WO2003076842A1

WO2003076842A1 - Apparatus and method for testing pipes

Info

Publication number: WO2003076842A1
Application number: PCT/EP2002/002789
Authority: WO
Inventors: Emil Edwin; Tore Arnesen; Håvard ØSTGAARD
Original assignee: Borealis Technology Oy
Priority date: 2002-03-13
Filing date: 2002-03-13
Publication date: 2003-09-18
Also published as: AU2002367761A1

Abstract

A method and apparatus are disclosed for making metallurgical tests of the long pipes found in the pyrolysis section of a petrochemical cracker reactor. The apparatus (1) comprises three major parts, the first being contained in a housing (3), the second being a test device and associated apparatus (4) and the third being a telescopic rod (5) interconnecting the other elements. The test device (4) comprises a shoe (6) to which are mounted standard measurement sensors (7). The shoe is mounted on a mounting head (9) which is rigidly connected to the top of a telescopic rod (5). The sections of the rod are arranged to slide in relation to each other to allow the telescopic rod (5) to extend from a length of about one metre to up to 12 metres. Within the telescopic rod (5) is provided a flexible polyethylene rod (14), the distral end (15) of which is secured to the upper end of the telescopic rod (5). The other end of the flexible rod (14) is coiled on a turntable (40). The flexible rod passes out of the rod housing (22 via outlet passage (25) and is guided via rollers (27) and guide members (28) into the telescopic rod (5). A motor (30) is used to drive the flexible rod via a toothed wheel (31). Control unit (35) controls the motor and monitors the position of the test device. Inuse, the flexible rod is extended, thereby extending the telescopic rod (5) which causes the test device to be raised up and along the surface of the pipe.

Description

APPARATUS AND METHOD FOR TESTING PIPES

The present invention relates to a method and apparatus for making tests, such as metallurgical tests, of elongate members such as the long pipes found in the pyrolysis section of a petrochemical cracker reactor.

In a petroleum cracker, large hydrocarbon molecules such as ethane and propane from natural gas, or heavier liquids such as naphtha and gas oil frorή petroleum are split into smaller molecules. This is often done to provide olefins such as ethylene that are useful in themselves, or may be used in polymerisation processes.

In the case of ethane and propane, the gas is heated to above about 800°C at which point bonds within the molecule break, producing a range of smaller molecules . The desired products are then separated out . The same principle applies when cracking heavier substances, but since the molecules are much larger, a far greater range of smaller molecules is provided. Although such processes provide a smaller yield of olefins, many other useful by-products are produced.

In a typical ethane cracker plant, the cracking takes place in a pyrolysis section. Here, ethane is pumped through a maze of 100-150mm diameter tubes located within a furnace where- it is heated up to about

800°C and cracks. The ethane never comes into direct contact with the source of heat, if it were to do so it would ignite disastrously.

Ethane is pumped through the pyrolysis section at a very high rate. The residence time of any individual molecule is a few seconds or less in older plants and less than a one tenth of a second in more modern plants . It is important that the flow rate is kept this high in order to prevent the cracking process from running away. If it were to do so, the ethane would crack not into the desired products, but into methane or even carbon (coke) and hydrogen. A further measure that is taken to control the possibility of runaway is the mixing of steam with the ethane before it is fed to the furnaces . This has two beneficial effects. The first is to lower the temperature necessary for the cracking to take place and the second is to reduce the amount of coke formed and deposited on the inside of furnace tubes .

It will be appreciated that the combination of steam, hydrocarbons and very high temperatures poses a significant safety problem. As a result, great efforts are made to design plants that are safe, and once these have been constructed they must be maintained in a safe and useful condition. In particular, it is of the greatest importance that regular checks be made of critical components in the system. As discussed above, the pipes in the pyrolysis section carry a large quantity of highly combustible chemicals that must be kept at high temperature whilst being safely isolated from the heat source of the furnace.

