Inspection of steel pipelines by method of the contactless magnetometry with KMD-01M system

Ph.D. Valery Saxon, CEO

Andrew Sergeev, Director of Industrial Safety Dept.

Alexander Prokazin, Technical Director of директор Industrial Safety Dept.

JSC «Polyinform», Saint-Petersburg, Russia.

Inspection of steel pipelines by method of the contactless magnetometry with KMD-01M system

The total length of trunk oil pipelines in Russia is over 50 000 km, gas pipelines – around 200 000 km. At the moment more then 50% of trunk pipelines are under operation for more then 25 years. During the exploitation the constant decreasing of characteristics due to their aging takes place. The parameters of products transportation should be reduced according to the results of the inspection, which negatively impacts on their productivity.

Each year the volume of needed inspections and repairing increases as well as the amount of pipelines breaks due to high worn-out state and corresponding need to liquidate the aftermath of emergency situations. In 2009 inRussia the amount of the breaks reached 25 thousands, means on average 500 breaks weekly. Experts-ecologists consider that the annual loss of oil products due to the accidents is not less then 5 millions tones, and the most part of the oil can not be collected and the polluted soil often can not be recultivated. Meanwhile, oil and gas pipeline accidents have caused enormous damage to the environment. The emission of gas is often accompanied by the ignition that may harm not only the local ecosystem, but also the infrastructure. Oil spills can irreversibly affect the hydrological objects, even at a long distance from the accident location.

Working conditions of gas and oil pipelines are characterized by both the climatic stress from outside and process loads associated with the aggressiveness of the pumped product, as well as mechanical shock and cyclic loads during operation. In addition, the pipeline is experiencing considerable bending forces associated with the movement, or freezing (frost heave) of soil, this leads to the appearance of the stress-deformed states (SDS), which in turn can initiate stress corrosion.

Early diagnosis of the technical state of pipelines allows preventing accidents caused by damage of pipelines during their operation and minimizing the cost of maintenance and repair work. However the inspection itself is quite costly, since it is often associated with the changes of a pipeline’s operation mode, and even the complete stop of product transportation, which leads to significant indirect losses.

The large number of pipelines is not ready at all for inspection by the most popular methods, for example, in-tube defectoscopy (smart pigs). The absence of receiving-release chambers, special valves, linear actuators, the complex geometry of the pipeline, which does not allow applying the smart pigs, all these significantly limit the application of this method. Meanwhile, according to various estimates, up to 40% of the total length of pipelines or even more is not equipped for in-tube inspection.

Also the problem of inspection of underwater pipelines still has no complete solution, being extremely actually for heavily watered spaces of Western Siberia, as well as offshore platforms, subsea pipelines. Most often the inspection of subsea pipelines is reduced to divers' or sonar survey, and only rarely the in-tube inspection is applied, as the price of possible jam of a pig, calibrator or a shell is too high in this case.

Different methods of inspection are used for technical inspection of pipelines. The variety of methods is associated with a variety of both the pipeline and the conditions of their use. And it is obvious that there can not be a single universal method suitable for all pipelines, and giving a comprehensive and accurate description of the technical condition.

One of the most widespread methods is magnetic. This method is based on the analysis of the magnetic fields of distribution occurring at the locations of defects cause changes in the mechanical and physical parameters of the pipeline. While using this method the metal of a pipe may be pre-magnetized to saturation, or measurements are made in an applied magnetic field. Such defectoscopes often are part of smart pig equipment, since the ultrasonic in-tube inspection methods have their limitations of use: they require a thorough cleaning of the walls from the sediments, the inability of the two-phase fluid. Nevertheless, the magnetometric method is widely used as a method for the contact diagnostics, for example, eddy current.

The main disadvantage of this method is the need to provide the direct access to the pipeline, i.e. to raise a pipeline to the surface or trenching at specific points. It requires a lot of resources and at areas of high watering the pipeline may be difficult to achieve.

Feasibility of using a magnetometric method without direct access to a pipe’s metal was a problem for a long time. There are magnetometers capable for determining the stress in the pipe’s metal, but attempts of the remote detection of local defects with small linear dimensions, faced with the lack of sensitivity of the primary magnetic transducers, which traditionally used fluxgate magnetic field sensors, as well as an insufficient number of magnetic field components measured. The disadvantage of the flux-gate sensor is high level of self noise, which limits its sensitivity as well as the relatively large mass of the core, and the high requirements to the parameters of the reference oscillator.

Based on the modern requirements of the contactless magnetometric diagnostics the specialists of POLYINFORM developed KMD-01M system. It uses the innovative sensors based on the latest achievements in the field of magnetic transducers. The principle of operation of these sensors is based on the anisotropic magneto-resistance effect (AMR effect).

