The invention relates to methods for nondestructive testing of trunk gas pipelines quality, in particular, to the provision of a flaw detector - pig explosion protection during the in-tube flaw detection of a gas pipeline.

"Method for Protecting against Explosion during an In-Tube Flaw Detector Operation and a Protection System Device" (Patent RU 2301940, IPC F17D5/00, G01M3/00, published on June 27, 2007) is the closest to the claimed solution in the number of common features.

A known protection method implies that the flaw detector power supply is interrupted when the ambient pressure is negative with respect to the atmospheric pressure.

A known device of the in-tube flaw detector protection system comprises at least one section of the in-tube flaw detector provided with a source for supplying power to instruments and devices thereof, a power supply switch and a pressure control device connected to a pressure sensor which is located in such a way that it is enabled to measure pressure in the medium surrounding the said section, at that, the pressure control device is connected to the power supply switch in such a way that it is enabled to control the said switch for interrupting the power supply when the pressure of the section surrounding medium is negative with respect to the atmospheric pressure. Besides, the device comprises another sensor identifying the flaw detector no-motion in a pipe, at that, the output of the flaw detector no-motion sensor and the output of the said pressure control device are connected to AND circuit in such a way that it is enabled to control the switch for interrupting the power supply. An odometer could be applied as a no-motion sensor.

The drawback of the said method for protecting against explosion and of the protection system device is that during the displacement of air by gas, the excessive pressure of the gas-air mixture in a launching trap with respect to the atmospheric pressure, when power to flaw detector instruments is supplied, could not ensure the mixture explosion safety. When filling a launching trap with gas, residual air in the trap is inadmissible. Besides, unauthorized power supply to the flaw detector instruments seems possible in the presence of an explosible gas-air mixture in the launching trap immediately after the started displacement of air by gas, which is going naturally under gas pressure exceeding the atmospheric pressure.

Low-frequency electromagnetic transmitters and receivers used for identifying in-tube flaw detectors - pigs moving inside pipelines are known. For example, Aprodit Company produces low-frequency transmitters PNT and receivers NPR in series. Transmitter PNT generates a magnetic field pulsating with the low frequency of 22 Hz. This signal passes through metal pipeline walls, soil or water above a pipeline, as well as through a reinforced concrete floor. The transmitter is set on a body of an in-tube flaw detector - pig.

Serial transmitter PNT is equipped with an autonomous power supply, emits a continuous or intermittent signal.

Receiver NPR is a portable autonomous device, which is used for searching and determining a location of an in-tube flaw detector - pig equipped with transmitter PNT emitting electromagnetic waves with the frequency of 22 Hz.

«Device for determining the location of cleaning and inspection pigs in the pipeline» (Patent RU 21 10729, IPC F17D5/00 published on May 10, 1998) is known. The device comprises the transmitter set on the pig, and receiver with an antenna for receiving the transmitter's signals located above the pipeline. The transmitter emits signals within the range of frequencies from 7 to 1 1 Hz with the duty ratio, which is set depending on the pig velocity. The transmitter comprises a hermetically sealed container encasing the autonomous power supply, which is connected via the electronic switch controlled by a supply voltage monitoring unit with the modulator, the output of the modulator is connected to the generator, the output of the generator is connected to the emitting antenna. The transmitter's signal receiver comprises the decoder, the input of the decoder is connected to the output of the amplifier-converter, and the output of the decoder - with a monitoring and indication device.

The drawback of known devices identifying the location of a flaw detector - pig in the pipeline is that they could not be additionally used for transmitting signals on the execution of normal operation modes of the flaw detector - pig kicked to the launching trap, and also during the flaw detector - pig movement through the pipeline in the course of the in-tube inspection and on reaching the receiving trap. For example, the operation mode of the transmitter PNT (continuous or intermittent) is definitely set using the remote control before the kicking of the flaw detector - pig to the launching trap prior to the in-tube pipeline inspection. Thus, the emission from the transmitter PNT could not be modulated in time to form signals on the execution of normal operation modes of the flaw detector - pig after its kicking to the launching trap.

The invention object is to increase the explosion protection efficiency of an in-line inspection tool during its location in explosible areas of a gas pipeline by means of obtaining and application of additional information concerning the power supply of the instrument compartment and the execution of normal operation modes of the tool using the receipt and analysis of signals from a low-frequency electromagnetic transmitter controlled by the tool onboard computer. The claimed method for protecting against the explosion of an in-line inspection tool implies that the tool is brought to the launching trap of a trunk gas pipeline with the tool's instrument compartment supply circuits disconnected from a power supply unit, while air is displaced by natural gas in the launching trap, the increase of gas-air mixture excessive pressure with respect to the atmospheric pressure is monitored, the instrument compartment power supply circuits are connected to the power supply unit, the linear section of a trunk gas pipeline is inspected, the tool is brought to the receiving trap, while natural gas is displaced by air in the launching trap, the natural gas pressure decrease is monitored, the instrument compartment supply circuits are disconnected from the power supply unit, the tool is withdrawn from the receiving trap.

In contrast to the known method, the claimed method implies the connection of the instrument compartment supply circuits to the power supply unit at the pressure guaranteeing the absence of explosible gas mixture, for example, 3 atm in the launching trap, and the instrument compartment supply circuits are disconnected when the pressure is decreased to, for example, 3 atm in the receiving trap, with an additional monitoring of the instrument compartment power supply and the execution of normal operation modes of the in-line inspection tool according to signals from low-frequency electromagnetic transmitter.

