GB2036321A

GB2036321A - Ultrasonic flaw detection

Info

Publication number: GB2036321A
Application number: GB7938220A
Authority: GB
Original assignee: Steel Castings Research and Trade Association
Current assignee: Steel Castings Research and Trade Association
Priority date: 1978-11-07
Filing date: 1979-11-05
Publication date: 1980-06-25
Also published as: GB2036321B

Abstract

In ultrasonic flaw detection the production of an effective coupling of the transducer and the component has hitherto involved the application by brushing, spraying, drip feeding and the like of a couplant fluid to the surface of the component which has the disadvantage that excessive quantities of couplant fluid are spilled and wasted. Couplant fluid is saved by continuously supplying it to the operative surface of the ultrasonic transducer 5 by way of bores (not shown) and an annular opening 12, the ultrasonic transducer being surrounded by an extraction chamber having an annular opening 16, there being vacuum applied to the extraction chamber by way of bore 19 to remove continuously couplant fluid from the vicinity of the operative surface. <IMAGE>

Description

SPECIFICATION Ultrasonic flaw detection This invention relates to ultrasonic flaw detection and is particularly concerned with the ultrasonic transducer which generates the sound waves to be transmitted through materials, components or structures for the purpose of detecting flaws.

Hitherto, whenever a component has required to be subjected to non-destructive testing the ultrasonic transducer or probe has been applied to the surface of the component and moved across the surface of the component until such time as means associated with the probe have shown the presence of a flaw. However, in order to ensure that the sound waves are properly transmitted through the component it has been necessary to apply a coupiant fluid to the surface of the component, and the probe presses on to the couplant fluid.

Couplantfluid is normally applied to the surface of the material such as by brushing, spraying, drip feeding from a reservoir or by pumping. All such methods are relatively simple and effective but have the disadvantage that excessive quantities of couplant fluid are spilled and wasted, a problem magnified when an automatic or semi-automatic inspection system is being employed. Attempts have been made to collect spilled couplant fluid but in very many instances such as when the component is very large or of a complex shape such collection attempts have been extremely inefficient, complex and expensive.

A further problem, particularly with hand held transducers is that variations in the contact pressure applied to the transducer by the ultrasonic operator can produce signal amplitude variations as a consequence of inconsistent coupling conditions, and these variations can be clearly seen in the received signal. For many applications of ultrasonic non-destructive testing, measurements of the amplitude of the received signal are made and it is important therefore that any variations in the thickness or the condition of the couplant layer are minimised. Another problem concerning ultrasonic non-destructive testing is that in certain applications, especially where the surface of the component or structure undergoing ultrasonic examination is rough textured, the contact face of the ultrasonic transducer can suffer severe abrasion, seriously impairing the life of the transducer.

According to the present invention, a method of ultrasonic testing comprises continuously supplying couplant fluid to the operative surface of an ultrasonic transducer, surrounding the ultrasonic transducer with an extraction chamber, and applying vacuum to the extraction chamber, whereby couplant fluid is continuously removed from the vicinity of the operative surface of the ultrasonic transducer.

According to a further aspect of the invention, ultrasonic testing equipment comprises a housing in which the ultrasonic transducer is secured, a first annular wall within the housing forming with the outer surface of the ultrasonic transducer a chamber for the admission of couplant fluid, a second annular wall on the housing, the second wall co-operating with the first wall to form an annular extraction chamber, and there being connection means to the first chamber for the supply of couplant fluid and connection means to the extraction chamber for the application of vacuum. Preferably the first annular wall has a length such that with the ultrasonic transducer secured in place, the annular wall projects beyond the operative surface of the ultrasonic transducer.

