-FIELD OF INVENTION
This invention relates to a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall. The crawling machine travels vertically upward/downwards, horizontally, and also on slanted and overhead surface.
BACKGROUND OF INVENTION
Power utility boiler furnace is surrounded with a plurality of tubes known as waterwall tubes. These tubes are mostly vertical but in certain region, it may be slanted or horizontal. These tubes undergo erosion, corrosion and overheating, which are subjected to other damage mechanisms and need to be checked periodically, normally during overhauling of the units for detection of defects, mostly thinning of assets their condition and decide for their localized replacement to avoid forced outage of the unit. Mostly the visual and ultrasonic spot thickness measurements are carried out on the accessible or identified locations of these tubes for their condition assessment. However, the approach for condition assessment of waterwall tubes is inadequate due to following reasons:
Location of greatest loss of thickness (both axial and
circumferential position) is not accurately known. Hence, with
the spot measurement approach, there is probability of missing
the maximum thickness loss spot in the measurement.
The spot measurement does not provide any information on
cross-sectional loss of thickness.
As the measurement is generally carried out at fixed elevations,
it does not give complete information on healthiness of entire
waterwall tubes.
It does not provide adequate information on planning of the
replacement of waterwall tubes.
Reference may be made to the following citations:-
US 3690393:- A magnetic wheel having axial end faces oppositely polarized magnetically, is maintained thereby in rolling contact with a magnetic flux conducting path. The wheel when driven propels a vehicle frame along the path without reliance on traction. Rolling contact is maintained by the magnetic field established by the flux extending between the end faces through the surface of the path producing contact holding forces acting on the non-polarized rim of the wheel.
US 4789037:- A self propelled vehicle for traversing a surface of magnetic material having two or more endless tracks incorporating a plurality of permanent magnets spaced along each track to create a magnetic field of a strength to attach the vehicle to the surface being traversed. Each permanent magnet comprising a bar of magnetised ceramic magnetic material extending in a direction transverse of the track clamped between a pair of magnetic metal plates. The metal plates each extending beyond one face of the ceramic bar at opposite edges of that face to provide respective magnetic poles of opposite polarity so in use only these poles contact the surface being traversed and the ceramic bar is spaced from the surface being traversed.
US 6125955:- An improved magnetic wheel for a vehicle that moves over ferromagnetic surfaces. The vehicle includes an articulating, remotely controlled chassis that is constructed around a variable frequency motor. Drive axles extend from spring biased torsion hubs and are supported at resilient bushings at each wheel. Each wheel includes a number of adjoining annular permanent magnet pole sets. Permanent magnet disks are arrayed around the circumference of each pole set. At least one pole set is secured to a wheel hub and the others are supported from
resiliently mounted registration pins. The resiliency mounted pole sets are able to flex with encountered irregularities at the work surface as the axle tracks and independently flexes with the surface changes.
US 4828059;- A wall-crawling machine comprises a body, a plurality of guide wheels rotatably mounted on the body, at least one crawler track extending around the guide wheels, a plurality of permanent magnets disposed on an outer surface of each of the crawler tracks, and a guide device provided on the respective crawler tracks for selectively restraining or releasing the crawler track from moving relative to the body in a direction perpendicular to a plane on which the permanent magnets travel.
US 3777834;- A magnet vehicle supportedly adhered to and adapted to run over an inclined wall surface of a structural member made of a strong magnetic material such as iron and steel, characterized in that said vehicle can be altered of its direction of travel as desired on said surface.
US 6564815B2:- A mobile robot for cleaning, stripping, reconditioning or refurbishing a coating on a metal work piece has a remote controlled power module for locomotion and a working head for removing the coating. The robot is held on the metal work piece by magnets mounted on the robot but spaced from the work piece.
In order to increase the reliability of waterwall tube inspection, continuous tube scanning system is required, which can carry the sensor for different regions of the vertical tubes for detection of defects and thinning.OBJECTS OF THE INVENTION
The primary object of the present invention is to provide a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall, which can travel vertically upward and downward, horizontally, and on slanted & overhead tubes for inspection of entire boiler waterwall tubes.
Another object of the present invention is to provide a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall, which is simple in construction.
Still another object of the present invention is to provide a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall, which is efficient.
Yet another object of the present invention is to provide a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall without any magnetic direct or indirect contact with the traversing tubes.
