CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of Angolan patent application no. (to be obtained) filed on February 7, 201 1 , the specification of which is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] The technical field relates to methods for non-destructive inspection of welds using an ultrasonic phased array transducer system and, more particularly, it relates to methods for inspecting the root zone, the surface zone, the volume and the fusion wall of a weld as well as the heat affected zone.

BACKGROUND

[0003] Since they are used in corrosive environments, pipelines including an internal protection layer of a corrosion resistant alloy (CRA) have been commonly used over the last decade. These pipelines typically include a relatively thin CRA layer (generally between 3 mm and 5 mm) superposed inside a standard carbon steel pipe and bonded thereto. The corrosive resistant alloy varies in accordance with the required chemical and mechanical properties but is typically Inconel® 625 or 825, Stainless steel 316, 22% chrome, Duplex or Super Duplex alloy.

[0004] Two approaches are generally used to superpose and bond the CRA layers to the carbon steel pipe. A first method consists of hot-rolling a CRA layer to a carbon steel plate, often referred to as hot rolled clad pipelines. A thin layer of a third material can be interposed between the CRA and the carbon steel to reduce steel hardening and improve metallurgical bonding. A second method consists of welding the CRA layer inside the carbon steel pipe, often referred to as weld overlaid clad pipelines.

[0005] With a CRA cladding, weld inspection is more challenging. Ultrasonic inspection methods for carbon steel welds are well known. However, the conventional methods cannot be used for austenitic welds and dads due to the grain structure which causes the material to be highly anisotropic and to induce scattering and significant signal attenuation and deviation (American Welding Society. 1986. Handbook on the Ultrasonic Examination of Austenitic Welds. 1986. ISBN 9997643585).

[0006] Thus, methods were developed for hot rolled clad using phased array automated ultrasonic testing (AUT) instruments. These methods allow greater flexibility compared to conventional AUT methods.

[0007] Hot rolled clad produces a substantially flat steel-to-clad interface as well as a flat internal face. Thus, the inspection challenge is strictly related to the grain structure and the dissimilar materials that are bonded together. The interface steel-clad as well as the internal face with weld overlaid clad are characterized by a variable geometry. This variable geometry prohibits the use of ultrasounds skipping on the internal face. There is thus an additional challenge in addition to grain structure and, more particularly, a method must be developed for non-destructive inspection with an uneven internal surface.

[0008] There is thus a need for a new non-destructive method for inspecting pipeline welds for overlaid clad and hot rolled clad pipelines.

BRIEF SUMMARY OF THE INVENTION

[0009] It is therefore an aim of the present invention to address the above mentioned issues. [0010] According to a general aspect, there is provided a method for inspecting a weld in a structure having a base material with a first surface and a second surface and the weld has a weld center line extending between the first and the second surfaces, the method comprising : Superposing at least one ultrasonic phased array transducer able to transmit and detect ultrasonic radiation, to the first surface above the weld; Emitting from the phased array transducer at least one channel including multiple beams of longitudinal compression waves incident towards the weld center line; Detecting radiation resulting from at least one of reflection and diffraction of the compression waves of the at least one channel; Extracting information from the detected radiation, and; Correlating the extracted information to provide an indication from which the likelihood of a defect in the weld be discerned.

[0011] In an embodiment, the at least one ultrasonic phased array transducer is one ultrasonic phased array transducer mounted in a wedge having a resilient contact surface, the contact surface being juxtaposed to the first surface. The wedge can have a void wedge angle. The multiple beams of a first one of the at least one channel can have a void refracted angle. The at least one channel can comprise a second channel of multiple beams and a third channel of multiple beams, the second and third channels having a non-void refracted angle. The refracted angle of the second and the third channels can range between about 5° and 60° with opposed orientations and, in an alternative embodiment, the refracted angle of the second and the third channels can range between about 20° and about 30° with opposed orientations.

[0012] In an embodiment, the longitudinal compression waves are emitted at a nominal frequency ranging between 2 and 15 MHz. [0013] In an embodiment, the at least one ultrasonic phased array transducer detects flaws about 2.5 mm below the first surface where the transducer is superposed and about 2.0 mm above the second surface opposed to the first surface.

