Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light

Definitions

• the present invention relates to a system, apparatus and method for testing elongate objects, such as pipe, and is directed toward the problem of detecting corrosion, defects or other anomalies to the pipe under conditions where access and/or visual inspection of the pipe is either not possible or impractical.
• the method of the present invention enables corrosion on an elecromagnetical permeable elongate member, such has a pipe, to be detected quite effectively. More specifically, this method enables much of the irrelevant information (reflections, electromagnetic noise) to be elimiated from the wave form, and then the wave forms processed in a particular manner to enable clearer identification of variations in the wave form that would indicate corrosion.
• a nearside and far side electric or electromagnetic pulses (waves) are transmitted from, respectively, nearside and farside spaced transmitting locations on the elongate member. The pulses (waves) travel toward one another to intersect at intersecting locations on the elongate member.
• the farside pulses are received as wave forms at a receiving location after intersection with related nearside pulses.
• the transmission of the nearside and farside pulses are synchronized so that the intersections of the near side and far side pulses (waves) occur at spaced intersecting locations on the elongate member.
• the wave forms of at least two of the far side pulses (waves) which are spaced from one another are combined to form a composite wave form.
• a variation of variations are ascertained- fronrt the composite wave form as a means of detecting corrosion.
• one of the wave forms of the two wave forms that are to be combined is inverted and then added to the other of the waveforms being combined to create a difference waveform, and variations in the difference wave form are ascertained as a means of detecting corrosion.
• the nearside pulses which pass through points of intersection that are adjacent to one another are considered to be sequential nearside pulses, with the order of sequence being the same as the order in which the points of intersection are spaced along the elongate member.
• the combining of the nearside waveforms is accomplished in a pattern such that first and second adjacent wave forms are combined to make a first composite waveform, the second waveform and an adjacent third waveform are combined to make a second composite waveform, the third waveform is combined with an adjacent fourth waveform to make a third composite waveform, with the pattern repeating itself with subsequent pairs of waveforms from adjacent farside pulses.
• Adjacent composite wave forms are compared with another as a means of detecting corrosion.
• a reference wave form is established by creating composite wave forms resulting from pulses that intersect at non- corroded areas of the elongate member, and identifying composite waveforms that differ from the reference composite waveform by a phase shift and/or dispersion and/or amplitute and and/or wave distortion. Corrosion that is present between two adjacent points of intersection on the elongate member is detected by comparing a composite wave form resulting from combining the difference waveform overlapping the point of intersection with difference wave forms on opposite sides of the overlapping composite waveform.
• corrosion that is present at a point of intersection of two wave forms can be detected by deriving two difference waveforms by combining the waveform at the point of corrosion with adjacent waveforms to form two difference wave forms which are then compared. Also, two additional difference wave forms that are on opposite sides of, and adjacent to, the two difference waveforms which are analyzed to detect the corrosion are compared with the two difference waveforms which are combined at the point of intersection as a means of detecting corrosion.
• Figure 1 is a somewhat schematic view of the system of the present invention being in its operative position where it is being used in testing a length of insulated pipe;
• Figure 2 is a graph illustrating one way in which data can be taken and presented in accordance with the present invention, this graph plotting propagation time against distance from A to B and again from B to A giving a reversed profile;
• Figures 2A and 2B are schematic drawings showing the intersection of two pair of pulses at adjacent spaced locations
• Figure 3 is a graph which displays a curve in the lower part of the graph which represents a composite wave form resulting from both the near side of far side pulses traveling along the pipe section under test, and the curves at the upper part of Figure 1 showing resulting wave forms at different locations, using the method of the present invention
• Figure 4 is a graph which is similar to the upper part of the graph of Figure 3 , displaying separately a first resulting wave form identified at the zero location shown in Figure 3
• Figure 5 is a graph similar to Figure 4, but showing separately the resulting wave form identified at the 25 location shown in Figure 3 ;
• Figure 6 is a graph similar to both Figures 4 and 5, but showing separately the resulting wave form at the 50 location of Figure 3;
• Figures 7A through 71 are a series of simplified illustrations of wave forms to demonstrate certain principles of different wave forms
• Figures 8A through 8E and Figures 9A through 9E are two series of Figures similar to those of Figures 7A through 7E, and to illustrate further the certain principles of difference wave forms;
• Figure 10 is an illustration of the paths of the electromagnetic wave components traveling along a section of pipe.