Thus, in use, with the housing and the ultrasonic transducer applied to the surface of a component, the first annular wall contacts the component and thereby spaces the operative surface of the ultrasonic transducer at the correct distance away from the surface of the component. That couplant fluid admitted to the first chamber, it flows from there to the gap between the component and the operative surface of the transducer component to provide correct acoustic coupling. As the pressure of couplant fluid builds up, and when the housing with the ultrasonic transducer is moved across the surface of the component there is inevitably spillage of couplant fluid between the first annular wall of the housing and the surface of the component. A high proportion is sucked into the extraction chamber as a consequence of the applied vacuum.By ensuring that the second annular wall on the housing is of somewhat shorter length than the first annular wall, the application of vacuum to the extraction chamber draws air into the extraction chamber from around the housing, thus assisting considerably the passage of couplant fluid into the extraction chamber.

To ensure a constant supply of couplant fluid to the chamber for the admission of couplant fluid, it is preferred to utilise a pump having a controllable flow rate such as a centrifugal pump or constant volume pump although any other suitable supply means can be provided such as by utilising a compressed air source to force the couplant from a reservoir to the admission chamber. The vacuum required for the collection of the couplant fluid can be generated by any suitable means but it is preferred to utilise a venturi vacuum generating system activated by compressed gas, the source for which can be an on-site compressed air line or a portable cylinder of compressed gas.

Because the couplant fluid effectively passes between the first annular wall and the surface of the component there is considerable reduction in wear of the transducer, although it is preferable for at least the front end of the first annular wall to be either coated with or formed from an abrasion resistant material. A flexible skirt may also be provided circumferentially fitted around the housing to improve fluid retention when used on rough or non-horizontal surfaces.

To allow greater versatility it is preferred that the ultrasonic transducer is adjustably mounted in the housing to allow its replacement by an ultrasonic transducer of different characteristics.

Thus, the ultrasonic transducer can be a push fit in the housing and there may be provided adjustment means to position the ultrasonic transducer such that the distance from the edge of the first annular wall from the operative face of the housing is correctly set. A clamping ring may be provided to secure the ultrasonic transducer to the housing with an interposed sealing ring to prevent the escape of couplant fluid rearwardly of the housing.

The construction of the invention constitutes a considerable improvement in the feeding and collection of couplant fluid to the operative face of the ultrasonic transducer and at the same time ensures that correct acoustic coupling is brought about in a manner that substantially eliminates any wear by abrasion of the operative face of the ultrasonic transducer. The construction also provides for the minimizing of the variation of the signal that can be caused by the variable contact pressure applied by the operative.

One embodiment of the invention will now be described, by way of example only, with respect to the accompanying drawings, in which Figure 1 is a perspective view from above of ultrasonic testing equipment according to the invention; Figure 2 is a perspective view from below of the device of Figure 1; Figure 3 is a sectional side elevation generally along the line 3-3 of Figure 1; and Figure 4 is a sectional side elevation generally along the line 4-4 of Figure 1.

In the drawings ultrasonic testing equipment comprises a housing formed by an upper housing member 1 and a lower housing member 2 in screw threaded engagement with each other. As shown by Figure 3, the upper housing member 1 has a generally cylindrical extension 3 extending through the lower housing member 2, and of a length such as to allow the lower end of the extension 3 to lie marginally inside the bottom of the lower housing member 2. A bore 4 through the upper housing member 1 and its extension 3 receives an ultrasonic transducer 5, the transducer having a diameter to be a tight fit against an annular shoulder 6 in the bore of the upper housing member 1. The transducer 5 is further secured in place by a locking ring 7 compressing a resilient sealing ring 8 between the shoulder and the transducer.

In a boss 9 on the upper housing member 1 an inlet hole 10 is provided communicating by a passage 11 with the annular gap formed between the transducer 5 and the wall of the bore 4 of the upper housing member 1 and its extension 3.

Thus, with a suitable nipple (not shown) in engagement with the inlet hole 10, couplant fluid can be admitted through the inlet hole 10 and along the passage 11 to the annular gap, which then constitutes an inlet chamber, from where couplant fluid can escape through the gap 12 at the lower end to cover the operative surface of the ultrasonic transducer.

