MEASUREMENT SYSTEM THERE FOR

The invention relates to a method for measuring cement/cementitious elements, such as piping, preferably cement piping made from asbestos cement. The piping relates to fluid distribution systems, such as water carrying means.

Piping such as water distribution systems relating to water carrying means are widely applied for the distribution of fluids. This piping can be made of different materials including cement, more specifically asbestos cement, and/or polymer materials, for example. One of the problems in piping, specifically in piping for water carrying means, and more specifically in piping made of asbestos cement, is leakage of water from the piping system. This is caused by deterioration of the piping material. Leaching in cement piping significantly reduces the lifetime and/or strength of a water supply system. Fresh water is lost, ln practice some water systems even lose up to 40% of the water supply. To prevent pollution of the remaining water a substantial overpressure needs to be maintained in the piping. Therefore, determining the condition of the piping is important.

Conventional measurement techniques for inspection of cement piping involve the use of surface penetrating radar (SPR) and phenolphthalein test. This requires digging up the pipes for the measurements. This is rather costly, time-consuming and inefficient.

It is known to use a sensor system to achieve some indication of the piping condition. This often involves low frequency ultrasonic testing for measurement of cement based structures.

In practice these measurements suffers from the problem that there are many unknown parameters involved, such as a thickness of the piping, signal loss, non-linear behaviour of piping material, piping composition etcetera. Furthermore, the accuracy of these measurements is often limited partly due to the acoustical attenuation of the boundary layer between the healthy and degraded piping material. This results in a limited resolution and damping of the signal. This is even increased further when applying higher frequencies. This renders it difficult to determine the piping condition.

An object of the present invention is to provide a method for measuring cement elements, such as cement piping, that obviates or at least reduces the aforementioned problems and provides a better indication for the actual element/piping condition and/or is more efficient as compared to conventional methods.

This object is achieved with the method for measuring cement elements, such as piping, with the method according to the invention comprising the steps of:

- providing a measurement system configured to move inside or along the element; - performing ultrasonic measurements at a number of measurement locations along a measurement distance along the length of the element;

- measuring the time-of-flight at the measurement locations along the measurement distance; and

- analysing the measured time-of-flights and calculating a deterioration value at the measurement locations along the measurement distance with an analysing module and determining a deterioration ratio between the highest and lowest deterioration values along the measurement distance.

The condition of the cement element, in particular cement piping, may deteriorate or degrade due to leaching of calcium, acidic attack, carbonation, biodegradation, sulphate attack, for example. The method according to the invention can be applied advantageously to

cement/cementitious elements. In particular, the method is advantageously applied to cement piping, preferably cement piping made from asbestos cement. Although the invention is described for cement piping it will be understood that the method can also be applied to other

cement/cementitious elements and where is referred to piping it also relates to other

cement/ cementitious elements .

Providing a measurement system that is configured to move inside and/or along the piping/element enables in-line/at-line inspection. Such in-line inspection obviates the need for digging up the cement piping/element. The cement material preferably relates to so-called asbestos cement. The pipes in a presently preferred embodiment are part of a water carrying means for a water supply system. It will be understood that the method may also be applied to other cement piping or cement elements. The measurement system preferably involves a pipeline inspection gauge that is capable of moving along the element or piping and performing ultrasonic measurements.

According to the present invention, the ultrasonic measurements are performed in a number of measurement locations over a measurement distance along the length of the piping or element. At each measurement location the so-called time-of-flight is measured. The method according to the invention uses the reduction in sound speed due to a deteriorated cement-based structure as an indication of the amount of deterioration or degradation of the piping or piping segment.

Analysing the measured time-of-flights at the number of measurement locations along the measurement distance provides a measure of the deterioration or degradation of the cement piping/element as a whole and/or of the cement piping/element at an individual location. This measure enables calculating a deterioration value at the individual measurement locations along the measurement distance with an analysing module. Next, a deterioration ratio can be determined between the highest and lowest deterioration values along the measurement distance. This ratio is preferably determined for every individual measurement location. In addition to the ratio between the highest and lowest deterioriation values also other measures/values can be used as a measure in the method of the invention, such as the variance in the measurements, mean value, peak value, rms value and/or distribution. This may further improve the accuracy of the measurement and/or any decision that takes into account this measurement, such as whether repair or maintenance of the piping is required.

