WO2012165960A1

WO2012165960A1 - System for monitoring wear of a piping element for transporting slurry

Info

Publication number: WO2012165960A1
Application number: PCT/NL2012/050381
Authority: WO
Inventors: Johannes Jonathan PAAUW; Jorrit Constantijn VAN DIJK
Original assignee: Ihc Holland Ie B.V.
Priority date: 2011-05-31
Filing date: 2012-05-31
Publication date: 2012-12-06
Also published as: NL2006871C2

Abstract

The invention relates to a system for monitoring wear of a piping element (40) for transporting slurry. The system comprising: - two electrically conductive wires (10, 20) at least partially embedded in the piping element, both wires (10, 20) comprising a detection region (11, 21), - a monitoring unit (30) comprising at least a first terminal (A) and at least a second terminal (B), the two electrically conductive wires (10, 20) being connected in between the first and second terminals (A, B). A first wire (10) of the two electrically conductive wires comprises a first resistor (12) provided in between the detection region (11) and the first terminal (A) and a second wire (20) of the two electrically conductive wires comprises a second resistor (22) provided in between the detection region (21) and the second terminal (B).

Description

System for monitoring wear of a piping element for transporting slurry

TECHNICAL FIELD

The invention relates to a system for monitoring wear of a piping element for transporting slurry, such as a sealing ring, the system comprising:

- two electrically conductive wires at least partially embedded in the piping element, both wires comprising a detection region that is relatively closest to an inside of the piping element through which the slurry is to be transported,

- a monitoring unit comprising at least a first terminal and at least a second terminal, wherein the two electrically conductive wires can be connected in between the first and second terminals, the monitoring unit being arranged to supply an electrical signal to the two electrically conductive wires and monitor an electrical parameter in response to the electrical signal. STATE OF THE ART

Dredging equipment comprises many piping elements for transporting slurry (sand and water mixture), such as conduits, tubes, pumps, dividers, (shut-off) valves, sealing rings, joints, rubber hoses and the like.

Sealing rings may be used to connect piping elements in a reliable and fluid-tight manner. Sealing rings may be made of a flexible or resilient material, such as rubber. For instance, valves may comprise such a sealing ring.

All piping elements are prone to wear, especially sealing rings made of a flexible material. As a result of the abrasive nature of the slurry, the piping elements may wear from the inside due to erosion.

In addition to that, sealing rings provided in valves may wear out as a result of opening and closing of the valve.

This wear should be monitored in order to repair or replace the piping element before it causes malfunction, for instance leakage or breakage of the piping element.

However, visual inspection of piping elements from the inside is relatively difficult and cumbersome. The piping elements may be located at locations that are difficult to reach. Also, the piping elements may be relatively small making inspection from the inside difficult. Furthermore, inspection from the inside may require shutdown of the installation of which the piping element forms part. In the prior art solutions are provided to monitor the wear of piping elements from the outside.

For instance, WO0070326A1 describes an erosion detector and a method of determining erosive wear within a conduit. The conduit has an outer metallic wall lined with a wear resistant lining of a moulded composite. A conductor is embedded within the lining during formation thereof. The conductor extends substantially about the circumference of the conduit and is spaced from the interior surface by a selected distance. Means are provided to monitor electrical continuity of the conductor. Once the lining wears and the conductor is broken, a continuity test will indicate that the lining has worn to the depth to which the conductor was embedded within the lining.

A similar device is described in US5634497A. According to this document a hose for suction and discharge of ore slurry or any other abrasive material is provided. The hose presents a sensor fixed to the referred hose which indicates the total or partial wear of the internal layer of the hose by means of the connection with first and second layers of braided copper wires.

Further variants are described in GB2348727A, US 2004/0065377 and

JP58135932A. For instance, JP58135932A describes that a continuous conductor is woven in an expansion joint made of rubber to detect a change in electric properties of the conductor.

GB2132773 A describes a system for detecting the presence of fluid in the thermally insulating layer on a pipe, i.e. to detect if a fluid penetrates the outer layer of the pipe.

In DE10024478A1 a process for determining a leak in a pipe for an electrically conducting fluid is provided, which comprises applying a first insulating layer followed by a conducting layer and a second insulating layer on the inner wall of the pipe, and measuring the resistance between an electrode in contact with the fluid and the conducting layer during the operation of the pipe.

