GB2371416A

GB2371416A - Conduit inspection apparatus

Info

Publication number: GB2371416A
Application number: GB0128673A
Authority: GB
Inventors: Thomas Payne; Stuart Campbell Arrol
Original assignee: Mitsui Babcock Energy Ltd
Current assignee: Doosan Babcock Ltd
Priority date: 2000-12-02
Filing date: 2001-11-30
Publication date: 2002-07-24
Anticipated expiration: 2021-11-30
Also published as: GB0128673D0; GB0029442D0; GB2371416B

Abstract

Conduit inspection apparatus comprises an access sleeve 12 attached to an adaptor 11, a cable 13 with grooves and a leader cable 14 attached to a leading end 13a of the cable 13. The grooves extend laterally across the cable 13 and a number of sensors are placed along the cable 13. Sleeve 12 is inserted into a tail pipe 4 and air is delivered to the adaptor 11 through an inlet 24. The cable 13 is fed into the adaptor 11 and drag forces over the grooves urge cable 13 through the sleeve 12 and through either tube 6 or 7. The adaptor 11 comprises an outer portion and an adjustable inner syringed shaped portion for regulating the air flow. Cable 13 is removed by reversing the air flow and the driving fluid may also be an inert gas or water. The grooves may be in the form of ripples or fins.

Description

Cable Transport System This invention relates to a cable transport system and in particular to a method for the inspection of a conduit and to apparatus for use in said method.

It is desirable and often necessary to undertake an internal inspection of a conduit to help locate such things as cracks or other flaws. It may also be desirable to determine certain parameters, for example temperature, along the length of the conduit to establish, for example in the case of a heat exchanger, its efficiency. In all cases, a sensor or a number of sensors are usually attached to a length of cable which is pushed down the conduit. However, in the case of a coiled conduit or a conduit having a number of bends the force required to be applied to the end of the cable must rise dramatically to carry the cable around each successive bend. This is known by those skilled in the art as the "windlass effect"

which will be described more fully later. Hence, inspecting a conduit with a large number of bends using this method is not very economical due to the substantial forces required. In some cases it may not be viable to use this inspection technique because the conduit or the cable itself may not be able to withstand the forces necessary to transport the cable around all the bends.

The present invention is directed to overcoming at least some of the above mentioned problems and as such has special relevance to the internal inspection of such conduits in the form of coiled tubes, for example, heat exchangers, boilers and steam generator equipment.

According to the invention there is provided apparatus for facilitating internal access to a conduit comprising a cable member having an irregular surface passable freely along a conduit, and a pressurised fluid supply means connectable to a conduit to supply a stream of pressurised fluid to the cable member to urge the cable along a conduit.

The fluid exerts a drag force along the whole length of the cable member as opposed to simply applying a force to the end of the cable as in the prior art which creates a "windlass effect".

Preferably, the irregular surface of the cable member comprises grooves or ripples on the surface thereof.

The irregular surface of the cable member increases the drag force exerted thereon by the fluid.

Preferably, the grooves or ripples extend along the surface of the cable member in a direction generally perpendicular to a centre line of the cable member.

Preferably, the cable member has a plurality of ripples spaced at intervals along its length.

Alternatively, the irregular surface comprises circumferential fins extending perpendicularly from and radially about the cable member.

Preferably, the grooves, ripples or fins extend partially or completely about the cable member.

Preferably, the inspection apparatus further includes a leading member attachable to a leading end of the cable member.

Preferably, the leading member comprises a flexible length of cable, of plastics material for example, which is lighter in weight and shorter in length than the cable member.

Preferably, the pressurised fluid supply means comprises a partially pressurised system.

Advantageously pressure is supplied by a compressor.

Preferably, the pressurised fluid used to urge the cable along the conduit is air. Alternatively, an

inert gas may be used. Optionally, the pressurised fluid may be a liquid, for example, water.

Preferably, the pressurised fluid supply means includes an adapter having a cable inlet, a cable outlet, a channel portion located therebetween and a pressurised fluid inlet located along the channel portion and intermediate the cable inlet and cable outlet.

