GB2155390A

GB2155390A - Method and apparatus for testing tube surfaces

Info

Publication number: GB2155390A
Application number: GB08406508A
Authority: GB
Inventors: George White Lewthwaite; Ivor Murray Morrison Gunn
Original assignee: UNITED KINGDOM AUTOMIC ENERGY
Current assignee: UNITED KINGDOM AUTOMIC ENERGY
Priority date: 1984-03-13
Filing date: 1984-03-13
Publication date: 1985-09-25
Also published as: GB8406508D0

Abstract

The inside surface of a tube (11) is examined by making a cast in the tube and then examining the surface of the cast. A block (13) is inserted into the tube (11) with a cutout to form a casting space into which casting material is injected through a tube (19) extending into the tube. In one arrangement (Figures 5 and 6), the casting space is defined by a former which can be moved sideways in the tube. <IMAGE>

Description

SPECIFICATION Methods and apparatus for testing tube surfaces This invention relates to methods and apparatus for testing tube surfaces, particularly the inside surfaces.

According to one aspect of the invention apparatus for obtaining a cast of the interior surface of part of a tube comprises a device for insertion into the tube to form at least a part of the boundary of a space in which said part interior surface is exposed, and a feed conduit for extending into the tube and delivering casting material to the space.

The feed conduit may be associated with a rod adapted to engage the device.

Elongate means may be connected to the device for use in removing the device from the tube.

The device may include means engageable with the surface to define the space, and means for moving the engageable means laterally into engagement with the surface. Said means for moving may comprise a lever pivoted to the device. Means may be provided for locating the device axially in the tube.

According to another aspect of the invention, a method of obtaining a cast of the interior surface of part of a tube comprises inserting into the tube a device which defines with said part interior surface at least part of the boundary of a space to which the part interior surface is exposed, and inserting casting material into the space.

The invention may be performed in various ways and two specific embodiments with possible modifications will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view of apparatus for obtaining a cast; Figure 2 is a vertical section of a boiler tube showing the apparatus of Fig 1 in use; Figure 2A is a side view of a plastics plug; Figure 2B is an end view from the left of Fig 2A; Figure 3 is a perspective view of a cast; Figure 4 illustrates assessment of cast height; Figure 5 is a cross-section on line 5-5 of Fig 6; and Figure 6 is a longitudinal section of another apparatus.

Referring to Figs 1 and 2, the apparatus 10 is used to obtain a cast of the inside surface of a tube, for example the water-side surface of a boiler tube 11 connected at one end to a tube-plate 12. In practice, the plate 12 would support a plurality of adjacent tubes 11.

The apparatus 10 comprises a plastics plug 13, for example of PTFE, which is cylindrical of circular cross-section but provided with a longitudinal flat surface 14 extending the length of the plug 13 produced by removing a segment of the cylinder, the segment subtending an angle of about 120 at the cylinder axis G as shown dotted in Fig 2B. The dimension d of Fig 2A may for example be 0.1cm.

Removal of the segment reduces the risk of the plug jamming in the tube when being removed. A tubular shroud 15 has a portion removed at one end to leave a nose portion 16 of a cross-section substantially the same as the segment removed from plug 13. A loading rod 17 extends in the shroud up to the end 18 at one end of nose 16 and projects beyond the other end of the shroud. A feed tube or conduit 19 extends though, and is movable axially in, the shroud 15 in the space not occupied by the rod 17.

A flat metal foil 20 having an area similar to face 14 and with an upturned end 21 is provided, and a segment shaped gauze 22 of the same but slightly smaller shape as the foil.

The plug 13 is a close fit when placed in tube 11.

The method of obtaining a cast is as follows.

a. Two moles 30, 31 of foamed plastics compatible with the tube wall and the casting material are pushed into the tube 11 to be inspected to a depth such that when inserted and resting on the moles the plug 13 is opposite the portion 40 of the tube wall containing a defect to be replicated.

b. The feed tube 19, which is of sufficient length to extend from a few millimeters below the top 23 of the plug to a convenient length beyond the top 24 of the tube plate 12, is filled with casting material in the form of Silicon-rubber for example that sold under the name Silcoset-105 by Ambersil Limited of Basingstoke, England laced with sufficient hardener to ensure that the mixture will set within a reasonable period, for example between 3 and 24 hours.

c. The plug 13, foil 20 and gauze 22 are pushed into position using the loading rod 17, using control cables 26, 27 to keep the components together, and controlling the orientation of the loading rod to achieve the correct, final orientation of the plug 13.