As is shown more particularly by Figure 4, the downward extension 3 to the upper housing member 1 has an outer annular wall 13 and the lower housing member 2 has an inner annular wall 14 which combine to form an extraction chamber 1 5 having an inlet gap 1 6 at the lower end. Cooperating bosses 17 and 18 on the upper and lower housing members are provided with cooperating outlet holes 19, 20 which outlet holes are intended to receive a nipple (not shown) for connection to a source of vacuum.Thus, in use, with the housing 1, 2 with the ultrasonic transducer 5 applied to the surface of a component and spaced from the surface of the component by four bearings 21 located in housings in the lower part of the extension 3, couplant fluid admitted through the inlet chamber 4 and through the gap 12 flows over the surface of the component to effectively couple the ultrasonic transducer with the component. As the pressure of the couplant fluid builds up and when the housing is moved across the surface of the component there is inevitable spillage of couplant fluid but with vacuum applied through the outlet holes 19, 20 to the extraction chamber 15 a high proportion of the fluid is sucked into the extraction chamber as a consequence of the applied vacuum.

By spacing the lower end of the housing from the component by the bearings, air is drawn into the extraction chamber from around the housing thus assisting considerably the passage of couplant fluid into the extraction chamber.

To ensure a constant supply of a controlled flow of couplant fluid to the inlet chamber, it is preferred to connect the inlet hole 10 to a source of couplant fluid via a centrifugal pump or constant volume pump having a manually controlled flow rate.

Although not shown, it is preferred that the outlet hole 1 9 is connected to a storage container for couplant fluid, which storage container can be evacuated by an appropriate vacuum generating system. Thus, couplant fluid drawn into the extraction chamber 20 can be delivered to the storage container to be stored either for subsequent recycling or disposal.

Claims

1. A method of ultrasonic testing comprising continuously supplying couplant fluid to the operative surface of an ultrasonic transducer, surrounding the ultrasonic transducer with an extraction chamber, and applying vacuum to the extraction chamber, whereby couplant fluid is continuously removed from the vicinity of the operative surface of the ultrasonic transducer.

2. Ultrasonic testing equipment comprising a housing in which the ultrasonic transducer is secured, a first annular wall within the housing forming with the outer surface of the ultrasonic transducer a chamber for the admission of couplant fluid, a second annular wall on the housing, the second wall co-operating with the first wall to form an annular extraction chamber, and there being connection means to the first chamber for the supply of couplant fluid and connection means to the extraction chamber for the application of vacuum.

3. Ultrasonic testing equipment as in Claim 2, wherein the first annular wall has a length such that with the ultrasonic transducer secured in place, the annular wall projects beyond the operative surface of the ultrasonic transducer.

4. Ultrasonic testing equipment as in Claim 2, wherein discrete projections are provided on the housing to form bearing surfaces.

5. Ultrasonic testing equipment as in Claim 4, wherein the discrete projections are formed by hard metal balls set in recesses in the housing.

6. Ultrasonic testing equipment as in any of Claims 2 to 5, wherein the housing is of two part construction in screw threaded engagement, an upper housing member having an extension extending through a lower housing member, the ultrasonic transducer fitting in a bore through the upper housing member and its extension, and forming with the wall of the bore a chamber for the admission of couplant fluid, and the extension and the lower housing member forming between them an extraction chamber.

7. Ultrasonic testing equipment as in any of Claims 2 to 6, wherein a pump having a controllable flow rate of couplant fluid to the chamber is provided for the admission of couplant fluid.

8. Ultrasonic testing equipment as in any of Claims 2 to 7, wherein the ultrasonic transducer is adjustably mounted in the housing to allow its replacement by an ultrasonic transducer of different characteristics.

9. Ultrasonic testing equipment as in Claim 8, wherein the ultrasonic transducer is a push fit in the housing.

10. Ultrasonic testing equipment as in Claim 7 or Claim 8, wherein adjustment means to position the ultrasonic transducer such that the distance from the point of contact with the component from the operative face of the housing is correctly set.

11. Ultrasonic testing equipment as in any of Claims 2 to 10, wherein a clamping ring is provided to secure the ultrasonic transducer to the housing with an interposed sealing ring to prevent the escape of couplant fluid rearwardly of the housing.

12. Ultrasonic testing equipment substantially as hereinbefore described with reference to the accompanying drawings.