Pig for inspecting a tubular object

Abstract

A pig 30 for inspecting a tubular object 42, comprises: a body 32; a transducer 34 including a plurality of transducer elements 38 arranged about a circumference of the body, each element operable to transmit a beam; and a controller programmed to operate the elements as one or more apertures in plural operating modes, each aperture comprising multiple transducer elements, wherein each operating mode is preprogrammed to define a number of transducer elements in the or each aperture and beam transmission timings of the elements of each aperture, each operating mode differing from each other by the number of elements and / or beam transmission timings of the elements of each aperture. The controller is programmed to dynamically modify which transducer elements are in each aperture during inspection and responsive to inspection conditions, and / or adjust beam transmission timings. The elements form an ultrasonic phased array transducer operating with synthetic apertures.

Description

The invention relates to a pig, preferably an untethered, single-bodied pig, for inspecting a tubular object. Such tubular objects may come in a variety of shapes, such as straight, bent, serpentine and meandering. Tubing systems in refining furnaces, boilers, fired heaters and other fixed industrial processing apparatuses typically have a sinusoidal path to optimise the exposure of the contents of the tubing systems to heat. Such a sinusoidal path is frequently referred to as being serpentine. Other connecting pipelines, which may be above ground, below ground or under water, can be treated in a similar way for both cleaning and testing using controlled pigs. In a typical tubing system, a product to be treated usually passes through the tubing system that has horizontally and / or vertically set tubes, and the passage of the product through the tubing system may be in a horizontal direction, a downward direction, an upward direction, or a combination thereof. Some tubing systems may include a section of closely packed tubes that may be used to, for example, raise a temperature of the product to be treated by way of convection heating. The pre-heated product may then be passed to a subsequent section of the tubing system in which there is more space between the tubes, and such tubes may be heated by way of radiant heating. Typically, in both sections, the tubing system includes straight tube sections joined by bent tube sections, which may be semi-circular (also known as U-bends) or may be box headers with sharp bends in the form of 90 degree turns, sometimes referred to as "horseshoes" and / or "mule ears". Other tubing systems may include at least one helical coiled tube or at least one arbour coiled tube. The term "pig" (or otherwise known as pipeline inspection gauge) is used to refer to devices that are passed through a pipe or tubing whether for cleaning purposes or for monitoring the condition of the pipe or tubing. Pigs may be used for aiding separation of product from the pipe or tubing, in particular identifying material build-up on interior walls of the pipe or tubing, for fluid transport separation, etc. Pigs may be used to inspect, detect and record conditions of a pipe or tubing from the inside to check the surface conditions of the interior and / or exterior of the pipe or tubing, to check for material deposits on the interior and / or exterior walls of the pipe or tubing and to check for degradation and irregularities in the pipe or tubing. This is important because, if a pipe or tubing is blocked, breached or has a compromised structural integrity during its operation, it could not only lead to costly and disruptive unscheduled downtime but also result in life threatening conditions for nearby people. In addition it is known to wrap or encase pipelines in insulation material. Carrying out inspection of such pipelines from the inside may avoid costly time and effort in removing the insulation material for the purpose of exposing the pipeline's outer surface. In order for efficient and safe operation of a tubing system, it is important that the tubing system is not only periodically cleaned and free from deposits, but also inspected to ensure the walls of the tubing system are free from undesirable deposits, tube material condition anomalies, wall thinning and / or various forms of metallurgical degradation. Inspection of a pipe or tubing may be performed to assess the need for cleaning and / or repair or to assess the effectiveness of previous cleaning and / or repair. Conventionally inspections of a pipe or tubing have been performed online through viewing windows and / or by inspecting the pipe manually during shutdown of the pipe or tubing. Monitoring of the condition of a pipe or tubing has also been conventionally carried out by radiography, precision monitoring of flow and pressure, thermal imaging, and hand-held non-destructive testing (NDT) such as ultrasonic testing (UT). However, each of these techniques is limited in its usefulness and has its disadvantages. Manual NDT can be time consuming, for example taking 6-7 days fully to inspect an entire furnace, and also requires abrasive cleaning of the outer wall of the tubing system of the furnace in order to enable successful inspection. Furthermore, a furnace would normally need internal scaffolding to enable the inspection to be carried out, thus costing considerable time. Thermal imaging usually involves searching for hotspots as an indication of contamination, but is not suitable for inspecting closely packed tubes such as seen in convection heating sections. When monitoring is carried out whilst the furnace is in operation, some areas of the tubing system may not be visible through the viewing windows. Furthermore, the far side of the tubing system is either difficult or impossible to monitor using the conventional monitoring techniques. Accordingly it may be necessary to replace one or more sections of the tubing system according to a supplier-provided lifetime warranty, which can result in not only unnecessary replacement of tube sections but also unnecessary and costly downtime of the tubing system. In subsea situations and where accessibility is prevented by normal means, use of controlled pigging can present a unique option for cleaning and material inspection. Alternatives, such as use of skilled / qualified divers or submersible remote operated equipment, can introduce additional dangers and restrictive or prohibitively high costs. It is known to provide a tethered pig with monitoring equipment and to send it through a pipe. Operation of the equipment is controlled from outside the pipe via a cable. Responses detected by the on-board monitoring equipment are transmitted back along the cable to an external monitoring unit. According to a first aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam); and a controller programmed to operate the plurality of transducer elements as one or more apertures in a plurality of operating modes, the or each aperture comprising multiple of the plurality of transducer elements, wherein each operating mode is preprogrammed to define a number of transducer elements in the or each aperture and define beam transmission timings of the transducer elements of the or each aperture, each operating mode differing from the or each other operating mode by the number of transducer elements in the or each aperture and / or the beam transmission timings of the transducer elements of the or each aperture. The operation of the plurality of transducer elements as one or more apertures in each operating mode may involve, for example, measurement