[0014] In an embodiment, the at least one phased array channel covers a volume zone of the weld including a volume and a fusion wall of the weld and a heat affected zone.

[0015] In an embodiment, the information extraction comprises extracting at least one of an amplitude and a relative position of the reflected waves. The extracting step can further comprise extracting a relative position of the diffracted waves. The extracted information correlation can comprise sizing the defect. The sizing can be carried out with at least one of a back- diffraction sizing method and an amplitude method.

[0016] In an embodiment, the structure is a pipeline and the weld joins a first metal pipeline section and a second metal pipeline section. The at least one ultrasonic phased array transducer can be superposed to an external surface of the pipeline sections and can cover a cap of the weld from the first pipeline section to the second pipeline section. The weld can be an austenitic weld. The weld can be a girth weld.

[0017] In an embodiment, the weld has a substantially V-shaped cross- section with a weld cap located at a base of the V-shaped cross-section and a root located in a tip of the V-shaped cross-section.

[0018] According to another general aspect, there is provided a method for inspecting one of a root zone and a surface zone of a weld in a structure having a base material with a first surface and a second surface and the weld has a weld center line extending between the first and the second surfaces, a root, and the surface zone being opposed to the root, the method comprising: Superposing at least one ultrasonic phased array probe able to transmit and detect ultrasonic radiation, on the first surface of the structure, opposed to the inspected one of the root zone and the surface zone, the at least one probe having at least a 16 mm aperture; Emitting from at least one ultrasonic phased array probe, longitudinal compression waves towards the inspected one of the root zone and the surface zone, the longitudinal compression waves being characterized by a refracted angle ranging between about 30° and about 70°; Detecting the radiation resulting from at least one of reflection and diffraction of the compression waves; Extracting information from the detected radiation; and Correlating the extracted information to provide an indication from which the likelihood of a defect in the weld be discerned.

[0019] In an embodiment, the at least one phased array probe comprises at least two phased array probes, each being positioned on a respective side of the weld.

[0020] In an embodiment, the inspected one is the root zone.

[0021] In an embodiment, the ultrasonic phased array probes are ultrasonic phased array probes mounted in a wedge having a non-void wedge angle.

[0022] In an embodiment, the ultrasonic phased array probes carry out a focalized linear scan of the one of the root zone and the surface zone.

[0023] In an embodiment, the refracted angle ranges between about 45° and 70° with opposed orientations.

[0024] In an embodiment, the longitudinal compression waves are emitted at a nominal frequency ranging between 2 and 15 MHz.

[0025] The root zone can include the root of the weld and the second surface of the structure. [0026] In an embodiment, the extracting step comprises extracting an amplitude and a relative position of the reflected waves. The extracting step can further comprise extracting a relative position of the diffracted waves.

[0027] In an embodiment, the extracted information correlation comprises sizing the defect. The sizing can be carried out with at least one of a back- diffraction sizing method and an amplitude method.

[0028] In an embodiment, the structure is a pipeline and the weld joins a first metal pipeline section and a second metal pipeline section. The ultrasonic phased array probes can be superposed to an external surface of the pipeline sections. The weld can be an austenitic weld. The weld can be a girth weld. The weld can have a substantially V-shaped cross-section with a weld cap located at a base of the V-shaped cross-section and the root is located in a tip of the V-shaped cross-section.

[0029] In this specification, the term "phased array probe assemblies" is intended to mean wedges including at least one phased array transducer or probe that is capable of transmitting and detecting ultrasonic radiation and, more particularly, multiple beams.

[0030] In this specification, the term "phased array" is intended to mean a multi-element ultrasonic transducer (typically with 16, 32, or 64 elements) used to generate steered beams by means of phased pulsing and receiving.

