APPARATUS AND METHOD FOR DETERMINING WHEN TO REPLACE A SEAL COMPONENT OF A SEAL ASSEMBLY

Abstract

A computer implemented method of determining when to replace a seal component of a seal assembly includes obtaining an indication of an accumulation of acoustic emission energy emitted from the seal component over a period of time and determining an estimate of remaining lifetime of the seal component based on the indication.

Claims

1. A computer implemented method of determining when to replace a seal component of a seal assembly, the method comprising: obtaining an indication of an accumulation of acoustic emission energy emitted from the seal component over a period of time; and determining an estimate of remaining lifetime of the seal component based on the indication.

2. The method of claim 1, wherein: the determining an estimate of remaining lifetime of the seal component is further based on a baseline acoustic emission energy.

3. The method of claim 2, wherein: the determining an estimate of remaining lifetime of the seal component is further based on a comparison between the indication and the baseline acoustic emission energy.

4. The method of claim 1, wherein: the indication is obtained by a sensor for sensing the acoustic emission energy emitted from the source of the acoustic emission energy.

5. The method of claim 4, comprising: modifying the indication by an attenuation function, wherein the attenuation function has a value which depends on the distance of the sensor from a source of acoustic emission energy.

6. The method of claim 4, comprising: modifying the baseline acoustic emission energy by an attenuation function, wherein the attenuation function has a value which depends on the distance of the sensor from a source of acoustic emission energy.

7. The method of claim 5, wherein: the value of the attenuation function varies exponentially with distance of the sensor from the source of acoustic emission energy.

8. The method of claim 1, wherein: the determining an estimate of remaining lifetime of the seal component based on the indication comprises: squaring the indication to obtain a squared indication; determining a total acoustic emission energy emitted from the source of acoustic emission energy over the period of time based on the squared indication.

9. The method of claim 1, wherein: the determining an estimate of remaining lifetime of the seal component is further based on a rate of change of the acoustic emission energy over a period of time.

10. The method of claim 1, wherein: the determining an estimate of remaining lifetime of the seal component is further based on the indication being independent of temperature of the sensor.

11. The method of claim 1, further comprising: replacing the seal component once the estimate of remaining lifetime has elapsed.

12. A controller configured to perform the method of claim 1.

13. A system comprising: a sensor for attachment with a seal assembly and configured to measure an indication of acoustic emission energy emitted from the seal assembly when the seal assembly is in use; and the controller of claim 12.

14. An apparatus comprising: a seal assembly; a sensor attached to the seal assembly and configured to measure an indication of acoustic emission energy emitted from the seal assembly when the seal assembly is in use; and the controller of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Some embodiments will now be described, by way of example only, with reference to the figures, in which:

[0097] FIG. 1A illustrates an axial cross-section of a first seal assembly;

[0098] FIG. 1B illustrates an axial cross-section of a second seal assembly;

[0099] FIG. 2 illustrates a flow chart of a method of the present disclosure;

[0100] FIG. 3 illustrates a flow chart of a method of the present disclosure;

[0101] FIG. 4 illustrates a graph of experimental results with cumulative acoustic emission energy plotted against time;

[0102] FIGS. 5A and 5B illustrate a graph of experimental results with total acoustic emission energy emitted over a period of time plotted against wear of a seal component; and

[0103] FIG. 6 illustrates a flow chart of a method of empirically obtaining an attenuation function;

[0104] In the drawings like reference numerals are used to indicate like elements.

DETAILED DESCRIPTION

[0105] The present invention is applicable to all types of mechanical seal. For example, the invention is applicable to all types of end-face mechanical seals for use in rotating equipment. Herein the term rotating equipment may refer to any apparatus comprising a driver side and a driven side, wherein the driver side is coupled to the driven side by a coupling between two rotary shafts or between a rotary shaft and some other driven member. Examples of rotating equipment include: compressors and process pumps. End-face mechanical seal may be used to prevent leakage of fluid from an inboard side to an outboard side of the mechanical seal.