of a wall thickness of the tubular object or detection / identification / measurement of a defect in or on a wall of the tubular object. The defect may be on an inner side of the wall of the tubular object, inside the wall of the tubular object, or on an outer side of the wall of the tubular object. Non-limiting examples of pipe wall defects include cracks, corrosions, delamination, debonding and pitting. The configuration of the pig according to the invention enables modification of the beam map and profile used by the pig in the inspection of the tubular object. Furthermore, by preprograming the different operating modes, the pig is pre-set for inspecting tubular objects of different sizes. In a preferred embodiment of the invention, each operating mode is preprogrammed to define the number of transducer elements in the or each aperture and define the beam transmission timings of the transducer elements of the or each aperture so as to enable a full circumferential inspection of the tubular object. This enables the pig to carry out a full circumferential inspection of tubular objects of different sizes, which is a problem faced by conventional pigs with a fixed number of transducers due to the increase in measurement gaps with increasing tubular object diameter. The controller may be programmed to dynamically modify which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object. The controller may be programmed to form the one or more apertures by stepping along the plurality of transducer elements around the body. In embodiments of the invention, the controller may be programmed to: define a first set of multiple transducer elements in the or each aperture in an aperture firing event; and define a second set of multiple transducer elements in the or each aperture in a subsequent aperture firing event; wherein the second set of multiple transducer elements includes one transducer element or some transducer elements from the first set of multiple transducer elements. In such embodiments, the number of transducer elements in the first set of multiple transducer elements may be the same as the number of transducer elements in the second set of multiple transducer elements. In other embodiments, the number of transducer elements in the first set of multiple transducer elements may be different from the number of transducer elements in the second set of multiple transducer elements. In further embodiments of the invention, the controller may be programmed to change the number of transducer elements in the or each aperture between different aperture firing events of the or each aperture. In still further embodiments of the invention, the controller may be programmed to change the number of transducer elements in the or each aperture between consecutive aperture firing events of the or each aperture. Each transducer element may be operable to receive a reflected beam signal (e.g. an acoustic beam). The controller may be programmed to operate the plurality of transducer elements as: one or more transmission apertures for transmitting a beam; and one or more receive apertures for receiving a reflected beam signal . One or more of the plurality of transducer elements may form part of both a transmission aperture and a receive aperture at the same time. The number of transducer elements in the or each transmission aperture may be different from the number of transducer elements in the or each receive aperture. In embodiments of the invention, the controller may be programmed to simultaneously activate multiple apertures. Such simultaneous activation of multiple apertures may involve simultaneous activation of multiple transmission apertures and / or multiple receive apertures. This improves the ability of the pig to carry out a full circumferential and axial inspection of the tubular object as the pig moves along the tubular object. During the inspection of the tubular object, the operation of the pig may undergo autonomous, dynamic changes in response to a change in operating state of the pig and / or the tubular object, which may be expected or unexpected. In embodiments of the invention, the controller may be programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object. This enables the pig to continue accurate inspection of the tubular object under different operating states of the pig and / or the tubular object. In embodiments of the invention, the controller may be programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to change a beam depth focus responsive to a change in operating state of the pig and / or the tubular object. This is particularly beneficial under circumstances where beam focusing at different depths is required. In embodiments of the invention, the controller may be programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to change a beam resolution responsive to a change in operating state of the pig and / or the tubular object. This is particularly beneficial under circumstances where signal scattering is caused by deterioration in inner wall quality of the tubular object as a result of, for example, residue build-up, corrosion and / or pitting. In embodiments of the invention, the controller may be programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to apply a time-corrected gain to a reflected beam signal responsive to a change in operating state of the pig and / or the tubular object. Dynamic application of the time-corrected gain increases the reliability of the pig by ensuring that all reflected beam signals will have sufficient amplitude to be properly measured by the pig. The change in operating state of the pig and / or the tubular object may be detected based on measurements taken by the pig. For example, the change in operating state of the pig and / or the tubular object may be detected if the measurements are determined to be outside the normal measurement processing range of the pig. One or more additional sensors may be employed to detect the change in operating state of the pig and / or the tubular object. In embodiments of the invention, the change in operating state of the pig may include an incorrect position and / or orientation of the pig inside the tubular object. For example, the change in operating state of the pig may be due to the pig no longer being concentric with the tubular object. In further embodiments, the change in operating state may include a change in geometry of the tubular object. The change in geometry of the tubular object may include, but is not limited to,: a change in schedule (i.e. wall thickness) of the tubular object; a change in diameter of the tubular object; a change in internal radius of the tubular object; a change in internal radius of the tubular object due to a build-up of material (e.g. residue) on the tubular object; a change in form factor of the tubular object; and / or a change in internal surface roughness of the tubular object. In still further embodiments of the invention, the controller may be programmed to operate the plurality of transducer elements to vary a bandwidth, a pulse duration, a pulserepetition frequency and / or a frequency of the beam. This facilitates optimisation of the pig's inspection operation depending on the condition and / or size of the tubular object for improved inspection reliability and accuracy. Preferably each of the plurality of transducer elements is an acoustic transducer element. Each of the plurality of transducer elements may be an ultrasonic transducer element and / or a piezoelectric transducer element. It is envisaged that other types of transducer elements may be used, such as electromagnetic, laser or radio