Magnetoresistive effect (MR) means changes of the electrical resistance of the material under the action of an external magnetic field. One type of the magnetoresistance effect - anisotropic MR-effect (AMR) shows the accordance of the resistance value of the ferromagnetic film from the angle between the magnetization vector and the direction of its current there through. The direction of the magnetization vector of the film is determined, inter alia, by the direction of the external magnetic field. In AMR sensors both monolayer and multilayer structures can be used.

The principal feature of KMD-01M system is that it realizes the method of gradiometry i.e. readings from 4 sensors located in a 4 space points are compared to each other with the elaboration of the difference signal not only by the same name magnetic field components, but also by the full vector of magnetic induction. This is necessary to exclude the influence of homogeneous magnetic field of Earth to the magnetometric characteristics of sensors while it’s not required that the background filed should be homogeneous.

For correct work of three-dimensional magnetic field sensors group, used in the magnetometric diagnostic system, the actual task is to suppress the impulse noise. The solution is applying the noise suppress algorithm, based on median filter. Filtration is made for each coordinate of the magnetic induction vector. This allows using the system under strong electromagnetic pollution, for example, near power lines, which are often located in same corridor with the route of the pipeline.

As it has been already mentioned, each from four magnetoresistive sensors placed in the cruciform antenna block of the system is three-component i.e. it measures the magnetic field on axis X, Y, Z. Thus, KMD-01M system measures tree components of the filed in four points of space, as well as the difference between the same-name components, 3 magnetic induction vectors and their differences. The processing and control such massive of data requires applying powerful field computers of climate protected version. The polling frequency of sensors can be changed in the range of 30 to 300 Hz by an operator depending on the speed of moving on the pipeline route.

The software for control KMD-01M and for mathematical data processing is completely original and designed by "Polyinform." Totally the system obtained 7 patents and two certificates of state registration programs.

During inspection KMD-01M automatically performs the binding of geographical GPS-coordinates with high accuracy (up to 0.5 m), which allows the end of each measurement cycle building an electronic map of magnetic anomalies by assigning to each anomaly its coordinates. This allows automatically tracing of a pipeline as well as reducing the expenses on the execution of the additional defectoscopy control. Also system provides simultaneous measuring of the distance from the nearest fix point (control point, insert, valve etc) by means of digital odometer.

For working in the areas of abnormally high or low temperatures, when the laptop can be unstable KMD-01M system has a contactless data transmission from the antenna system to the control computer with the help of WI-FI. In this case, geophysicist may be in the car at a distance of up to 100m from the operator, moving along the pipeline route. This significantly widens the abilities of KMD-01M applying under extremely low and high temperatures. Also such structure of the system allows placing it on a various vehicles: cars, snowmobiles, etc. In this case, the productivity increases dramatically - up to 35-40 km. by one team per shift, without loss of diagnostic quality. Visualization magnetograms in real time mode, implemented in KMD-01M allows identifying the most significant anomalies with no post-processing of diagnostics data. This saves the time required for trenching and subsequent additional defectoscopy control.

The process of inspection using KMD-01M system 

The operator at the pipeline

The using of KMD-01M with the visualization in real-time is shown by a few examples:

1.          Carrying out the inspection of the technical condition of the main pipeline 32". Nature of the terrain is sandy desert. The detected magnetic anomaly is in the form of the stress-deformed states associated with the pressure of the sand dune, more than 10 meters in height, appeared during last few years before the examination.

Magnetogram 1

The upper magnetogram shows the changing of the full vector of magnetic induction of the pipeline, covered by the sand dune.

At 118 meters long section the high of the dune is more than 10 diameters of the pipe, so the data of the pipeline can not be read.

At places where the pipeline enters and exits the dune the stressed-deformed state of high level are detected, caused by the pressure of large amount of sand. This section was marked as conducive to accident.

 

Practically it’s often situation when stressed-deformed conditions significantly decrease as the result of digging out, except of cases when the stressed regards the changing of pipeline’s geometry. (Magnetogram 2)

 

Magnetogram 2

The magnetogram of changing of the full vector of magnetic induction shows significant stress, caused by curving of the pipeline due to the pressure of sand. No local defects discovered (see lower magnetogram).

 

KMD-01M system possesses high mobility and can be placed at different carriers. For example, it appeared reasonable to use snowmobile under the conditions of West Siberia. In this case the scope of work implemented during one shift increased several times without loosing the quality of inspection.

 

Currently we are intensively working on the development of two new versions of the KMD-01M: for an automatic underwater vehicle (AUV) (together with concern "Gidropribor Underwater weapon of Russia), designed to a depth of 500m and a hand-held device for the diagnosis of offshore platforms, pipelines, often located in the intertidal zone at depths of up to 50 meters, which makes it possible to use light diving equipment for production work.
Applying of the contactless magnetometric inspection method allows (additionally to the “traditional” methods) providing more complex solution of industrial safety for pipelines and reducing the risk of ecological catastrophes, related with hydrocarbons transportation.
 

Bibliography

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