The deterioration ratio provides an effective relative measurement at individual measurement locations along the piping or element. The advantage of this relative measurement is that the actual pipe material parameters are not essential for measuring the condition of the cement piping. These piping parameters involve wall thickness and piping composition, for example. Furthermore, this relative measurement reduces the adverse effects of signal loss and/or inaccurate data as well as the effect of the non-linear behaviour of the piping material. The dimensions and materials of the piping along a measurement distance tire substantially similar such that the relative measurement provides an effective deterioration ratio that provides a measure for the absolute condition of the piping or pipe segment that comprises the measurement distance.

In a preferred embodiment of the invention the method comprises the additional steps of:

- comparing the deterioration ratio for a measurement distance with a threshold; and

- if the ratio is above the threshold deciding to renew or repair the piping or element.

Determining the deterioration ratio over a certain measurement distance enables comparing this ratio with a certain threshold. This comparison provides a measure that can be taken into consideration when deciding to renew or repair the specific piping or piping segment. It is noted that this decision process can be made independent from the actual measurement and can be performed externally. The actual threshold may depend on the actual application and may involve information about the piping, regulation, available investment funds etc.

In one of the preferred embodiments the deterioration value comprises the measured sound speed. By determining the deterioration value based on the measured sound speed an effective relative indication of the condition at a specific measurement location can be determined. If information about wall thickness and/or piping composition is available, the absolute sound speed can be determined.

In a presently preferred embodiment of the invention there is at least one measurement location along the measurement distance, preferably the number of measurement locations along the measurement distance is above 1 (in ¹ ) per meter of the length of the piping, more preferably above 10 m ¹ , even more preferably above 100 m ¹ , and most preferably above 1000 m ¹ . Performing a relatively large number of measurements along a measurement distance enables making a number of comparisons of the measured values at the specific measurement locations. This enables providing an accurate ratio that relates the relative measurements of the time-of-flights that preferably relate to the measured sound speed. As mentioned earlier, the sound speed depends on the amount of deterioration/degradation of the piping. The measurements are preferably performed in a relatively short time interval by moving the measurement device along the piping on the inside or along a (external) surface thereof.

Preferably, the ultrasonic measurements are performed at two or more frequencies at one or more of the measurement locations. This measurement at more than one frequency provides additional information about the actual condition of the piping. For example, one of the further frequencies is at a relatively low frequency or a relatively high frequency. This provides additional information about the state of degradation.

In a further preferred embodiment of the invention the method comprises the step of comparing the deterioration value and/or deterioration ratio with historical data from a database.

By comparing the measurements with historical data the degradation or deterioration can be monitored in time. Optionally, this may trigger an additional threshold that can be used in a decision making process about repairing or renewing the piping or element. Therefore, in such embodiment, both the actual values and/or ratios and also the change and/or rate of change of these values or ratios can be used in the decision making process. This may further improve the monitoring of the piping or element.

Preferably, the method further comprises the steps of:

- comparing the change and/or rate of change of the deterioration value and/or

deterioration ratio for a measurement distance with a change threshold; and

- if the change and/or rate of change is above the change threshold deciding to renew' or repair the piping or element.

It will be understood that the threshold and/or change threshold can be chosen involving a number of different parameters, including regulation, investment funds etc.

In a presently preferred embodiment of the invention the ultrasonic measurement is performed at a measurement frequency in the range of 10 kHz- 100 MHz, preferably in the range of 0.1-10 MHz, more preferably in the range of 0.25-5 MHz, and most preferably in the range of 0.4- 2 MHz.

It is shown that performing measurements in the frequency ranges indicated here the time-of-flight is a reliable measure as it depends on the actual sound speed in the (piping) material that is substantially influenced by the presence of defects.

Preferably, the ultrasonic measurement comprises a measurement frequency in the range of 0.25-0.75 MHz for measurements on a piping having a wall thickness of up to 25 mm, preferably up to 23 mm. If an indication of the wall thickness is available the frequency can be chosen in view of this (rough) indication.

Preferably, the ultrasonic measurement comprises a measurement frequency in the range of 0.75-1.5 MHz on a piping or element having a wall thickness of above 20 mm, preferably above 23 mm.

It is also possible to combine the different frequencies with each other in a single measurement. This provides further information about the condition of the piping or element.

In a further preferred embodiment of the invention the method comprises the additional step of measuring an amplitude of the reflected signal and determining early stage degradation.

Experiments showed that it is possible to measure and determine the amplitude of the reflected signal to determine an early stage degradation effect of the piping or element. This provides an additional measurement. In a presently preferred embodiment this measurement of amplitude is used in combination with the ultrasonic measurements that were mentioned earlier ln particular, the amplitude measurement may provide an early indication of an increased risk of deterioration of the piping. For example, such indication can be used to determine the measurement intervals of the specific piping.