GB2254465A describes at least one wire being disposed within a liner in an area of concern in a conduit. The continuity of the wire is checked. If a wire is broken, this information can be displayed, indicating a potential problem with the liner. In case two wires are used, these wires form two separate circuits and except for a common source of electrical potential and ground are independent from one another. Both wires may comprise a resistor, the resistors are in parallel with each other and are selected to deflect a meter appropriately; for instance 200 Ohms for one resistor and 20 thousands Ohms for the other resistor.

SHORT DESCRIPTION

It is an object to provide a system for monitoring wear of a piping element for transporting slurry that is able to detect wear of a piping element in an easy and failsafe manner.

Therefore, according to an aspect, there is provided a system for monitoring wear of a piping element for transporting slurry, such as a sealing ring, the system

comprising:

- a monitoring unit comprising at least a first terminal and at least a second terminal, wherein the two electrically conductive wires can be connected in between the first and second terminals, the monitoring unit being arranged to supply an electrical signal to the two electrically conductive wires and monitor an electrical parameter in response to the electrical signal,

wherein a first wire of the two electrically conductive wires comprises a first resistor provided in between the detection region and the first terminal and a second wire of the two electrically conductive wires comprises a second resistor provided in between the detection region and the second terminal.

Such a system has the advantage that in case both detection regions are damaged, an electrical conducting path is created through the slurry, bypassing the first and second resistors. This will cause a significant change in the electrical signal that is measured in response to the generated electrical parameter, which can be detected relatively easily. Hereby it is ensured that breakage of both detection regions is detected in a fail-safe manner.

According to an embodiment the monitoring unit comprises a voltage source, wherein the electrical signal is an electrical voltage generated over the two electrically conductive wires and the monitoring unit is arranged to monitor an electrical current through the first and second terminals. The system may comprise a current meter to monitor the electrical current. According to an embodiment the monitoring unit comprises a current source, wherein the electrical signal is an electrical current generated through the two electrically conductive wires and the monitoring unit is arranged to monitor an electrical voltage over the first and second terminals. The system may comprise a voltage meter to monitor the electrical voltage.

According to an embodiment the wherein the electrical parameter is one of an electrical current through the first and second terminals, an electrical voltage over the first and second terminals and an electrical resistance between the first and the second terminals. The monitoring unit may be arranged to compute a resistance between the first and the second terminals. By determining the electrical parameter information can be obtained about the status of the first and second detection regions. Depending on the electrical resistance value of the slurry, breakage of one detection region will cause a relatively small change in the electrical parameter. However, once both the detection regions are worn and interrupted, a relatively high change in the electrical parameter will be detected. Also, this change will be in an opposite direction with respect to an initial value of the electrical parameter than the relatively small change.

According to an embodiment the monitoring unit is arranged to generate a wear indication signal, comprising information about the status of the first and second detection regions based on the monitored electrical parameter. Such a wear indication signal may be any kind of signal, including a audible signal, a visual signal or the like, to indicate that one or two detection regions are worn.

According to an embodiment the system is arranged to receive an electrical resistance value of the slurry, the first and second resistors being variable resistors and the monitoring unit is arranged to control the resistance of the variable resistors in response to the received electrical resistance value of the slurry.

Also, a system arranged to receive an electrical resistance value of the slurry has the following advantage, even when applied to a system not having variable resistors. If the electrical resistance value of the slurry is known, the change in the electrical parameter measured in response to the electrical signal or the change in the electrical resistance between the first and the second terminal can be estimated due to breakage of both detection regions. Based on this information, a threshold value can be determined for the electrical signal or resistance which needs to be reached before the system concludes that both detection regions are broken. According to an embodiment the system comprises a measurement device arranged to measure the electrical resistance value of the slurry. This is an

advantageous and accurate way to obtain information about the electrical resistance value of the slurry.