• Figures 11 - 16 are presentations of wave forms illustrating the difference wave forms produced in accordance with the method of the present invention.
• Figure 17 is a graph illustrating the wave forms in the first step of third embodiment of the present inventions.
• Figure 18 is a graph similar to Figure 17, showing the wave forms of a subsequent step in this third embodiment
• Figure 19 is a schematic drawing of the place for the antennas in this third embodiment
• Figure 20 is a graph similar to Figures 17 and 18 illustrating a third step in the third embodiment ;
• Figure 21 is a graph showing three of the wave forms of Figure 20, drawn to a scale emphasizing the vertical dimension of the waves;
• Figure 22 is a graph similar to Figure 21 showing the wave forms of Figure 21 and also the difference wave forms derived therefrom;
• Figure 23 is a graph similar to Figure 21 showing three of the waves moved together;
• Figure 24 is a graph showing a plurality of difference wave forms, where two areas of corrosion are being detected;
• Figure 25 is a graph derived from the earlier wave forms illustrating the difference in amplitude of the difference waves where corrosion exists;
• Figure 26 is a graph based on Figure 24, further emphasizing the differences in amplitude.
• FIG. 1 There is shown a pipe 10 having a section 11 which is under test.
• This pipe 10 is or may be a pipe or pipeline that would typically be used in the petroleum or petrochemical industry, where the pipe is made of steel and surrounded by a coat or layer of insulation.
• the apparatus 12 of the present invention is shown somewhat schematically in its operating position, testing the section 11 of the pipe 10.
• This apparatus 12 comprises a pulse generator 14, a signal analyzer 16, and interactive computer 18, and two transmitting/receiving antennas 20 and 22.
• the transmitted pulse When the transmitted pulse is received by one or the other of the antennas 20 or 22, this pulse is in turn transmitted to the signal analyzer. Certain analysis can immediately take place in the signal analyzer 16. Alternatively, the information relating to the pulse can be stored and analyzed at a later time. The computer performs certain control functions in the proper transmission and reception of the pulses and other functions . There are several ways in which an apparatus, such as the apparatus 12, can be used in detecting corrosion in pipes, and two of these will be discussed below. There is a first method where a single pulse is transmitted from the pulse generator 16 to one or the other of the antennas 20 or 22 to cause the wave form to travel from the location of that antenna 20 or 22 along the pipe 10 to the location of the other antenna 20 or 22 where the signal from the wave form is received.
• the distance between the sending location 20 and the receiving location 22 is ascertained accurately, and the timing of the time of transmission of the pulse from the antenna 20 or 22 to the other antenna 20 or 22 is measured very accurately (desirably to a fraction of a nanosecond or even to a very small fraction of a nanosecond) . If the section between the two test locations 20 and 22 is non- corroded, and if the pipe is uniform along its length, then the pulse will arrive at the receiving location 22 in a wave form which is in the same general pattern (except possibly for disturbances, such as a near by magnetic field, electromagnetic noise, etc.) . Also, the rate of travel of the pulse would remain substantially constant, provided the pipe remains uncorroded and uniform.
• One method of utilizing this technique is to send the pulse from the transmitting location to the receiving location over an uncorroded section of pipe of a know length and diameter, and known characteristics, relative to its transmission of electromagnetic waves. This would establish the time of travel of the wave from the transmitting to receiving location and the expected configuration of the wave form at the receiving location.
• Figure 1 can be used. However, instead of using a single pulse or series of single pulses, as in the method described above, both antennas 20 and 22 are used as both transmitting and receiving antennas in the same timeframe. Thus, as one pulse is transmitted from the antenna 20, one is also transmitted from the antenna 22. These pulses travel toward one another and "collide" at some intermediate location along the pipe. This meeting of the pulses will cause variations in both of the wave forms as they move through the area of collision toward the other antenna which is its receiving location.
• the point of collision along the length of the pipe can be caused to occur at any desired location along the length of the pipe. Then by changing the relative time transmissions of the pulses in small increments, this point of collision can be stepped along the length of the pipe.