Having said that, modern petrochemical cracking plants are designed to produce vast quantities of product at a very high rate. The effect on the profitability of a plant of the necessary downtime when carrying out these vital safety checks is significant. There is therefore a great incentive for these checks to be carried but expeditiously.^'"

Although the pipes and the pyrolysis section are made of specialist, high-grade steel, as noted above they are operating in a very harsh environment which inevitably, over time, leads to metallurgical problems. The presence of high temperatures can lead to a bulging and creep of the pipe walls. In addition, the chemicals found within the pipe can lead to oxidation and carburisation of the pipes. Carburisation means that the carbon content of the pipe is increased by the carbon from the reaction penetrating into the tubes . This increases the brittleness of the pipe, thereby increasing the risk of failure.

There are various known types of sensor devices that may be used to detect these problems in a process called NDT measurement. The principle applied is that selected instruments are attached to a carrier or "shoe" that may be passed over the pipe surface. The shoe is connected by wires to a control unit,... such. as. a. computer, that can analyse the output data. This can be done in real time such that, if a metallurgical problem is found, the location of the problem can be identified by the corresponding position of the shoe.

There are, however, various drawbacks associated with this known approach. One is that, as previously noted, modern cracker reactors are extremely big; the pipes found in the pyrolysis section may be 12 or 14 metres in length. Since they extend vertically, this makes it difficult and to some extent dangerous to manipulate the shoe manually. As a result, so-called "climbers" may be used to carry the shoe. These are remote operating vehicles (ROVs) which may be clamped to a pipe and are then capable of driving themselves up and down using a motor which drives wheels that run against the pipe wall .

Unfortunately, however, these devices are complex, heavy and may be difficult to control . The need to clamp the ROV into position on each^" pipe can make^' the operation time consuming. Where control problems occur, it may be difficult to identify exactly where metallurgical problems are located.

According to a first aspect of invention there is provided an apparatus for testing an elongate member, the apparatus comprising a sensor unit, a driver for driving the sensor unit along the elongate member and a controller, wherein the driver provides positional data indicating the position of the sensor unit to the controller and the sensor unit provides sensing data to the controller. Thus, by means of the present invention, the controller, which may be a computer or other similar data processing device, is provided with information concerning the condition of the elongate member (which may typically be a pyrolysis pipe as previously discussed) together with data describing which part of the pipe that information. concerns . - Thus, typically, a direct correlation is provided between the distance along the pipe (for example in mm from a datum point) and the data concerning the state of the pipe . In other words, the invention may be used to provide a map of the member being tested.

Although the invention is not limited to the use of any particular testing technique, it is primarily envisaged that metallurgical testing techniques be used. At least in the context of a pyrolysis pipe, it is preferred that the sensor be arranged to measure carburisation and/or oxidation and/or creep of the pipe. It will be appreciated that there are numerous ways in which the position of the sensor unit may be determined so that its position may be relayed to the controller. The sensor unit may, for example, be mounted to an ROV of the type previously discussed which may be further provided with apparatus to determine its position and to transmit that position, either by wires or wireless techniques to the controller. For example, the ROV may use known laser technology to measure its position from a datum point at the base of the pipe. This, together with data concerning the condition of the pipe may then be transmitted over short-range radio link to the controller.

However, it is preferred that the sensor unit be mounted to an extendable member. The base of such a member may be located on the ground at the foot of the pipe such that extension of the extendable member causes the sensor or to move up the pipe. By measuring the degree to which the extendable member is extended, the position of the sensor may be determined. This combination of drive means and position determination has the advantage of being rugged and avoids the problems associated with controlling an ROV.

Although, in principle, any suitable extendable member may be used, for example a "cherry picker" arrangemen ,.., the, constraints, .of., space. •.that,-Ξapply, .JLn ...the . context of a cracker plant (or many other environments where the invention may be useful) mean that compact arrangements are highly preferable. It is therefore preferred that the extendable member is telescopic, for example in the form of a telescopic rod, e.g. in the general form of a very large radio antenna.

This arrangement is believed in itself to be independently inventive and therefore, viewed from a further aspect, the invention provides an apparatus for testing an elongate, generally upright member, the apparatus comprising a sensor unit connected to a base unit by a telescopic support, the arrangement being such that the base unit may be placed at the base of the upright member such that extension of the telescopic support moves the sensor unit along the upright member.