According to an aspect there is provided a method for monitoring wear of a piping element for transporting slurry, such as a sealing ring, the method comprising:

- generating an electrical signal to two electrically conductive wires, the two electrically conductive wires being at least partially embedded in the piping element, both wires comprising a detection region that is relatively close to an inside of the piping element through which the slurry is to be transported,

- monitoring an electrical parameter in response to the electrical signal, wherein the first wire of the two electrically conductive wires comprising a first resistor provided in between the detection region and the first terminal and a second wire of the two electrically conductive wires comprising a second resistor provided in between the detection region and the second terminal,

wherein monitoring of the electrical parameter comprises:

- monitoring a change of the electrical parameter in a first direction to determine wear of one detection region, and

- monitoring a change of the electrical parameter in a second direction opposite to the first direction to determine wear of both detection regions. The first direction may be an increase or a decrease of the electrical parameter, the second direction may be opposite to the first direction so may be a decrease or an increase.

According to an embodiment the electrical signal is an electrical voltage generated over the two electrically conductive wires and monitoring the electrical parameter comprises monitoring an electrical current through the first and second terminals.

According to an embodiment the electrical signal is an electrical current generated through the two electrically conductive wires and monitoring the electrical parameter comprises monitoring an electrical voltage over the first and second terminals.

According to an embodiment the method comprises generating a wear indication signal, comprising information about the status of the first and second detection regions based on the monitored electrical parameter. According to an embodiment the first and second resistors are variable resistors and the method comprises

- obtaining an electrical resistance value of the slurry, and

- controlling the resistance of the variable resistors in response to the obtained electrical resistance value of the slurry. This allows to adjust the resistance of the variable resistors such that the resistance of the variable resistor is not too high or too low to ensure that wear of one or two detection regions will result in a significant change of the monitored electrical parameter.

According to an embodiment obtaining an electrical resistance value of the slurry comprises controlling a measurement device to measure the electrical resistance value of the slurry.

According to an aspect, there is provided a computer program product comprising data and instructions that can be loaded by a computer system, allowing said computer system to perform any one of the methods described above.

According to an aspect there is provided a computer readable medium provided with a computer program product according to the above.

According to an aspect, there is provided a computer arrangement arranged to perform any one of the methods according to the above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

FIG. 1 schematically shows a system according to an embodiment,

FIG.'s 2a-2c show the system in a more schematic way,

FIG. 3 schematically shows a system according to an alternative embodiment, and

FIG. 4 schematically shows a system according to a further embodiment.

The figures are only meant for illustrative purposes, and do not serve as restriction of the scope or the protection as laid down by the claims.

DETAILED DESCRIPTION

FIG. 1 schematically shows a system for monitoring wear of a piping element 40. The piping element 40 shown is a sealing ring. The sealing ring may be made of a flexible and resilient material, such as rubber or polytetrafluoroethylene (PTFE or Teflon) a plastic, a ceramic material or the like.

However, the embodiments may also be used in combination with other piping elements, such as conduits, tubes, pumps, dividers, (shut-off) valves, sealing rings, joints, rubber hoses and the like. The piping element may for instance be made of rubber, Teflon, plastic or a ceramic material.

The system as shown in Fig. 1 comprises a monitoring unit 30 and two electrically conductive wires 10, 20. These wires are with one end connected to a first terminal A and with a second end connected to a second terminal B. The wires 10, 20 run from the first terminal A, via the piping element 40 back to the second terminal B.

Part of the wires 10, 20 are embedded in the piping element 40 such that parts of both wires 10, 20 are located at a closest distance from an inside of the piping element 40. These parts of the wires are referred to as detection regions 11, 21.

The detection regions 11, 21 are positioned in the piping element 40 at such a distance from the inside of the piping element 40 until where wear is allowed. Once the wear reaches a detection region, the wires will be damaged and the electrical conducting path will be interrupted.

The two detection regions 11, 21 may be small or may extend along a substantial part of the circumference of the piping element 40. The two detection regions 11, 21 may be positioned at opposite positions with respect to each other of the piping element 40. One detection region may be positioned at the bottom of the piping element 40. According to an alternative embodiment, described in more detail below, the detection regions 1 1, 21 may be provided in two different lower quadrants of the piping element.

The detection regions 11, 21 may be provided at different depths with respect to the inside of the piping element 40 such that different degrees of wear can be monitored. In such an embodiment, the detection regions 11, 21 may be provided at the same location, one above the other. This allows to monitor different degrees of wear.

Both wires 10, 20 comprise an electrical resistor 12, 22. The first wire 10 comprises an electrical resistor 12 positioned in between the first terminal A and the detection region 11. The second wire 20 comprises an electrical resistor 22 in between the second terminal B and the detection region 21.