[0031] In this specification, the term "indication" is intended to mean detected ultrasound signals by the phased array transducers. Indications are identified as flaws or defects when they are characterized as an imperfection above a predetermined threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Fig. 1 is a schematic cross-sectional view of a weld joining two structure sections in accordance with an embodiment;

[0033] Fig. 2 is a schematic cross-sectional view of the weld shown in Fig. 1 and showing two creeping wave probe assemblies configured for inspecting a surface zone of the weld;

[0034] Fig. 3 is a schematic cross-sectional view of the weld shown in Fig. 1 showing a volume zone of the weld;

[0035] Fig. 4 is a schematic cross-sectional view of the weld shown in Fig. 1 and showing two phased array probe assemblies configured for inspecting a root zone of the weld;

[0036] Fig. 5 is a schematic cross-sectional view of the weld shown in Fig. 1 and showing the two phased array probe assemblies partially configured for inspecting the volume zone and the root zone of the weld;

[0037] Fig. 6 includes Fig. 6a and Fig. 6b and are schematic cross-sectional views of a weld including an internal clad layer and showing two phased array probe assemblies superposed to an external surface of the structure sections and each emitting a phased array channel towards the weld with a non-void refracted angle, Fig. 6a showing the phased array channel emitted by a first phased array probe assembly and Fig. 6b showing the phased array channel emitted by a second phased array probe assembly;

[0038] Fig. 7 is a schematic cross-sectional view of the weld shown in Fig. 6 and showing the phased array probe assembly superposed to a weld cap of the weld and emitting a phased array channel towards the weld with a refracted angle of 0°; [0039] Fig. 8 includes Fig. 8a and Fig. 8b and are schematic cross-sectional views of the weld shown in Fig. 6 and showing the phased array probe assembly superposed to the weld cap of the weld and emitting phased array channels towards the weld with a non-void refracted angle, Fig. 8a showing the phased array channel emitted by the phased array probe assembly in a first direction and Fig. 8b showing the phased array channel emitted by the phased array probe assembly in a second direction, opposed to the first direction;

[0040] Fig. 9 includes Fig. 9a and Fig. 9b and are schematic cross-sectional views of the weld shown in Fig. 6 and showing two phased array probe assemblies mounted on a respective side of the weld, superposed to the external surface of the structure sections and each emitting a focalized linear phased array channel towards the root zone of the weld with a non- void refracted angle, Fig. 9a showing the phased array channel emitted by a first phased array probe assembly and Fig. 9b showing the phased array channel emitted by a second phased array probe assembly; and

[0041] Fig. 10 is a graph showing a comparison of flaw sizing with the nondestructive ultrasonic inspection method and a conventional destructive method.

[0042] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

[0043] Referring to the drawings and, more particularly, referring to Fig. 1 , there is shown a schematic cross-sectional view of a weld 20 which can be inspected using the below detailed methods and apparatuses. [0044] The weld 20 is located at the junction of two juxtaposed structure sections 22, i.e. a first structure section 22a is connected to a second structure section 22b by means of the weld 20. In the embodiment shown, each one of the structure sections 22 is made of steel. In an alternative embodiment, each one of the structure sections 22 can be a steel structure clad with a corrosion resistant alloy (CRA) layer 26 (see Figs. 6 to 9). For instance and without being limitative, the CRA alloy can include nickel alloys, stainless steel, and other suitable alloys with an austenitic grain structure. The CRA layer 26 can be a hot rolled clad layer or a weld overlaid clad layer.

[0045] One skilled in the art will appreciate that the below detailed inspection methods can be applied to structures such as and without being limitative pipe sections which can include an internal or external clad layer or not. Furthermore, the composition of the structure to inspect and the weld material used to connect the sections of the structure can differ from the above-described examples.

[0046] More particularly, the weld 20 can be a girth weld joining together two pipe sections 22 (only a section thereof is shown), which can have been created during a method of laying an underwater pipeline from a floating vessel, for instance. One skilled in the art will appreciate that the below detailed methods can be applied to other suitable types of structures having a first surface and a second surface such as and without being limitative pressure vessels.

[0047] Moreover, the shape of the weld 20 can differ from the one shown in Fig. 1 .

[0048] For a pipe structure, conventionally, the pipe 24 defines the outside diameter and the external surface 29 of the structure sections 22 and the CRA layer 26 defines the inside diameter and the internal surface 31 of the structure sections 22 circumscribing the internal conduit Ί".