[0106] End-face mechanical seals comprise a mating ring and a primary ring. Both the mating ring and the primary ring are annular circular cylinders. The mating ring is positioned so that an axial face (e.g. seal face) of the mating ring opposes an axial face of the primary ring. The mating ring is disposed on the driving side of the rotary coupling and is positioned so that an axis of rotation of the rotary coupling is coincident with the central longitudinal axis of the mating ring. The mating ring has a fixed axial position relative to the shaft (or for example, relative to the pump casing). In other words, the mating ring does not move relative to the shaft. The mating ring may be mounted to the shaft or to another stationary part of a rotating equipment e.g. a pump casing or a seal plate. The mating ring is rotatable about the axis of rotation of the rotary coupling e.g. by the shaft which drives the rotating equipment. The primary ring is disposed on the driven side of the rotary coupling and positioned so that an axis of rotation of the rotary coupling is coincident with the central longitudinal axis of the primary ring. The primary ring is configured to be movable axially relative to the mating ring e.g. the primary ring can move axially (e.g. float) relative to the mating ring to vary the gap between the primary ring and the mating ring.

[0107] In the examples shown in FIGS. 1A and 1B the mating rings are stationary mounted and the primary rings are shaft mounted.

[0108] A seal fluid provides a thin film of fluid between the opposing faces of the primary ring and the mating ring. For example, the seal fluid may be fluid sealed by the mechanical seal provided by the primary ring and the mating ring. For example, the seal fluid may comprise any of the following types: process fluid; a buffer fluid; and, a barrier fluid. The type of seal fluid for a given mechanical seal may depend on the general mechanical seal arrangements as described by the API682 standard et alia. The thin film, sometimes referred to as a fluid film, generates hydrostatic forces (e.g. forces which are present regardless of whether the mating ring is stationary or rotating) and hydrodynamic forces (e.g. forces which are present only when the mating ring rotates) which are exerted on the mating ring and primary ring. Grooves may be provided on the mating ring (e.g. logarithmic spiral grooves) which are involved in generating the hydrodynamic forces, for example, when the mating ring rotates, the grooves may shear the seal fluid flow towards the central longitudinal axis of the mating ring which increases the pressure of the seal fluid flow.

[0109] FIG. 1A illustrates an axial cross-section of a first seal assembly 100A. FIG. 1B illustrates an axial cross-section of a second seal assembly 100B Both the first seal assembly 100A and the second seal assembly 100B are designed for containment of process fluid which may comprise hazardous fluids and light hydrocarbons.

[0110] The first seal assembly 100A comprises: a pump casing 102; a pump shaft 104; a seal cartridge 106; a primary ring 108; a mating ring 110; and, a channel 112 for receiving a process fluid.

[0111] The pump shaft 104 is disposed through a central hole of the primary ring 108. The pump shaft 104 is disposed through a central hole of the mating ring 110. The pump casing 102 encloses at least a portion of any of: the pump shaft 104; the primary ring 108; and, the mating ring 110. The seal cartridge 106 encloses at least a portion of any of: the pump shaft; the primary ring 108; and, the mating ring 110.

[0112] The channel 112 is delimited by channel sides. A portion of the primary ring 108 forms at least part of the channel sides of channel 112. A portion of the mating ring 110 forms at least part of the channel sides of channel 112. A portion of the pump casing 102 forms at least part of the channel sides of channel 112. A portion of the seal cartridge 106 forms at least part of the channel sides of channel 112.

[0113] The primary ring 108 is configured to the rotate about and relative to the pump shaft 104. The mating ring 110 is configured to the resist rotation about and relative to the pump shaft 104. The channel 112 is configured to receive a flow of process fluid.

[0114] The second seal assembly 100B comprises: a pump casing 152; a pump shaft 154; a seal cartridge 156; a inboard primary ring 158; a inboard mating ring 160; an outboard primary ring 178; an outboard mating ring 180; a first channel 162 for receiving a process fluid; a second channel 182 for receiving a buffer fluid.

[0115] The pump shaft 154 is disposed through a central hole of the inboard primary ring 158. The pump shaft 154 is disposed through a central hole of the inboard mating ring 160.

[0116] The pump shaft 154 is disposed through a central hole of the outboard primary ring 178. The pump shaft 154 is disposed through a central hole of the outboard mating ring 180. The pump casing 152 encloses at least a portion of any of: the pump shaft 154; the inboard primary ring 158; the inboard mating ring 160 the outboard primary ring 178; and, the outboard mating ring 180. The seal cartridge 156 encloses at least a portion of any of: the pump shaft; the inboard primary ring 158; the inboard mating ring 160 the outboard primary ring 178; and, the outboard mating ring 180.