• the wave form resulting from the collision will be different from a reference, wave form which would occur where the collision point is at a non- corroded section of pipe.
• the antennas 20 and 22 could be used only as transmitting antennas and two additional antennas could be used as receiving antennas. Further, other transmitting and receiving devices could be used, such as by making a direct electrical connection to the pipe.
• the present invention is particularly adapted for extracting information from the wave forms resulting from the dual pulse method described above .
• a first embodiment of the method of the present invention is described in the following text, with reference to Figures 2A-2B through Figures 9A-9E.
• a second embodiment is also disclosed later herein, using in part the same principles as the first embodiment, and this will be described later with reference to Figures 10 - 16.
• Figures 2A and 2B are schematic illustrations of the operation of the dual pulse method.
• Figure 2A there is schematically shown a one hundred foot length of pipe. It will be assumed that the pulse travels along the length of the uncorroded pipe at the rate of one foot per nanosecond.
• the near side pulse is transmitted into the pipe at the location NS (near side location) at a point in time indicated at zero.
• the second pulse is transmitted into the pipe at the far side location (designated FS) , and in this particular example, it is assumed that the second far side pulse is transmitted into the pipe forty nanoseconds earlier than the time the near side pulse is transmitted into the NS location. Therefore, it can be seen that when the far side pulse has traveled along the length of the pipe for forty nanoseconds to reach a location indicated at the sixty foot location, the near side pulse is transmitted at time zero from the near side location.
• the near side and the far side pulses travel toward one another, each traveling thirty feet until they intersect at the thirty foot location on the one hundred foot pipe. At the intersection, the two pulses interact with one another, and the far side pulse continues it path of travel to the near side (NS) location. Also, the near side pulse after passing through the point of intersection continues its course of travel toward the far side (FS) location.
• each of the pulses is a somewhat complex wave form.
• a wave form travels along the length of the pipe, it is subject to attenuation, distortion, interference and dispersion.
• each wave can be considered as having what we might term wave components made up of earlier and later arrivals.
• There is a first arrival which will travel the shortest course from the transmitting to the receiving location.
• the first arrival will travel along the top surface of the pipe in a straight line.
• second arrivals which are pulse components which follow a helical path once around the pipe to arrive at a short time later.
• third, fourth, fifth, ....etc. arrivals which come at yet later times.
• This curve, designated 50 is a composite curve which results from the combination of both the near side and the far side pulses. In this instance, one transmission takes place at the near side, and the receiving antennae is also located at the near side. The portion of the curve indicated at 52 represents the near side pulse being transmitted into the pipe at the transmitting location.
• the portion of the curve indicated at the general area of 54 represents a portion of the composite wave that arrives at the near side receiving location, this being a combination of the far side wave and near side wave components. As indicated above, there are reflections, refractions, late arrivals, etc., which complicate the wave form.
• FIG. 2B shows a second dual pulse operation where the transmission time of the far side pulse has been delayed by four nanoseconds, so that it is transmitted thirty six nanoseconds before the transmission of the near side pulse. It can be seen that after the far side pulse has traveled thirty six feet, the transmission of the near side pulse takes place. Thus when the near side pulse is transmitted, the far side pulse is at the sixty four foot location, and the two pulses intersect at the thirty two foot location.
• the composite wave form which results from the transmission and intersection of pulses as shown in Figure 2A is stored in the memory.
• the second composite wave form resulting from the transmission of the near side and far side pulses in accordance with Figure 2B is also received.
• the second composite wave form resulting from the test operation of Figure B is subtracted from the composite wave resulting from the test operation in Figure 2A.
• Figure 4 illustrates the single curve indicated at "0" in Figure 3;
• Figure 5 illustrates only the curve indicated at "25” in Figure 3; and
• Figure 6 illustrates only the curve indicated at "50” in Figure 3.
• wave forms indicated at "0", "25”, and “50" in the top part of Figure 3 are actual wave forms extracted from adjacent wave forms similar to the ones shown in the lower part of Figure 3. It is important to note that if the composite wave form is not formatted correctly, the difference between adjacent wave forms does not provide the "effect" wave forms shown in Figure 3.