The extendable member may be caused to extend in any suitable manner, but it is particularly preferred for this be done by means of a flexible rod which may be extended upwards in order to' push the sensor unit 'and telescopic rod. The rod is preferably made of polyethylene and may be steel reinforced. It is most particularly preferred that the flexible rod be located within the telescopic rod. The flexible rod may have its distal end located near the upper end of the extendable member. Its proximal end may be coiled up within a housing to save space.

It is not critical how the flexible rod is driven, for example rubber rollers driven by a motor may engage the sides of the flexible rod by friction. However, it is better if a more positive means engagement be used. Thus, in a preferred form of the invention, the flexible rod is provided with engagement means such as indentations, holes, ribs, teeth or the like and the which may positively be engaged by a corresponding member driven by a motor. A particularly convenient arrangement is to have equally spaced indentations such as blind-bores..formed..i _a.-J.ine...along, .the flexible, rod. These may be engaged by the pins or teeth of a gear wheel. In this way, a particularly reliable and positive drive is provided.

A further advantage of this general arrangement is that the indentations or other engaging means provide a convenient way in which the degree of extension of the rod, and therefore the position of they sensor, may be determined. This may be achieved by means of a secondary gear wheel engaging the indentations etc.. With this arrangement, the number of rotations of the gear wheel indicates the position of the sensor.

However, it is particularly preferred that the gear wheel that drives the flexible rod also provides the positional data. This may be done by providing a separate sensing device for measuring the rotation of the gear wheel. Alternatively, the motor that drives the gear wheel may be a stepper motor or the like such that the degree of rotation of the motor is known automatically as it is operated.' Indeed, in this way- the speed of movement of the sensor device may be accurately controlled and its position known instantly.

Preferably the apparatus has a base unit that is arranged so that it may be held firmly in position, either by its own weight, by attaching it to the member that is being tested, by providing means to fasten it to the ground etc. This assists in ensuring that the sensor unit is kept in the correct position. If necessary, means- may be provided to press the telescopic member towards the upright member, for example by a spring, or to hold it in position by means of hydraulics etc, to ensure that the sensor unit maintains correct register with the upright member. In most cases it would be appropriate for means to be the provided to push the sensor against the upright member with a predetermined pressure . It may be useful to provide a magnet in association with the sensor to pull the sensor towards a •steel.---.pipe..

In many instances the reliability of the test data depends to a greater or lesser extent on the sensor unit being held firmly in position against the pipe. Although in many cases this may be satisfactory ensured by means of the previously described arrangements, it is preferred that a suitable sensing device be provided in, on, or associated with, the sensor unit so that this may be checked. A capacitance-based sensor is perhaps the most convenient use in these circumstances.

Preferably, the output from such a device is fed to the controller such that, if necessary, the drive may be stopped, an alarm sounded or some form of automatic remedial action be taken. For example, an actuator may be provided within the sensor unit to increase or decrease engagement with the pipe as desired.

The invention also extends to corresponding methods and therefore, viewed from a further aspect, the invention provides a method of testing an elongate member such as a pipe comprising the steps of providing a sensor unit, using a driver to drive the sensor unit along the member, and supplying data to a controller, wherein the driver provides positional data indicating the position of the sensor unit to the controller and the sensor unit provides sensing data to the controller.

From a still further aspect, there is provided a method of testing an elongate, generally upright member, comprising the steps of providing a sensor unit connected to a base unit by a telescopic support, placing the base unit near to a lower part of the upright member, and extending the telescopic support to move the sensor unit along the upright member.

Preferably the above-defined methods are implemented using the apparatus of one or more aspects or preferred forms of the invention as previously described.

As set forth above, the invention is particularly applicable to the maintenance-of•, petroleum cracker reactors. Thus, from a still further aspect, the invention provides a method of monitoring the condition of a petroleum cracker plant using the above-described apparatus and/or method.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings :

Figure 1 is a schematic, partly sectional side view of an apparatus according to the invention; and

Figure 2 is a schematic, partially sectional plan view of an apparatus shown in Figure 1.

