GB2027199A

GB2027199A - Process and apparatus for the ultrasonic testing of tubes and rods

Info

Publication number: GB2027199A
Application number: GB7921973A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1978-06-27
Filing date: 1979-06-25
Publication date: 1980-02-13
Also published as: IT1121852B; FR2430010A1; IT7923719A0; JPS556287A; DE2828643A1

Abstract

A process and an apparatus for the ultrasonic testing of tubes and rods moving axially without rotation has fixed testing heads 3,3',3'' which are replaceably mounted in testing head holders 1 and are individually connected to electronic evaluating means. The testing heads provided at regular intervals over the circumference of the testpiece to give 100% coverage (Figs 2 and 3, not shown) transmit sound through the testpiece and the test results of the individual sound sources are evaluated separately. The process and apparatus have particular application in the testing of tubes or rods with an external diameter up to 100 mm. Testing speeds of up to about 500 m/hour are possible. Internal and external tube defects are detectable (Fig. 4, not shown). <IMAGE>

Description

SPECIFICATION Process and apparatus for the ultrasonic testing of tubes and rods The present invention relates to a process for the ultrasonic testing of tubes and rods travelling in a straight line through an apparatus with fixed testing heads, particularly for external tube diameters of about 100 mm, and to an apparatus for performing the process.

According to test requirements such as, for example DIN 1 7 175, seamless and welded high quality tubes have to be subjected to full ultrasonic testing over their entire circumference.

With the considerable increase in the production of high quality tubes, the test capacities of ultrasonic testing equipment have had to be further extended and partially automated.

Up to the present time, test capacities have only been increased by extending the test equipment.

However, this is no longer economically viable, as the costs of transportation, warehouses and staff increase out of all proportion to the throughput when the number of apparatus is increased, and this particularly affects tubes in the smaller size range.

The following known test methods are preferred for ultrasonic testing: 1. Fixed testing heads with the testpieces transported helically through the test equipment.

In this method, multiple oscillator testing heads are used to increase the pitch of the spiral, and this has led to a considerable increase in the costs of the apparatus. Moreover, in this method, the upper limits of the testing speed have been reached and used to the full owing to the high cycle sequence required for the electronic testing equipment because of the high speed of rotation of the testpieces.

A major disadvantage of this method is the very high cost on the roller beds. With tubes in the smaller size range, in particular, it is difficult to transport tubes rotating at high speed without causing impact and at the same time advance these tubes through the test apparatus.

In most cases, the ends of the test pieces cannot be tested adequately as they cannot be tested end to end because of the great impact.

Another disadvantage of this method is the accuracy of guiding of the testing head holders, since in contrast to rotary apparatus, the mechanical coupling is effected only on one side and therefore, because of inertia, the holding means cannot easily follow all the movements of the testpiece.

2. tn rotary testing equipment, the entire surface of the testpiece is again scanned helically. The testpieces travel in a straight line through a rapidly rotating cylindrical testing head holder fitted with testing heads. This method has the advantage that there is no need for large drives or guides for the rotating testpieces. The testing capacities are limited both by the speed of rotation of the testing head holders and also by the complicated mechanical drive.

A disadvantage of both methods is that lengthwise defects cross directly over the sound field, depending on the direction of incidence of the sound. This means that defects can only be detected for a short time, irrespective of their length. As a result, depending on the detectability of the defects, there is a limit to the permissible frequency of impulses and the maximum possible testing speed is restricted; furthermore, defects below a certain length (in the region of the diameter of the sound field) can only be detected statistically, which means that it is impossible to determine the defect length automatically.

We have sought to provide a process whereby tubes and rods can be tested at extremely high throughput speeds without rotating the testpieces or test equipment (rotary test equipment}, and to provide an apparatus for performing the process.

Accordingly in one aspect the present invention provides a process for the ultrasonic testing of a tube or rod testpiece travelling in a straight line through an apparatus with fixed testing heads, wherein sound is transmitted through the testpiece simultaneously by sound sources distributed around the entire circumference which touch one another with their sound cones and test results from individual sound sources are evaluated separately.

In another aspect the present invention provides an apparatus for the ultrasonic testing of a tube or rod testpiece which comprises a fixedly mounted, totally replaceable, cylindrical testing head holder with testing heads inserted at regular intervals over the circumference in replaceable manner, each test head being individually connected to an electronic evaluating means.

Preferably, the waves of sound are formed into beams by focussing and the number of sound sources is determined by the total coverage of the circumference of the testpiece. In a preferred embodiment the readouts of defects for each sound source are given separately and the evaluation detection ranges of the sound sources are subdivided.

The testing heads are preferably mounted offset relative to one another and the testing head holder is replaceable and held in position by a quick-release mechanism.