transducer elements. The plurality of transducer elements may be arranged in a same row about a circumference of the body. It will be appreciated that the invention may comprise a single row of transducer elements or multiple rows of transducer elements about the circumference of the body. The plurality of transducer elements may include multiple transducer elements arranged on a curved surface of the body to form a curved array of transducer elements (e.g. multiple transducer elements forming a ring about the circumference of the body), or may include multiple transducer elements arranged on a flat surface of the body to form a flat array of transducer elements (e.g. multiple transducer elements forming a hexagon or other polygon about the circumference of the body). The pig is preferably an untethered and / or single-bodied pig. The pig preferably has a unitary body. The configuration of the pig according to the invention enables a more compact arrangement of the transducer elements and a more compact size of the pig without sacrificing the inspection capabilities of the pig. This in turn enables the pig to be used across a wider range of shapes and sizes of tubular objects. It will be appreciated that the pig may be tethered, multi-bodied and / or has a nonun itary body. According to a second aspect of the invention, there is provided a method of operating a pig for inspecting a tubular object, the pig comprising: a body; and a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam), wherein the method includes the steps of: operating the plurality of transducer elements as one or more apertures in a plurality of operating modes, the or each aperture comprising multiple of the plurality of transducer elements, wherein each operating mode defines a number of transducer elements in the or each aperture and defines beam transmission timings of the transducer elements of the or each aperture, each operating mode differing from the or each other operating mode by the number of transducer elements in the or each aperture and / or the beam transmission timings of the transducer elements of the or each aperture. The features and advantages of the first aspect of the invention and its embodiments apply mutatis mutandis to the features and advantages of the second aspect of the invention and its embodiments. The method of the invention may include the steps of: operating the plurality of transducer elements as one or more apertures in one of the plurality of operating modes to inspect a tubular object with a first diameter; and operating the plurality of transducer elements as one or more apertures in another of the plurality of operating modes to inspect another tubular object with a second diameter, the first and second diameters being different from each other. The method may include the step of dynamically adjusting a number of transducer elements in the or each aperture and / or adjusting beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object. The following paragraphs describe further aspects of the invention. According to a third aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam; and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to dynamically modify which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object. According to a fourth aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducers arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam); and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to form the one or more apertures by stepping along the plurality of transducer elements around the body. According to a fifth aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam); and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to: define a first set of multiple transducer elements in the or each aperture in an aperture firing event; and define a second set of multiple transducer elements in the or each aperture in a subsequent aperture firing event; wherein the second set of multiple transducer elements includes one transducer element or some transducer elements from the first set of multiple transducer elements. The number of transducer elements in the first set of multiple transducer elements may be the same as the number of transducer elements in the second set of multiple transducer elements. Alternatively the number of transducer elements in the first set of multiple transducers may be different from the number of transducer elements in the second set of multiple transducer elements. According to a sixth aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam); and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to change the number of transducer elements in the or each aperture between different aperture firing events of the or each aperture. According to a seventh aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam (e.g. an acoustic beam); and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to change the number of transducer elements in the or each aperture between consecutive aperture firing events of the or each aperture. According to an eighth aspect of the invention, there is provided a pig for inspecting a tubular object, the pig comprising: a body; a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam; and a controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object. According to a ninth aspect of the invention, there is provided a method of operating a pig for inspecting a tubular object, the pig comprising: a body; and a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam, wherein the method includes the step of: operating the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements; and dynamically modifying which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object. According to a tenth aspect of the invention, there is provided a method of operating a pig for inspecting a tubular object, the pig comprising: a body; and a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam, wherein the method includes the step of: operating the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements; and dynamically adjusting a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object. The features and advantages of the first and second aspects of the invention and their embodiments apply mutatis mutandis to the features and advantages of each of the third to tenth aspects of the invention and their embodiments. That is to say, each of the embodiments of the first and second aspects of the invention is combinable with each of the third to tenth aspects of the invention and their embodiments. It will be appreciated that two or more of the third to tenth aspects of the invention may be combined as a single embodiment. It will be appreciated that the use of the terms "first" and "second", and the like, in this patent specification is merely intended to help distinguish between similar features, and is not intended to indicate the relative importance of one feature over another feature, unless otherwise specified. Within the scope of this patent application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and the claims and / or the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and all features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which: Figure 1 shows a pig according to an embodiment of the invention; Figures 2 and 3 shows a transducer ring of the pig of Figure 1; Figure 4 shows a close-up of the transducer elements mounted on the transducer ring of Figures 2 and 3; Figure 5 shows an aperture comprising multiple transducer elements; Figure 6 compares ultrasonic beams respectively generated by a linear array of transducer elements and a convex array of transducer elements; Figure 7 illustrates radial offsets between outer transducer elements and inner transducer elements of a convex array of transducer elements; Figure 8a to 8c show the beam map and profile of the ultrasonic beam generated by a convex array of transducer elements, without any time delay laws applied; Figures 9a to 9c show the beam map and profile of the ultrasonic beam generated by a convex array of transducer elements, with time delay laws applied; Figure 10 shows results of CIVA simulations; and Figures 11 and 12 show examples of sequences of firing events for an array of transducer elements. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interests of clarity and conciseness. A pig for inspecting a tubular object is shown in Figure 1 and is designated generally by the reference numeral 30. The pig 30 comprises a body 32 that comprises an intermediate portion 34 arranged between two end portions 36 so that the intermediate portion 34 and the end portions 36 are co-axially aligned along the length of the pig 30. The cross-section of each of the intermediate portion 34 and end portions 36 is substantially circular but may vary in shape in other embodiments. The intermediate portion 34 is in the form of a transducer ring onto which a transducer comprising a plurality of transducer elements 38 is mounted, as shown in Figures 2 to 4. The transducer elements 38 are arranged in a single row about the entire circumference of the body 32 at a predetermined pitch Y and diameter. Preferably the transducer elements 38 have the same length X and the same width Z. The transducer elements 38 are encapsulated by an epoxy resin (not shown), which not only mechanically holds the transducer elements 38 in place but also acts as a matching layer. The intermediate and end portions 34,36 together define a single body 32 of the pig 30, i.e. a single-bodied pig 30. Each end portion 36 may be covered by a respective end cap on which an alignment implement is mounted. The alignment implements are configured to, in use, engage an interior wall of the tubular object so as to align the pig 30 relative to the tubular object. Each alignment implement may comprise a plurality of radially extending resilient brushes or a resilient flange. In the embodiment shown, the plurality of transducer elements 38 is a plurality of ultrasonic transducer elements that are operable to both transmit and receive an ultrasonic signal (or signals). Each transducer element 38 includes a piezocomposite crystal, which functions as a transmitter to convert an electrical signal supplied by an electronic component into a transmitted ultrasonic signal. The transmitted ultrasonic signal is transmitted towards the wall of the tubular object and is then reflected off an internal or external surface of the wall of the tubular object, or off material build-up on an interior or exterior wall of the tubular object, back towards the piezocomposite crystal. In this way, the piezocomposite crystal is able to receive a first reflected ultrasonic signal from the internal wall surface of the tubular object, and also receive a second reflected ultrasonic signal from the external wall surface of the tubular object. The piezocomposite crystal then functions as a sensor that converts the received (reflected) ultrasonic signal(s) into an electrical signal (or electrical signals) for analysis. In other embodiments, the plurality of transducer elements may be a plurality of transducer elements configured to transmit other types of acoustic signals or electromagnetic radiation signals. For example, each transmitter may be a laser or radio transmitter. It will also be appreciated that, in other embodiments of the invention, each transducer element may include a transmitter and receiver that are separate from each other. Each of the intermediate and end portions 34,36 defines a bore therein along its length. A bore of each end portion 36 is connected to a respective end of a bore of the intermediate portion 34 so that the bores of the end portions 36 combine with the bore of the intermediate portion 34 to define an overall bore of the pig 30. The pig 30 includes a controller 40 and a power supply device (e.g. a battery) that is stored inside the bore of the pig. The controller 40 is shown schematically in Figure 2. The controller 40 may be, for example, a computer or a processor. The pig 30 further includes a printed circuit board that is stored inside the bore of the pig 30. The controller 40 and the power supply device are preferably mounted onto the printed circuit board. Flexible electrical connections (e.g. electrical wires) are used to connect the transducer elements 38 to the printed circuit board. This is so that the controller 30 can send control signals for operating the transducer elements 38 and receive information collected by the transducer elements 38. The pig 30 preferably comprises a storage media device, such as a memory card, configured to store the information collected by the plurality of transducer elements 38. The storage media device is preferably stored inside the bore. The following operation of the pig 30 is described with reference to inspection of a pipe 42 but it will be appreciated that the pig 30 may be used to inspect other types of tubular objects. The pig 30 of the invention is designed to provide a full circumferential inspection (i.e. 100% wall coverage) across a range of pipe diameters and improved reliability. The full circumferential inspection may be performed to, for example, measure a wall thickness of the pipe 42 or detect / identify / measure a defect in or on a wall of the pipe 42. The defect may be on an inner side of the wall of the pipe 42, inside the wall of the pipe 42, or on an outer side of the wall of the pipe 42. Non-limiting examples of pipe wall defects include cracks, corrosions and pitting. In this case 100% wall coverage refers to the circumference of the pipe 42, specifically an ultrasonic beam transmitted by the transducer elements 38 interacting with 100% of the pipe's outer diameter (OD) circumference, i.e., no gaps between measurement spots. Wall coverage is calculated using the following formula: nTx x BW Wall Coverage % = --------------------x 100, Pipe OD Circumference where, nTx is the number of transducer elements 38 and BW is the ultrasonic beam width. The main challenge with achieving 100% wall coverage is due to the pipe's OD circumference being far greater than the pig's circumference on which the transducer elements 38 are mounted. Conventionally intelligent pigs use single transducers that transmit and receive the ultrasonic signal, which required a significant circumferential overlap between transducers. This resulted in challenges of packaging the required number of transducers into the pig whilst maintaining a suitable size to navigate through complex pipe network geometries, such as pipe bends and meanders. In the invention, the controller 40 is programmed to operate the plurality of transducer elements 38 as multiple apertures 44 (also referred to as synthetic apertures), with each aperture 44 comprising multiple transducer elements 38. This allows each aperture 44 to function as a phased array ultrasonic transducer so that the shape and size of the ultrasonic beam transmitted by each aperture 44 can be controlled. For example, the ultrasonic beam transmitted by each aperture 44 can be focused or steered. Such control over the shape of the ultrasonic beam is achieved through application of different time delay laws applied by the controller 40 to each individual transducer element 38. A time delay law is the timing difference applied to each individual