Sensor probe and pipeline construction and method

A sensor and carrier device are provided in combination with a pipeline for either placing a sensor element within the flow stream of the pipeline or a device to divert flow outside of the pipeline to measure a parameter of the conditions within the pipeline or of the gas flowing through the pipeline. The configuration of the probe comprising the carrier and sensor is such as to reduce the possibility of structural failure of the probe.

BACKGROUND OF INVENTION

The present invention is directed to a pipeline construction and method of operation which presents a sensor to fluid in or from the flow stream of fluid flowing through the pipeline.

Pipelines are used to convey fluids (liquid and/or gas), for example, natural gas or other hydrocarbon gases and/or liquids and are well-known in the art. It is common in such pipelines to monitor various parameters of their operation. Examples of monitored parameters include pressure, temperature, fluid speed, energy content and sometimes the component mix of the fluid flowing through the pipeline. Typically this can be done in one of three broad ways. First, when it is desired to measure a parameter, a probe is temporarily installed in the line, the reading taken and the probe removed. However, oftentimes such an approach would require the shutting down of the pipeline to effect installation and removal of the probe. A second method is the use of a probe that is permanently or semi-permanently mounted to the pipeline having a portion thereof projecting into the interior of the pipeline. A third method is the use of a drive device to automatically, upon a given signal, for example, after a predetermined time period, insert the probe into the pipeline and remove the probe from the pipeline. All these methods are well known in the arts. See for example, U.S. Pat. Nos. 4,346,611, 5,756,906, 6,259,523 and 6,338,359.

Pipelines can contain delicate equipment therein, for example, a turbine type fluid speed monitoring device, valves and the like. Should a probe break loose, it can cause damage to equipment contained in the line in addition to requiring its repair or replacement. Oftentimes, gas is moved through pipelines at high and ultra high speeds, sometimes subsonic and sometimes supersonic. It has been found that in operation, the probe and possibly a sensor and its carrier can break from forces acting on the probe. To reduce bending moments, oftentimes the probes are short but this limits the location within the pipeline in which the parameter to be monitored can be sensed or extracted. The location of the sensing or sampling can affect the reading or output of the sensor usually carried by a carrier portion of the probe. For example, gas speed will vary with position transversely across the pipeline. Generally, in laminar flow, the gas speed profile will be a parabola with the maximum gas speed being in the center of the pipe and the minimum speed being at the pipe wall. Temperature may also vary depending upon where across the pipe cross section the measurement is taken. Likewise, pressure may also vary by where the reading is taken across the pipe. The longer the carrier, the greater the bending moment is that is applied to the measuring device because of the increased force from the increased surface area of the carrier and the longer moment arm due to the increased length of the carrier.

Another source of force application to a carrier and sensor is induced vibration. There may be two sources of vibration in a flow stream in a pipeline. One is the vibration of the pipeline from the fluid flowing therethrough which may be transmitted to the probe and carrier. Another source of vibration is caused by separation of the flowing fluid from the carrier as it moves around the carrier and, depending upon where the flow separates from the carrier, vortices will form on the “backside” or downstream side of the carrier. These vortices can induce vibration in the carrier and/or sensor, and should that vibration be resonant, can cause structural failure of the probe and perhaps damage to downstream equipment from the probe moving downstream with the flowing fluid.

Work has been done to try to prevent carrier and probe failure. Reference can be made to API 14.1.7.4.1 for probe design. A formula is provided for calculating the maximum length of a probe as a function of its outer diameter. The solution suggested by this publication is that to prevent damage from resonant vibration, the length of the probe should be limited in the manner described in the reference.

A brief discussion of vibration may also be found in Mark's Standard Handbook for Mechanical Engineers, 10thEdition, at page 3–47.

A problem further complicating the design of carriers and sensors is that a pipeline is not constant in operation. The rate of flow, temperature and pressure change over time. The fluid in the pipeline may also change. Thus, a carrier and sensor designed to be acceptable only at one set of operating conditions may not always be appropriate for the pipeline since the operating conditions may change, complicating the solution to the problem of carrier design because one could not match the design of the carrier to operating conditions that would prevent resonant frequency vibration. It is pointed out that it is not clear, if it is resonant frequency vibration alone or in combination with other factors that causes the failure of carriers, although some in the art assume that it is, further complicating the solution to the problem of carrier failure.