The invention further relates to a measurement system for measuring

cement/cementitious elements, such as cement pipes, the measuring system according to the invention comprising:

- a moveable frame configured for moving in or along the element;

- a sensor system attached to the frame and comprising:

- a transducer for providing and receiving a number of ultrasonic measurement signals over a measurement distance along the length of the element, wherein the transducer is configured for repeatedly performing a measurement at a specific location along the measurement distance and measuring the time-of flight at the measurement locations along the measurement distance;

- an analysing module that is configured to receive measurement data comprising the ultrasonic measurement signal over the measurement distance and is configured to calculate a deterioration value at the measurement locations along the measurement distance and determining a deterioration ratio between the highest and lowest deterioration values along the measurement distance; and

- a measurement output that is configured to output data from the analysing

module.

The system provides similar effects and advantages as described for the method ln an embodiment of the invention the measurement system can also be referred to as a piping inspecting gauge that is capable of moving inside the interior of the pipe to enable performance of the measurements.

Preferably, the measurement system comprises a database with historical measurement data and a comparing module that is configured to compare the deterioration value and/or deterioration ratio with historical data from the database. As was already mentioned in relation to the method according to one of the presently preferred embodiments of the invention this comparison enables making a better decision on repair or renewal of the piping or element. The decision making process may use a threshold value that is determined on the basis of regulations, investment funds, etcetera.

Preferably, the sensor system comprises 10 or more transducers, more preferably 12 or more transducers, and most preferably 16 or more transducers. By providing a number of transducers substantially the entire inner surface/circumferential of the piping/element can be measured almost simultaneously. This improves the accuracy of the entire measurement process and thereby improves the quality of the decision making process.

Preferably, the measurement system comprises a floating device that enables movement of the system along the measurement distance of the piping/element. It will be understood that other alternatives could also be envisaged for movement of the measurement system inside or along the piping/element.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

- Figure 1 schematically show's the method of the invention;

- Figure 2 shows a schematical setup of the measurement system of the invention; and

- Figure 3 shows an embodiment of the measurement system according to the

invention.

Measurement process 2 (figure 1) starts with receiving 4 of a measurement request and providing 6 of a measurement system. To enable the measurements, the measurement system is moved 8 inside the piping and performing 8 the measurements. In analysing step 12 the deterioration or value is determined with the measurements and is optionally related to detailed conventional measurement to receive further information. In a next determination step 16 the ratios are determined. Optionally, historical data is collected 18. The ratios are compared in comparing step 20 with a threshold and/or optionally with the historical data. In the decision making process 22 a decision is made for repair or renewal and is optionally followed by the actual maintenance in maintenance step 24.

Measurement system 102 (figure 2) measures pipe wall 104. Wall 104 comprises first layer 106 and second layer 108 that are separated by boundary layer 110. Schematically illustrated is a defect 112. Measurement system 102 further comprises transducer 1 14 that is controlled by processor 116 that sends and/or receives instructions/signals 118. Transducer 114 sends measurement signals 120, 122, 124. In the illustrated embodiment measurement signal 120 measures the surface of first layer 106, second measurement signals 122 measures boundary layer 110, and third measurement signal 124 measures the second layer 108. In the illustrated embodiment measurement system 102 comprises an external controller 126 that is connected to processor 116 and to database 128 that stores historical data, if available.

Piping 130 (figure 3) is provided with central axis 132 and extends over length P.

Measurement distance L comprises a number of measurement locations 134. Sensor system 136 measures at the individual measurement locations 134 involving transducer 114 and processor 116. In the illustrated embodiment sensor system 136 comprises first disk 138 and second disk 140 that are connected with shaft 142. Between disks 138, 140 there is provided measurement disk 144 on shaft 142. A number of transducers is provided on measurement disk 144. Second disk 140 comprises battery 146 and inpul/output connections 148. lt will be understood that alternative configurations of measurement system 102 is possible.

Piping 130 with internal diameter D, and external diameter D ₀ having wall thickness d is preferably periodically measured with measurement system 102. This involves moving sensor system 136 over piping segment P over at least a measurement distance L to enable measurement at the different measurement locations 134. Processor 126 controls sensor system 136 and collects data from database 128. Processor 126 sends and/or receives data or signals 150 from and to sensor system 136, preferably also when sensor system 136 moves in a direction A along central shaft 132.

It will be understood that different alternative embodiments of sensor system 136 and measurement system 102 can be envisaged. For example, disks 138, 140 can be replaced by a floating device and/or processor 126 can be provided in an internal manner with sensor system 136.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged. Although the invention is described for a cement piping it will be understood that the method can also be applied to other cemenl/cementitious elements.