• the "effect” time rise, slope, amplitude, dispersion and absolute time, among many parameters that are effected by corrosion
• the difference wave form will be displaced in time with respect to other adjacent pairs. This time displacement is a good indication of the condition of the pipe, provided it can be meaningfully interpreted.
• the difference wave forms shown here are examples of- the wave forms that are well defined, but are very difficult to extract real time information. (See Figures 4, 5 and 6. Note particularly Figure 6 at the "knee" of the wave form is not well defined, and could be selected anywhere from a point near thirty two hundred to forty two hundred, a range of one hundred nanoseconds.
• the peak is well defined.
• the peak is not just a voltage difference between two different response wave forms, but it is determined by the shape factors involved with the leading edge of the two adjacent wave forms. For example, if the two adjacent wave forms are displaced more in time than any two other adjacent wave forms, it will result in an increase of amplitude.
• " -.E" (peak) is a function of time. It is also a function of actual amplitude difference between two different wave forms. Also, if the leading edge of one wave form is distorted as a result of corrosion, this distortion will result in a change of amplitude in the difference wave form and a shift in the position of the peak with respect of time.
• the peak is very sharp and the shape of the difference wave forms extremely uniform.
• the pipe has anomalies (e.g. corrosion)
• the shape of the difference wave form is significantly altered and the corrosion effect (CE) displaced by major differences in the leading edge.
• This peak shift is much easier to instrument and measure than other parameters. Also this peak shift is an indicator of the cumulative effect of all individual parameters and effect the electromagnetic response, even if they might be very difficult to measure individually. As the pipe degrades, the peak distorts more readily because of the complex contribution of all driving forces. In a perfect system, every difference pulse should be identical. Hence, measuring the time associated with the first peak occurring after an indefinite knee of a differential pair, provides an effective way of extracting critical information and measuring the corrosion effect.
• Figure 7A shows a rather simple wave form 60 which is drawn, for convenience, in straight lines.
• Figure 7B shows the same wave form at 62, but offset one unit from the wave form 60.
• Figure 7C shows the summation of the wave forms 60 and 62 as the wave form 64. It is possible to drive meaningful information from the wave form in Figure 7C where the wave. forms are added, but it is preferred to first one of the wave forms and then add the two together. This is done in Figure 7D which shows the wave form 60, with the offset wave form 62 inverted, and the summation of the wave 60 and the inverted wave 62 accomplishes a subtraction of the wave forms of Figure 7A and 7B. This results in the difference in the difference wave form 66 shown in Figure E.
• FIG 7F the wave form 74 is shown, exactly in the same form and position as the wave form 60 of Figure 7A. Then the same wave form is shown in Figure 7F at 76, inverted and shifted two units from the wave form 74. Then when the wave form 76 is subtracted from the wave form 74, there is the difference wave form 78 shown in Figure 7G. It will be noted that with the wave form 76, spaced two units away from the wave form 74 (instead of one unit, as in Figures 7A and 7B)has an amplitude which is twice the amplitude Of the difference wave form 66. This illustrates that if the time displacement of the wave forms increases, the amplitude of the difference wave form would be expected to increase. This is simply by way of illustration, and relates to only one particular facet of detecting corrosion from the difference wave form.
• Figure 8A through 8E For purposes of further analysis, reference is made to Figure 8A through 8E and to Figures 9A through 9E.
• Figure 8A there is shown a wave form 80, and in Figure 8B a second advanced wave form 82 which has been attenuated and delayed, presumably because of encountering corrosion in the pipe.
• Figure 8C shows the summation of these, this being the wave form 84.
• Figure 8D shows the same wave form 80 and the adjacent wave form 82 inverted.
• Figure 8E shows a difference wave form 86 which results by subtracting the wave form 82 of Figure 8B from the wave form 80 of Figure 8A.
• Figure 9A shows a wave form 88 which is the same as the wave form 80 of Figure 8A.
• Figure 9B shows a second wave form 90 delayed by one unit, and having a different slope along the leading edge.
• Figure 9C shows the summation wave form at 92.
• Figure 9D shows the wave form 88 and the second wave form 90 inverted.
• Figure 9E shows the difference wave form at 94.
• four of the figures show difference wave forms, these being the difference wave form 66 in Figure 7E, the difference wave form 78 in Figure 7G, the difference wave form 86 in Figure 8E, and the difference wave form 94 Figure 9E.