In the process of the present invention, the testpiece is moved through a cylindrical testing head holder. However, the testing head holder does not rotate about the axis of the tube but is stationary.

Scanning of the entire surface of the testpiece, without any gaps, is achieved by the fact that testing heads are arranged so close together round the entire testing head holder that the beams of sound cover the entire surface of the testpiece.

Since the number of testing heads requires increases sharply with the increase in the diameter of the testpieces, owing to the enlarged surface area of the testpieces to be tested, this process is particularly suitable for testing tubes or rods in the smaller size range, e.g. the entire range of boiler pipes or jackets.

There is no technical upperlimit to the range of dimensions which can be tested; the only limit is that imposed by economics and the question of justifiable expense.

With tubes below a certain diameter, the process according to the invention is considerably cheaper from the point of view of the apparatus than known processes. The process and apparatus of the present invention have particular application in the testing of tubes or rods with an external diameter of up to 100 mm.

The advantages of the new process are as follows: 1. Testing speeds of up to about 500 m/h are possible.

2. There is no rotation of the tubes. Consequently there is reduced expenditure on mechanical roller beds and guides.

3. There is no rotation of the testing heads. Therefore, mechanically less complicated testing headl holders and hence simpler construction can be used.

4. The ends of the tubes can be tested, as the tubes can travel end to end.

5. The length of longitudinal defects can be determined, as the test heads are guided past the defects so as to travel paraliel to them; this also facilitates the scanning of any defects indicated.

6. There is a certain detection of defects less than about 6 mm long.

7. There is easier replacement of the testing head holders which are dependent on the dimensions of the tubes.

The present invention is further illustrated in the accompanying drawings which schematically show an apparatus according to the invention for testing an external tube diameter of about 38 mm.

In the drawings: Figure 1 is a cross section through a testing head holder; Figure 2 is a detail of a portion of testpiece; Figure 3 is a detail of the testing head holder; Figure 4 is a view of the read-outs of an internal and an external defect on the picture screen; Figure 5 is a front view of the entire apparatus; and Figure 6 is a plan view of Figure 5.

Figure 1 shows a cross section through a testing head holder 1 with a tube 2 which is to be tested.

In the cylindrical testing head holder 1, six testing heads 3 are arranged so that they direct sound at the tube 2, the middle point of which coincides with that of the testing head holder 1, in such a way as to fulfill the conditions for the sound incidence.

The testing heads 3 shown are all pairs of associated testing heads 3, 3' and 3". The space between the testing head holder 1 and the surface of the tube is filled with coupling water.

In the view shown in figure 1 , the diameter of each beam of sound meeting the outer surface of the tube is about 10 mm. In order to concentrate the sound beams, all the testing heads are fitted with convex ancillary lenses 4. This ensures that all the sound rays in a beam meet the surface of the tube at the same angle of impact. In the example illustrated, this angle of impact is always 190.

Thus, for these three beams, angles of incidence in the material of about 450 are obtained.

To make the drawing clearer, only those sound beams from the testing heads 3 which strike the testpiece anticlockwise are shown in the testpiece.

The testing heads 3 which make contact in the clockwise direction are arranged, in the example shown here, so that monitoring of the operation is carried out by means of the sound transmitted from the cooperating pairs of heads 3, 3' or 3" in reverse. However, it is also possible for the two testing heads of a pair of testing heads to be arranged so that monitoring of the operation can be carried out by means of the beams reflected directly on the outer surface of the tube 2, for example from 3 to 3 and vice versa. If three testing heads transmitting sound in each direction of rotation of the tube are arranged in a cross-sectional piane, only T of the whole outer surface of the tube to be tested is covered Therefore, in order to cover 1 09/0 of the entire surface, even more testing heads than are shown here are required.

The arrangement required for 100% coverage is shown in Figure 2.

This Figure shows the development of the outer surface of a section of tube which is to be soundtested.

The area shown on the left are covered by the testing heads 3, 3' and 3" shown in Figure 1.

In order to fill all the remaining outer surface without leaving any gaps, another three testing planes each having three pairs of testing heads are required. Operation in the circumferential direction-in Figure 2 the surface development-is offset from one testing plane to the next. Thus, for example, a total of 24 testing heads are required for the dimensions 38x4. This corresponds to the electronic equipment required in present testing equipment. However, the mechanical equipment required is considerably less.

The development in Figure 3 shows the offset arrangement of the testing heads in the testing head holder 1.

