Home\Services\Smart pigging and inspection\Smart pigging with the use of magnetic flaw detectors MFL/CDP and (or) TFI/AFD, including high resolution

Smart pigging with the use of magnetic flaw detectors MFL/CDP and (or) TFI/AFD, including high resolution

With the emergence of high resolution magnetic pigs with sensors on the basis of Hall transducers, it is now possible to solve a set of tasks on the identification of defects of different types for one run of a smart pig. The defects are as follows: 

  • Metal loss of factory and corrosion nature;
  • Cracks and anomalies in welding joints and cracks in a barrel of pipeline;
  • Non-magnetic inclusions;
  • Interwall laminations;

The main advantages of magnetic flaw detectors over ultrasound ones:

  1. A capacity to work in any work environment – gases, liquids and liquid-gas mixtures (multi-phase streams). Ultrasound propagates only in homogeneous liquids that are free from gas bubbles and suspensions. The presence of even a small gas factor leads to an inevitable loss of a piece of information. A piece of information can be lost in water-flooded oil pipelines as well since there is a water-oil environment division, ultrasound tends to reflect from the environment division with different velocities which leads to a signal loss or the emergence of false signals.
  2. The inspection result is significantly less dependent on a degree of purification of the pipeline’s intracavity, especially corrosion pockets. Ultrasound does not propagate in paraffine, sand, proppant, clay and other deposits which leads to a loss of a positive signal and imposes specific requirements to a degree of purification of the pipeline’s intracavity, although deep pittings and pits are in general hard to clean from deposits.
  3. The absence of a sensor hardware threshold of sensitivity and delay flip flop.

    Explanation: The ultrasound flaw detector’s operating principle lies in the emission of a square pulse with the use of an ultrasound piezoelectric originator, the registration of pulses reflected from the inner and external pipeline walls and the measurement of time intervals between the leading edges of the emitted and reflected pulses. Physical peculiarities of the ultrasound signal registration and their conversion into electrical pulses lead to the formation of the so-called “tails” of the first reflected pulse from the inner pipeline wall when it is amplified to a great extent (up to 22 dB). A “tail” can be registered as a reflected pulse from the external wall and at the same time a false signal emerges that can be interpreted as a wall thickness reduction. The described situation leads to the necessity to use a delay flip flop in the measurement system. It is calculated by a time factor and is, as a rule, 40% of the time that a signal needs to propagate from the inner wall to the external wall. As a result, the ultrasound flaw detector allows measuring the depth of defects of up to 60% of the pipeline wall thickness, i.e. it has a dead area. It is impossible to measure deeper defects; it is only possible to establish a fact that the depth of this defect is more than 0.6t (t – wall thickness). In other words, two defects of 0.61t and 0.85t require an immediate and obligatory AFDT (Auxiliary Flaw-Detection Testing), however the pipeline operation conditions can allow doing without decreasing the work pressure in the first case and require to do it in the second one.
  4. A capacity to register and measure defects of any geometrical shape regardless of the defect edge steepness.

    Explanation: the propagation principle of a lens-focused transducer of an ultrasound signal of narrow shape provides for its reflection from the defect walls as follows: the angle of incidence is equal to the angle of reflection. As a consequence, the signal reflected from the defect walls with steep edges does not return to the transducer which is at the same time a signal originator and a signal receiver. First of all, it relates to such defects as pits, pitting, deep and narrow guide marks, scratches. The said fact is supported by the impossibility to register cracks in a barrel of pipe and other flat type defects that are longitudinally placed in relation to a pipe wall, with the use of ultrasound flaw detectors having a standard configuration.
  5. A capacity to register defects when a flaw detector moves at high velocities. 

    Explanation: Since a transducer is at the same time a signal originator and a signal receiver, there is a terminal maximum velocity at which it can move within a pipeline. The transducer receives the reflected signal at this velocity with due regard for its own dimensions and movement in the longitudinal direction, relevant time needed for the reflected signal to return from the pipeline walls. As a rule, there are issues with registering the reflected signal at a velocity of more than 2 m/s (Taking into account the standard transducer scanning frequency of 300 Hz, the center of the ultrasound transducer moves 6.6mm in the longitudinal direction at a velocity of 2 m/s, which correlates to the size of the transducer itself and therefore to its capacity to receive the degraded reflected signal.
  6. The main advantage of magnetic flaw detectors is their capacity to register defects (cracks, incomplete penetrations, incomplete fusions) and welding joint anomalies (sink marks, undercuttings, excessive penetration, etc.) and crack-like defects in a barrel of pipe, which is technically impossible to do if you use the ultrasound technology (see above).