• FIG. 10 shows a relatively short section of pipe, where there is a transmitting location 102 and receiving location 104.
• these locations 102 and 104 are both at the top of the pipe and aligned.
• the straight line lengthwise axis between the points 102 and 104 is indicated at 106. Since this axis 106 is the shortest path between the points 102 and 104, the first arrival path would be along the path indicated at 108, which is coincident with the axis 106.
• first arrival wave component 108 there are two second arrival wave components, the travel paths of which are indicated at 110 and 112. It can be seen that each of these are helical paths, which travel longitudinally and through a helical curve of 360°. Then the third arrivals are indicated at 114 and 116, and these also are helical paths, but with a total circumferential component of travel of 720°.
• the second arrival has a longer path of travel than the first arrival
• the third arrival has a yet longer path of travel than the second arrival, etc. If there is corrosion on the pipe, at least some of these later arrival pulse components will pass through the area or areas of corrosion and that path component will be delayed, attenuated, and/or otherwise modified.
• Figure 11 illustrates the wave forms obtained by the second embodiment of the present invention.
• the vertical axis represents voltage (measured in volts)
• the horizontal axis measures time, with each increment representing ten nanoseconds.
• the numeral one thousand actually represents one hundred nanoseconds
• the numeral two thousand represents two hundred nanoseconds, etc.
• the wave forms presented in Figure 11 extend over a full five hundred nanoseconds.
• the particular tests from which these curves were developed were done over a pipe section one hundred and sixty feet length (i.e. the transmitting location was one hundred and sixty feet away from the receiving location) .
• the dual pulse method was utilized, as indicated above. Since the entire pipe is encircled by electromagnetic energy, the effect of corrosion anywhere on the pipe will appear in the difference wave form obtained by intersection of the pulses at the location of corrosion.
• the first steps in the second embodiment in the method of the present invention are substantially the same as those of the first embodiment. More specifically, a first testing operation was performed by transmitting the near side and far side pulse in timed relationship so that these would meet at a predetermined point of intersection. There is a composite wave form resulting from this first test operation and that is stored. Then, as described in the presentation of the first embodiment, there is a second operation in timing of the far side pulse so that it was either advanced or delayed so that the point of intersection was shifted, and the result was a composite wave being recorded that had components of the far side pulse shifted somewhat from the previous composite wave. As described in the first embodiment of this method of the present invention, one of the composite wave forms is subtracted from the other to get a difference wave form.
• the next step is to plot the second difference wave form 122, but the second difference wave form 122 is shifted to the left, and is also lowered somewhat so that the second difference wave form 122 is aligned with and a short distance below, the first difference wave form 120.
• the two wave forms 120 and 122 match each other rather closely.
• These two difference wave forms 120 and 122 were derived from adjacent composite wave forms, and both of these composite wave forms resulted from a dual pulse operation where the pulse is intersected at a noncorroded area (or at least a very lightly corroded area) of the pipe under test.
• the upper composite wave results from a difference wave form where a reference point of intersection was that at the 125.3 feet mark, while the second difference wave form 122 was made up of adjacent composite wave forms at a reference location 129.6.
• Figure 12 shows two other reference wave forms 124 and 126, resulting from two adjacent pair of composite wave forms at reference locations at the 34.6 and 38.9 foot locations on the pipe section under test. These composite wave forms also resulted from the far side and near side pulses of each test operation intersecting at a noncorroded (or very lightly corroded) area of the pipe section under test.
• the lower wave form 128 has a reference of 43.2. This was at a somewhat corroded pipe section having a corrosion index of 1.0262. (The corrosion index is a scale which is utilized by the inventor in rating areas of corrosion. A rating of 1.000 would be no corrosion and the higher the number, the greater the severity of corrosion) .
• the lower wave form 128 has at two areas something of a phase shift, indicated at 130 and 132.
• Figure 15 shows as the upper wave form the same wave form 136 which is the lower wave form in Figure 14, and a new difference wave form 140 taken at a reference location of 160 feet on the pipe.
• These wave forms resulted from composite wave forms developed with the intersecting locations being at more highly corroded areas.