[0117] The first channel 162 is delimited by first channel sides. A portion of the inboard primary ring 158 forms at least part of the first channel sides of first channel 162. A portion of the inboard mating ring 160 forms at least part of the first channel sides of first channel 162. A portion of the pump casing 152 forms at least part of the first channel sides of first channel 162. A portion of the seal cartridge 156 forms at least part of the first channel sides of first channel 162.

[0118] The second channel 182 is delimited by second channel sides. A portion of the inboard primary ring 158 forms at least part of the second channel sides of second channel 182. A portion of the inboard mating ring 160 forms at least part of the second channel sides of second channel 182. A portion of the outboard primary ring 178 forms at least part of the second channel sides of second channel 182. A portion of the outboard mating ring 180 forms at least part of the second channel sides of second channel 182. A portion of the seal cartridge 156 forms at least part of the second channel sides of second channel 182.

[0119] The inboard primary ring 158 is configured to the rotate about and relative to the pump shaft 154. The inboard mating ring 160 is configured to the resist rotation about and relative to the pump shaft 154. The outboard primary ring 178 is configured to the rotate about and relative to the pump shaft 154. The outboard mating ring 180 is configured to the resist rotation about and relative to the pump shaft 154. The first channel 162 is configured to receive a flow of process fluid. The second channel 182 is configured to receive a flow of barrier fluid or a buffer fluid.

[0120] In use, the inboard primary ring 158, the inboard mating ring 160, and the process fluid are configured to provide an inboard mechanical seal. In use, the outboard primary ring 178, the outboard mating ring 180, and either the barrier fluid or the buffer fluid are configured to provide an outboard mechanical seal.

[0121] The inboard seal faces a process side e.g. the inboard seal seals against a process side. The outboard seal faces an atmospheric side e.g. the outboard seal seals against an atmospheric side.

[0122] In examples comprising two mechanical seals (e.g. an inboard mechanical seal and an outboard mechanical seal), two acoustic emission sensors may be provided e.g. a first acoustic emission sensor and a second acoustic emission sensor. In such examples, the first acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components the inboard mechanical seal and the second acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components of the outboard mechanical seal.

[0123] In examples comprising two mechanical seals (e.g. an inboard mechanical seal and an outboard mechanical seal), two acoustic emission sensors may be provided e.g. a first acoustic emission sensor and a second acoustic emission sensor. In such examples the first acoustic emission sensor may be closer to the source of acoustic emission than the second acoustic emission sensor.

[0124] The first acoustic emission sensor may obtain an indication of an acoustic emission energy emitted from a given acoustic event which is greater in magnitude (e.g. a greater amplitude) than an indication of the same acoustic event obtained by the second acoustic emission sensor. There may be a phase shift between the indication obtained by the first acoustic emission sensor and the indication obtained by the second acoustic emission sensor. In such examples, the first acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components the inboard mechanical seal and the second acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components of the outboard mechanical seal. Additionally, the first acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components of the outboard mechanical seal and the second acoustic emission sensor may be configured to obtain an indication of an accumulation of acoustic emission energy emitted from one or more components of the inboard mechanical seal. In such examples, indications obtained by first acoustic emission sensor may be filtered to remove indications emitted from the outboard mechanical seal and to retain indications emitted from the inboard mechanical seal and, indications obtained by second acoustic emission sensor may be filtered to remove indications emitted from the inboard mechanical seal and to retain indications emitted from the outboard mechanical seal.

[0125] In examples comprising two mechanical seals (e.g. an inboard mechanical seal and an outboard mechanical seal), one acoustic emission sensor may be provided. A probability of a particular event based

[0126] The condition monitoring system may be configured to monitor performance indicator parameters in a seal to determine an operating condition of the seal.

[0127] The performance indicator parameters may include any of: temperature; and, magnitude of acoustic emission (e.g. an indication of the acoustic emission energy as described herein).

[0128] The performance indicator parameters may include the change with respect to time of any of: temperature; and, magnitude of acoustic emission (e.g. an indication of the acoustic emission energy as described herein). For example, the change of the parameters may be obtained over a set period of time (e.g. 1 second).

[0129] The performance indicator parameters may be obtained by any suitable sensor.

[0130] Embodiments of the present disclosure provide a method for determining an estimate of remaining lifetime of a seal component in a seal assembly. The seal component of the seal assembly for which an estimate of remaining lifetime may be determined may be a mating ring or a primary ring. In some examples, the estimate of remaining lifetime may be determined for the combination of the mating ring and the primary. The estimate of remaining lifetime of the seal component depends on a given seal assembly.