Preferably, the adaptor comprises an inner portion moveable within an outer portion.

Preferably, the inspection apparatus further includes an access sleeve insertable into an auxiliary conduit for easing insertion of the rippled cable into a conduit where access to a conduit is via an auxiliary conduit.

Typically, the sleeve is used in the case where access to the coiled conduit is via an auxiliary conduit of larger diameter.

Preferably, the access sleeve is of a durable material capable of withstanding the pressurised fluid, for example a braided pressure hose and which is also flexible to negotiate bends in the auxiliary conduit.

Preferably, the access sleeve is in the form of a hollow tubular member.

Preferably, the access sleeve has a bore generally equal to that of the conduit.

In another aspect of the present invention there is provided a method for facilitating internal access to a conduit comprising inserting a cable having an irregular surface into the conduit, the cable being of a size allowing it to pass freely along the conduit, and feeding a pressurised fluid to the conduit to urge the cable along the conduit.

The pressurised fluid enters the fluid inlet and exits into the conduit creating a venturi effect along the channel portion between the cable inlet and the pressurised fluid inlet urging the cable along the conduit by the drag force exerted thereon by the pressurised fluid. This effect minimises the fluid losses at a gland of the cable inlet.

Preferably, the cable member is urged along the conduit by providing drag along the whole length of the cable member.

Preferably, the method includes the steps of increasing the drag force exerted on the cable member, inducing tension in the cable member, and rotating the drum unwinding the cable member therefrom and urging it through the conduit.

Preferably, the cable member is capable of transporting a sensor. The sensor transported along the conduit is monitored and readings on an external

monitoring instrument are taken to provide a continuous trace of the condition of the conduit. Optionally, a number of sensors can be provided along the length of the rippled cable.

The readings taken may be, for example, readings relating to the temperature within the conduit or relating to the structural integrity of the conduit wall.

After readings have been taken, the cable member is removed from the conduit by reversing the direction of flow of the pressurised fluid or simply by removing the pressurised fluid supply and winding the cable member onto the drum.

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only with reference to the accompanying drawings in which : Fig. 1 is a cross sectional front view showing only partial detail of a boiler vessel and its internal tubing for inspection in accordance with the method of the present invention; Fig. 2 is a view from above and the side of a portion of the boiler vessel of Fig. 1 having a section of its side wall removed showing in more detail the internal tubing;

Fig. 3 shows an adaptor and access sleeve of the apparatus of the invention attached to the boiler vessel of Fig. 1; Fig. 4 shows progress of rippled cable in accordance with the invention through the adaptor and access sleeve of Fig. 3 and along the helical tubing of the boiler vessel; Fig. 5 is a length of the rippled cable of the apparatus of the invention clearly showing the rippled surface; Fig. 6 is a view similar to Fig. 4 with the adaptor and access sleeve removed; Fig. 7 is a view similar to Fig. 6 showing the complete superheater header and feedwater header of the boiler vessel; Fig. 8 is a cross sectional side view of the rippled cable passing through the adaptor and along a portion of helical tubing; Fig. 9 is a cross sectional view of the adaptor of Fig. 8 showing an inner syringe shaped portion able to be screwed within an outer receiving portion; Fig. 10 is a side view of the inner syringe shaped portion of the adaptor of Fig. 9;

Fig. 11 is a similar view of the adaptor of Fig.

9 showing the syringe portion fully inserted into the receiving portion; Fig. 12 shows an operator inserting the rippled cable into the coiled tubing of a boiler vessel mockup; Fig. 13 is a plot showing the relationship between the number of bends in a coiled tubing and the force necessary to transport the cable therethrough according to the invention; Fig. 14 shows the forces exerted on the whole length of the cable when transporting the cable through the coiled tubing according to the invention; Fig. 15 shows the forces exerted on a portion of the cable of Fig. 14 when the tension in the cable is increased; Fig. 16 is a plot similar to Fig. 13 showing the relationship observed in a cable transport system of the prior art, using hand force alone; Fig. 17 shows the forces exerted on a cable required to prevent the cable from slipping when wrapped on a windlass drum in the cable transport system of Fig. 16; and

Fig. 18 shows the forces exerted on a portion of the cable when the tension in the cable is increased in the cable transport system of Fig. 17.