transducer element 38 to control its beam transmission timing. Furthermore, the number of the transducer elements 38 in a given aperture 44 can be varied so as to change an aperture size of the aperture 44 and thereby change the shape, size and intensity of the transmitted ultrasonic beam. The ability to vary the aperture size and apply time delay laws to the transducer elements 38 within the aperture 44 allows for greater control over the ultrasonic beam generated by the aperture 44. This flexibility ensures that the desired performance of the pig 30 can be met. To achieve the desired performance, the parameters of the aperture 44 (aperture length L, transducer element width W, gap between transducer elements G and total number of transducer elements in the aperture) need to be optimised. A schematic showing these parameters can be seen in Figure 5. Values for the parameters were defined through simulations and modelling as well as manufacturing limitations. The transducer ring's diameter constrains the pitch between consecutive transducer elements 38 depending on the number of transducer elements 38 used in the pig 30. In a first non-limiting example, for a transducer ring diameter of 56 mm, the pitch between consecutive transducer elements 38 would be 1.37mm if 128 transducer elements were used. In a second non-limiting example, for a transducer ring diameter of 56 mm, the pitch between consecutive transducer elements 38 would be 0.69mm if 256 transducer elements were used. The inventors performed Huygen modelling to determine the required transducer element widths and the likelihood of focussing being achieved with an aperture based on a convex array of transducer elements with a 28mm radius. These models showed that focussing could be achieved using a 1.37mm pitch. The convex array of the transducer elements means that the range of beam steering and the level beam focussing achievable by the aperture will not be as good as a linear array of transducer elements. Figure 6 compares (A) the ultrasonic beam generated by four transducer elements in a linear array and (B) the ultrasonic beam generated by four transducer elements in a convex array with a 28mm radius. Time delay laws were not applied to either array. It can be seen from Figure 6 that the linear array of transducer elements formed a centralised beam while the convex array of transducer elements did not form a centralised beam. The convex array of transducer elements can be operated by applying time delay laws to the transducer elements. In this particular case, the time delay laws are calculated based on the radial offsets for the two outer transducer elements compared to the two inner transducer elements (indicated by the vertical lines in Figure 7). This is to compensate for different path lengths travelled by signals from the outer transducer elements and by signals from the inner transducer elements due to the curvature of the transducer ring. Figures 8a, 8b and 8c respectively show the beam map and profile of the ultrasonic beam generated by three, four and five transducer elements of a convex array with a 28mm radius (transducer element width = 1.25mm, pitch = 1.37mm), without any time delay laws applied. Figures 9a, 9b and 9c respectively show the beam map and profile of the ultrasonic beam generated by three, four and five transducer element s of a convex array with a 28mm radius (transducer element width = 1.25mm, pitch = 1.37mm), with time delay laws applied. In Figure 8b, the simultaneous firing of the four transducer elements results in no centralised beam but instead results in a beam map in which predominantly destructive interference is occurring. In Figures 8a and 8c, a small localised centralised beam is present due to one of the transducer elements being centrally positioned as a result of the odd number of transducer elements within the aperture. However, the localised centralised beams in Figures 8a and 8c are much smaller than the centralised bream generated by the linear array of transducer elements shown in Figure 6(A). On the other hand the application of time delay laws to the convex array of three, four and five transducer elements effectively removes the radial offsets between the transducer elements and thereby removes or minimises the destructive interference. This enables the convex array of transducer elements to generate an ultrasonic beam with a beam map and profile that is similar to that of the ultrasonic beam generated by the linear array of transducer elements, as shown in Figures 9a, 9b and 9c. Accordingly, through use of phased array transducing, an aperture based on a convex array of transducer elements is capable of generating a uniform centralised ultrasonic beam capable of performing pipe inspection. The three beam profiles presented in Figures 9a, 9b and 9c represent each beam profile at the water-wall interface of the three pipe diameters (namely 4, 5 and 6 inches). The profiles show how the side lobes of the beam signal are most significant for the 4-inch pipe. This is due to the shorter water path causing near-field interference to be present. The beam profiles also show how the peak amplitude of the beam signal remains relatively consistent across the different pipe sizes. Following on from the Huygens modelling, semi-analytical simulations were performed by the inventors using CIVA software. The aim of the CIVA simulations were to validate the beam profiles obtained through the Huygens simulations and to understand the different beam widths that could be obtained by applying the time delay laws. Overall, the CIVA simulations provided additional confidence in the performance of the convex array of transducer elements by showing good agreement with the Huygens modelling. Figure 10 shows (A) the beam map, (B) the inline beam profile, (C) the normal beam profile and (D) the simulation setup of the CIVA simulations. The simulations also showed that variable beam widths could be achieved by varying the time delay laws applied. Exemplary array parameters were determined by modelling and simulations along with the manufacturing constraints: • Pitch = 1.37 mm • Transducer element width = 1.22 mm • Gap between transducer element s = 0.15 mm • Transducer element length = 6 mm. • Number of transducer elements in pig = 128 • Transducer ring diameter = 56 mm Using these parameters, initial approximations of the wall coverage can be generated. Conventionally wall coverage calculations were performed using the transducer diameter as the beam width. This is not a true representation of the beam width, as it does not consider natural focussing of beam spread that occurs to the signal as it propagates. However, as this is a conventional, it has been used to show approximate wall coverage values for the pig 30 of the invention compared to conventional pigs that do not use phased array transducing, across different pipe diameters. The pig size remains unchanged across the different pipe diameters. Pipe Diameter (inches) Wall Coverages (%) Conventional Example 1 Conventional Example 1 Invention 4 26.7 53.5 190.0 5 21.6 43.3 153.7 6 36.3 72.6 129.0 The pig 30 of the invention achieved over 100% wall coverage for all pipe diameters. Any value above 100% wall coverage is due to overlapping beam coverage. In contrast, the conventional pigs were unable to achieve 100% wall coverage for any of the pipe diameters. As a result, conventional pigs of different sizes would be required to inspect the pipe diameters, and multiple runs would be required to achieve the 100% wall coverage. The 100% wall coverage achieved by the pig 30 of the invention is due to the operation of the