d. An additional volume of casting material is pumped (using an hypodermic syringe) into the feed tube 19 thereby displacing the same volume into the cavity 41 between the foil 20 and the inner surface 25 of the tube 11. The amount of this additional material depends on the tube dimensions but is calculated to displace just enough material to fill the cavity 41. The Silcoset 105 is sufficiently viscous to require a positive pressure to move it along the tube 19.

e. After a short interval, the feed tube 19 is withdrawn into the shroud 15 and the loading rod, shroud and feed tube are withdrawn from the boiler tube 11.

f. A small polytainer filled with a sample of the laced Silcoset 105 is lowered to rest on top of the plug 13.

g. The tube 11 is flooded with nitrogen from a suitable source and sealed.

h. After a sufficient time has elapsed (see above) the polytainer is recovered and a check made that the contents have set.

The plug 13 is removed using its control cables 26.

j. The casting, within which the wire gauze 22 is now embedded, is removed using the control cable 27 attached to the gauze.

k. The moles 30, 31 are blown by compressed air up through the tube 11 the inside surface 25 of which can then be inspected with an introscope if desired.

It may be required to take castings from up to 8m below the surface of the tube plate.

An example of a casting thus obtained is shown at 42 fig 3 including a bulge 43 corresponding to a hole on the inner surface of the tube 11. The outer surface of the bulge or projection 43 corresponds to the surface of the hole and there is substantial similarity in the morphology of the projection and the hole.

The dimension of bulge 43 may for example be Imm diameter and 305 m high. The height of the projection 43 may be determined using a travelling microscope by focussing first on the peak and then the root of the projection. The projection is viewed as shown in fig 4 for good accuracy rotation about axis C should be minimal.

In some cases the tube 11 has an inner sleeve thus reducing the cross-section of the tube bore and the arrangement of figs 5, 6 may be suitable.

The tube inner surface is shown at 60. The sleeve inner surface is shown at 61. A cassette 62 in one side has a central hollow or window 63 open at one side and a passage 64 in one end of the pe ripheral wall of the cassette window 63 receives the feed tube 19 with a push fit. The loading rod 65 is trapezium in section and fixed to a flat side 66 of the cassette, the opposite side 67 of the cassette being curved to match the surface 60. The dimension A is half the diameter of surface 60. A lever 68 is pivoted at 69 to the rod 65. When the rod and cassette and previously charged feed tube are pushed into the sleeve the lever 68 is in the position 70.When the cassette is in the desired orientation and resting on mole 31 a control cable 71 is pulled to move the lever 68 to the full line position thus moving the rod 65 and cassette 62 sideways to bring cassette surface 67 against surface 60. Fig 5 is a plan view as the cassette passes through the sleeve.

The casting material is then forced into window 63 as above and a cast obtained. Upward movement of rod 65 will move the lever 68 towards Position 70 Permitting sideways movement of the cassette and withdrawal of the apparatus, or a stiff rod can be inserted to displace the lever 68.

Thus, when the cassette is at the correct depth and resting on a previously loaded foam mole it is pushed sideways by the positioning lever operated through its control cable and brought into close contact with the tube wall. Silcoset-105 is then displaced into the cassette via the previously charged feed tube and provides a replica of that position of the tube wall exposed in the window in the cassette. After a suitable interval of time the casting machine may be removed. If the initial upward movement does not displace the positioning lever there is enough clearance between the loading rod and the sleeve to be able to use a suitable push rod.

The casting contained within the cassette may either be cut out, or the cassette may be removed from the machine and clamped to suitable inspection devices.

The casts of selected regions of the interior surfaces of tubes can be examined later at leisure.

Claims

1. Apparatus for obtaining a cast of the interior surface of part of a tube comprises a device for insertion into the tube to form at least a part of the boundary of a space in which said part interior surface is exposed, and a feed conduit for extending into the tube and delivering casting material to the space.

2. Apparatus as claimed in Claim 1 including means engageable with the surface to define the space, and means for moving the engageable means laterally into engagement with the surface.

3. Apparatus as claimed in Claim 2 in which said means for moving comprises a lever pivoted to the device.

4. Apparatus as claimed in Claim 1, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

5. A method of obtaining a cast of the interior surface of part of a tube comprises inserting into the tube a device which defines with said part interior surface at least part of the boundary of a space to which the part interior surface is exposed, and inserting casting material into the space.