Referring to the drawings and initially to Figs 1 to 5, there is illustrated a conduit inspection apparatus according to the present invention for inspecting a boiler vessel 1.

The boiler vessel 1 is a conventional boiler vessel of a generally cylindrical shape having a superheater header 2 at a top external end 3 of the boiler 1 and a steam tail pipe 4 extending downwardly from the header 2 and inwardly of the vessel 1. The tail pipe 4 bi-furcates at one end 5 remote from the header 2 leading to two helical tubes 6 and 7.

With the exception of Fig. 2 and to promote clarity of drawings, only the helical tube 7 is shown. Both helical tubes 6 and 7 have return pipes (not shown) attached to the ends thereof remote from the steam tail pipe 4 and terminate at a feedwater header 10.

The conduit inspection apparatus, the assemblage of which will be described below and can be seen most clearly in Figs. 3 and 4 includes an adaptor 11, an access sleeve 12 in the form of a pipe or hose being open at both ends, a rippled cable 13 and a leader cable 14 attached to a leading end 13a of the rippled cable 13.

The leader cable 14 is shorter in length, lighter and more flexible than the rippled cable 13 and is of a flexible metallic or plastics type material. These properties help the leader cable 14 and hence the rippled cable 13 to negotiate very tight bends in the tube 7, for example, the bifurcation 5.

Ripples 15 in the form of circumferential grooves extend laterally across the surface of the rippled cable 13. The rippled cable 13 also has a number of sensors (not shown) placed along its length.

The adaptor 11 generally comprises an outer cylindrical shaped receiving portion 16 and an inner syringe shaped portion 17. The outer cylindrical shaped receiving portion 16 has a generally cylindrical shaped bore 18 therein running from an open end 19 thereof to a lip 20 substantially midway along the receiving portion 16. From the lip 20, the bore 18 tapers to form a channel 21 at an end of the receiving portion 16 remote from the open end 19. The channel 21 has a cable inlet 22 and cable outlet 23.

An air inlet 24 is located in a side of the receiving portion 16, intermediate the lip 20 and the cable inlet 22.

The syringe portion 17 has a channel 25 running the length thereof having a cable inlet 26 and cable outlet 27.

The syringe portion 17 has a screw thread on a portion of its outer surface (not shown) engageable

with a corresponding screw thread (not shown) of the receiving portion 16 allowing the syringe portion 17 to be adjustable within the bore 18 between the open end 19 and the lip 20 such that the channel 25 of the syringe portion 17 lies along the same centre line x-x as the channel 21 of the receiving portion 16.

This is seen most clearly in Figs. 9 and 11.

Adjusting the position of the syringe portion 17 within the bore 18 of the receiving portion 16 controls the flow of fluid within the adaptor 11 and helical tube 7.

The conduit inspection apparatus further includes a winding drum (not shown) which is mounted on a horizontal swivelling spindle (not shown). A trailing end of the rippled cable 13 is anchored on the drum, the drum being provided, at the curved surface thereof with a continuous helical groove for locating the rippled cable 13 when it is wound onto the drum.

Before inspection, any water or fluid within the steam tail pipe 4 or helical tube 7 is first removed through the feedwater header 10 by blowing air through the steam tail pipe 4 from a compressor.

Failure to remove the water in this way could suggest a blockage within the piping of the boiler vessel 1.

