Method and apparatus for measuring a parameter of a multiphase flow

The present invention comprises method of measuring a parameter of a multiphase flow of a fluid and apparatus therefore. The apparatus comprises a buffer chamber apparatus that is operably fluidly coupled to a pipe bearing a fluid comprised of components of different densities. The buffer chamber apparatus has structure that defines a substantially fluid tight chamber that is in flow communication with the fluid borne in the pipe. One or more ports are defined in the chamber structure whereby the fluid in the chamber may be selectively accessed for sensing a parameter of the fluid. The fluid in the chamber resides in a substantially stable state promoting the separation of the different density components of the fluid.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to measuring a parameter of a 
multiphase flow in a pipe. More particularly, the present invention 
relates to buffer chamber assemblies which are coupled to a pipe proximate 
a pipe tap. The buffer chamber assembly serves as a means to sense 
parameters of the fluid in the pipe, to sample the fluid in the pipe, and 
to introduce fluid to the flow in the pipe, while resisting the clogging 
of the pipe tap. 
2. Description of the Prior Art 
Pipe taps, particularly pipe taps that are coupled to parameter measuring 
devices, such as pressure measuring devices, are typically ineffective 
when used on pipes carrying fluids which tend to clog. The clogging that 
attends the flow of some fluids that are typically transported in pipes 
rather quickly partially or fully occludes the tap opening, thereby 
affecting the accuracy of the parameter measurement. The tap in the pipe 
may be remotely located and clearing of a clogged condition may pose 
considerable problems, not the least of which is the potential need to 
shut down flow in the pipe during the cleaning operation. 
U.S. Pat. No. 5,312,137 by Nee discloses a safety shield for capturing 
corrosive fluids escaping from a joint in a piping system. The safety 
shield includes an aperture to encircle a pipe and an outlet. Devices may 
be included which measure the conditions within the shield. 
U.S. Pat. No. 4,040,289 by Clark discloses a method and an arrangement for 
air testing of sewer lateral connections. The tester is pressurized with 
air over the lateral connection location and the air pressure monitored. 
If the tester holds pressure, the connection is deemed leakage proof. 
U.S. Pat. No. 5,330,720 by Sorbo discloses a system for detecting gaseous 
emissions from a mechanical coupling. The housing comprises a 
semi-permeable material which allows the gases to escape while preventing 
foreign matter from entering the housing. 
U.S. Pat. No. 5,022,271 by Hannon, Jr., discloses a pressure sensing device 
for pipes carrying corrosive or abrasive fluids. The device measures 
pressure in the pipe by the movement of a thin metal wall incorporated 
into the pipe. The thin metal wall includes pleats or folds which allows 
the wall to move inwardly or outwardly in response to changes in pressure. 
U.S. Pat. No. 4,840,068 by Mayhew, Jr. discloses a pressure sensor assembly 
which measures pressure by the movement of a diaphragm included in a pipe 
wall. A chamber upon which the pressure sensor is mounted contains a 
pressure sensing fluid kept separate from fluid in the pipe by the 
flexible diaphragm. The flexible diaphragm flexes outward or inward 
causing the sensing fluid to pressurize of depressurize. There is no 
mixing of the pipe fluid and the sensing fluid. 
U.S. Pat. No. 5,347,868 by Shigesada discloses a pressure gauge designed 
for use in measuring the pressure of thixotropic (colloidal) liquids. The 
object of the invention is to prevent aggregation stagnation of the fluid 
by controlling the stagnation of a magnetic coating liquid in the vicinity 
of a pressure sensor. Aggregation of fluid near the pressure gauge is 
subsequently reduced. 
There is a need for a pipe tap which resists clogging and minimizes the 
corrosive effect on parameter sensors from corrosive fluids being 
transported in the pipe. The pipe tap should be inexpensive to manufacture 
and highly effective. Such a buffer chamber assembly must reduce clogging 
near a parameter sensor, thereby making more accurate readings as to the 
various parameters of the fluid. Additionally, such a buffer chamber 
assembly should be simple to use, especially when readings must be taken 
in the field under potentially hostile environmental conditions. Such a 
buffer chamber assembly should also utilize existing tools for mounting on 
pipes rather than requiring specialized equipment. 