[0131] In examples, primary seal rings may comprise carbon-graphite. In examples, mating rings may comprise silicon carbide.

[0132] A seal assembly may vary in structure for a given use. As provided by the present disclosure there exists a principle capable of general application wherein, seal components of seal assemblies may have varying lifetimes, dependent on physical properties of particular system, for example: the size of the seal components of the seal assembly; the type of seal fluid used; and/or any other property described herein. The estimated lifetime of different seal components of different seal assemblies may be determined based on characteristics of the seal component of the seal assembly and its use, such as: an indication of an accumulation of acoustic emission (AE) energy emitted from the seal component over a period of time; a baseline acoustic emission energy; a comparison between the indication and the baseline acoustic emission energy; a modification of the indication by an attenuation function; squaring the indication to obtain a squared indication and determining a total acoustic emission energy emitted from the source of acoustic emission energy over the period of time based on the squared indication; rate of change of the acoustic emission energy over a period of time. In examples any of the indications may be filtered e.g. the indications may be passed through any of: a high-pass filter; a low-pass filter; and, a bandpass filter. Knowing these parameters, an estimated lifetime of the seal component in the seal assembly can be determined. This can enable maintenance and replacement of the seal components before they become worn to a deteriorated state.

[0133] The computer implemented methods of determining when to replace a seal component of a seal assembly described herein may be implemented by a computer, for example, a controller. The computer is configured to: obtain an indication of acoustic emission energy emitted from the seal component over a period of time and the computer may perform one or more numerical estimation methods on the indication; and, determine an estimate of remaining lifetime of the seal component based on the indication which are arrived at through the numerical estimation method. The numerical estimation methods may be performed in accordance to any of the principles laid out in Numerical Recipes in C: The Art of Scientific Computing. In some examples, the indication may be a function V, which depends on time (e.g. V(t)). The numerical estimation may comprise squaring the indication to obtain a square indication, V.sup.2. The square indication may be integrated with respect to time between limits the 0 to T wherein, T, is the period of time over which a rotating equipment is operated. The numerical estimation may comprise performing an numerical integration on the squared indication, for example, using any of: the midpoint rule; the trapezoidal rule; Newton-Cotes formulas.

[0134] A first example of a computer implemented method of estimating the remaining lifetime of a seal component of a seal assembly will now be described with reference to FIG. 2.

[0135] Obtain 5201, an indication of acoustic emission energy emitted from the seal component over a period of time.

[0136] The indication, V, is obtained by a sensor mounted on the seal assembly, for example, an acoustic emission sensor such as any of those described herein. In this example, the indication is a proportional to the magnitude of acoustic emissions detected by the sensor per unit time.

[0137] The acoustic emission energy emitted by the seal component at an instant in time is proportional to the square of the indication at the instant in time. The total acoustic emission energy, E.sub.Ti, emitted over a period of time, T.sub.i, is proportional to the square of the indication, V.sup.2, integrated with respect to time over the period of time, T.sub.i. This may expressed mathematically as:

E.sub.T.sub.i=∫.sub.0.sup.T.sup.iV.sup.2(t)dt

[0138] Thus, it can be seen that indication, V, is indicative of the acoustic emission energy emitted from the seal component.

[0139] Determine S202, an estimate of remaining lifetime of the seal component based on the indication.

[0140] For example, the following mathematical relationship between: a total lifetime of the seal assembly, T.sub.b; the baseline acoustic emission energy, E.sub.b; total acoustic emission energy, E.sub.Ti; and, the estimated remaining lifetime, T.sub.u, may be used to determine the estimated remaining lifetime, T.sub.u. The relationship may be expressed mathematically as:

[00007]$T_b.Math.\left(1-\frac{E_{\mathrm{Ti}}}{E_b}\right)=T_u$

[0141] Another example computer implemented method of estimating the remaining lifetime of a seal component of a seal assembly will now be described with reference to FIG. 3.

[0142] Obtain, S301, by a sensor for sensing the acoustic emission energy emitted from the source of the acoustic emission energy, an indication of an accumulation of acoustic emission energy emitted from the seal component over a period of time.

[0143] The sensor may be an acoustic emission (AE) sensor, for example, a piezoelectric AE sensor. In examples wherein the sensor is an AE sensor, the sensor is configured to sense an acoustic emission and output an indication comprising a voltage indicative of the magnitude of the acoustic emission. For example, the magnitude of the voltage may be proportional to the magnitude of the acoustic emission.