In use, and after the fluid has been removed from the vessel 1, the access sleeve 12 is placed within the steam tail pipe 4. The sleeve 12 should be of a flexible type material, for example a flexible

braided hose, allowing the sleeve 12 to negotiate the bends along the tail pipe 4. A leading end 29 of the sleeve 12 when fully inserted in to the tail pipe 4 should fall short of the opening of the helical tube to be investigated. The cable outlet 23 of the adaptor 11 is attached to an opening of the sleeve 12 at a trailing end 30 thereof. An air supply line 31 delivers air to the adaptor 11 through the air inlet 24. The passage of the air through the channel 21 creates an air flow through the tail pipe 4 and tube 7. A gland (not shown) at the cable inlet 26 minimises fluid loss.

As can be clearly seen from Fig. 3, the leading end 29 of the sleeve 12 falls short of the opening of the helical tube 7 but extends beyond that of the helical tube 6, as it is intended in this embodiment to investigate helical tube 7.

This prevents the cable 13 being carried into the wrong helical tube. Alternatively, or in addition, the tube not being investigated, which in this embodiment is the helical tube 6 can simply be blocked off. This can be done by blocking the exit of the feedwater header pipe 8 (not shown) located on the feedwater header 10.

A length of the rippled cable 13 is then unwound from the drum which freely rotates on the swivelling spindle. The leader cable 14 which is attached to the leading end 13a of the rippled cable 13 is inserted into the cable inlet 26 of the syringe

portion 17. The air from the supply line 31 on passing into the channel 21 creates a secondary air flow in the channel 25 in the direction of the arrow A as shown in Fig. 9 which urges the cable 13 towards the channel 21.

The cable 13, on passing into the channel 21 of the receiving portion 16 meets the air from the supply line 31 travelling in the same direction. The natural drag force exerted by the passage of the air over the cable 13 is amplified by the ripples 15 on its surface and it is this drag force which urges the cable 13 through the sleeve 12 and helical tube 7.

The drag force exerted on the cable can be controlled by regulating the air flow in the supply line 31; the higher the air velocity through the adaptor 11 the greater the drag force transferred to the cable 13. Air flow is also regulated by adjustments of the syringe portion 17 within the bore 18 to optimise fluid flow and minimise fluid losses at the cable inlet 22.

Generally, the smaller the diameter of pipe through which the rippled cable 13 travels the greater will be the fluid velocity and hence the drag force exerted thereon by the driving fluid. As such, the inside diameter of the sleeve 12 is generally equal to that of the helical tube 7 so that the drag force exerted on the cable 13 in the helical tube 7 will be equal to that in the sleeve 12. This ensures a

smooth transition of the cable 13 from the tail pipe 4 to the helical tube 7 via the bifurcation 5.

The leader cable 14 is of a flexible material, for example flexible metallic or plastics material, and further helps smooth transition of the cable 13 from the tail pipe 4 to the helical tube 7 via the bifurcation 5.

Although the applicants do not wish to be bound by any theorem, in order to understand more clearly the present invention and the problems it seeks to overcome, a brief description of the problem known as the"windlass effect"experienced in the prior art is explained below.

THE WINDLASS EFFECT Consider a cable wrapped around a Windlass drum as shown in Fig. 17. Suppose that at one end of the cable a tension T is applied in an attempt to pull the cable around the drum and suppose that a tension T'is applied at the other end of the cable so as just to prevent the cable from slipping. The cable is then in equilibrium under the action of the applied tensions and the reaction and friction at the surface of the drum. Let the angular position at which T is applied be 9.

Consider an element of the cable as shown in Fig. 18.

Since this element is in equilibrium the net force on it must be zero.

Resolving forces tangential to the circumference:

(T+AT) Cos (AO/2) = pR + T Cos (AO/2) (1) where AO = is the angle subtended by the element AT = is the change in tension over the element R = is the frictional force on the element

R = is the normal reaction on the element p. = is the coefficient of friction

as Ae -7 0 I equation (1) becomes :

dT =) HR (2) Resolving forces normal to the circumference : T Sin (AO/2) + (T + AT) Sin (AO/2) = R (3)

as AO-4 0, equation (3) becomes :

T dO = R (4) Combining equation (2) and (4) gives : dT = T d# (5) Equation (5) is a separable differential equation which can be written as 1/T dT = d# (6) Integrating both sides of the above equation (6) we get: Ln T = go + C (7) Where C is the constant of integration.