SUMMARY OF THE INVENTION 
In keeping with the principles of the present invention, the objects are 
accomplished with the unique configuration of a buffer chamber operatively 
connected to one or more countersunk pipe taps. The combination of those 
elements in the present invention results in a device which is easy to 
install and remove and is simple and inexpensive to manufacture. 
The buffer chamber assembly is designed to cause the separation of fluids 
passing through a pipe. Separation is accomplished by passing the fluids 
through pipe taps in the pipe wall and into a buffer chamber. Separation 
then occurs as the denser fluid sinks to the bottom of the buffer chamber 
while fluid or fluids of lower density move toward the top of the chamber. 
Separation of fluids is critical when one or more of the fluids has the 
potential for clogging in the vicinity of the pressure measuring device 
used to measure pressure of the fluid. Clogging, or the accumulation of 
material with a different viscosity than the bulk of the fluid, may cause 
a pressure differential across the clogged material. That pressure 
differential would then result in inaccurate pressure readings from the 
pressure measuring device. 
The present invention, by causing separation of the fluids carried in a 
pipe, causes only a selected fluid or fluids to come in contact with the 
pressure measuring device. Preferentially, those fluids are less likely to 
clog. For instance, in a pipe carrying oil and water, the buffer chamber 
assembly could be used to separate the oil from the water. Because oil 
generally has a lower density than water, oil will rise to the top of the 
buffer chamber while water will sink to the bottom. Because water has less 
clogging potential than oil, in this instance a pressure sensor port, 
which allows communication between the buffer chamber and the pressure 
measuring device, should be located near the bottom of the buffer chamber. 
Consequently, there is a reduced likelihood that clogging will occur in 
the vicinity of the pressure measuring device. Additionally, since there 
is effectively no flow in the buffer chamber after the initial fluid from 
the pipe has flooded the buffer chamber, one of the separated fluids in 
the chamber could be drawn off through a port, leaving only the more 
benign fluid in the buffer chamber. 
Similarly, another advantage of the present invention is the separation of 
fluids when one or more of the fluids has corrosive properties which would 
be deleterious to the pressure measuring device. In that instance, 
separation of the fluids coupled with an appropriate placement of the 
parameter tap in the buffer chamber would allow only the less caustic 
fluid or fluids to come in contact with the parameter measuring device. 
A further advantage of the present invention is that by including a port in 
the buffer chamber, fluids from the pipe flow may be sampled by 
withdrawing a sample through the port and additives that affect the flow 
as desired may be introduced to the flow in the pipe by injection through 
the same port. 
The present invention comprises a buffer chamber apparatus that is operably 
fluidly coupled to a pipe bearing a fluid of different densities. The 
buffer chamber apparatus has structure that defines a substantially fluid 
tight chamber that is in flow communication with the fluid borne in the 
pipe. One or more ports are defined in the chamber structure whereby the 
fluids in the chamber may be selectively accessed for sensing a parameter 
of the fluid. The fluid in the chamber resides in a substantially stable 
state promoting the separation of the different density fluids by gravity.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purpose of describing the features of the present invention, the 
buffer chamber assembly is discussed in operative connection to a pipe. 
The pipe is generally used for the transport of fluids, such as oil and 
water in liquid form, although the term fluid is not intended to be 
limited only to liquids. 
To measure a fluid parameter, such as the pressure of the fluid, at a given 
location on a pipe, pipe taps are made in the wall of the pipe. These pipe 
taps allow fluid to escape. If the fluid flows into a fixed volume, the 
fluid retains the approximate parameter of the fluid travelling in the 
pipe that is sought to be sensed. When measured, the parameter in the 
fixed volume can be calibrated to give an accurate reading as to the 
parameter of the fluid flowing in the pipeline. 
