Monitoring pipes

Details Monitoring pipes Monitoring pipes

2000-09-18

2002-11-05

Williams, Hezron (Department: 2856)

Measuring and testing

Vibration

By mechanical waves

C073S625000, C073S628000

Reexamination Certificate

active

06474165

ABSTRACT:

This invention relates to monitoring pipes, and refers in particular to the use of ultrasonics to characterize liquid-filled pipes.
The owners of liquid-filled pipelines frequently wish to monitor the condition of those pipes. The uncertainties may include the material type, internal diameter, and thickness of the pipe, the material type, and thickness of any internal lining if present, the presence of corrosion on the internal surface of the pipe, the presence of corrosion on the external surface of the pipe, damage to the lining, the thickness of any deposits of material on the internal surface of the pipe or of the lining if present, the presence and extent of circumferential cracks, the presence and extent of longitudinal cracks, and the position of features such as bends, offtakes, valves and joints. In view of the high cost of replacing pipework, and the potential consequential damage due to fluid loss from a break in the pipework, it can be justifiable for the owner to carry out regular surveys of the condition of the pipework from within the pipe using a vehicle transported along inside the pipe. In some circumstances it is be important not to disturb any deposits on the pipe wall. In these cases the condition needs to be assessed without contacting the wall.
So-called ‘intelligent pigs’ are frequently used inside high-pressure gas pipelines to detect the presence of corrosion and other defects. The earliest vehicles were magnetic flux leakage devices. A powerful magnetic field is used to saturate the steel wall, and any defects in the pipe wall induce anomalies in the magnetic field downstream which are subsequently detected by the ‘pig’. This device requires steel pipe with no internal lining, with no internal deposit, demands close contact with the wall, and has a high power requirement. Thus, it fails to match many of the requirements described above. Even in steel pipes the flux leakage method fails to detect longitudinal cracks very well. The magnetic flux leakage method has been applied successfully to fluid-filled unlined steel pipes, but the success was contingent upon the pipes being carefully cleaned of any deposit before the flux leakage device was used.
To detect longitudinal cracks, other vehicles inside high-pressure gas pipelines use ultrasonic transducers in shear mode. Fluid-filled resin wheels are pressed closely against the wall of the pipe, and used to couple ultrasonic shear waves into the wall. Ultrasonic waves in this instance refer to elastic waves at high frequencies in the hundreds of kilohertz (and even low megahertz) ranges. A compression wave is analogous to the visible motion transmitted along a stationary line of railway wagons when struck by a heavy diesel locomotive. A shear wave is analogous to the manner in which a side-winder snake manages to make forward progress by wriggling its body. The shear waves induced by the fluid-filled resin wheels travel circumferentially around the pipe, and are detected by adjacent wheels. In principle this technique can detect longitudinal cracks. It is evident though, that in many respects the method fails to address the full problem of condition monitoring described above. The fluid-filled wheels are required inside the gas pipe because the high impedance mismatch between gas and solid result in a near total reflection at the inner surface of the pipe if the waves were launched in the gas. This limitation does not apply in liquid-filled pipes for compressive waves. The liquid can provide a good coupling between compressive waves in the liquid and in the solid.
In the oil industry, ultrasonics have been used in reflection mode as caliper tools to measure the diameter of wells deep underground. Such wells are generally filled with liquids of various types. A tool inserted into the well projects an ultrasonic compression pulse radially through the liquid, and measures the time take for the first reflection to return from the wall. After the well has been drilled it is usually lined with a steel casing to keep it open. Cement is injected behind the casing into the space between the casing and the rock as drilled. An ultrasonic tool is sometimes used in cased wells to check the bond between the casing and the cement. An ultrasonic pulse penetrates through the steel casing, through the cement, and into the rock. The quality of reflection from the casing-to-cement interface is a measure of the quality of the cement bond to the casing. A good bond gives a lower-magnitude reflected pulse than the situation where a fluid-filled micro-annulus has developed between the casing and the cement. Another oil industry tool uses ultrasonic waves in refraction mode. An ultrasonic pulse is projected at an angle to the steel wall, and it couples by refraction into the casing and into the rock behind the casing. The transmitted pulse is detected by a receiver also at an angle to the wall, so a second refraction is required to detect the transmitted signal. The presence of a micro-annulus indicating a poor cement bond prevents good transmission into the rock, and this gives a received signal which differs from that which obtains when the bond is a good one.
Another method used inside steel pipes is commonly referred to as remote-field eddy current. An induction coil creates a magnetic field axially along the pipe whose return path is partly along the pipe wall and partly along the surrounding medium. The flux normal to the pipe wall is measured by probes close to the wall. Defects cause measurable disturbances in that flux. The method cannot be used in non-magnetic pipe, and gives no information about lining or deposits. As with magnetic flux-leakage devices, this device requires the wall inner surface to be cleaned of any deposits before being used.
Ultrasonic methods are used inside pipes in a reflection mode to determine pipe diameters and to detect the presence of a micro-annulus in cement surrounding the pipewall. They are also used in refraction mode to detect the presence of a micro-annulus in cement surrounding the pipewall. They have also been used in both reflection and refraction modes to detect flaws in pipes. However, in all these cases the material of the wall is assumed to be known so that the speed of sound in the wall material is known. And in none of the above cases is there presumed to be any lining or deposit on the inner surface of the wall. This invention sets out to combine ultrasonic methods in reflection, refraction and reflection-refraction modes so as to identify the materials of the pipewall, the lining and any interior debris prior to using this information to size the pipewall, radius and thickness, the lining and any debris and then to identify features such as cracks, corrosion and fittings.
The invention proposes for this purpose Apparatus for the characterization of a liquid—filled pipe, which Apparatus comprises:
1. a vehicle capable of fitting inside the pipe and of being transported by the liquid along the pipe.
2. the vehicle carrying rings of several ultrasonic transducers, preferably disposed at equidistance circumferentially around the ring and the rings arranged such that:
2.1 one ring of transducers operates in the reflection mode purely radially.
2.2 two rings of transducers operate as a pair displaced axially to each other. The pair is used in a longitudinal refraction mode. One ring of transducers emits pulses along the pipe at the critical angle to the wall such that the wave is refracted as waves travelling within the debris, lining and pipewall, and the refracted wave is received by the other ring of transducers.
2.3 the emit ring of transducers of the refraction mode pair also has the capability of receiving reflected echoes, this being a refraction/reflection mode.
2.4 one ring of transducers is used in a circumferential refraction/reflection mode. Each transducer emits pulses in a radial plane but at the critical angle circumferentially to the wall such that the wave is refracted as a circumferential wave along the debris, lining and pipewall and the transducer receives

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