[0049] As mentioned above, the shape of structure to be inspected can differ from a tubular pipe. However, for the surface of the structure including a weld cap 34 will be referred to as the external surface 29 of the structure 20 and the surface of the structure including a weld root 36 will be referred to as the internal surface 31 of the structure 20.

[0050] The weld 20 defines a weld center line 33 that is substantially perpendicular to the external and internal surfaces 29, 31 of the structure sections 22.

[0051] The integrity of the weld 20 and its surrounding area must be inspected for quality and safety reasons. One way to inspect structure welds 20 is through an ultrasonic-based non-destructive inspection system.

[0052] For inspection purposes, the weld 20 can be divided into four inspection zones. Referring to Fig. 2, there is shown that the first inspection zone is a surface zone 32 including the weld cap or bead 34, which protrudes above the external surface 29 of the structure sections 22. The surface zone 32 also extends a few millimeters under the external surface 29 of the structure 22. It can be inspected using creeping wave probe assemblies 35 which are typically efficient to detect about 0.5 millimeter (mm) high surface breaking defects up to about 4 mm deep. The creeping wave probe assemblies 35 are superposed to the external surface 29 of the structure 22, each being located on a respective side of the weld 20.

[0053] A second inspection zone is a volume zone 37 located below the weld cap 34, starting about 2.5 mm deep and including the volume and the fusion wall of the weld 20 as well as the heat affected zone (HAZ), as shown in Fig. 3. It starts about 2.5 mm deep from the external surface 29 to about 2 mm above a root 36 of the weld 20.

[0054] A third zone is a root zone 40 which is located below the volume zone 37 and includes the root 36 of the weld 20 and the internal surface 31 of the structure sections 22, close to the weld 20, as shown in Fig. 4.

[0055] As it is known in the art, one of the methods for partially inspecting the volume zone 37 and the root 36 includes twin phased array probe assemblies 38 superposed to the external surface 29 of the structure sections 22, each being positioned on a respective side of the weld 20, as shown in Figs. 5 and 6. Each one of the twin phased array probe assemblies 38 produces a phased array channel 41 , including multiple longitudinal beams, incident to the weld 20. The phased array channels 41 produced by the two phased array probe assemblies 38 cover the weld 20 from about 10 mm deep from the external surface 29 to the root 36 or the internal surface 31 . The probes (or transducers) included in the phased array probe assemblies 38 emit multiple angle beams at various angles as shown in Fig. 6. The angle shown in the figures are the refracted angles (or angles of refraction). This is known as an azimuthal scan (or sector scan) for volumetric and side wall fusion indications. [See for instance, Introduction to Phased Array Ultrasonic Technology Applications, R/D Tech, 2004, paragraph 4.2.5, page 175.]

[0056] An alternative method to the azimuthal scan for inspecting the same zone can include emitting several channels of a single longitudinal beam each (instead of one channel including multiple beams).

[0057] For both the azimuthal and the alternative scan methods described above, the beams at different angles are emitted consecutively with a few microseconds between each beam as it is known in the art. [0058] However, the azimuthal and its alternative scan methods do not inspect the upper section of the volume zone 37 as shown in Figs. 5 and 6. High angle longitudinal beams, over about 70°, are difficult to control, calibrate, and analyze. There is thus a blind zone in the upper part of the volume zone 37 when inspecting a weld 20 with both methods. The angle is measured relative to a normal line to the surface where the probe assembly 38 is positioned.

[0059] Another method for inspecting the volume zone 37 is described in reference to Figs. 3, 7, and 8 wherein a phased array probe assembly 42 is superposed to the cap 34 of the weld 20 and the structure sections 22, in a manner such that it entirely covers the weld cap 34, i.e. along the longitudinal axis A (Fig. 1 ) of the structure sections 22. Furthermore, a contact surface 43 of the probe assembly 42, i.e. the one in contact with the external surface 29 of the structure 22 and the weld 20, is resilient and conforms to the surface to which it is superposed, including the weld cap 34.