apertures to carry out phased array transducing. The true measure of wall coverage is achieved through the actual beam width of the ultrasonic signal, and not the size of the transducer element 38. Since the beam width can be focused or defocused depending on the time delay laws and aperture size used, the beam profile can be optimised for the pipe diameter that is being inspected. As shown and discussed, the size of the beam generated is dependent on the defined number of transducer elements 38 in each aperture 44 and on the applied time delays laws to define the beam transmission timings of the transducer elements 38 in each aperture 44. Therefore, to achieve the desired 100% wall coverage, the aperture size and time delay laws will be set so that the beam width is greater than the required beam width, BWReq, for 100% wall coverage, given by: Pipe OD Circumference BWRea = —---------------. Req nTx Using this equation, the BWReq for the different pipe diameters and 128 transducer elements are: • 4" pipe diameter = 2.8 mm • 5" pipe diameter = 3.5 mm • 6" pipe diameter = 4.1 mm The phased array transducing design of the pig 30 of the invention can therefore meet the required aim of 100% wall coverage across the range of pipe diameters. A given array of transducer elements 38 may form part of both a transmission aperture 44 (for transmitting an ultrasonic beam) and a receive aperture 44 (for receiving a reflected ultrasonic beam signal). The array of transducer elements 38 may be configured so that the transmission aperture 44 consists of one number of transducer elements 38 while the receive aperture 44 consists of a different number of transducer elements 38. This is because the required aperture sizes for transmitting and receiving ultrasonic signals may be different. The following exemplary operation of the pig 30 is described with reference to a four-transducer element transmission aperture and a two-transducer element receive aperture but it will be appreciated that other sizes of transmission and receive apertures can be used. Figures 11a to 11c show a sequence of firing events for an array of transducer elements 38. Figure Ila shows a first firing event in which four consecutive transducer elements (transducer elements 1, 2, 3, 4) are simultaneously fired as a four-transducer element transmission aperture 44a. The transmitted ultrasonic beams from the four transducer elements combine to form a composite ultrasonic beam. Figure 11b shows a second firing event in which four consecutive transducer elements (transducer elements 2, 3, 4, 5) are simultaneously fired as a four-transducer element transmission aperture 44b. The second firing event takes place after the first firing event and uses three of the four transducer elements (transducer elements 2, 3, 4) of the first firing event in combination with the next transducer element (transducer element 5) in the array. The other transducer element (transducer element 1) of the first firing event is deactivated. Figure 11c shows a third firing event in which four consecutive transducer elements (transducer elements 3, 4, 5, 6) are simultaneously fired as a four-transducer element transmission aperture 44c. The third firing event takes place after the second firing event and uses three of the four transducer elements (transducer elements 3, 4, 5) of the second firing event in combination with the next transducer element (transducer element 6) in the array. The other transducer element (transducer element 2) of the second firing event is deactivated. The sequence of firing events continues by moving along the array of transducer elements while maintaining the aperture size. Figure 12 shows a sequence of firing events for one-quarter of the 128 transducer element s when a four-transducer element aperture is used. In each firing event, a total of 8 active transducer elements will be used, with four consecutive transducer elements forming a transmission aperture and another four consecutive transducer elements forming another transmission aperture. The two transmission apertures are spaced apart from each other. Figure 12 also shows that the inner transducer elements of the transmission apertures are also used to form receive apertures. In each firing event of the sequence, new transmission and receive apertures are formed, similarly to the sequence of firing events described with reference to Figures 11a to 11c. The sequence of firing events in Figure 12 applies mutatis mutandis to the other three-quarters of the 128 transducer elements. The simultaneous activation of multiple apertures 44 improves the ability of the pig 30 to carry out a full circumferential and axial inspection of the pipe 42 (as the pig 30 moves along the distance of the pipe 42). The extent of the axial wall coverage is dependent on the firing rate of the transducer elements 38 in relation to the speed of the pig 30 travelling through the pipe 42. The same pig 30 may be used to inspect different pipes with different diameters but using different aperture sizes and / or different time delay laws. For example, a three-transducer element aperture may be used for a smaller pipe diameter while a five-transducer element aperture may be used for a larger pipe diameter. The controller 40 of the pig 30 is programmed to operate the transducer elements 38 in a plurality of operating modes. Each operating mode is preprogrammed to define a number of transducer elements 38 in each aperture 44 and define beam transmission timings of the transducer elements 38 of each aperture 44. Each operating mode differs from the or each other operating mode by the number of transducer elements 38 in each aperture 44 and the beam transmission timings of the transducer elements 38 of each aperture 44. This allows the beam map and profile of the ultrasonic beam for each operating mode to be optimised for the pipe 42 to be inspected. For example, as the pipe diameter decreases, the beam width can be reduced to increase beam resolution while simultaneously optimising overlapping beam coverage in the full circumferential inspection of the tubular object. This is because a wall coverage excessively exceeding 100% indicates that the beam width is too large, which means that the inspection is not being performed at an optimum resolution. Preprograming the different operating modes enables the pig 30 to be pre-set for inspecting pipes of different diameters. This is in contrast to using the same operating mode of the pig 30 for inspecting pipes of different diameters, which results in a less than optimal inspection for some of the pipes. The provision of the various preprogrammed operating modes removes the need to use multiple pigs to inspect different pipes. During the inspection of the pipe 42 by the pig 30, the operation of the pig 30 may undergo autonomous, dynamic changes in response to a change in operating state of the pig 30 and / or the pipe 42, which may be expected or unexpected. These autonomous, dynamic changes may be performed by programming the controller 40 to dynamically adjust a number of transducer elements 38 in each aperture 44 and / or adjust beam transmission timings of the transducer elements 38 of each aperture 44 responsive to a change in operating state of the pig 38 and / or the pipe 42. Nonlimiting examples of such autonomous, dynamic changes are described as follows. In a first example, the time delay laws applied to the transducer elements 38 within an aperture 44 may be dynamically tuned based on an internal radius of the pipe 42. Internal radius measurements performed by the pig 30 use the first reflected ultrasonic beam signal received from the water-wall