Both electrical resistors 12, 22 may have a similar resistance value or may have a different resistance value. By using difference resistances, information may be retrieved about which detection region 11, 21 is damaged.

The electrical resistors 12, 22 may have a resistance that is of the same order of magnitude as the electrical resistance R_si of the slurry between the first and the second detection regions 11, 12.

According to a preferred embodiment, the electrical resistors 12, 22 have a resistance that is higher than the electrical resistance R_si schematically shown in Fig. 2c of the slurry between the first and the second detection regions 11, 21, preferably at least a factor 2 higher or more preferably at least a factor 5 higher.

In order to be able to detect the interruption of one detection region 11, 21, the electrical resistors 12, 22 may be chosen not too high with respect to the resistances Ri i, R₂i schematically shown in Fig. 2c, for instance not more than 4,5 times higher.

For instance, the electrical resistance R12, R22 of the electrical resistors 12, 22 may be chosen to be within the range: 2,25 < R12, 22 Rw < 4,5, wherein Rw is an estimate for the resistance through the slurry. So, Rw is an estimate for R_si, Rn and R21 as shown in Fig. 2c. Such an estimation is accurate in situations where R_si ~ Rl 1 ~ R21.

In case R_si > Rn, R21 (for instance more than a factor 3), it is preferred to select the electrical resistance R12, R22 of the electrical resistors 12, 22 within the range: 1 <

The electrical resistors 12, 22 may be variable resistances with a variable resistance value as shown in Fig. 3, which may be controlled by the monitoring unit 30 described. The monitoring unit 30 may further be arranged to receive information about the typical resistance of the fluid being transported through the piping element 40, for instance by receiving input from a user or a remote system via interface unit 37

(explained in more detail below), or, as schematically shown in Fig. 3, by receiving information from a measurement device 50. The measurement device 50 may be formed by one or more probes that is/are positioned in contact with the fluid being transported through the piping element 40. The monitoring unit 30 may be formed as a computer arrangement comprising a processing unit 35 and a memory unit 36. The processing unit 35 is arranged to communicate with the memory unit 36. The memory unit 36 may comprise

programming lines and instructions readable and executable by the processing unit 35 allowing the processing unit 35 to function according to the embodiments described. The processing unit 35 may write data to the memory unit 36.

The monitoring unit 30 further comprises an interface unit 37. The processing unit 35 may be arranged to communicate with the interface unit 37. This interface unit 37 may be a user interface, allowing the processing unit 35 to receive instructions from a user, for instance via a keyboard KE and to communicate information to a user, for instance via a display DI.

The monitoring unit 30 may further comprise a terminal unit 33, comprising the first and second terminals A, B. The terminal unit 30 is shown in more detail in Fig.'s 2a - 2c. The monitoring unit 30 may comprise an electrical source, such as a voltage source 31 (see Fig. 2a), to supply an electrical signal to the two electrically conductive wires 10, 20. The terminal unit 33 may further comprise an electrical meter, such as a current meter 32 (see Fig. 2a), to measure an electrical parameter in response to the electrical signal.

The electrical source may also be a current source, in combination with a voltage meter as electrical meter.

The monitoring unit may further comprise an energy source, such as a battery or accumulator and/or may be arranged to be connected to an external energy source.

The system is designed in such a way that in case both detection regions 11, 21 are damaged, a new electrical conducting path is created between the first detection region 11 and the second detection region 21 via the fluid being transported by the piping element 40, bypassing both resistors 12, 22. This new electrical conducting path will cause a significant change in the electrical parameters of the circuit which can be registered in an easy and fail-safe manner by the monitoring unit.

The functioning of the system will now be described in more detail with reference to Fig.'s 2a -2c in which the system is depicted in a more schematic way. The terminal unit 33 is provided with an electrical voltage source 31. The system may further comprise a current meter 32 to monitor the electrical current running through the wires 10, 20.

Fig. 2a shows the situation in which both detection regions 11, 21 are intact and current will flow through the first and second wire 10, 20. A corresponding electrical current (Iintact) may be measured by current meter 32 and a corresponding resistance (Rintact) between the first and the second terminals A, B may be computed by the monitoring unit 30.