Referring to the Figures, wherein like numerals indicate like components 
throughout, the buffer chamber assembly of the present invention is shown 
generally at 10. With regard to FIGS. 1-3, the buffer chamber assembly 10 
has two major components; a chamber 12 and a retaining strap 14. The 
buffer chamber assembly 10 is depicted associated with a pipe 15 used to 
transport fluids. 
The chamber 12 is preferably composed of a non-permeable, corrosion 
resistant material which is able to withstand the pressures of the fluid 
that is being transported in the pipe 15, such as aluminum or steel. In 
certain applications, the chamber 12 may be formed of a thermoplastic of 
polyvinyl chloride material where the pressures are relatively low and to 
take advantage of the corrosion resistance properties of such material. 
Generally, the chamber 12 may have a number of different shapes; the 
chamber 12 depicted in FIG. 1 being generally a cube. In this embodiment, 
the retaining strap 14 compressively couples the chamber 12 to the pipe 
15. The chamber 12 comprises a chamber body 16 and two opposed sides 18. 
The chamber body 16 comprises a generally u-shaped frame 19. The frame 19 
has two flat coplanar mounting panels 20 at the two ends of the u-shaped 
frame 19. The mounting panels 20 each include a threaded hole 26 defined 
therein. 
A curved body panel 22 connects the two mounting panels 20. The curved body 
panel 22 is generally a segment of a half cylinder that must be fit to the 
outside circumference of the pipe 15. Accordingly, the outside surface of 
the curved body panel 22 has radius that is very slightly greater than the 
radius of the particular pipe 15 that the chamber 12 is intended to be 
mated to. The curved body panel 22 presents a sealing face for 
establishing a sealing engagement with the pipe 15. A chamber port 24 is 
defined in the curved body panel 22. The chamber port 24 is preferably a 
generally elongated orifice. 
Referring to FIG. 3, heater 25 may be mounted to the body 16. The heater 25 
is useful to transfer heat through the structure of the body 16 to heat 
the fluid in the chamber 12 as desired. The heater 25 is typically an 
electrical heater and is connected to an electrical power source by 
electrical leads (not shown). 
Valve port 28 and sensor port 30 are defined in the body 16. Threaded 
bushings (not shown) are typically utilized in conjunction with the ports 
28, 30. Such bushings are threaded into the ports 28, 30 and project 
therefrom. Nuts 32 produce fluid-tight pressure fits for the retention of 
pipe fittings 34 to the valve port 28 and sensor port 30. 
The valve port 28 and the sensor port 30 are typically displaced from one 
another in elevation as the chamber 12 is mounted on the pipe 15. As 
depicted, the valve port 28 is elevated above the sensor port 30. The 
valve port 28 is positioned to draw off air trapped within the chamber 12 
or to draw off the lighter of two separable fluids that are contained 
within the chamber 12. The valve port 28 may be sealed off after removal 
of fluid as desired. The heavier of the two separable fluids will act upon 
the sensor port 30. 
Parameter sensing of the fluid in the chamber 12 may be done in a number of 
ways. As depicted in FIG. 2, lines 33, connected to the valve port 28 and 
sensor port 30 may be further connected to a manometer, pressure gauge, or 
transducer. As depicted in FIG. 3, a sensor device 35 is attached to the 
outer surface of the chamber 12 and is located proximate to the sensor 
port 30. The sensor device 35 may sense such fluid parameters as the 
pressure or temperature of the fluid in the chamber 12. A protecting 
barrier 36 is attached to the inside of the chamber 12 and is located 
proximate to the sensor port 30. 
The chamber sides 18 are generally rectangular with an edge comprising a 
semi-circular curved section 40 that generally matches the curvature of 
the curved body panel 22. The chamber sides 18 are held clamped to the 
side margins of the chamber body 16 by plurality of pass through bolts 44. 