[0144] The acoustic emission energy emitted by the seal component at an instant in time is proportional to the square of the indication at the instant in time. The total acoustic emission energy, E.sub.Ti, emitted over a period of time is proportional to the square of the indication integrated with respect to time over the time interval, T.sub.i. This may expressed mathematically as:

E.sub.T.sub.i=∫.sub.0.sup.T.sup.iV.sup.2(t)dt

[0145] Thus, it can be seen that indication, V, is indicative of the acoustic emission energy, E.sub.Ti, emitted from the seal component over the period of time, T.sub.i.

[0146] Optionally, the raw acoustic emission data obtained may be filtered (for example, by a high pass filter, for example, with a flat bandpass, for example a Butterworth high pass filter) to obtain filtered acoustic emission data. The filtered acoustic emission data may be considered the indication, V. The cut off of the filter may be, at least 50 kHz, or at least 100 kHz, or at least 150 kHz.

[0147] A root-mean-squared (RMS) of value of either of: the raw acoustic emission data; or, the filtered acoustic emission data; may be used to obtain an RMS acoustic emission data. The RMS acoustic emission data may be considered the indication, V.

[0148] In some examples, the indication and/or the sensor may be analogue. In some examples the sensor may be a microphone which may be analogue. The microphone may be configured to sense an acoustic emission and output an indication comprising a voltage indicative of the acoustic emission. For example, the microphone may be configured to sense acoustic emissions outside of the range of frequencies audible to humans e.g. frequencies greater than those audible to humans. In examples, the magnitude of the voltage of the may be proportional to the magnitude of the acoustic emission. Accordingly, the total acoustic emission energy may be obtained from the acoustic emission by any of the ways described herein.

[0149] Optionally, modify, S302, the indication by an attenuation function.

[0150] The attenuation function accounts for dissipation and/or damping of acoustic emissions as the acoustic emissions propagate from the seal component to the sensor. The attenuation function has a value which depends exponentially on the distance of an acoustic sensor from a source of acoustic emission energy. The attenuation function, ƒ(x), takes an argument, x, which is the distance between the source of acoustic emissions and the sensor. The attenuation function, ƒ(x), may relate the total acoustic emission energy measured over the period of time, E.sub.T, to the total acoustic emission energy emitted from the source over the period of time, E.sub.0:

E.sub.T=E.sub.0ƒ(x)=E.sub.0e.sup.−k.sup.1.sup.x

[0151] Where, k.sub.1, is an attenuation factor.

[0152] Alternatively, modify, S302a, the baseline acoustic emission energy by the attenuation function.

[0153] In this alternative step, the attenuation function, g(x), takes an argument, x, which is the distance between the source of acoustic emissions and the sensor. The attenuation function, g(x), relates the baseline acoustic emission energy which would be measured at a sensor, E.sub.b, to the baseline acoustic emission energy which would be measured at the source, E.sub.bsource:

E.sub.b=E.sub.bsourceg(x)=E.sub.bsourcee.sup.−k.sup.2.sup.x

[0154] Where, k.sub.2, is an attenuation factor.

[0155] In examples, each of the baseline acoustic emission energy and the indication may be obtained by a sensor a set distance away from the site of acoustic emissions. As the acoustic emissions for obtaining the baseline acoustic emission energy and the indication travel through the same impedances (e.g. the material of the seal assembly between the source of acoustic emission and the sensor for obtaining the baseline acoustic emission energy and the indication) the attenuation of each signal due to the impedances will be approximately the same. Accordingly, in such examples, there is no need to determine an attenuation function because the effects of attenuation on the obtained signals will already be accounted for (e.g. the signal in each case will be attenuated by an approximately equal amount). Therefore, the two signals will be directly comparable without the need to obtain and apply an attenuation function.

[0156] Determine, S303, an estimate of remaining lifetime of the seal component based on: the indication; a baseline acoustic emission energy.

[0157] As detailed above, the indication, V, of the accumulation of acoustic emission energy emitted over the period of time may be used to obtain a value of the accumulation of acoustic emission energy emitted over the period of time, Rh.

[0158] The indication may be modified as set out in optional step S302 and may be omitted. For example, when the attenuation of the obtained baseline acoustic emission energy and the indication are already accounted for.