[0060] For instance and without being limitative, the contact surface 43 of the probe assembly 42 can include a resilient material layer 48. In a non- limitative embodiment, the resilient material layer 48 is located peripherally of the probe assembly (or wedge) 42. The resilient material layer 48 defines the outer contact surface 43 of the probe assembly 42 with the structure 22 to inspect. It matches and conforms to the surface of the structure 22 including the weld cap 34 and it is designed to ride on the weld cap 34. Since it is designed to ride on the weld cap 34, it is substantially resistant to friction. In a non-limitative embodiment, the contact layer 48 is made of neoprene (about 6 mm thick) covered outwardly by a polyimide film such as Kapton®. [0061] To conform to the surface to which it is superposed and in addition to the resilient contact surface 43, the probe assembly 42 has an internal cavity filled with liquid such as water. Thus, the liquid also conforms to the surface to which it is superposed. More particularly, the probe assembly 42 has an at least partially unsealed bottom surface of its housing, i.e. it includes at least one opening or slit defined therein, to permit liquid contained in the internal cavity to flow therethrough. The probe assembly 42 is further designed to maintain a volume of liquid in the housing cavity to ensure that the volume of the cavity between the bottom surface of the transducer inserted in the probe housing and the surface that is being examined, e.g. such as the weld 20, is filled with liquid. One skilled in the art will appreciate that other liquids than water or gels can be used provided that they conform to the inspected surface including the weld cap 34 and that ultrasounds can travel therethrough.

[0062] In a non-limitative embodiment, the ultrasonic covering scheme extends from about 2.5 mm deep from the external surface 29 to about 2 mm above the internal surface 31 , for substantially any thickness of weld 20.

[0063] By positioning the probe 42 above the weld cap 34, substantially parallel to one of the external surface 29 and the internal surface 31 of the structure sections 22 and substantially perpendicular to the weld 20, the weld cap 34 can remain on the weld 20 for inspection of the volume zone 37 of the weld 20.

[0064] For inspecting the volume zone 37, phased array channels including a plurality of longitudinal compression waves are used. As shown in Fig. 7, a first one 46 of the channels includes multiple beams having a refracted angle of 0° (or angle of refraction). The channel 46 is substantially perpendicular to the external surface 29 to which the probe assembly 42 is superposed and substantially parallel to the weld center line 33.

[0065] Referring now to Figs. 8a and 8b, two other channels 44 are shown wherein the angle of refraction is non-void. In Fig. 8a, the channel 44 is oriented towards the second structure section 22b while in Fig. 8b, the channel 44 is oriented towards the first structure section 22a. The channels 44 carry out a linear scan (often referred to as E-scan) of the volume zone 37, i.e. a movement of the acoustic beam along the major axis of the array without any mechanical movement. The channels 44 have a refracted angle ranging between about 5° and about 60°. In an embodiment, the multiple beams of the channels 44 have a refracted angle ranging between about 20° and about 30°. One skilled in the art will appreciate that the angle of incidence of the longitudinal compression waves differs from the refracted angle and it can be calculated through well known methods (Snell-Descartes law or law of refraction).

[0066] The channels 44, 46 are emitted sequentially by the phased array transducer of the probe assembly 42. The interval between the emission of the channels 44, 46 is in the order of the few microseconds.

[0067] The refracted and incident angles are measured relatively to a normal line to the surface where the probe assembly 42 is positioned.

[0068] The probe (or transducer) (not shown) included in the probe assembly 42 emits longitudinal compression waves at a nominal frequency ranging between 1 and 15 MHz and, in another embodiment, at a nominal frequency ranging between 2 and 5 MHz.

[0069] The phased array probe assembly 42 has a wedge angle, or incidence angle, i.e. the angle defined between the upper wedge surface and the lower or contact wedge surface 43, of about 0°, i.e. both surfaces are substantially parallel to one another.

[0070] The above-describe inspection method provides volumetric indications of the volume zone 37 of the weld 20 and its surrounding area.