The plurality of bolts 44 are disposed within corresponding bores (not 
shown) in each of the chamber sides 18 that are in registry when the sides 
18 are disposed on the chamber body 16. The bolts 44 are passed through 
the bores in a first chamber side 18, through the interior of the chamber 
12, and through the corresponding bore in the second chamber side 18 with 
the threaded end thereof projecting beyond the second chamber side 18. The 
ends of the bolts 44 are retained by burl nuts 46. A gasket material is 
provided between the sides 18 and the body 16 resulting in a pressure seal 
when the burl nuts 46 are tightened down. The gasket material is of a type 
compatible with the fluids introduced into the chamber 12 and having 
properties which allow adequate pressure differential to be maintained 
without failure of the gasket material. 
A gasket 48, as depicted in FIG. 3, is disposed on the outer surface of the 
curved section 22 and is held in compressive engagement between the buffer 
chamber assembly 10 and the pipe 15. The gasket 48 substantially surrounds 
the chamber port 24 and has a slot (not shown) defined therein that is in 
registry with the chamber port 24 so that the gasket 48 does not cover the 
chamber port 24. The material that is used to form the gasket 48 is 
selected much as the material for the gasket material that is provided 
between the sides 18 and the body 16, bearing in mind the pressure 
requirements and the properties of the fluid that is being transported in 
the pipe 15. 
The second major part of the buffer chamber assembly 10 is the retaining 
strap 14. The retaining strap 14 is preferably composed of a strong but 
flexible material such as steel. The retaining strap 14 is formed in a 
generally semicircular shape and, when mated to the chamber 12 defines a 
circular opening therein that has a diameter that is slightly greater than 
the outside diameter of the pipe 15 to which the particular buffer chamber 
assembly 10 is to be mated. The retaining strap 14 has flanges 64 formed 
at the two ends thereof. Each of the flanges 64 has a face 65 that is 
adapted to mate with the mounting panels 20. Each flange 64 has a bore 
(not shown) defined therein that is in registry with the threaded hole 26 
defined in the opposing mounting panel 20. The retaining strap 14 is 
compressively coupled to the chamber 12 and to the pipe 15 by the bolts 62 
being threaded into the threaded holes 26. By threading the bolts 62 into 
the holes 26, the gasket 48 is compressed between the pipe 15 and the 
outer surface of the curved section 22, creating a fluid-tight seal 
between the buffer chamber assembly 10 and the pipe 15. 
The buffer chamber assembly 10 is operatively connected to a pipe 15. The 
pipe 15 has an inner surface 74 and an outer surface 76. Taps 72 are 
defined extending through the wall of the pipe 15, extending from the 
inner surface 74 to the outer surface 76. The taps 72 generally taper in 
diameter from a larger diameter at the outer surface 76 to a smaller 
diameter at the inner surface 74 as distinct from the more usual bores 
comprising traps that have a singular diameter the full distance from the 
inner surface 74 to the outer surface 76 of the pipe 15. When the buffer 
chamber assembly 10 is installed on the pipe 15, care is taken to ensure 
that the taps 72 are aligned with the chamber port 24 so that there is 
fluid communication between the fluid in the pipe 15 and the chamber 12 of 
the buffer chamber assembly 10. 
FIG. 4 is a second preferred embodiment of the invention. FIG. 4 depicts a 
buffer chamber assembly 10 comprising two opposed chambers 12. Each of the 
chambers 12 of the present embodiment is constructed substantially as 
described above. By using two opposed identical chambers 12, the need for 
a retaining strap 14 is eliminated. The chambers 12 are joined by bolts 62 
which are disposed in the flanges 64 and are secured by nuts 66. A 
plurality of taps 72 are defined equiangularly around the circumference of 
the pipe 15. 
For the embodiment shown in FIG. 4, the chamber port 24 of each of the 
chambers 12 is aligned with the pressure taps 72. The chambers 12 are 
secured by operatively joining bolts 62 and nuts 66. 
FIG. 5 is a third preferred embodiment of the invention shown in FIG. 1-3. 