[0159] A deterioration energy may be obtained based on the indication. A deterioration energy, E.sub.d, may be defined as the total acoustic emission energy emitted over the deterioration time, T.sub.d. For example, the deterioration energy, E.sub.d, may be defined as the sum of M snaps of acoustic emission energy, E.sub.Ti. This may be expressed mathematically as:

E.sub.d=E.sub.T.sub.1+E.sub.T.sub.2+ . . . +E.sub.T.sub.M=Σ.sub.i.sup.ME.sub.T.sub.i=Σ.sub.i.sup.M∫.sub.0.sup.T.sup.iV.sup.2(t)dt

E.sub.d=∫.sub.0.sup.T.sup.1V.sup.2(t)dt+∫.sub.0.sup.T.sup.2V.sup.2(t)dt+ . . . +∫.sub.0.sup.T.sup.MV.sup.2(t)dt

[0160] Advantageously, summing over a plurality of snaps of acoustic emission energy reduces the amount of processing power required to integrate the indication of acoustic emission energy. For example, the load on a device configured to perform the integration (e.g. a computer; e.g. an analogue integrator) may be reduced.

[0161] The deterioration energy E.sub.d, may be proportional to the deterioration wear, W.sub.d, of the seal component over the deterioration time, T.sub.d. This may expressed mathematically as:

E.sub.d=K.sub.E-WW.sub.d

[0162] Where, K.sub.E-W, is a constant of proportionality.

[0163] A wear regime comprises a relationship between acoustic emission energy from a seal component at per unit time and a magnitude of wear of the seal component per unit time. In the present example, the wear regime of the seal component comprises a linear relationship between the acoustic emission energy per unit time, Ė, and the magnitude of wear per unit time, {dot over (W)}. This may expressed mathematically as:

Ė=c{dot over (W)}

[0164] Where, c, is a constant of proportionality.

[0165] The deterioration energy, E.sub.d, which is based on the indication is compared to a baseline acoustic emission energy, E.sub.b. The baseline acoustic emission energy, E.sub.b, is the expected acoustic emission energy to be emitted by a seal component over its expected lifetime, T.sub.b. For example, the expected lifetime of the seal component may be five years. Therefore, a baseline acoustic emission energy data, E.sub.b, for such a seal component would be the expected acoustic emission energy to be emitted by a seal component over five years of use.

[0166] A mathematical relationship between: the total lifetime of the seal assembly, T.sub.total; the baseline acoustic emission energy, E.sub.b; the deterioration energy, E.sub.d; and, the estimated remaining lifetime, T.sub.u. The relationship may be expressed mathematically as:

[00008]$T_{total}.Math.\left(1-\frac{E_d}{E_b}\right)=T_u$

[0167] By using the relationships between: [0168] Baseline acoustic emission energy, E.sub.b; baseline acoustic emission indication, AE.sub.base; and, total lifetime of the seal assembly, T.sub.b:

E.sub.b=AE.sub.base.Math.T.sub.b [0169] Estimated remaining acoustic emission energy, E.sub.u; baseline acoustic emission indication, AE.sub.base; and, the estimated remaining lifetime, T.sub.u:

E.sub.u=AE.sub.base.Math.T.sub.u

[0170] Replace, S304, the seal component once the estimate of remaining lifetime has elapsed.

[0171] Operation of the rotating equipment is ceased. The seal assembly is dismantled such that access to the deteriorated seal component is provided. Then the deteriorated seal component is replaced with a new seal component.

[0172] To determine an estimate of remaining lifetime of the seal component, any of the following constraints may additionally be adhered to.

[0173] The total acoustic emission energy, E.sub.T, is linear to operational wear, W.sub.T. In other words, the ratio of the total acoustic emission energy, E.sub.T, and operational wear is equal to a constant of proportionality, c.sub.1. This may be expressed mathematically as:

[00009]$\frac{E_T}{w_T}=c_1$

[0174] Seal fluid may affect the severity of contact between seal faces of the seal assembly. In examples, carbon dioxide provides higher contact severity than light oil. Accordingly, the wear may depend on the seal fluid used.

[0175] The total acoustic emission energy, E.sub.T, is linearly proportional to seal area of the seal component, A. In other words, the ratio of the total acoustic emission energy, E.sub.T, and seal area, A, is equal to a constant of proportionality, c.sub.2. This may be expressed mathematically as:

[00010]$\frac{E_T}{A}=c_2$

[0176] For example, doubling the seal area, A, doubles the acoustic emission energy emitted over the period of time, T, provided the same asperity surface load is constant and the lubricating fluid in each case is the same.