[0071] Information included in the reflected and diffracted radiation detected by the transducer included in the phased array probe assembly 42 is extracted and correlated to provide an indication from which the likelihood of a defect in the inspected weld zone can be discerned, as it will be described in more details below. For instance, the amplitude and the relative position of two detected waves or beams can be extracted from the reflected radiation and diffraction of the waves or beams.

[0072] For instance, information such as and without being limitative, the height, the depth, and the length of the defect can be extracted from the reflected radiation and diffraction of the waves or beams.

[0073] Once again the multiple inspection beams are emitted sequentially with a few microseconds between each beam as it is known in the art. For instance and without being limitative, the channel 46 can be first emitted, followed by channel 44 on a first side of the weld 20 and channel 44 on a second, opposed side of the weld 20.

[0074] One skilled in the art will appreciate that, in an alternative embodiment (not shown), the transducer 42 can be superposed to the internal surface 31 of the structure 22, i.e. the surface opposed to the weld cap 34. In this alternative embodiment, the ultrasonic covering scheme extends from about 2.5 mm deep from the internal surface 31 to about 2 mm above the external surface 29. [0075] To complete the inspection of the weld 20, other channels 52 of multiple beams can be used, as it will be described in further details below in reference to Figs. 4 and 9. To inspect the root zone 40 including the internal surface 31 of the joint 20, two twin phased array probe assemblies 54 are used to produce two other phased array channels 52, 52 that cover the root zone 40. The transducers or probes included in the twin phased array probe assemblies 54 are used to accurately discriminate and size about 0.5 mm high defects located in the root zone. One skilled in the art will appreciate that more than two probe assemblies 54 can be used for inspecting the root zone 40. For instance and without being limitative, two probe assemblies 54 can be provided on each side of the weld 20.

[0076] The two probe assemblies 54 are superposed to the external surface 29 of the structure sections 22 (or any other structure) and positioned on each side of the weld 20, as shown in Fig. 4. Each one of the transducers of the twin phased array probe assemblies 54 carries out a focalized linear scan (often referred to as E-scan) of the root zone 40 as shown in Fig. 9, incident to the weld 20, i.e. movement of the acoustic beam along the major axis of the array occurs without any mechanical movement. The equivalent focal law is multiplexed across a group of active elements; linear scans are performed at a constant angle and along the phased array probe length. For angle beam scans, the focal laws typically compensate for the change in wedge thickness. In some industries this term is used to describe a one-line scan.

[0077] Typically the two phased array probe assemblies 54 are positioned at a substantially similar distance from the weld center line 33. However, one skilled in the art would appreciate that the probe assemblies 54 can be positioned at a different distance from the weld center line 33, for instance if the thickness on both sides of the weld 20 is not the same. [0078] The multiple beams of the channels 52 have a refracted angle (or angle of refraction) ranging between about 30 ⁰ to 70°. In an embodiment, the refracted angle is between about 45° to about 60°. Once again, one skilled in the art will appreciate that the angle of incidence of the longitudinal compression waves differs from the refracted angle and that it can be calculated as mentioned above.

[0079] Accordingly, in a non-limitative embodiment, the phased array probe assemblies 54 have a wedge angle, or incident angle, of about 19 ⁰ for a steel pipe. The incident angle of the emitted ultrasound beams is thus about 19°. One skilled in the art will appreciate that the incident angle and the wedge angle vary in accordance with the inspected material and the desired refracted angle.

[0080] The probes (or transducers) (not shown) included in the probe assemblies 54 emit longitudinal compression waves at a nominal frequency ranging between 1 and 15 MHz and, in another embodiment, at a nominal frequency ranging between 2 and 5 MHz.

[0081] The phased array probes of the probe assemblies 54 have an aperture above about 16 mm and, in an embodiment, above about 20 mm. The aperture is the width of the transducer element or group of elements pulsed substantially simultaneously, with few microseconds between each.

[0082] The probe assemblies 54 have an internal cavity filled with a polymer such as rexolite®, a cross linked polystyrene microwave plastic. However, one skilled in the art will appreciate that liquids including water, gels or other solids can be used provided that it has a known ultrasound propagation speed and a relatively limited ultrasound attenuation.