• Several features should be noted. In observing the peak location at 142, and the two peak locations at 144 and 146, it can be seen that there are substantial amplitude differences with regard to the second and third peaks between these curves 136 and 140. In addition there is significant phase shift indicative of corrosion anomalies.
• the presence of corrosion is detected by a method which might be termed "whole wave analysis", which involves looking not only at the leading portion of the wave, but also a much greater time span of the wave form which also contains significant information. It also becomes apparent that valuable information is obtained from portions of the wave form as far along the wave form as two hundred to four hundred nanoseconds or longer from the first arrival of the electromagnetic pulse. Further, the location of the corrosion can be located within reasonably close tolerances by properly synchronizing the pulses so that the point of intersection is known. Also, it should be noted that these readings were taken on the same section of pipe, but with the intersection being moved to different locations.
• the pulses will be transmitted from the far side and near side locations, and in this particular embodiment, the wave form which is to be analyzed to detect corrosion is the far side pulse arriving at a receiving location adjacent to the transmitting location at the near side. Also, in this third embodiment , the time intervals between the transmissions of the far side pulse will remain constant. Thus, to synchronize the pulses so that the point of intersection stepped along the length of the pipe, for each transmission, the near side pulses shall be advanced in timing by a short increment so that the point of intersection of the pulses will be stepped in a left to right direction across Figure 18.
• FIG. 19 there is shown a section of pipe 170 having a Near side transmitting antenna 172 and a far side transmitting antenna 174. There is a receiving antenna 176 spaced from the transmitting antenna 172 a short distance toward the far side transmitting antenna 174. Initially, the far side transmitter remains inactive so that the far side transmitting antenna 174 is not transmitting any signal. The near side transmitter is activated to transmit a series of timed pulses which are synchronized with regular time intervals. This is done in a manner that each subsequent pulse is advanced four nanoseconds relative to the preceding pulse.
• the first pulse would be sent at 0 seconds .
• the second pulse would be transmitted four nanoseconds before the two second interval .
• the third pulse would be sent eight nanoseconds sooner than the four second interval .
• the first pulse would be sent twelve seconds before the 8 second interval, etc.
• the first pulse is transmitted at 0 nanoseconds, the next pulse indicating as having a four nanosecond advance, the third pulse at 8 nanoseconds advance, with these advances continuing on down to the 18th pulse which has been advanced by 72 nanoseconds relative to the initial pulse at 0.
• Each pulse from the near side antenna 172 passes by the receiving antenna 176, and the pulse is recorded, with the wave forms indicated at 178. It is to be recognized that in most all instances, there is a certain amount of outside electromagnetic, electrical noise, echoes, refractions, etc. that tend to obscure or "clutter" the signal.
• Each of these pulses 178 is recorded in the memories of the control unit, including all the various extraneous influences on the signal, plus the portion of the signal attributable to the pulse itself. As will be discussed subsequently herein, these pulses 178 that are recorded are used as reference pulses which are subtracted in a subsequent step in the method of the third embodiment .
• the far side transmitter is activated so that regularly timed pulses are transmitted from the antenna 174 into the pipe section 170 i.e. without any advancing or delay in the timing.
• Each transmission at the near side is synchronized with the transmission at the far side.
• the next pulse from the near side is advanced four nanoseconds from the designated time period from the previous pulse.
• the far side pulse is transmitted at a time period so that the pulses from the near side and far side antennas 174 intersect at the location of the receiving antenna 176.
• the next pair of pulses are transmitted with the Near side pulse being advanced by four seconds, so the point of intersection is spaced two nanoseconds closer to the far side.
• the third pulse is advanced by eight seconds so that the intersection of the spaced and additional two nanoseconds toward the far side. It can be seen that the first pair of pulses intersecting at the antenna 176 that the peaks of theses pulses come close to coinciding. It can be seen that subsequent pairs of pulses are transmitted and with the near side pulses being advanced four nanoseconds on each transmission, relative the far side pulse, the pattern of the wave which is received at the antenna 176 comprises a first peak 182 which is attributable to the near side pulse passing by the antenna 176, and a second peak 184 which is attributable to the near side pulse reaching the antenna at a later time .
• the far side pulse that is received by the antenna 176 is the one which is analyzed to determine whether the corrosion exists.