FIG. 5 shows a buffer chamber assembly 10 which comprises a circular 
chamber 12. Similar to the embodiment shown in FIG. 4, the flanges 64 are 
joined by a bolt 62 which is held secure by nuts 66. For the embodiment 
shown in FIG. 5, the chamber 12 is made to encircle the pipe 15 and is 
held securely in place by joining the flanges 64. Flanges 64 are joined by 
operatively connected bolts 62 and nuts 66. 
FIG. 6 is a fourth preferred embodiment of the invention shown FIG. 1-3. 
FIG. 6 shows a buffer chamber assembly 10 with a flushing system 82. The 
flushing system 82 communicates with the chamber 12 through the injection 
port 84. The injection port 84 provides a pressure-proof seal between the 
reservoir 86 and the chamber 12. The reservoir 86 holds the fluid which 
will be introduced into the buffer chamber assembly 10 by a small pump 
(not shown). The reservoir 86 is preferably constructed of a material 
which is impervious to degradation by the fluid contained within the 
reservoir 86. The pressure bearing capacity of the pump (not shown) must 
be adequate to allow greater pressurization of the fluid before the valve 
88 than that of the fluid within the chamber 12 so that fluid travels from 
the reservoir 86 to the chamber 12. 
For the embodiments shows in FIGS. 1-3 and 6, assembly of the buffer 
chamber assembly 10 is accomplished by simply aligning the chamber port 24 
with the pressure taps 72. The flanges 64 of the retaining strap 14 are 
then aligned with the threaded holes 26. Bolts 62 are disposed in flanges 
64 to secure the threaded holes 26. 
FIGS. 7-10 depict a fifth preferred embodiment of the buffer chamber 
assembly 10 of the present invention. In this embodiment, the chamber body 
16 of the chamber 12 is unitary, being formed from a single block of 
substantially homogeneous material. The material may be a metallic 
material such as aluminum or stainless steel or it may be a plastic 
material. The unitary chamber body 16 requires milling or other material 
removal methods to form the chamber cavity 102 defined therein. By being 
unitary, this embodiment design eliminates the need for the opposed sides 
18 as depicted in previous embodiments. 
The unitary chamber body 16 has a chamber cavity 102 defined therein. The 
chamber cavity 102 is comprised of two elements, a chamber port 
interconnect 104 and a chamber bore 106. The chamber port interconnect 104 
fluidly couples the chamber port 24 to the chamber bore 106. As indicated 
in FIG. 9, the chamber port interconnect 104 is trapezoidal in cross 
section, expanding at the intersection with the chamber bore 106 to 
increase the volume of the chamber cavity 102. 
The chamber bore 106 is a bore defined through the chamber body 16. The 
longitudinal axis of the chamber bore 106 is transverse to the center axis 
of the chamber port interconnect 104. The first terminus of the chamber 
bore 106 defines the valve port 28 and the second terminus of the chamber 
106 defines the sensor port 30. Both the valve port 28 and the sensor port 
30 have threads 108 defined therein to accommodate the insertion of 
bushings therein. Further, either the valve port 28 or the sensor port 30 
may be plugged by threadingly engaging a suitable plug in the threads 108 
thereof in instances where such port 28, 30 is not required for the 
particular application of the buffer chamber assembly 10. 
The buffer chamber assembly 10 depicted in FIGS. 7-10 may be operably 
coupled to the pipe 15 by using a retaining strap 14 as previously 
described. Alternatively, pins (not shown) may be inserted through the 
mounting bores 100 such pins have a length that is greater than the width 
dimension of the buffer chamber assembly 10 so that the ends of the pins 
project on either side of the buffer chamber assembly 10. A tightenable 
strap (not shown) connects the two ends of the pins exposed on a side of 
the buffer chamber assembly 10 to an end of a similar pin positioned on 
the far side of the pipe 15. Tightening such strap sealingly couples the 
buffer chamber assembly 10 to the pipe 15. 