Equation (7) can be rewritten: T = K e # (8) If we now apply the boundary condition that T = T' when 0 = 0 we get K = T', hence: T = T' e # (9) Equation (9) can be rewritten as:

T = T'erz (10) Where 9 = 27m n = number of turns As the number of turns increase the tensile force required to move the cable rises dramatically as illustrated in Fig. 16.

OVERCOMING THE WINDLASS EFFECT Alternatively, consider the analysis of a cable transport system whereby the cable is transported by drag forces distributed along the whole length of the cable by means of fluid flow, according to the invention.

Consider an element of the cable as shown in Fig. 15. Since this element is in equilibrium the net force on it must be zero.

Resolving forces tangential to the circumference: (T+AT) Cos (AO/2) + p,. R = f r AO + T Cos (AO/2) (1) where AO = the angle subtended by the element AT = is the change in tension over the element pR = is the frictional force on the element R = is the normal reaction on the element g = is the coefficient of friction r = is the helix radius f = is the drag force per unit length of cable

as AO-4 0, equation (1) becomes : dT + go = f r dO (2) Resolving forces normal to the circumference: T Sin (##/2) + (T+AT) Sin (AO/2) = R (3) as ## # 0, equation (3) becomes: T dO = R (4) Resolving equations (2) and (4) gives: dT + T d# = f r dO (5) Equation (5) is a separable differential equation and can be written as: 1/ [f r/p.-T] dT = d# (6) If we integrate both sides of equation (6) we get: - Ln [fr/ - T] = # + C (7) Where C is the constant of integration.

Equation (7) can be re-written as:

[fr/-T] = K e-PO If we now apply the boundary condition that T = 0 when 0 = 0 we get K = f r/, hence : T = f r/ [1-e'] (8) Equation (8) can be rewritten as : T = (frizz [1-e'] Where e = 21m and n = number of turns As the number of turns increases the tensile force required to move the cable tends to a constant value of fr/ as illustrated in Fig. 13. There is no exponential rise in required tensile force as the

number of turns increase, hence the-Windlass Effect" is overcome. Therefore, the force required on the end of the cable 13 to transport the rippled cable 13 through the helical tube 7 of the present invention can be

described by the equation :

F = (t--) J. l

Where ; F = Force on end of cable r = Helix radius f = Drag force per unit length of cable = Coefficient of friction n = number of coils The graph of Fig. 13 clearly shows that the critical force required to urge the cable 13 through the tube 7 is very small and that this force will generally urge the cable through a tube with a large number of bends.

Comparatively, the force required to transport a cable through the helical tube 7 by a force on the end of the cable alone is given by the following equation : F = T'exp (27B) Where :

F = Force exerted on end of cable T'= Small resistant force experienced by cable (normally estimated) n = number of coils p = co-efficient of friction The graph of Fig. 16 for a typical cable clearly shows that the force required to transport such a cable beyond the first few coils in the helical tube 7 increases greatly and continues to do so as the number of bends in the helical tube 7 increases.

If necessary once the cable 13 has been fully inserted into the helical tube 7, the adaptor 11 is disconnected from the sleeve 12 and the remaining cable pulled through the adaptor 11. The sleeve 12 is then removed from the tailpipe 4, the rippled cable 13 being left in place in the conduit. The cable 13 is then connected to monitoring equipment (not shown) where readings from the sensors of the cable 13 can be logged. This allows parameters such as temperature to be taken for each section of the helical tube 7.

Once the inspection of the tube 7 has been completed the rippled cable 13 is simply removed by reversing the air flow in the conduit.

This can be done by connecting an air supply to the feedwater pipe 8 at the feedwater header (10). The speed of removal of the cable 13 can be controlled by regulation of the air supply.

It will be appreciated that while the driving fluid in this embodiment is air, other suitable fluids may be used, for example inert gases or water.