[0177] In examples, the wear may be characterised by a specific wear coefficient W.sub.c. The specific wear coefficient is directly proportional to wear volume, V.sub.w, and inversely proportional to the product of force applied tangentially to the surface of the seal face, F, and load applied tangentially to the surface of the seal face, L. This may be expressed mathematically as:

[00011]$W_c=\frac{V_W}{FL}$

[0178] Wear may be determined by the level of asperity contact and the type of seal fluid. For a poor lubricating seal fluid (e.g. less lubrication) the wear coefficient (wear volume/load*distance) is greater than for a well lubricating fluid (e.g. more lubrication). It has been observed that the amount of energy required to abrade a given amount material does not change when seal fluid is changed (e.g. the amount of energy to abrade a given amount of material is invariant with respect to seal fluid.

[0179] A mechanical seal for a poorly lubricating seal fluid may be designed differently to a mechanical seal for a well lubricating seal fluid that seals a well lubricating fluid. For example, a greater load can be applied to seal closing forces to reduce leakage in a mechanical seal for a well lubricating seal fluid. If a mechanical seal is used for both poorly lubricating seal fluids and well lubricating seal fluids, the mechanical seal may be limited to use with operating parameters suitable for the poorly lubricating fluid (e.g. operating parameters may include any of: speed; sealing pressure) in order to achieve a minimum guarantied seal lifetime.

[0180] For example, if a pressure differential is low at the inboard seal, increased severity of contact is more likely on the inboard seal than on the outboard seal which still operated at higher pressure differential to atmospheric pressure.

[0181] The indication may also be received by a controller via a communication interface such as over a network or where appropriate direct measurement may be performed by appropriate measurements. For example direct measurements of the indication may be taken by any appropriate apparatus such as those discussed herein.

[0182] To support the present disclosure tests were conducted using with four separate type mechanical seal assemblies. Acoustic emission sensors were attached to each of the seal assemblies. Each of the PAC wide band sensors were configured to measure AEs from each of seal assemblies.

[0183] A first seal assembly was attached to a first rotating equipment. The first seal assembly had a hydraulic balance ratio of 100% (unbalanced) and the first rotating equipment operated continuously for 13 days (e.g. a test period of approximately 300 hours). A second seal assembly was attached to a second rotating equipment. The second seal assembly had a hydraulic balance ratio of 100% (unbalanced) and the second rotating equipment operated continuously for 300 hours. A third seal assembly was attached to a third rotating equipment. The third seal assembly had a hydraulic balance ratio of 80% (balanced) and the third rotating equipment operated continuously for 600 hours. A fourth seal assembly was attached to a fourth rotating equipment. The fourth seal assembly had a hydraulic balance ratio of 100% (unbalanced) and the fourth rotating equipment operated continuously for 600 hours.

[0184] Hydraulic balance ratios of 100% and 80% ensure permanent contact between the seal face components at controlled but different severities of load. After cessation of operation of the respective rotating equipment, the wear of each seal component was obtained. The wear may be obtained by finding the difference between a measurement of the seal component taken before operation of the seal assembly and a measurement of the seal component taken after cessation of operation of the rotating equipment. An axial length of the seal component may be measured before operation and after cessation of the operation of the rotating equipment. The raw acoustic emission signals obtained from each seal assembly was filtered by a 100 kHz Butterworth high pass filter to obtain filtered acoustic emission data. A RMS of value of the filtered acoustic emission data was obtained from the filtered emission data to obtain RMS filtered acoustic data.

[0185] FIG. 4 shows cumulative RMS filtered acoustic data, measured in volts, against time, measured in days.

[0186] Table 1 below summarises the results of the tests on each of the first through fourth seal assemblies.

TABLE-US-00001 TABLE 1 First Second Third Fourth seal seal seal seal assembly assembly assembly assembly Seal Wear 1.15 1.1 1 1.5 (% of total wear allowance) Test period 12.43 12.43 25.81 25.81 (days) Contact AE 61.7470 54.5498 44.6463 66.4802 Energy (V) Contact AE 4.967 4.388 1.729 2.57 Energy rate (V per day) Wear rate 0.0925 0.0885 0.0385 0.058 (% of total wear allowance per day)

[0187] The results of the deterioration tests on the John Crane® type 3648 seal demonstrate that there exists a relationship between acoustic emission energy and wear.