The pipe testing apparatus, shown generally at 1, is illustrated in use testing a pipe 2. The apparatus comprises three major parts, the first being contained in a housing 3 , the second being a test device and associated apparatus 4 and the third being flexible rod 5 interconnecting the other elements . There is also an associated computer control unit (not shown) . The pipe 2 is^{" "}a^"portion"of a pipe found in^' a pyrolysis furnace of- a- cracker reactor.

With reference first to the test device, etc. 4, this comprises a shoe 6 to which are mounted standard NDT measurement sensors 7. In addition, however, a capacitance distance sensor 8 is also provided. This is arranged to detect the distance between a shoe 6 and pipe 2.

The shoe 6 is detachably mounted on a mounting head by means of machine screws 10. This enables the head to be removed as necessary either for maintenance purposes or to enable it to be substituted for a different shoe containing different types of sensing equipment. An electrical plug and socket arrangement 11 is provided to facilitate electrical connection between the sensors and the remainder of the apparatus via a flexible coiled cable 12.

Mounting head 9 is rigidly connected to the top of .telescopic,,rod 5. The telescopic rod .compr ses,;^., number- of tubular sections 13 arranged concentrically in the manner of a conventional radio antenna. These sections 13 are arranged to slide in relation to each other in order to allow the telescopic rod 5 to extend from a length of approximately one metre to up to 12 metres . (It will be appreciated that a reduced number of sections 13 is shown in the interests of clarity) .

Within the telescopic rod 5 is provided flexible polyethylene rod 14, the distal end 15 of which is secured to the upper end of the upper section of telescopic rod 5. Otherwise, the flexible rod is free to slide within the telescopic rod 5. The lower end of the telescopic rod 5 is rigidly fixed to the upper surface of housing 3 and is' also securely attached to further attachment points within the housing. The housing contains most of the remaining components of the apparatus and is attached to a rigid base member 24 formed of thick steel plate in order to provide ballast for¹ the apparatus. The base member is in turn mounted on four heavy-duty castors 21 which enable the apparatus to be manoeuvred into position.

Mounted on top of base 20 is rod housing 22 which, as may best be seen from Figure 2, has a generally circular interior profile apart from outlet passage 25. As be seen from Figure 2, the rod housing holds the proximal end of a flexible rod 14 which is coiled up inside it. The rod lies on a passive turntable 40 which rotates as the rod is extended. The flexible rod 14 is not otherwise connected to the rod housing 22.

As may also be seen from this figure, the upper surface of the rod is provided with a series of equally spaced blind bores 26 arranged in a line along its entire length.

The flexible rod passes out of the rod housing 22 via outlet passage 25 and is guided via guide rollers 27 and guide members 28 into telescopic rod 5 where its distal end 15. is .attached..AS.., previously described..

Between the rod housing 22 and the guide rollers and guide members there is provided a motor 30 that drives gear wheel 31. The teeth 32 of the gear wheel are in the form of pins sized to engage with blind bores 26 in flexible rod 14. The gear wheel 31 is arranged to engage the flexible rod in the manner of a rack-and- pinion such that rotation of the gear wheel 31 causes the flexible rod to move into or out of the telescopic rod 5. The motor contains a counter for determining the number of rotations of the gear wheel 31.

The motor 30 is controlled by means of a motor controller 35. This receives output from the counter via a cable 41 and controls the motor via cable 42. The ^■ motor controller 35 is connected to an external control unit, which in this case is a suitably programmed computer a (not shown), by means of control cable 36. The computer control unit is also connected via cable 36 and flexible cable 12 to the test device so that the latter provides 'data the computer.

In order to use the apparatus 1, it is firstly manoeuvered to the base of pipe 2. This is facilitated by castors 21. The apparatus is normally moved with the telescopic rod 5 set at its shortest. If necessary, the apparatus 1 can be secured to the pipe 2 by flexible belt or the like.

Once approximately in position, the position of the apparatus is finely adjusted in order to engage the shoe 6 properly in relation to the pipe 2. As previously discussed, the shoe 6 is essentially conventional and so its alignment procedure corresponds to that which would be used with a manually operated shoe .