It will be appreciated that the grooves can be of any form which make the surface of the cable irregular, for example ripples and fins.

It will also be appreciated that the jet of air used to initially clear the coiled tubes of fluid before transporting the cable 13 therethrough may be provided by the driving fluid used to transport the cable.

It will further be appreciated that the cable 13 may be connected to the monitoring equipment as it passes through the conduit allowing a single sensor attached to the cable 13 to take readings at various sections of the conduit.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail.'

Claims

CLAIMS 1. Apparatus for facilitating internal access to a conduit, comprising a cable member having an irregular surface passably freely along a conduit, and a pressurised fluid supply means adapted to be connectable to a conduit to supply a stream of pressurised fluid to the cable to urge the cable along a conduit.
2. Apparatus as claimed in Claim 1, wherein the irregular surface of the cable member comprises grooves or ripples on the surface thereof.
3. Apparatus as claimed in Claim 2, wherein the grooves or ripples extend along the surface of the cable member in a direction generally perpendicular to a centre line of the cable member.
4. Apparatus as claimed in any of Claims 1 to 3, wherein the irregular surface comprises circumferential fins extending perpendicularly from and radially about the cable member.
5. Apparatus as claimed in claim 4, wherein the grooves, ripples or fins extend partially or completely about the cable member.
6. Apparatus as claimed in any preceding claim, wherein the inspection apparatus further includes a leading member attachable to a leading end of the cable member.
7. Apparatus as claimed in Claim 6, wherein the leading member comprises a flexible length of cable which is lighter in weight and shorter in length than the cable member.
8. Apparatus as claimed in any preceding claim, wherein the pressurised fluid supply means comprises a partially pressurised system.
9. Apparatus as claimed in any preceding claim, wherein the pressurised fluid is air, an inert gas, or a liquid.
10. Apparatus as claimed in any preceding claim, wherein the pressurised fluid supply means includes an adapter having a cable inlet, a cable outlet, a channel portion located therebetween and a pressurised fluid inlet located along the channel portion and intermediate the cable inlet and cable outlet.
11. Apparatus as claimed in Claim 10, wherein the adaptor comprises an inner portion moveable within an outer portion.
12. Apparatus as claimed in any preceding claim, wherein the inspection apparatus further includes an access sleeve insertable into an auxiliary conduit for easing insertion of the rippled cable into a conduit where access to a conduit is via an auxiliary conduit.
13. Apparatus as claimed in claim 12, wherein the access sleeve is in the form of a hollow tubular member.
14. Apparatus as claimed in claim 13, wherein the access sleeve has a bore generally equal to that of the conduit.
15. Apparatus as claimed in any of claims 12 to 14, wherein the access sleeve is of a durable material.
16. Apparatus as claimed in any of claims 12 to 15, wherein the access sleeve is of a flexible material.
17. A method for facilitating internal access to a conduit comprising inserting a cable member having an irregular surface into the conduit, the cable member being of a size allowing it to pass freely along the conduit, and feeding a pressurised fluid to the conduit to urge the cable member along the conduit.
18. A method as claimed in Claim 17, comprising creating a venturi effect along the channel portion of the adaptor between the cable inlet and the pressurised fluid inlet, and urging the cable member along the conduit by the drag force exerted thereon by the pressurised fluid.
19. A method as claimed in Claim 17 or Claim 18, comprising providing drag force along the whole length of the cable member.
20. A method as claimed in any of claims 17 to 19, wherein the cable member transports a sensor or sensors.
21. A method as claimed in Claim 20, comprising transporting the sensor/sensors along the conduit and taking readings on an external monitoring instrument.
22. A method as claimed in any of Claims 17 to 21, comprising reversing the direction of flow of the pressurised fluid and removing the cable member from the conduit.
23. Apparatus for facilitating internal access to a conduit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
24. A method for facilitating internal access to a conduit substantially as hereinbefore described with reference to and as shown in the accompanying drawings.