SUMMARY OF THE INVENTION
The present invention discloses a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall, which is capable of travelling to different regions of the waterwall tubes alongiwht sensors and camera mounted on it for condition assessment of the tubes, thereby increasing area of coverage and reliability. The crawler comprising of a driving motor with plurality of clamped permanent magnets with an air gap greater than 1 mm between the tube surface and the magnet. The magnets are not in contact with the tubes.
STATEMENT OF INVENTION
According to this invention there is provided a magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall comprising of a motor with a plurality of clamped permanent magnets not in contact with said tubes.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig. 1 shows : magnetic crawler of the present invention. Fig. 2 shows: line diagram of the present invention.
DETAIL DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWING;
The present invention provides a magnetic crawler driven by means of a driving motor wherein the crawler can travel on a ferromagnetic tube surface vertically upward/downward and on slanted and overhead surface.
The crawler is provided with a plurality of clamped permanent magnets mounted in pockets made preferably of Aluminium and mild steel. An air gap of more than 1mm is maintained between the tube surface and magnetic pocket. Thus, neither the magnets nor the pockets are in contact with the tubes.The clamped magnets placed in the metallic pockets provide a magnetic attraction force between the crawler and the tubes on which the vehicle moves. Clamped magnets are positioned in suitable direction with the tube.
Further, non metallic wheels made of synthetic material are provided with the crawler wherein the wheels are curved to have maximum area of contract with the surface. The wheels are driven by the motor. Driving mechanism comprises of mechanical chain drive with a reduction gear box and with a gear ratio of more than 1.
Advantageous features
1. Thorough inspection of boiler waterwall tubes.
2. The crawling machine works without direct and indirect contact of magnetic material with the traversing surface.
3. It simplifies the process of taking the sensors/tools etc to the far reaching area of waterwall for inspection. Hence, it can reduce the requirement of scaffolding arrangement at different elevation of the boiler and in turn, reduces the waterwall tube inspection time of the boiler thereby helping in reduction of overhaul period apart from saving in scaffolding exclusively made for tube inspection.
4. Ash deposited on waterwall tubes does not affect the functioning of the system due to non magnetic contract with surface.
5. Additionally, sensors, probes and camera can be attached to this for inspection of the nearby waterwall tubes.
6. It can carry weight up to about 15 kg excluding its own weight.
7. It can move vertically upward/downward, horizontally, slanted and overhead on ferromagnetic tubes/pipes of boiler waterwall.
Applications
• It can be used for testing of magnetic tubes of boiler (like Waterwall tubes, S/H, R/H tubes)
• It can sense the defect (pits, thinning, geometrical distortion like bulging, crack, deposits or any other flaws causing inhomogeneity in magnetic field) including thickness loss along entire cross section of the tube including its ID.
• As the sensor is non contact type, it can be mounted on a crawler for continuous length inspection of the boiler waterwall tubes.
Principle of working
• Sensor is based on penetrative magnetism to sense the defect including thickness loss from entire cross section of the tube including its ID.
• It senses the distorsion in the incidental electromagnetic field due to changes in the wall of tube on account of pits, thinning or any other flaws causing inhomogeneity in magnetic field.
• Excitor coil provides the required current excitation suitable to material properties and dimension. Magnetic field due to excitor coil penetrates the entire thickness of the test component (tube).• Any distortion causes in the field by the inhomogeneity in the material on account of defect, swelling, thickness variation is sensed by the received coil in differential configuration.
• Any residual signal sensed by receiver coil is processed further and is displayed on the CRO for further analysis and interpretation.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following

WE CLAIM:
1. A magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall comprising of a motor with a plurality of clamped permanent magnets not in contact with said tubes.
2. A magnetic crawler as claimed in claim 1, wherein the magnets are positioned in the metallic pockets providing a magnetic attraction force between the crawler and tubes.
3. A magnetic crawler as claimed in claim 1 or 2, wherein the magnets are located in suitable direction with the tube.
4. A magnetic crawler as claimed in any of the preceding claims, wherein the crawler is provided with a plurality of wheels, which are curved to have maximum area of contact with the surface.
5. A magnetic crawler as claimed in any of the preceding claims, comprising of a driving mechanism having chain drive with a reduction gear box.
6. A magnetic crawler as claimed in any of the preceding claims, wherein the crawler may be attached with sensor, probe, odometer and camera for inspection of nearby waterwall tubes.
7. A magnetic crawler as claimed in any of the preceding claims, wherein the crawler can move vertically upward/downward, horizontally, slanted and overhead on ferromagnetic tubes/pipes of boiler waterwall.
8. A magnetic crawler for monitoring ferromagnetic tubes of boiler waterwall substantially as herein described with reference to the accompanying drawing.