bodies.
The power source unit for MPI equipment primarily consists of a dry type step-down transformer (TR1) (415V/20V & 160KVA). There are 5nos of pneumatic cylinders (1, 2, 3, 11& 15) installed inside the MPI equipment, which are suitably arranged to establish connections between the transformer (TR1) secondary and the output ports (7a, 7b & 7c).
The secondary of the transformer (TR1) is connected to the output ports either directly or through the full wave bridge rectifier assembly by charging or discharging the pneumatic cylinders (11 & 15). By this theMPI equipment (A) is capable of delivering either AC or FWDC current output for MPI inspection. At normal state of the cylinders 11 & 15 the FWDC current output will be connected to the output ports and when the cylinders (11 & 15) are charged the AC current output will be connected to the output ports.
The connector plate (17) connected to the piston shaft of cylinder no. 15 is connected to the copper bus bar (4). From the bus bar (4), the bunch of flexible cables (6) are made to the copper mesh plates fitted on the piston shaft of cylinders (1, 2 or 3). When any one the cylinder is charged the piston shaft of that cylinder will provide high current output to that particular output ports (7a, 7b & 7c).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 – Electrical schematic drawing of the changeover mechanism of MPI equipment Figure 2 – Elevation diagram of the connection of air cylinders with the bus bar Figure 3 – Front view schematic diagram of the connection of air cylinders with the bus bar Figure 4 – AC-DC common point change over arrangement diagram Figure 5 – AC-DC (+ve) point change over arrangement diagram

Figure 6 – High current cable connections during MPI testing of a typical valve body using the proposed method
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION:
As shown in Figure A, the newly developed apparatus and method for the Magnetic particle inspection testing of Valve body consists of;
Pneumatic cylinder (1): This is a pneumatic cylinder operated through electro-magnetic solenoid valve. A copper mesh plate is fitted at the end of piston shaft which is connected to the set of copper cables (6). When the cylinder is charged the high current from the cable (6) is fed to the output port (7a).
Pneumatic cylinder (2): This is a pneumatic cylinder operated through electro-magnetic solenoid valve. A copper mesh plate is fitted at the end of piston shaft which is connected to the set of copper cables (6). When the cylinder is charged the high current from the cable (6) is fed to the output port (7b).
Pneumatic cylinder (3): This is a pneumatic cylinder operated through electro-magnetic solenoid valve. A copper mesh plate is fitted at the end of piston shaft which is connected to the set of copper cables (6). When the cylinder is charged the high current from the cable (6) is fed to the output port (7c).
Bus bar (4): This is a copper bus bar which establishes interconnection between copper mesh plate (17) connected to the piston shaft of cylinder (15) and the set of flexible cables (6).
Insulation bush (5): This is a Teflon bush mounted on the main frame of the MPI equipment to firmly hold the high current bus bar. It also provides an insulation between the bus bar and the main frame (10) of the MPI equipment.

Flexible Current Cable set (6) : This is the rubber insulated flexible copper cable which is used for establishing connections between copper bus bar (4) and the copper mesh plate fitted on the piston shaft of pneumatic cylinders (1, 2 & 3).
Output port (7a): This is a copper plate provided for connecting the high current output cables to the MPI equipment (A). The other end of the plate is connected to a copper meshplate (9a), fitted on the insulation plate (8a).
Output port (7b): This is a copper plate provided for connecting the high current output cables to the MPI equipment (A). The other end of the plate is connected to a copper mesh plate (9b), fitted on the insulation plate (8b).
Output port (7c): This is a copper plate provided for connecting the high current output cables to the MPI equipment (A). The other end of the plate is connected to a copper mesh plate (9c), fitted on the insulation plate (8c).
Insulation plate (8a, b, c) : This is a insulation plate fitted on the equipment body and it supports the copper plates (7a, b & c).
Copper mesh (9a, b, c) : These are the copper mesh plates which are fitted to the output port copper plates (7a, b, c) and are supported by the insulation plates (8a, b, c) respectively.
Supporting Post (10): This is a metal post mounted on the equipment main frame. It supports the copper busbar (4) and it is insulated by the insulation bush(5).
Pneumatic cylinder for common point (11): This is a pneumatic cylinder, which is provides the electrical connection to the common port (com) of the MPI equipment (A). When the cylinder is in discharged state the DC common point (12) and when the cylinder is charged the AC common point (14) is connected to the flexible cable (13).

Copper Plates for DC Output (12): This is a copper plate with a mesh fitted at one end which faces the copper mesh (13) mounted on the piston shaft of pneumatic cylinder (11). It is connected to the DC common point.
Copper Mesh (13): This is a copper mesh connected to the piston shaft of pneumatic cylinder (11). The copper mesh is connected to the common port (com) of the MPI equipment (A).
Copper Plates for AC Output (14): This is a copper plate with a mesh fitted at one end which faces the copper mesh (13) mounted on the piston shaft of pneumatic cylinder (11). It is connected to the AC output of the transformer (TR1) secondary.
Pneumatic cylinder (15): This is a pneumatic cylinder, which is provides the connect the AC/DC (+ve) point to the bus bar (4). When the cylinder is in discharged state the DC +ve point (16) and when the cylinder is charged the AC common point (18) is connected to the flexible cable (17) through which it is connected to the bus bar (4).
Copper Plates for DC Output (16): This is a copper plate with a mesh fitted at one end which faces the copper mesh (17) mounted on the piston shaft of pneumatic cylinder (15). It is connected to the DC +vepoint.
Copper Mesh (17): This is a copper mesh connected to the piston shaft of pneumatic cylinder (15). The copper mesh is connected to the bus bar (4).
Copper Plates for AC Output (18): This is a copper plate with a mesh fitted at one end which faces the copper mesh (17) mounted on the piston shaft of pneumatic cylinder (15). It is connected to the AC output of the transformer (TR1) secondary.

WE CLAIM:
1. An “Electro-Pneumatic Changeover mechanism for High Current Port in Magnetic Particle Inspection Equipment” comprising:
- Pneumatic cylinder (1 to 3) operated through electro-magnetic solenoid valves which are used for selection of output ports.
- Pneumatic cylinder (11 to 15) operated through electro-magnetic solenoid valves which are used for AC/DC change over.
- Busbar (4) establishing interconnection between copper mesh plate (17) connected to the piston shaft of cylinder (15) and the set of flexible cables (6).
- Output port (7a, b, c) provided for connecting the high current output cables to the MPI equipment (A), the other end of the platesare connected to a copper mesh plate (9a, b, c), fitted on the insulation plate (8a, b, c) respectively.
- Insulation plate (8a, b, c) disposed on the equipment body to support the copper plates (7a, b & c).
- Copper mesh (9a, b, c) disposed to the output port copper plates (7a, b, c) and are supported by the insulation plates (8a, b, c).
- Pneumatic cylinder for common point (11) provides the electrical connection to the common port (com) of the MPI equipment (A).
- Pneumatic cylinder (15) provides connection AC/DC (+ve) point to the bus bar (4).

2. A method to change over mechanism, wherein
a) DC common point (12) through switching is connected to the flexible cable (13) when the cylinder (11) is in charged state
b) AC common point (14) is connected to the flexible cable (13) when the cylinder is in charged state.
3. The method as claimed in claim 2, wherein
a) DC + ve point (1b) is connected to the bus bar (4) through flexible cable (17) when the cylinder (15) is in discharged state
b) AC common point (18) is connected to the bus bar (4) through flexible cable (17), when the cylinder is in charged condition.