interface. If these measurements are outside of the normal measurement processing range of the pig 30, the controller 40 adjusts the time delay laws to ensure that the most suitable and effective time delay laws are used based on the calculated internal radius. The preference is to maintain 100% wall coverage while ensuring that the beam width is not too small or too large when changes to the pipe's geometry occur. This is beneficial for pipe inspections in which a change of pipe schedule or diameter occurs, or when there is a significant level of residue (coke or scale etc.) left on the internal wall of the pipe 42, restricting the overall diameter. In a second example, the beam width may be dynamically adjusted to account for variations in internal surface roughness or surface finish of the pipe 42, which may arise due to build-up of residue on the internal wall or corrosion and defect formation. Such adjustment of the beam width changes the beam resolution to account for these variations. For example, corrosion and pitting results in a rougher surface, which results in the ultrasonic beam signal being scattered. To limit the amount of scattering and inspect the rough surface with greater accuracy, the beam width can be reduced, thereby focusing the ultrasonic beam and enabling a higher resolution inspection. The need to transition between the standard resolution inspection and the higher resolution inspection may be determined by an amplitude scan performed by the pig 30. If low amplitude internal wall reflections are obtained and wall thickness measurements are not able to be calculated, then the higher resolution inspection (with a smaller beam spot size) will be activated. For example, the standard resolution inspection may involve a coarse measurement density with a large spot size, while the higher resolution inspection by the pig 30 may involve a smaller spot size that focuses on regions of poor results, i.e. where wall thickness measurements were not able to be calculated. For example, the apertures 44 may be operated to perform an inspection of the pipe 42 in an initial sweep of the circumference of the pipe 42. In the initial sweep, beam measurements are spread evenly across the circumference of the pipe 42 to obtain uniform beam resolution, and an even beam spot size is used for inspecting the entire circumference of the pipe 42. The beam spot size can be increased or decreased by adjusting the number of transducer elements 42 in each aperture 44 and / or the time delay laws. Increasing the beam spot size permits the beam measurements to be spread further apart from each other to cover the circumference of the pipe 42. On the other hand, decreasing the beam spot size enables finer measurement to be carried out. Therefore, if an area of concern (e.g. damage, material build-up, defect) is identified in the initial sweep, additional beam measurements may be performed by using a smaller beam spot size in the area of concern. In this way the beam resolution is dynamically adapted by the controller 40 in response to a change in operating state of the pipe 42, which permits more optimised measurement. In a third example, the controller 40 may be programmed to dynamically adjust a number of transducer elements 38 in each aperture 44 and / or adjust beam transmission timings of the transducer elements 38 of each aperture 44 so as to apply a time-corrected gain to a reflected ultrasonic beam signal responsive to a change in operating state of the pig 30 and / or the pipe 42. For larger diameter pipes where the water path is greater, the signal that reaches the pipe wall has low ultrasonic energy in comparison to the smaller diameter pipes with shorter water paths. Therefore, as compensation, a time variable gain is applied. This is a gain that increases with time accounting for the natural decay in ultrasonic signals, caused by attenuation. Different time-corrected gain profiles are required for different water paths. The implementation of a different time variable gain profile compared to the pre-set profile will depend on the signal amplitudes and the internal radius measurements. If the signal amplitudes are too low and the internal radius reading is greater than expected, a new time variable gain profile can be introduced and used to process the results. This will provide greater reliability by ensuring that all reflections have sufficient amplitude to be processed accurately. In a fourth example, the controller 40 may be programmed to dynamically adjust a number of transducer elements 38 in each aperture 44 and / or adjust beam transmission timings of the transducer elements 38 of each aperture 44 so as to change a beam depth focus responsive to a change in operating state of the pig 30 and / or the pipe 42. This is particularly beneficial under circumstances where beam focusing at different depths is required in order to accurately inspect the condition of the pipe 42. The use of autonomous, dynamic changes to the operation of the pig 30 increases its performance by counteracting changes in the operating state of the pig 30 and pipe 42 that might adversely affect the reliability and accuracy of the inspection results. Optionally the controller 40 may be programmed to dynamically adjust a number of transducer elements 38 in each aperture 44 and / or adjust beam transmission timings of the transducer elements 38 of each aperture 44 responsive to an incorrect position and / or orientation of the pig 30 inside the pipe 42. For example, the change in operating state of the pig 30 may be due to the pig 30 no longer being concentric with the pipe 42, which changes the relative position of the pig 30 to the internal wall of the pipe 42 and thereby changes the water path length travelled by the ultrasonic signals. Further optionally, the controller 40 may be programmed to operate the plurality of transducer elements 38 to vary a bandwidth, a pulse duration and / or a frequency of the ultrasonic beam. Also, pre-set time delay laws can be defined to depth focus the beam, allowing for improved sensitivity towards internal or external defects. It will be appreciated that the plurality of transducer elements 38 may be operated as apertures 44 in pulse-echo mode (whereby the same aperture 44 transmits and receives the ultrasonic signal) or in pulse-catch mode (whereby one aperture 44 transmits the ultrasonic signal and another aperture 44 receives the ultrasonic signal). The pulse-catch mode may be used for detecting radial defects in the pipe 42. Other ways of operating the transducer elements 38 as apertures include, but are not limited to, chirp pulse mode or coded excitation mode. In areas of clean pipe, one measurement is typically sufficient to get an accurate wall measurement. In corroded or otherwise damaged / unclean areas, averaged measurements would be useful for obtaining accurate wall measurements. Accordingly multiple measurements of the corroded or otherwise damaged / unclean areas can be dynamically averaged. It will be appreciated that the above numerical values are merely intended to help 5 illustrate the working of the invention and are not necessarily limiting on the scope of the invention. The listing or discussion of an apparently prior-published document or apparently prior-published information in this specification should not necessarily be taken as an 10 acknowledgement that the document or information is part of the state of the art or is common general knowledge. Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed 15 in combination with any and all preferences and options for all other aspects, features and parameters of the invention.