All the above-mentioned advantages coupled with the use of the state-of-the-art achievements in sensor technology and microprocessor technology, achievements in the field of miniaturization, use of high-tensile and wear-proof materials, allowed developing a new generation of magnetic inspection pigs that have high technical characteristics and can register and measure geometrical parameters of all types of defects with a high degree of certainty. The practical use of such pigs resulted in a situation when pipeline operators (such as BP, SHELL, PHILIPS, etc.) stopped using ultrasound technologies. Needless to say that gas pipeline operators did stop using them as well since the use of ultrasound technologies requires expensive “batching” (liquid plug creation) procedures to be performed, which also leads to economic losses related to the violation of transported product pumping-over operation schedules

The refusal to use ultrasound technologies is mainly due to a significant economic benefit – a single pig run is always less expensive than two pig runs because (amongst other things) it allows reducing Customer’s indirect expenses on the organization of an additional run and follow up of an inspection pig. In such a case the Customer does not lose any information and if it uses technical innovations it even receives information of higher quality.



  • To receive truly high-quality information it is necessary to achieve a high resolution and use a dynamic scanning system that provides for information of high quality with a stable resolution (measurement pitch) in situations when a movement velocity changes within the range of up to 5 m/s; when a stream moves at a high velocity, an active velocity regulatory system should be used;
  • The use of contactless multi-channel profile logging significantly increases the quality of information when geometrical parameters of a pipeline are inspected and it completely eliminates the possibility to register false defects that are characteristic of contract profile logging at a high velocity of an inspection pig and are related to a rebound (bound) of contract measurement sensors from the pipeline inner wall – this effect is particularly noticeable in gas pipelines and pipelines with a multi-phase stream;
  • Control over a pipeline wall’s magnetization level directly in the course of diagnostics truly allows verifying the reliability of received information;
  • The use of magnetic pigs with longitudinal magnetization allows receiving significant additional information on a pipeline, without repeating it if there are several methods used (ultrasound and magnetic) – information on longitudinal-oriented defects (cracks, stress corrosion cracking, etc.), anomalies and defects in longitudinal welding joints;
  • Design solutions aimed at ensuring a high mechanic stability of diagnostic equipment components, a capacity to pass turns with 1.5D radius, a small size and independent pipeline kicking systems that allow pipeline pigging without the need to reconstruct pig receivers;


Magnetic MFL Inspection Scrapers of the 3rd Generation (СDP)


cdp.jpg cdp-eng.jpg

The implementation of technical innovations in inspection MFL pigs resulted in new achievements:

А) The resolution capacity of magnetic MFL inspection scrapers:

  • 2.5 mm in the longitudinal direction;
  • 5.5 mm in the traversal direction.
What are the benefits?

Many pigs in the diagnostics market (including ultrasound ones) have a standard resolution of 3.3х8.0 accordingly or even worse. When this equipment is used for measuring parameters of a defect that has geometrical dimensions of 60х60mm, 18 measurements in the longitudinal direction will be made, at the same time 7 sensors will be in the defect’s area in the traversal direction.

So we will receive 24 measurements with the use of 10 sensors for a magnetic MFL pig.

An important benefit of this high resolution of MFL pigs is a capacity to register informatio with a high degree of certainty deep pittings (“puncture”, weld hole) that lead to pipeline leakage and are the most often reason for accidents at field pipelines (A report of D.Eng.Sc., Professor V.N. Antipyev, Director of the Expert Organization “Energy-2” at the seminar “New Technologies and Materials for the Construction and Repair of Pipelines” according to the 5FP program of the European Commission, Tyumen, November 2003).

In this regard, the use of magnetic NDT with a high resolution for inspecting field pipelines is considered to be the best choice.

B) Transducer scanning (sampling) frequency – 2,000 Hz.

The use of transducer scanning at a high frequency coupled with the use of the dynamic scanning system (the frequency is directly proportional to the flaw detector’s velocity) guarantees a stable resolution for MFL pigs at 2.5mm in the longitudinal direction covering the whole range of velocities of up to 5 m/s.

Important remark: Declaring a resolution to be at 3.3 mm for the majority of diagnostics companies at a transducer scanning frequency of 300 Hz means that the declared resolution is ensured only at velocities of up to 1 m/s. The resolution becomes worse at higher velocities and defect identification and measurement specifications are not complied with!

Example: Equipment with outdated electronics used by the majority of diagnostics companies has a resolution capacity in the longitudinal direction that decreases at a velocity of 2 m/s and a scanning frequency of 300 Hz to 6.6 mm and at a velocity of 4 m/s – to 13.3mm! (Defects larger than 10mm are not identified at all). Inspection MFL equipment has a stable resolution of 2.5 mm at a velocity of up to 5 m/s.

