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, 10th Edition, 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.