Thus, there is a need for an improved probe design that will reduce the risk of probe failure.

SUMMARY OF THE INVENTION

The present invention involves the provision of a pipeline construction comprising a section of pipe and a probe configured to reduce the risk of failure.

The present invention also provides for a method of measuring or monitoring a gas pipeline operating parameter.

Like reference numerals throughout the various Figures designate like or similar parts or constructions.

DETAILED DESCRIPTION

The referenced numeral1designates generally a pipeline construction comprising at least one pipe section2through which fluid flows. The fluid may be gas, liquid or a combination thereof. In a preferred embodiment of the present invention, the fluid flowing through the pipeline1is a hydrocarbon gas such as natural gas, methane, propane and the like which may contain liquid(s). In laminar flow, and as seen inFIG. 1, the fluid speed profile is generally in the shape of a parabola as seen on the left-hand end of the pipe section2inFIG. 1. Flow speeds, on average across the flow path, are on the order of at least about 50 ft/sec, up to several hundred ft/sec, and in the case of natural gas, can be on the order of approximately 100 ft/sec. The pipe sections2are typically round and the diameter of the pipe section can be any suitable diameter ranging from on the order of 2 inches to 24 inches or can be even larger. The length of such pipelines1can be in the miles or hundreds of miles. At certain locations along the length of the pipeline1, various measuring or monitoring devices5are provided in or associated with the pipeline construction at mounting locations provided for the use of such devices5. Measuring or monitoring devices5may include a sensor device6,FIG. 5, such as pressure sensors, temperature sensors, fluid speed sensors, chemical analysis, energy content and the like, as are well known the art, may be provided. The sensor6may have at least a portion in the interior12of the pipe section2or may be external of the interior. As best seen inFIGS. 1 and 2, a measuring device, designated generally5, is mounted to the pipe in any suitable manner. As seen inFIG. 1, the device5includes an elongate probe7suitably mounted to the pipe section2and extends through a port9into the interior12of the pipeline1and pipe section2. The probe7includes a carrier portion8adapted to receive and support a sensor6or other device. The carrier portion8may also be a device itself, e.g., a flow stream diverter with a diversion channel in flow communication with an external instrument as described below in reference to the structure ofFIGS. 2 and 6. The port9provides an opening providing access between the exterior11and interior12of the pipeline1and pipe section2. The mounting of the device5to the pipe section2may be by any suitable means as is known in the art, e.g., threaded, welded or a flange connection. As shown inFIG. 1, a coupling collar14is made part of the pipeline2as, for example, by mechanical attachment, integral formation therewith, welding or the like. The device5includes a mounting connector17to which the probe7is secured in a sealed manner. The mounting of the probe7to the connector17can be by a permanent mounting as by welding or other form of permanent securement, or non-permanent mounting such as frictional engagement and threaded connectors and is preferably sealed to prevent the escape of fluid from the interior12to the exterior11. Such connections are well-known in the art. The connector17can be provided with a hexagonal shape for using a wrench to effect threaded engagement at20between the connector17and collar14. The mounting may also be non-permanent or temporary. Such connection can be effected through the use of pipe threading and sealant such as tape made from polytetrafluoroethylene (PTFE). Such mountings are well-known in the art. Carrier8has an exposure length L1which is an exposed length to the interior12as shown inFIG. 1. The carrier8has a leading edge25and a trailing edge27with the leading edge25being on the upstream side of the carrier8and the trailing edge27being on the downstream side of the carrier8. The probe7, as seen for example inFIGS. 3,4, includes an outer sheath29,29A respectively forming a portion of the carrier8with a longitudinally extending channel30,30A respectively with a sensor device6therein. The sensor device6may be in the form of a thermocouple, strain gage pressure measuring device or other sensor devices. The channel30,30A may be used to function as a pitot tube, or a device to measure the constituents of the flowing fluid, for example, an energy meter, or the like. Such sensors are well-known in the art and may be acquired from Welker Engineering of Sugar Land, Tex.

