Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
2000-07-20
2002-12-03
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
C324S345000, C324S258000, C324S225000, C324S207120, C324S207240
Reexamination Certificate
active
06489771
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to pipeline monitoring systems and more particularly concerns a sensor for detecting passage of a “pig” through a pipeline.
Operators of pipelines use pigs in a variety of activities including the separation of different liquids or gasses as they are conveyed through the pipeline and cleaning the pipeline of foreign materials. Generally, the pipeline operator uses mechanical or “dumb” pigs for such applications. Sensing the passage of “dumb” pigs through pipelines is historically accomplished by mechanical means. Intrusive threaded adapters are welded in place with spring-loaded shafts extending into the pipe. The shafts are temporarily deflected by the pig as it moves through the pipe and a spring-loaded lever or flag is released to give a visual indication of the pig's passage. By locating many of the intrusive pig “signalers” along the pipeline, the operator can monitor the progress of a pig through the line by the sequential release of the flags. Occasionally, operators need to ascertain the condition of their pipeline. “Dumb” pigs are not useful in these applications so active “smart” pigs with sensors and recording means are used. “Smart” pigs have a circumferential array of sensors which spring radially to snug them against the inside of the pipe to measure the pipe wall thickness about every eighth of an inch as the pig moves through the pipe.
Intrusive adapters are fraught with problems. For one, an annular high-pressure rotary or sliding shaft seal is necessary to prevent product inside the pipe from escaping as the shaft moves in either direction. Moreover, while many products carried by the pipeline are not corrosive to steel, they do make the annular high-pressure rotary or sliding seal of an intrusive signaler very difficult to achieve. Another problem is that, in preparation for the next pig passage, the operator expends considerable field time manually compressing the flag springs and ensuring that their detents are properly positioned to hold the springs compressed. To reduce the field time required to monitor the system, a multi-contact electrical switch could be actuated by the flag to power a local elevated incandescent signal lamp and/or possibly a remote readout panel. Even so, before the next pig passage, the operator would still have to return to each site to compress the flag spring, check the signal lamp and record any failures or malfunctions in his log. A further problem with intrusive adapter systems is that pipeline terrain is often mountainous, arid or subsea with exposure to ice heaves, mud slides, earthquakes, hurricanes, lightening, forest fires and other hazards that could damage signalers previously logged as fully functional. Another serious problem is that gaseous products separated by “dumb” pigs are a hazard to the spring-loaded shaft because the pigs often become temporarily stuck on welds in the pipe or at low spots along the line. Pressure slowly builds behind the stuck pig and eventually when it becomes unstuck the pig is, for a distance of several hundred yards, accelerated to speeds much faster than the average speed of the product. The shafts of the signalers are, therefore, sometimes sheared off as the high speed pig encounters them. Whatever the cause, if any of the welded threaded adapters are defective, maintenance or replacement involves great expense. The pipe must be exposed so that the defect can be viewed. Chippers remove the protective corrosion coating, grinders gently remove some of the smaller defects, cutting torches remove some of the larger defects and welders reweld the original threaded adapter to the pipe. If the original threaded adapter is not reusable, it is removed from the pipe with a cutting torch and its replacement is welded to the pipe. After approval of the work by a quality control group, the pipe must be sandblasted and coated with anti-corrosive material.
The use of “smart” pigs introduces additional problems. For example, “smart” pigs are very rigid and can only tolerate roughly a 20% reduction in pipe diameter. Consequently, all of the intrusive components must often be removed from the pipeline to prevent damaging the “smart” pig and also to prevent the “smart” pig from damaging the intrusive signaler. In “smart” pigs which use magnetic sensors, the magnets are so strong that they saturate the magnetizable steel pipe wall so that, as the “smart” pig moves its magnets beyond the previously saturated steel pipe regions, the regions do not return to zero magnetization but retain roughly 20% of the magnetization. For magnetic sensor “smart” pig systems, the industry standard signal frequency of 22 Hz adopted about 20 years ago for transmitters is lower than power line frequencies of 50 Hz and 60 Hz and lower than the first subharmonic for line powered cathodic protection systems at 25 Hz and 30 Hz. However, some European electric railroads use 50 Hz/3, or 16.6 Hz with a first subharmonic at 8.3 Hz. Therefore, this frequency results in a significant noise problem which is barely addressed by improved active filters and algorithms. For systems with their antenna close to the pipe, the noise ratio at 22 Hz is well beyond the capabilities of the lower power, battery powered, active filters required by the industry. This signal to noise ratio gets worse as the system operating frequency is lowered towards static or DC because of the electrical railroad frequency at 16.6 Hz/8.3 Hz, the AC components of the cathodic protection systems at 50 Hz/25Hz, the DC components of the same systems and the static residual 20% magnetization after “smart” pig runs.
The industry's standard portable non-noise canceling single antenna for sensing industry standard 22 Hz transmitters and its associated waveforms are illustrated in
FIGS. 1 and 2
. Since the industry standard transmitters generate an AC magnetic flux signal they can be sensed by the industry standard antennas when they are motionless in a magnetic steel pipe. This function can be done with either a clockwise or counterclockwise winding equally well, and the operator is free to inadvertently reverse the phasing of the induced EMF e
1
by rotating the entire antenna A
1
. Consequently, while known sensors are used to indicate the presence of a pig in a pipeline, the direction of motion of the pig in the pipeline is not indicated by the sensor. For clarity, all of the physical components in
FIG. 1
are shown in cross sectional views along their centerlines except for the permanent magnet PM and the last half turn of the winding W. The last half turn completes the output circuit and contributes to the induced EMF e
1
. This permits the magnetic flux lines F
1
, F
2
and F
3
to be drawn on the surface of the cross section where they are inside the entity. In the production antenna winding, thousands of turns of fine copper magnet wire are used to provide the needed sensitivity. However, in
FIG. 1
, the winding W is shown as a uniformly spaced solenoid of magnet wire to permit the details of the core C, winding W, magnetic fluxes F
1
, F
2
and F
3
and induced EMF e
1
to be graphically presented. To minimize perturbations in the flux paths F
2
and F
3
threading through the magnetic steel core C of the antenna A
1
, a winding W and a core C of equal length L
1
are used. This fully distributed winding W further makes the axes of symmetry Z
1
and zero crossing Z
2
of the antenna A
1
coincident and perpendicular to the axis of movement X of the permanent magnet PM. If there were no permanent magnet PM and no pipe P, the residual magnetic flux F
3
from the magnetic core C of the antenna A
1
would close upon itself in a static fashion, thus inducing no EMF. If there were no pipe P and a permanent magnet PM moved uniformly in relation to the antenna A
1
, when the centerline of the permanent magnet PM crossed the axis of symmetry Z
1
, for each positive induction in the winding W by each line of dynamic magnetic flux F
2
there would exist by reason of symmetry an equal and opposite induc
Aurora Reena
Catalano Frank J.
Lefkowitz Edward
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