[0083] One skilled in the art will appreciate that the probe assemblies 54 and the probe assemblies 38 used for the azimuthal scan for volumetric and side wall fusion indications can be the same probe assemblies, i.e. the same probe assemblies can be used for the azimuthal scan for volumetric and side wall fusion indications and the root zone scan. The channels emitted for both zone inspections are emitted consecutively with a few milliseconds between each emission, as it is know in the art.

[0084] For all the above described methods and embodiments, the probes are superposed to the external surface 29 of the structure or pipeline. However, one skilled in the art will appreciate that the probes could be superposed to the internal surface 31 of the structure or the pipeline. However, the shape of the contact surface 43 of the probe assemblies may have to be modified to conform to the surface to which it is juxtaposed. Furthermore, if the probes are superposed to internal surface 31 of the structure or the pipeline, i.e. the one substantially in line with the root 36, the above-described method to inspect the root zone 40 can be used to inspect the surface zone 32 of the weld 20.

[0085] Phased array probes used typically include a linear assembly of crystals that allows electronic control over beam steering and focalization spot in only one axis, the active axis. In such a case, the axis perpendicular to the active axis is referred to as "passive axis"; in which axis no change can be electronically induced to the acoustic beam.

[0086] Alternative phased array probes are designed with their crystals not aligned on a single straight line, but distributed in more than one dimension. This distribution allows electronic control on beam steering and focalization spot in more than one axis.

[0087] One skilled in the art will appreciate the above described methods can be used with all suitable kind of phased array probes capable of focalization and beam steering in one or more axes and directions in order to increase performances such as sensitivity and accuracy in the secondary axis.

[0088] For a girth weld inspection, all the probe assemblies are mounted for movement together in the circumferential direction around the pipes, so that the entire weld may be inspected in one revolution. However, one skilled in the art will appreciate that the weld may be inspected in more than one revolution.

[0089] As one skilled in the art will appreciate, in each one of the channels, the beams are emitted consecutively with a few microseconds between each emission.

[0090] By combining the above-described techniques, the defects, flaws, or imperfections of the weld area can be characterized by their dimensions such as their length, height and depth.

[0091] As one skilled in the art will appreciate, zone sections can be inspected by two or more of the above-described methods. For instance, in an embodiment, the lower section of the volume zone is inspected by the phased array probe superposed to the weld as well as the phased array probes inspecting the root zone.

[0092] Furthermore, all of the above-detailed methods for inspecting a weld can be combined. Combination of methods improves the accuracy of the overall inspection. However, one can select one or several of the above- detailed methods in accordance with his particular needs.

[0093] For weld overlaid clad pipes, a zone discrimination technique, which is usually used for pipeline girth weld inspection, cannot be used since the weld scan plan is not specifically divided into zones. A method referred to as "back-diffraction" can be used to size the detected indication. This technique requires a software that provides a three dimensional display and specialized sizing cursors and tools, as it is known in the art.

[0094] The back-diffraction method comprises measuring the relative time of flight difference between diffraction signals of a defect. This is similar to traditional time of flight diffraction (TOFD) with the exception that the signal is received by the same probe that emitted the ultrasound signal. The equation to calculate the height of an indication is:

UT2-UT1

H = —

p

[0095] where H is the defect height (vertical extension), and UT ₂ are the UT paths for the lower tip and the upper tip respectively, and β is the ultrasonic refracted angle in the material [F. Jacques, F. Moreau & E. Ginzel. 2003. Ultrasonic backscatter sizing using phased array - developements in tip diffraction flaw sizing. Insight - Non-Destructive Testing and Condition Monitoring. November 2003, Vol. 45, 1 1 , pp. 724- 728 - which is hereby incorporated herein by reference].

[0096] With the back-diffraction sizing method, one will look for evidence of diffracted signals originating from the indications (or the detected signals). The height assessment can be performed using the true depth measurement between the signals coming from the upper part of the indication and the lower part of the indication.

[0097] Measurement can be done on diffracted signals in combination with the reflected signals. The sizing method is a time based measurement and is not amplitude dependant.