At least a portion, and preferably a majority of the length L1of the carrier8that is exposed to the flow path of fluid within the interior12, is configured as by cross sectional shape and/or surface treatment, e.g., dimpling or roughening as discussed below. Preferably, the entirety of the length L1is uniformly shaped or relatively uniformly shaped as seen in transverse cross section, as for example, inFIGS. 3–5. A uniform cross section helps effect simple sealing as with a resilient seal32such as an elastomeric O-ring,FIG. 2. The cross sectional shape, as for example as seen inFIG. 3, has a length L2, which is measured in the general direction of flow of the fluid through the pipeline interior12, extending between the leading edge25and the trailing edge27along the longitudinal axis of the transverse cross section. The carrier8also has a width, W, as measured as the maximum width in a direction transverse to the length L2. The ratio of L2to W should be at least about 1.5:1, preferably at least about 2:1, and most preferably, at least about 3:1. The carrier8has its longitudinal axis generally normal to the longitudinal axis of the pipe section2and is generally normal to the general direction of fluid flow in the pipe section2. The contour of the leading edge25is preferably generally arcuate or generally round while the trailing edge27may be any suitable shape and can be rounded as seen inFIGS. 3,4or pointed. Preferably, the side surfaces34,35generally converge from behind the leading edge25toward the trailing edge27along at least a portion of the length L2of the carrier8. As seen inFIG. 4, convergence starts at about the midpoint of L2A.

To effect an appropriate configuration, discussed above, if desired, the leading edge25may be roughened, as for example, by knurling, dimpling or other means of forming a roughened leading surface to move the point of flow separation farther back along the sides34,35to a point more toward the trailing edge27than without roughening. Roughening may permit a change in the above-described length to width ratio allowing reduction in the length to width ratio as defined above.

The probe7, at least for the carrier portion8extending into the interior12of the pipeline1, has a drag coefficient, when the leading edge25and longitudinal axis of the transverse cross section are pointed upstream.FIG. 7shows a relationship between drag coefficient and the ratio of the length L2to the width W (denoted generically as L/W onFIG. 7in conformance with standard nomenclature.) The drag coefficient is less than about 0.7, preferably less than about 0.6, and most preferably less than about 0.4 when measured at a Reynolds number of 50,000. A description of drag coefficient (also referred to as absolute drag coefficient) may be found in Marks' Standard Handbook for Mechanical Engineers, Tenth Edition at pages 11–67, 68. There, drag coefficient, Cd=D/qS where D is drag, q is dynamic pressure and S is the maximum cross section. As used in this specification and in the claims, the term drag coefficient is the drag coefficient value as measured at a Reynolds number of 50,000 even though the Reynolds number of the fluid in the pipeline may be higher or lower than 50,000. The drag coefficient will vary as the Reynolds number varies for the same transverse cross sectional probe shape. Further, by use of the configuration, such as those shown inFIGS. 3–5, a larger moment of inertia is provided than for a round tube because of the increased dimension L2relative to a round tube having the same diameter as the width W.

The cross sectional configuration of the carrier8is such as to keep the separation of the flow around the probe from becoming turbulent far enough toward the trailing edge27so as to reduce the induced vibrations to above or below a resonant frequency for the carrier8. For a round probe, the maximum recommended probe length as set forth in API 14.1.7.4.1 may be calculated in accordance with the following equation:
L2=[(Fm×4.38×OD×10)/(S×V)]×[(E/r)×(OD2+ID2)]1/2

Fm=Virtual mass factor—a constant to take into account of the extra mass of the cylinder due to the fluid surrounding it and vibrating with it.

S=Strouhal number=dependent on the Reynolds No. & shape of the cylinder, but can be taken as 0.4 for worst case or 0.2 as suggested by API Chapter 8.

E=Modulus of Elasticity of probe material (kg/cm2)

ρ=Density of probe material (kg/m3)

According to the American Engineering System, the equation is:
L=[[(Fm×1.194×OD)/(S×V)]×[(E/r)×(OD2+ID2)]1/2]1/2

Fm=Virtual mass factor—For a gas, Fm=1.0 and for water and other liquids Fm=0.9

E=Modulus of elasticity of probe material (per psi)

ρ=Density of probe material (g/cc)

Other methods of determining the maximum length are disclosed in the referenced API publication. The probe depth L1is shown inFIG. 1and is L in both of the above equations.