Figure 4 shows a view of the ultrasonic readouts for an internal and external defect by a testing head. The path of the read-out along the time axis of the screen of an ultrasonic apparatus is produced as a tube having an inner and outer groove in a testirig head holder 1 set to these defects with a testing head 3 is rotated in the holder. The extents of the base on the time axis of read-outs E1 and EA each correspond to the diameter of an outer surface according to Figure 2 scanned by a testing head 3.

Description of read-out EA of the external defect: The amplitude of the read-out of the external defect is of varying height as the tube rotates. It fluctuates according to the type of testing head, the construction of the ancillary lenses and the distance of the testing head. In this example of a tube measuring 38x4, the fluctuation is about 5dB, corresponding to an opened-out outer surface of 8 mm, with an oscillator diameter at 6 mm.

However, if these deviations are too great, it is possible to subdivide the evaluation ranges AEB, for internal defects and AEBA for external defects so that any fluctuations in sensitivity which may occur can be balanced out.

In the example shown in Figure 4, the three echoes EjA, E2A and E3A of the external defect have the amplitudes AE1A AE2A and AE3A.

In order to evaluate these three echoes equally, the read-out expectation range AEBA is divided into three ranges. Since different evaluation thresholds can be set, the echoes EtA, E2A and E3A can be evaluated equally within limits of about 2dB.

Key to Figure 4: Es = transmitted impulse E0=surfaceecho E, = internal defect echo EA = external defect echo E;A = 1 st external defect echo E2A = 2nd external defect echo E3A = 3rd external defect echo AE,A = amplitude of the 1 st external defect echo AE2A= amplitude of the 2nd external defect echo AE3A = amplitude of the 3rd external defect echo AEBi = read-out expectation range for internal defect AEBA = read-out expectation range for external defect In the above examples, the process of the present invention is explained solely with reference to longitudinal defects.

however, the process can also be used for transverse defects and for testing wall thickness. The arrangement and number of testing heads used depends on the type of testing to be carried out.

Readily replaceable testing head holders 1 are required in order to test the entire range of dimensions with the process of the present invention.

If in focus, diameter of the oscillator and the focal point are carefuly chosen, it is possible to test external tube diameters which are very close together with one testing head holder 1. The test apparatus is equipped so that mechanical pre-adjustment for the next tube dimension can be carried oul within the apparatus.

Figures 5 and 6 show an apparatus in accordance with the present invention. The run-in portion of the apparatus consists of a V-shaped roller bed with driven rollers 5 and a pair of rollers 6 of the drive mechanism. A threaded spindle 7 is provided, for centrically displacing the roller pairs 6. A spring 8 operating mechanically, hydraulically or pneumatically is provided, for generating a defined normal force. In the centre of the entire apparatus, which is mounted on a stand and can be made up of individual components, is the testing head holder 1 which is held in position by a quick-release mechanism 10 containing, for example, a toggle 11 to brace it.

The testing component itself consists of the testing head holder 1, the size of which depends on the dimensions of the tube. Incorporated in this testing head holder 1 are as many testing heads 3, 3' and 3" as are required to test the whole of a tube 2 moving in a translatory motion through the testing head.

The run-out portion of the apparatus is identical to the run-in portion i.e. it, too, consists of a pair of drive rollers 6 and a driven roller 5 for the run-out roller bed.

Claims

1. A process for the ultrasonic testing of a tube or rod test piece travelling in a straight line through an apparatus with fixed testing heads, wherein sound is transmitted through the testpiece simultaneously by sound sources distributed around the entire circumference which touch one another with their sound cones and test results from individual sound sources are evaluated separately.

2. A process as claimed in Claim 1, wherein read-outs of defects for each sound source are given separately.

3. A process as claimed in Claim 1 or 2, wherein the waves of sound are formed into beams by focussing.

4. A process as claimed in any of claims 1 to 3, wherein the number of sound sources is determined by the total coverage of the circumference of the testpiece.

5. A process as claimed in any of claims 1 to 4, wherein the evaluation detection ranges of the sound sources are subdivided.

6. An apparatus for the ultrasonic testing of a tube or rod testpiece which comprises a fixedly mounted, totally replaceable, cylindrical testing head holder with testing heads inserted at regular intervals over the circumference in replaceable manner, each test head being individually connected to an electronic evaluating means.

7. An apparatus as claimed in Claim 6, wherein the testing heads are mounted offset relative to one another.

8. An apparatus as claimed in Claim 6 or 7, wherein the testing head holder is replaceable and held in position by a quick-release mechanism.

9. A process for the ultrasonic testing of a tube or rod testpiece substantially as herein described and with reference to the accompanying drawings.

10. An apparatus for the ultrasonic testing of a tube or rod testpiece substantially as herein described and with reference to the accompanying drawings.

11. Any novel element, or combination or elements, herein described and/or shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same invention as, any of the preceding claims.