If the piping element 40 wears from the inside as a result of erosion caused by the slurry, first, one of the detection regions 11, 21 will be damaged, thereby breaking the electrical conducting path of one of the first and second wires 10, 20. This is schematically shown in Fig. 2b, in which by way of example the second detection region 21 is broken. Current will still be able to run through the second wire via the slurry. The resistance of the slurry is symbolized by the symbolic resistor R₂i depicted in Fig. 2b. As a consequence, the resistance of the second wire 20 will increase, depending on the electrical resistance R₂i of the slurry between the two broken parts of the detection region 21. Consequently, the current meter 31 will monitor a decrease of current (I_one damaged < Iintact)- A corresponding resistance (Rone damaged > Rintact) between the first and the second terminals A, B may be computed by the monitoring unit 30.

As a result of further wear, the other detection region 11 may also be broken, as schematically depicted in Fig. 2c. Current will now be able to run through the first and second wires 10, 20 and resistors 12, 22 via the slurry. The resistance of the slurry is symbolized by the symbolic resistors Rn and R₂i depicted in Fig. 2c. However, an additional electrical conducting path is also created via the second wire 20, the second detection region 21, the slurry, the first detection region 11 and the first wire 10. This additional electrical conducting path is schematically depicted in Fig. 2c with a symbolic resistor R_si, representing the resistance of the slurry between the first and second detection region 11, 21. This additional electrical conducting path bypasses the resistors 12, 22.

Salt water has a resistance in the order of 18.5 Ω/cm, fresh water has a resistance in the order of 1667 Ω/cm. As the resistance of the resistors 12, 22 is at least significantly higher than the resistance R_si of the slurry, this will result in a significant increase of the current as measured by the current meter 31 : (Ι^₀ damaged > Iintact > lone damaged)- A corresponding resistance (Rtwo damaged < Rintact < Rone damaged) between the first and the second terminals A, B may be computed by the monitoring unit 30.

As will be understood based on the above, the current that is measured when one detection region is damaged will be lower than the initial current Iintact, while the current measured when both detections regions are damaged will be higher than the initial current Iintact- This reduces the risk of wrong interpretation of the measurements.

Fig. 3 shows a further embodiment, in which the electrical resistors 12, 22 are variable electrical resistors 12, 22, controllable by the monitoring unit 30. The monitoring unit 30 may be arranged to receive information about the resistance of the fluid which is transported through the piping element 40, compute a desirable resistance value for the variable electrical resistors 12, 22 and change the variable electrical resistors 12, 22 accordingly.

The monitoring unit 30 may receive information about the resistance of the fluid via the interface unit 37 or from measurement device 50, for instance via terminal unit 33. The measurement device 50 may be formed by one or more probes that is/are positioned in contact with the fluid, for instance inside the piping element 40.

According to a further embodiment, the detection regions 11, 21 may be positioned near the underside of the piping element 40, although not in the lowest point of the piping element 40. Most wear will not occur at the bottom of the piping element 40, but typically occur halfway the two lower quadrants.

Fig. 4 schematically shows such an embodiment in which two detection regions 11, 21 are provided in opposite lower quadrants of the piping element 40. The quadrants as referred to are formed by imaginary horizontal and vertical lines through the centre of the piping element 40.

Fig. 4 shows a cross-sectional view of a piping element, in which an angle a is shown, indicating the angle associated with the position of the detection region 1 1 with respect to lowest point of the piping element. The angle a is taken with respect to an imaginary vertical line V through a central body axis B of the piping element 40. Angle a may be chosen 0° < a < 90°, or preferably 10° < a < 80° or more preferably 10°<a<20°.

LIST OF FIGURE ELEMENTS

10, 20 electrically conductive wires

11, 21 detection regions

12, 22 electrical resistor

30 monitoring unit

31 voltage source

32 current meter

33 terminal unit

35 processing unit

36 memory unit

37 interface unit

A first terminal

B second terminal

KE keyboard

DI display

R21, R22 resistance through fluid for damaged detection regions 11, 21 respectively

Rsi resistance through fluid in between first and second detection region 11, 21

40 piping element

50 measurement device

Claims

1. System for monitoring wear of a piping element (40) for transporting slurry, such as a sealing ring, the system comprising:

- two electrically conductive wires (10, 20) at least partially embedded in the piping element, both wires (10, 20) comprising a detection region (11, 21) that is relatively close to an inside of the piping element (40) through which the slurry is to be transported,

- a monitoring unit (30) comprising at least a first terminal (A) and at least a second terminal (B), wherein the two electrically conductive wires (10, 20) can be connected in between the first and second terminals (A, B), the monitoring unit (30) being arranged to supply an electrical signal to the two electrically conductive wires (10, 20) and monitor an electrical parameter in response to the electrical signal,

characterized in that a first wire (10) of the two electrically conductive wires comprises a first resistor (12) provided in between the detection region (11) and the first terminal (A) and a second wire (20) of the two electrically conductive wires comprises a second resistor (22) provided in between the detection region (21) and the second terminal (B).

2. System according to claim 1, wherein the monitoring unit (30) comprises a voltage source (31), wherein the electrical signal is an electrical voltage generated over the two electrically conductive wires (10, 20) and the monitoring unit (30) is arranged to monitor an electrical current through the first and second terminals (A, B).

3. System according to claim 1, wherein the monitoring unit (30) comprises a current source, wherein the electrical signal is an electrical current generated through the two electrically conductive wires (10, 20) and the monitoring unit (30) is arranged to monitor an electrical voltage over the first and second terminals (A, B).

4. System according to any one of the preceding claims, wherein the electrical parameter is one of an electrical current through the first and second terminals (A, B), an electrical voltage over the first and second terminals (A, B) and an electrical resistance between the first and the second terminals (A, B).

5. System according to any one of the preceding claims, wherein the monitoring unit (30) is arranged to generate a wear indication signal, comprising information about the status of the first and second detection regions (11, 21) based on the monitored electrical parameter.

6. System according to any one of the preceding claims, wherein the system is arranged to receive an electrical resistance value of the slurry, the first and second resistors (12, 22) being variable resistors and the monitoring unit (30) is arranged to control the resistance of the variable resistors in response to the received electrical resistance value of the slurry.

7. System according to claim 6, wherein the system comprises a measurement device (50) arranged to measure the electrical resistance value of the slurry.

8. Method for monitoring wear of a piping element (40) for transporting slurry, such as a sealing ring, the method comprising:

- generating an electrical signal to two electrically conductive wires (10, 20), the two electrically conductive wires (10, 20) being at least partially embedded in the piping element, both wires (10, 20) comprising a detection region (11, 21) that is relatively close to an inside of the piping element (40) through which the slurry is to be transported,

- monitoring an electrical parameter in response to the electrical signal,

characterized by the first wire (10) of the two electrically conductive wires comprising a first resistor (12) provided in between the detection region (11) and the first terminal (A) and a second wire (20) of the two electrically conductive wires comprising a second resistor (22) provided in between the detection region (21) and the second terminal (B),

wherein monitoring of the electrical parameter comprises:

- monitoring a change of the electrical parameter in a second direction opposite to the first direction to determine wear of both detection regions.

9. Method according to claim 8, wherein the electrical signal is an electrical voltage generated over the two electrically conductive wires (10, 20) and monitoring the electrical parameter comprises monitoring an electrical current through the first and second terminals (A, B).

10. Method according to claim 8, wherein the electrical signal is an electrical current generated through the two electrically conductive wires (10, 20) and monitoring the electrical parameter comprises monitoring an electrical voltage over the first and second terminals (A, B).

11. Method according to any one of the claims 8 - 10, wherein the method comprises generating a wear indication signal, comprising information about the status of the first and second detection regions (11, 21) based on the monitored electrical parameter.

12. Method according to any one of the claims 8 - 11, wherein the first and second resistors (12, 22) are variable resistors and the method comprises

- obtaining an electrical resistance value of the slurry, and

- controlling the resistance of the variable resistors in response to the received electrical resistance value of the slurry.

13. Method according to claim 12, wherein obtaining an electrical resistance value of the slurry comprises controlling a measurement device (50) to measure the electrical resistance value of the slurry.

14. Computer program product comprising data and instructions that can be loaded by a computer system, allowing said computer system to perform any one of the methods according to claim 8 - 13.

15. Computer readable medium provided with a computer program product according to claim 14.

16. Computer arrangement arranged to perform any one of the methods according claims 8 - 13.