When the test is ready to start, a signal from the computer control unit causes the motor 30 to start to turn. The gear teeth 32 of gear wheel 31 engage with the holes 26 in flexible rod 14, thereby pulling the rod out of rod housing 22 and pushing it up the inside of an telescopic-rod .5..Since .the, flexible rod is._;. fa.sjfcened,,£p the upper end of telescopic rod 5, this results in the telescopic rod 5 extending, thereby moving mounting head 9 and shoe 6 upwards . This causes the sensors 7 to move slowly along the pipe in a vertical direction and as they do so, data is sent via flexible cable 12 and cable 36 to the computer control unit.

Since the motor 30 is under control (via motor controller 35) of the control unit the position of the sensor seven at any given time is known. Thus, the computer control unit maps the sensor data to the sensor position. In a simple form, the computer can provide output which correlates sensor output to the distance travelled by the shoe. By simply marking the initial position on the pipe for use as a datum position the location of any metallurgical problem found in the pipe during the test can really be identified by measurement after the test has been completed.

In addition to the conventional sensors 7, the shoe 6""also comprises a capacitance^-' sensor 8 which detects whether the shoe is correctly aligned in relation to the pipe 2. This also provides a signal to the control unit and if it is determined that the position is incorrect (for example if a shoe is too far from pipe) , the computer control unit will cause the motor to stop and sound an alarm signal .

The telescopic rod is allowed to extend until a shoe reaches the top of a pipe 2. At this point it may be retracted quickly, the test having been completed, or it may be retracted at a slower rate to enable the test to be repeated as a check. Once the telescopic rod is fully retracted the apparatus 1 may be moved to a different location to start another test.

Claims

laims

1. An apparatus for testing an elongate member, the apparatus comprising a sensor unit, a driver for driving the sensor unit along the elongate member and a controller, wherein the driver provides positional data indicating-position of the sensor unit to the controller,- and the sensor provides sensing data to the controller.

2. An apparatus as claimed in claim 1, wherein the controller is arranged to correlate the positional data and the sensing data.

3. An apparatus as claimed in claim 1 or claim 2 . wherein the sensor unit is arranged to measure carburisation and/or oxidation and/or creep.

4. An apparatus as claimed in claim 1, 2 or 3, wherein the sensor unit is mounted on an extendable member.

5. An apparatus as claimed in claim 4, wherein the extendable member is a telescopic rod.

6. An apparatus as claimed in claim 5 , wherein a flexible rod is provided for extending the telescopic rod.

7. An apparatus as claimed in claim 6 , wherein the flexible rod is provided with indentations that engage with a gearwheel driven by a motor.

8. An apparatus as claimed in claim 7 , wherein a counter is provided to determine the number of revolutions of the motor such that the movement of the sensor may be monitored.

9. An apparatus as claimed in any of claims 1 to 7 , wherein the rod is driven by a stepper motor and the stepper motor provides an output indicating the position of the sensor unit.

10. An apparatus as claimed in any preceding claim, wherein the sensor unit comprises a means for

'determining whether the . sensor.-sis .correctly positioned in relation to the elongate member it is testing.

11. An apparatus as claimed in claim 10, wherein the sensor unit comprises a capacitance probe for determining the distance between the sensor unit and the surface of the elongate member it is testing.

12. An apparatus as claimed in claim 10 or 11, wherein the said means for determining provides input to the controller such that the driver may be controlled in response to said input .

13. An apparatus for testing an elongate generally upright member comprising a sensor unit connected to a base unit by a telescopic support, the arrangement being such that the base unit may be placed at the. base of the upright member such that extension of the telescopic support moves the sensor unit along the upright member.

14. An apparatus as claimed in claim 13, wherein the telescopic supports is arranged such that sensor unit may be pressed against a pipe with a predetermined pressure.

15. A method of testing an elongate comprising the steps of providing a sensor unit, using a driver to drive the sensor unit along the member, and supplying data to a controller, wherein the driver provides positional data indicating the position of the sensor unit to the controller and the sensor unit provides sensing data to the controller.

16. A method of testing an elongate, generally upright member, comprising the steps of providing a sensor unit connected to a base unit by a telescopic support, placing the base unit near to a lower part of the upri^ht.^ember,_...and . extending the telescopic support.,,-to. move the sensor unit along the upright member.

17. The method of claim 15 or 16 comprising the use of the apparatus of any of claims 1 to 14.