[0188] In the present example, the primary ring comprises carbon graphite and the mating ring comprise silicon carbide. There was no measurable wear of the mating ring and therefore, the total seal wear comprises the wear on the primary. The reason for this is that in the seal assembly carbon-graphite wears more readily than silicon carbide.

[0189] In examples, the total seal wear may comprise the wear on both the primary ring and the mating ring. In examples, the primary ring and the mating ring may consist essentially of the same material, for example, silicon carbide and carbon-graphite.

[0190] FIG. 5A shows a scatter graph of the acoustic emission energy, measured in volts, against wear, measured in millimetres. A curve of best-fit is included to generalise the relationship between the acoustic emission energy and the wear. The relationship between the acoustic emission energy and the wear, in this example, is linear and accordingly a straight line is the most appropriate curve of best-fit for the data. The relationship between acoustic emission energy and wear may be extrapolated as shown in FIG. 5B.

[0191] A first wear regime comprises a relationship between acoustic emission energy from a seal component at per unit time and a magnitude of wear of the seal component per unit time. In the present example, the first wear regime of the seal component comprises a linear relationship between the acoustic emission energy per unit time, Ė, and the magnitude of wear per unit time, {dot over (W)}. This may expressed mathematically as:

Ė=c{dot over (W)}

[0192] Where, c, is a constant of proportionality.

[0193] In other seal assemblies the first wear regime may have a different functional form, for example, polynomial, exponential, or logarithmic.

[0194] In some examples, there may be more than one wear regime. For example a second wear regime comprising a relationship between acoustic emission energy from a seal component at per unit time and a magnitude of wear of the seal component per unit time.

[0195] A transition between a first and second wear regimes may occur when a parameter of the seal assembly changes. For example, an increase in the rate of change of total acoustic emission energy, E.sub.T, over a selected period of time (e.g. 1 second) may correspond to a transition from a first wear regime (e.g. an adhesive regime) to a second wear regime (e.g. an abrasive regime).

[0196] The attenuation function was obtained empirically and was found to comprise an exponential decay which depends on the distance, x, between the sensor and the source of acoustic emission. The modified acoustic emission energy, E.sub.mod, is related to the acoustic emission energy at the source of the acoustic emission, E.sub.0, by the following equation.

E.sub.mod=e.sup.−k.sup.3.sup.xE.sub.0

[0197] Wherein k.sub.3 is an attenuation factor.

[0198] The attenuation function may be obtained empirically. A method of obtaining an attenuation function empirically is shown in FIG. 6. The method of empirically obtaining an attenuation function shown in FIG. 6 comprises:

[0199] Simulate, S701, an acoustic emission in the seal assembly.

[0200] Simulation of AE may be performed by snapping a pencil lead break on an exterior surface of the seal assembly. For example, a pencil lead break may be snapped at the locations denoted as S1 to S7 in FIG. 1.

[0201] Measure, S702, a magnitude of the acoustic emission by a sensor.

[0202] The sensor may be any sensor described herein suitable for measuring acoustic emissions.

[0203] Measure, S703, a distance between the source of acoustic emission and the sensor.

[0204] The distance between a source of acoustic emission and the sensor may be measured by, for example, a ruler or a tape measure.

[0205] Obtaining a relationship between the magnitude of acoustic emission and the distance between source of AE and the sensor.

[0206] Repeat steps S701 through S703 until a sufficient number of data points have been obtained. For example, ten data points may be considered to be a sufficient number of data points in order to perform step S704.

[0207] Obtain, S704, a relationship between the magnitude of acoustic emissions and the distance of between the source of acoustic emissions and the sensor.

[0208] Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described and/or claimed herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates.

[0209] Any processors used in the computer system (and any of the activities and apparatus outlined herein) may be implemented with fixed logic such as assemblies of logic gates or programmable logic such as software and/or computer program instructions executed by a processor. The computer system may comprise a central processing unit (CPU) and associated memory, connected to a graphics processing unit (GPU) and its associated memory. Other kinds of programmable logic include programmable processors, programmable digital logic (e.g., a field programmable gate array (FPGA), a tensor processing unit (TPU), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM), an application specific integrated circuit (ASIC), or any other kind of digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof. Such data storage media may also provide the data store of the computer system (and any of the apparatus outlined herein).

[0210] Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

[0211] The condition monitoring system may be configured to perform any of the methods described herein. For example, the condition monitoring system may comprise a controller. The controller may be configured to perform any of the methods described herein.