• the following procedure is followed.
• Each of the wave forms 186 that result from the second step of this method are also stored in memory.
• the wave forms 178 are each subtracted from the corresponding wave forms shown in Figure 18 with the resulting wave forms being shown in at 188, Figure 20.
• What has occurred is that when the wave forms of Figure 17 are subtracted from the corresponding wave forms of Figure 18, the wave form from the near side, along with the extraneous noise, echoes, etc. is cancelled out so that what is left is the wave form 188 that essentially represents the far side wave form which is "uncluttered.”
• the overall result is that this facilitates the detection of variations in the wave form that originated from the far side.
• Figure 21 shows four adjacent wave forms 190 which are the same wave forms 188 of Figure 20, except that vertical dimension has been increased substantially so that the slope of these wave forms 190 is steeper. It can be seen in Figure 21 that each of these four wave forms 190 are very similar to one another. This would indicate that there is little or no corrosion in the area where the wave forms 190 have intersected.
• Figure 22 represents four adjacent wave forms resulting from four pulse transmissions which follow one after the other in sequence. These waves are designated 192-1, 192-2, 192-3 and 192-4. Each wave form is subtracted from the preceding wave to obtain a difference wave form. This is accomplished by first inverting the wave form 192-2 and then adding this inverted wave form to the wave form 192-1 to obtain a difference wave form which is 194-1 (this 194-1 being the difference wave form of the two wave forms 192-1 and 192-2) .
• a second difference wave form 194-2 is obtained by inverting the wave form 192-3 and adding this to the wave form 192-2 to obtain the difference wave form 194-2.
• the third difference wave form 194-3 is obtained in the same way by inverting the wave form 194-4 and adding this to the wave form 192-3.
• each of the three different wave forms 194-1, 194-2 and 194-3 are very similar to one another and have substantially the same amplitude.
• Figure 23 illustrates another technique utilized in this third embodiment.
• the four wave forms 194-1 through 194-4 are moved closer together, while leaving the wave forms unchanged. By moving these wave forms closer together, it is much easier to detect variations in the wave forms. Also, the different wave forms which would result from the arrangement of the wave forms in Figure 23 would be a much smaller anthitude. The effect of this is, however, that differences in amplitude between the peaks does not decrease when the wave forms are moved closer together. This further accentuates the differences in the wave forms .
• FIG. 24 To illustrate the wave forms where corrosion is being detected, reference is now made to Figure 24. There are shown 18 adjacent difference wave forms such as shown at 194-1, 194-2, and 194- 3 in Figure 22. It can be seen that the fourth wave form 196 and the fifth wave form 198 are configured rather differently than the adjacent wave forms shown immediately above and below these two wave forms 196 and 198. It will be noted that between the initial “hump” 199 and the second "hump" 200 of the wave form 196 there is a substantial dip at 201.
• the second peak or "hump" 202 of the wave form 198 has a much smaller amplitude. Further, it can be seen that the peak 203 of the first rise or "hump" 204 of the wave form 198 is shifted to the right. An alignment line 204 is drawn to show the shift from the alignment line at the left.
• FIG. 25 is a graph where the points of peak amplitude for adjacent difference wave forms has been prepared by drawing lines connecting adjacent peak points. It can be seen that the peak indicator at 206 is much greater than the rest of the peak points, and this would indicate an area of corrosion. The peak indicated at 208, while not having the height of the peak at 206, still rises above the others. This would indicate that corrosion would likely be encountered at the location at the pipe represented by the point 208 which would be the peak of the difference wave form of two adjacent wave forms where the corrosion was at or near the location of intersection.
• Figure 26 is a graph similar to Figure 25, . where the amplitude of the points in Figure 25 have been amplified in a matter to further accentuate the differences.
• near side and far side can be reversed.
• the far side pulse being the pulse which is analyzed, and the near side pulse which has been advanced to cause the point of intersection to be stepped along the elongate number (pipe)
• this arrangement could be reversed.
• both the near side pulses arriving at the far side, and the far side pulses arriving at the near side could each be received and analyzed.

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• 1998
  • 1998-06-04 CA CA2293500A patent/CA2293500C/en not_active Expired - Fee Related
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