Demand explanations as to compliance with specifications for diagnostics pigs at a velocity of more than 1 m/s 

C) Nowadays only when you use MFL pigs you meet the requirement of the Pipeline Operator Forum to specifications of smart inline pigs and to the performance of works in general (Version 2.1 as of November 6, 1998 is attached), as well as the obligatory requirement to control a pipeline wall’s magnetization level directly in the course of diagnostics. Moreover, the said requirement regulates a required pipeline wall’s magnetization range which provides for the registration of defects with a precision of 0.95 and it is possible to perform a linear calibration of such measurements. This range is from 10 to 30 kA/m.

What is this in aid of?

When a magnetization level is lower, information cannot be accurately calibrated with the required precision. This means that some defects, which will be identified, will be measured with a precision not in accordance with the declared specifications. Some defects in the form of deep “needle-like” pitting can be missed at all. Experts of leading pipelines operators do know about it.

Many diagnostics companies just do not specify magnetization parameters in characteristics of their diagnostics equipment.

“NTC ”Neftegazdiagnostika”, LLC, proposes to run diagnostics of pipelines with specific wall thickness parameters that ensures a magnetization range to be from 10 kA/m for the maximum wall thickness to 30 kA/m for the minimum wall thickness and to provide a true magnetization schedule along the route right after the run.

D) “NTC ”Neftegazdiagnostika”, LLC, offers its services on pipelines mapping with a high precision. As a result the Customer receives true profiles of pipelines beddings (vertical and horizontal), correlation of all registered peculiarities of a pipelines, including defects, in relative and world geographic coordinates, identification of such reference points as roads, water obstacles, communications, etc.


By using mapping information you significantly reduce the time required to find a defect (the search is carried out according to the coordinates with the use of GPS equipment) and cut excavation expenses. A pipeline can be correlated to the world geographic map (visualization). When conducting reinspections, it is possible to identify sections with pipelines shearing caused by external effects (landslides, underwater line sections, pump outs in frozen soil and swamplands), which are characterized by a pipeline material being in a stress condition.

E) All modern magnetic inspection MFL pigs, starting from the diameter of 16" and more, have a single-section design and independent pig launcher kicking means. All MFL pigs, regardless of their intended use, are capable of passing turns (bends) at a 90° angle and 1.5D radius, as well as segmented bends with an angle of up to 30°. They are distinguished by an increased mechanical stability of their structural components that reduces the risk of equipment getting stuck in a pipeline or of receiving low-quality or incomplete information due to damaged sensors or cable connections, to a minimum, which also reduces the likelihood that reruns will be necessary.


Inspection Scrapers of the 2nd Generation for Traversal Magnetization (AFD)


afd.jpg afd-eng.jpg

AFD inspection scrapers for traversal magnetization with a unique longitudinal and traversal resolution and absence of any spaces between main sensors. It is achieved because sensors are placed in a circle in two lines between the magnets, it provides a 100% guarantee that the full surface of a pipe wall will be covered.

A) The resolution capacity of AFD inspection scrapers for traversal magnetization:

  • 2.5 mm in the longitudinal direction;
  • 2,9 mm in the traversal direction — 100% surface coverage.

B) Transducer scanning (sampling) frequency: — 2,000 Hz.


AFD 14''


These are the first scrapers in the market that can truly identify stress corrosion and to show with a high degree of probability very thin longitudinal cracks that often lead to pipeline breaks. It is no secret that scrapers of the first generation do not possess the sensitivity that is necessary to identify narrow longitudinal-oriented defects and stress corrosion.


"Bumi Armada Caspian LLC is satisfied with NTC Neftegazdiagnostika LLC performance and services provided during installation of the repair clamps and expresses its gratitude for ability to solve challenging and technically complex issues promptly and at high quality standart."
"...The field works were performed within short timeframes and of the highest professional quality; preliminary reports on the diagnostics’ results were also issued in a timely manner."
"The inline inspection of sections of the oil pipeline, in-field flow lines performed by “NTC “Neftegazdiagnostika”, LLC was of the highest quality, even though the project was very difficult."
Show all
Clients and partners
  • Petrodar
  • rosen
  • South Stream
  • Halliburton
  • Al Qahtani
  • Saudi Aramco
  • Kaztransoil
  • weatherford
  • melnik
  • Eni-saipem
  • rnc
  • Bumiarmada
  • Gubkin
  • Rosneft
  • Achimgaz
  • NordStream
  • PI
  • LUKoil
  • Gazprom
  • TDW
  • TPS
  • Asia Trans Gas