Claims

1. A pig for inspecting a tubular object, the pig comprising:a body;a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam; anda controller programmed to operate the plurality of transducer elements as one or more apertures in a plurality of operating modes, the or each aperture comprising multiple of the plurality of transducer elements, wherein each operating mode is preprogrammed to define a number of transducer elements in the or each aperture and define beam transmission timings of the transducer elements of the or each aperture, each operating mode differing from the or each other operating mode by the number of transducer elements in the or each aperture and / or the beam transmission timings of the transducer elements of the or each aperture.

2. A pig according to Claim 1 wherein each operating mode is preprogrammed to define the number of transducer elements in the or each aperture and define the beam transmission timings of the transducer elements of the or each aperture so as to enable a full circumferential inspection of the tubular object.

3. A pig according to any one of the preceding claims wherein the controller is programmed to dynamically modify which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object.

4. A pig for inspecting a tubular object, the pig comprising:a body;a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam; anda controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to dynamically modify which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object.

5. A pig according to any one of the preceding claims wherein the controller is programmed to form the one or more apertures by stepping along the plurality of transducer elements around the body.

6. A pig according to any one of the preceding claims wherein the controller is programmed to:define a first set of multiple transducer elements in the or each aperture in an aperture firing event; anddefine a second set of multiple transducer elements in the or each aperture in a subsequent aperture firing event;wherein the second set of multiple transducer elements includes one transducer element or some transducer elements from the first set of multiple transducer elements.

7. A pig according to Claim 6 wherein the number of transducer elements in the first set of multiple transducer elements is the same as the number of transducer elements in the second set of multiple transducer elements.

8. A pig according to any one of the preceding claims wherein the controller is programmed to change the number of transducer elements in the or each aperture between different aperture firing events of the or each aperture or between consecutive aperture firing events of the or each aperture.

9. A pig according to any one of the preceding claims wherein each transducer element is operable to receive a reflected beam signal.

10. A pig according to Claim 9 wherein the controller is programmed to operate the plurality of transducer elements as: one or more transmission apertures for transmitting a beam; and one or more receive apertures for receiving a reflected beam signal.

11. A pig according to Claim 10 wherein the number of transducer elements in the or each transmission aperture is different from the number of transducer elements in the or each receive aperture.

12. A pig according to any one of the preceding claims wherein the controller is programmed to simultaneously activate multiple apertures.

13. A pig according to any one of the preceding claims wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of theor each aperture responsive to a change in operating state of the pig and / or the tubular object.

14. A pig for inspecting a tubular object, the pig comprising:a body;a transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam; anda controller programmed to operate the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements, wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object.

15. A pig according to Claim 13 or Claim 14 wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to change a beam depth focus responsive to a change in operating state of the pig and / or the tubular object.

16. A pig according to any one of Claims 13 to 15 wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to change a beam resolution responsive to a change in operating state of the pig and / or the tubular object.

17. A pig according to any one of Claims 13 to 16 wherein the controller is programmed to dynamically adjust a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture so as to apply a time-corrected gain to a reflected beam signal responsive to a change in operating state of the pig and / or the tubular object.

18. A pig according to any one of Claims 13 to 17 wherein the change in operating state of the pig includes an incorrect position and / or orientation of the pig inside the tubular object.

19. A pig according to any one of Claims 13 to 18 wherein the change in operating state of the tubular object includes a change in geometry of the tubular object.

20. A pig according to Claim 19 wherein the change in geometry of the tubular object includes: a change in schedule of the tubular object; a change in diameter of the tubular object; a change in internal radius of the tubular object; a change in internal radius of the tubular object due to a build-up of material on the tubular object; a change in form factor of the tubular object; and / or a change in internal surface roughness of the tubular object.

21. A pig according to any one of the preceding claims wherein the controller is programmed to operate the plurality of transducer elements to vary a bandwidth, a pulse duration, a pulse-repetition frequency and / or a frequency of the beam.

22. A pig according to any one of the preceding claims wherein each of the plurality of transducer elements is an ultrasonic transducer element and / or a piezoelectric transducer element.

23. A pig according to any one of the preceding claims wherein the plurality of transducer elements is arranged In a same row about a circumference of the body.

24. A pig according to any one of the preceding claims wherein the pig is an untethered and / or single-bodied pig.

25. A pig according to any one of the preceding claims wherein the body is a unitary body.

26. A method of operating a pig for inspecting a tubular object, the pig comprising: a body; anda transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam,wherein the method includes the steps of:operating the plurality of transducer elements as one or more apertures in a plurality of operating modes, the or each aperture comprising multiple of the plurality of transducer elements, wherein each operating mode defines a number of transducer elements in the or each aperture and defines beam transmission timings of the transducer elements of the or each aperture, each operating mode differing from theor each other operating mode by the number of transducer elements in the or each aperture and / or the beam transmission timings of the transducer elements of the or each aperture.

27. A method according to Claim 26 including the steps of:operating the plurality of transducer elements as one or more apertures in one of the plurality of operating modes to inspect a tubular object with a first diameter; andoperating the plurality of transducer elements as one or more apertures in another of the plurality of operating modes to inspect another tubular object with a second diameter, the first and second diameters being different from each other.

28. A method according to Claim 26 or Claim 27 including the step of dynamically adjusting a number of transducer elements in the or each aperture and / or adjusting beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object.

29. A method of operating a pig for inspecting a tubular object, the pig comprising: a body; anda transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam,wherein the method includes the step of:operating the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements; anddynamically modifying which of the plurality of transducer elements are selected to be in the or each aperture during an inspection of the tubular object.

30. A method of operating a pig for inspecting a tubular object, the pig comprising: a body; anda transducer including a plurality of transducer elements arranged about a circumference of the body, the or each transducer element operable to transmit a beam,wherein the method includes the step of:operating the plurality of transducer elements as one or more apertures, the or each aperture comprising multiple of the plurality of transducer elements; anddynamically adjusting a number of transducer elements in the or each aperture and / or adjust beam transmission timings of the transducer elements of the or each aperture responsive to a change in operating state of the pig and / or the tubular object.

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