[0098] A second method that can be used for sizing the weld defects, especially when the indications are too small to use the back-diffraction method, i.e. when there is no discernable tips of the diffracted signals, is an amplitude-based method.

[0099] Vertical extent of flaws detected on the angle beam channels can be assessed by a linear interpolation of amplitude.

[00100] As known in the art, the phased array probes are operated in accordance with a sequence of focal laws which cause the transducers of the arrays to create beams of ultrasonic sound radiations at a variety of different angles.

[00101] The defect sizing can be based on diffraction measurements and/or amplitude measurements, as it is known by one skilled in the art.

[00102] Example

[00103] A complete qualification process including sizing and macrographs of natural flaws was conducted based on DNV OS- F101 App. E to accurately measure the performance of the above- described sizing method on pipeline girth welds with a weld overlaid CRA clad.

[00104] This was done during the course of a project for the inspection of fatigue welds on FPSO with manifolds and clustered wells located in water depth up to a maximum of 2500 meters.

[00105] It was performed on five (5) defective welds of 32.2 mm thick wall including a 4.5 mm thick weld overlaid clad of Inconel® 625. The project specification required a system capable of detecting and accurately sizing surface-breaking flaws as small as 0.5 mm high by 12 mm long, and 1.5 mm high by 22 mm long for embedded ones. [00106] Defective welds were scanned with the pipe axis in a horizontal position. Scans were interpreted by two different operators for reliability.

[00107] From the five defective welds, 55 indications/imperfections and one (1 ) clear area were assessed by destructive testing (DT) for comparison with the AUT assessments. Indications to be assessed were chosen in order to provide an even distribution through the entire weld thickness (cf. Table 1 ). Population in root area is over represented to get a better knowledge of this critical area where no defect higher than 0.5 mm is typically allowed.

Table 1 : Depth distribution of defects.

[00108] These fifty-six (56) indications led to about 620 macro-sections.

[00109] Comparison between the above-described AUT methods and a conventional radiography testing (RT) was carried out. The AUT detected everything and more than what was detected by the RT. RT did not detect a defect that was at least thrice as long and high as the critical defect dimension. [00110] Before any destructive testing, welds were assessed by two independent operators to show the operator dependency on the results. For fifty-six (56) indications reported by macro-sectioning, differences in the sizing of only 15 defects were noticed and, more particularly,

• 1 difference of 1 mm in depth sizing;

• 1 difference of 2 mm and 5 differences of less than 1 mm in height sizing;

• a maximum difference of 17 mm in length sizing.

[00111] The small number of differences between the AUT interpretations of the two operators and the small differences between two sizing values for the same indication demonstrate consistency of the AUT results between the two operators. The above-described AUT method is therefore not dependent on operator for flaw detection and sizing.

[00112] Fig. 10 shows that, except for three (3) oversized defects, all other 53 flaws assessed during the qualification process are within ±1 mm sizing accuracy range. When the study is focused on the inside diameter (ID) and outside diameter (OD) flaws, the range improves to ±0.5 mm in accuracy, which are excellent results in comparison with the highest industry standards. With the above-detailed method, the probability of undersizing a flaw by more than 1 mm is about 2.2%.

Table 2: AUT vs. DT, including data from the two operators.

[00113] Table 2 indicates that 1 10 defect heights were evaluated plus two (2) flaw-free areas. For 60 embedded defects, the standard vertical sizing error was ±0.7 mm. For the surface-breaking flaws located either in the cap or the root surface, for 50 flaws, the standard vertical sizing error was 0.3 mm.

[00114] During this test, there was neither a defect missed nor any false positive alert made.

[00115] The above-described ultrasonic inspection method for pipe girth weld with weld overlaid clad of austenitic material and other pipes covers about 100% of the weld volume and detects indication as small as about 0.5 mm high in the root zone.

[00116] The above described methods allow inspection of weld overlaid CRA with a non-destructive procedure. As mentioned above, one skilled in the art will appreciate that the above described methods can be used for any type of suitable weld.

[00117] Several alternative embodiments and examples have been described and illustrated herein. The embodiments of the invention described above are intended to be exemplary only. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.