In use, the buffer chamber assembly 10 contains a fluid under a pressure 
that is related to the pressure within the pipe 15. Fluid passes from the 
pipe through the pressure taps 72. Fluid then passes through the chamber 
port 24 into the chamber 12. In the chamber 12, a composite or multiphase 
fluid separates, the denser fluid sinking to the bottom while less dense 
fluid floating to the top of the chamber 12. The protecting barrier 36 
prevents direct travel of fluid from the pressure taps 72 to the sensor 
port 30. Fluid fills the sensor port 30 and contacts the sensor 35. The 
sensor 35 measures the pressure in the fluid. When relatively 
incompressible fluids are carried in the pipe 15 the pressure measurement 
determined at the sensor 35 accurately represents the pressure in the pipe 
15. 
The heater 25 shown in FIG. 3 may be used to raise the temperature of the 
fluid in the chamber 12. By raising the fluid temperature, the viscosity 
of the fluid is reduced. Similarly, the flushing system 82 shown in FIG. 6 
would also result in lower viscosity fluid in the chamber 12. Lower 
viscosity fluid is less likely to clog the sensor port 30. Accuracy of 
pressure measurement is improved. 
The separation of fluids which occurs in the chamber 12 causes only the 
fluid of the highest density to enter the sensor port 30 when the sensor 
port 30 is located downward in relation to the remainder of the chamber 
12. Where fluids such as oil and water are transported through the pipe 
15, the water is the denser of the two fluids and thus enters the sensor 
port 30. Water cannot clog the sensor port 30 whereas oil may cause the 
port 30 to become clogged. Clogging of the sensor port 30 could cause a 
pressure drop across the clog, thus causing an inaccurate pressure reading 
by the pressure measuring device 34. The present system, therefore, 
provides a more reliable means for measuring fluid pressure in a pipe 15. 
The taps 72 are counter-sunk so that discontinuities in the fluid, such as 
solids or gas bubbles, do not become lodged in the taps 72. 
Discontinuities which are able to pass initially through the relatively 
smaller diameter of the tap 72 on the inner surface 74 will be small in 
comparison to the diameter of the taps 72 on the outer surface 76. This 
disparity in size between the discontinuity and the taps 72 diameter 
causes a smaller percentage of the surface area of the discontinuity to 
contact the taps 72 than if the discontinuity and the taps 72 were of 
similar size. Less contact between the discontinuity and the taps 72 
results in less potential for the discontinuity becoming lodged in the 
taps 72. Another advantage of the counter-sunk taps 72 is evident during 
initial flow of fluid from the pipe 15 into the semi-filled chamber 12. 
The fluid passing through the taps 72 expands as it passes from the inner 
surface 74 to the outer surface 76 through the taps 72. As the fluid 
expands its pressure drops. That pressure drop motivates any 
discontinuities partially blocking a given tap 72 to travel with the fluid 
flow and, therefore, leave the tap 72 and enter the chamber 12. Therefore, 
in at least two ways the taps 72 result in a lower probability of clogging 
than if the taps 72 were not counter-sunk. The small diameter of the tap 
72 on the inner surface 74 further results in less disturbance of fluid 
flow through the pipe 15. A disturbance-free flow is desirable to attain 
separated, laminar flow within the pipe 15. 
The function of the taper in the taps 72 is to prevent clogging. 
Specifically, oil bubbles, for example, which would otherwise clog a 
pressure line or transducer, will readily pass through the tapered tap 72 
having the same sized opening diameter at the interior surface of the pipe 
wall as a straight bored tap. The angle of taper must provide for an 
abrupt opening away form the sharp corner of the opening diameter at the 
interior surface of the pipe wall in order that the bubbles do not 
accumulate at the opening. 
It is understood that a number of modifications can be readily devised in 
accordance with the principles of the present invention by those skilled 
in the art without departing from the spirit and scope of the invention. 
Therefore, it is not desired to restrict the invention to the particular 
construction illustrated and described, but to cover all modifications 
that may fall within the scope of the appended claims.