When the shape of the carrier8is not uniform about a center point as is a round carrier, the carrier needs to be oriented where the leading edge25is pointed upstream and a line between the central point of the leading edge25and the trailing edge27(the longitudinal axis of the transverse shape) is generally parallel to the side wall portions of the pipe section2in which it is mounted, which is also generally parallel to the direction of flow within the pipe section2, assuming a laminar flow.

Resonant frequency or a close approximation may be calculated as in the specific example below.

Oscillation occurs when fs=fn. As above calculations show that they are not equal, the probe is not subject to resonance at its natural frequency and will not fail due to resonant vibration effects.

Bending Stress

Drag Force on Probe

The following fluid creates a pressure difference of:
deltaP=Cd×½×pf×V2

A Reference area

D Reference width

Re Reynolds Number Re=(υ×D)/μ

υ Free stream velocity

pf Fluid Density

Drag Force exerted parallel to approach flow.

Cd=1.5 Maximum plus buffer

Bending Moment

This pressure difference acts as a drag force on the probe creating a bending moment at the support point.
M=ΔP×Le×OD×(L−0.5×Le)

Bending Stress

The section Modulus for a hollow cylinder is given by:
Z=PI/32×(OD4−ID4/OD)

Resulting in a bending stress (Sb) of:

Since flow induced bending stress (Sb) is below the yield strength (Se) of the probe material, the probe will not fail due to gas flow induced bending stress.

For Re>10000

FIG. 2shows an alternative embodiment of the present invention. As compared toFIG. 1, the device ofFIG. 2includes a power drive51for effecting insertion of the probe7′ and extraction of the probe7′ from the interior12. Such power drives51are well-known in the art, an example of which is a Welker Model AID-3 and is disclosed in U.S. Pat. Nos. 4,631,967, and 6,761,757 the disclosures of which are incorporated herein by reference. The carrier8′ may be inserted by the power drive51upon an automated command or a manual command to either effect repair or replacement of the probe7′ or to have the probe7′ in the interior12only during the time when an operating parameter is being measured or monitored. The probe7′ is sealed by the seal32.

As seen, the probe7′ has its free-end53beveled and being sloped downwardly from its leading edge25towards its trailing edge27. In such a construction, the probe7′ can function as a pitot tube by having the opening or channel30′ therethrough having its open end61facing at least partially upstream. The channel30′ can then be a portion of a sensor6. It can also be part of a diverter, described below.

FIGS. 3–5illustrate various transverse cross sectional shapes and constructions of the probe7. As seen inFIG. 4, the transverse cross sectional shape is oval, and the probe is designated7A. Parts or components inFIGS. 4,5that are similar to the corresponding part or component inFIG. 3are designated with postscript A or B. As best seen inFIG. 5, the transverse cross sectional shape of the carrier8B is generally a teardrop.

FIG. 5shows another alternative embodiment of the present invention. The probe7B has a carrier member8B in the form of a thin wall tubular member having a hollow interior section73. The tubular portion of carrier72is preferably thin walled and can be machined or formed as for example as pipe is formed. The thickness of the wall of the carrier8B may be on the order of about 0.02 inches or greater. Preferably the thickness is on the order of about 0.05 inches to about 0.075 inches for carriers having a cross sectional area of about 0.3 to about 1.0 square inch. The tubular portion of carrier8B is preferably formed of a metal or metal alloy such as stainless steel. It may also be made of other suitable materials or a combination of materials including composites. The hollow interior73may contain a suitable casting or polling material75to help hold the sensor6in place. The filler75may also be in the form of a foam material. The filler75can be provided with a passage or channel30B therethrough for the mounting of the sensor6. The carrier8B may be open at both ends and suitably sealed at least on the exposed end with the filler75. Preferably, the interior73has a generally uniform cross sectional shape to facilitate manufacture of the carrier8B of the probe7B.

A flow stream diverter is shown inFIG. 6. In this embodiment, the carrier108has a through opening109in the wall110which provides for flow of a portion of the flow stream through the opening109and into the flow path111in the carrier108. The fluid in the flow path111may be conducted to test equipment outside the pipeline1by a suitable conduit, not shown for further processing or testing.