The main technical outcome, which is achieved following the implementation of the claimed method for protecting an in-line inspection tool from the explosion, consists in the increased degree of the explosion protection of the in-line inspection tool and a gas pipeline, and in the additional information providing for the prevention of undesirable explosible situation progress. The process of the in-line inspection tool kicking to the launching trap and the displacement of air by gas is held in conditions of explosible gas-air mixture generation. The explosible gas-air mixture contents in the launching trap to the point of almost complete replacement of air with gas. Gas to displace air is fed under the pressure of at most 0.2 MPa (2 kilogauss/cm ² ).

Air displacement is considered to be complete when the oxygen content in gas leaving the launching trap amounts at most 2% and determined by a gas analyzer (item 3.21 CIl 1 1 1 -34-96 "Code of the regulations on construction of trunk gas pipelines. Void pigging and testing of gas pipelines").

Consequently, for increasing the efficiency of the tool explosion protection, the instrument compartment power supply circuits should be connected to the power supply unit in the presence of not just excessive but higher excessive pressure in the launching trap, for example, 3 atm, guaranteeing the absence of explosible gas-air mixture in the trap.

The in-line inspection tool kicking is followed by the displacement of air by gas in the launching trap. At that, the valve opens to vent the gas-air mixture. Oxygen content in the gas-air mixture leaving the trap is monitored by a gas analyzer. When oxygen content in the gas-air mixture leaving the launching trap falls below 2%, the vent valve is shut off and gas pressure starts to increase in the launching trap. When the gas pressure in the launching trap equals 3 atm, the onboard computer according to a signal from the pressure alarm connects the instrument compartment power supply circuits to the power supply unit. Simultaneously, the onboard computer starts to receive the signal from the no-motion sensor. Consequently, it may surely be considered that while the connection of the tool's instrument compartment power supply circuits to the power supply unit, the explosible situation is fully absent in the launching trap, because the trap is completely filled with gas, and the tool is motionless.

Then gas pressure achieves the nominal value of 8 - 10 atm in the launching trap and normal operation of the gas pipeline inspection tool starts. The process of the in-line inspection tool withdrawal from the receiving trap and the displacement of gas by air is also conducted in conditions of an explosible mixture formation. The valve opens to vent gas. When gas pressure drops to 3 atm in the receiving trap, the onboard computer according to a signal from the pressure alarm disconnects the instrument compartment power supply circuits from the power supply unit. Consequently, it may surely be considered, that the disconnection of the instrument compartment takes place prior to the formation of the explosible gas-air mixture in the receiving trap.

The claimed method for protecting against the explosion of an in-line inspection tool allows for additional information on the operative condition of the tool kicked to the launching trap, stuck in the gas pipeline or reached the receiving trap before the tool withdrawal, by receiving a signals group from the low-frequency transmitter, modulated in time by the onboard computer. The modulation of a transmitter signal in time is done by the onboard computer by switching of power supply circuits in time.

The claimed device for protecting against the explosion of in-line inspection tool contents a hermetical instrument compartment with set inside electronic equipment, power supply unit, onboard computer, low-frequency electromagnetic transmitter, no-motion sensor, and an environmental pressure alarm. At that, the onboard computer executes the inclusion of the instrument compartment power supply circuits under the indications of environmental pressure alarm subject to the excessive pressure in the medium surrounding tool for the value guaranteeing the absence of explosible gas-air mixture in the launching trap. Low-frequency electromagnetic transmitter is connected to the tool power supply unit through the commutating switch controlled by the onboard computer. After the in-line inspection tool kicking to the launching trap, the onboard computer executing the given algorithm of a tool functioning, switches on the low-frequency transmitter power supply for time periods of different length. The emission from the low-frequency transmitter in the interval of determined length corresponds to the execution of the determined normal operation mode by the tool. For example: the instrument compartment power-up, onboard systems monitoring, readiness for normal operation, motion start, inlet valve run, supplying power to the diagnostics system, cruise condition and, afterwards, at the approaching to the receiving trap: the valve is run, arrived, power supply monitoring, pressure monitoring, and the instrument compartment power cut (termination of transmitter's emission). Besides, at the cruise condition while the trunk gas pipeline inspection the following signals could be produced; failure, emergency stop, disconnection of power supply from the diagnostics system, and the instrument compartment power cut (termination of transmitter's emission). All low-frequency signals are received and identified by the receiver with releasing of corresponding information to an operator display. Consequently, the operator receiving the credible information on the presence or absence of the instrument compartment power supply, can prevent the development of explosible situation giving timely orders on opening and closing of the inlet valve and launching (receiving) trap.

According to the requirements of pipelines flaw detection technology it is inadmissible to start the in-line inspection tool motion when the launching trap is filled with the product of transit. Therefore the signal from the tool no-motion sensor is connected to the input of the onboard computer, which is an accelerometer.

For increasing the reliability of a signal acquirement on the pressure value of the gas-air mixture in the launching (receiving) trap, three pressure relays with a pickup setting for the pressure of 3 atm are used as a pressure alarm, and signals are processed by the onboard computer using two out of three voting logic.

To increase the tool explosion safety the instrument compartment is filled with inactive gas and hermetically sealed.

The invention essence is illustrated by the drawing.

Fig. 1 shows the system device scheme for protecting the in-line inspection tool from the explosion.

The method for protecting the in-line inspection tool from the explosion is considered by the example of the device presented in Fig. 1.

The system device scheme for protecting the in-line inspection too! from the explosion applies special functional capabilities of the following devices that constitute the tool and located in the instrument compartment 1 ; power supply unit 3, onboard computer 5, no-motion sensor 6, environmental pressure alarm 7 and low-frequency electromagnetic transmitter 8. Moreover, the power bus of the instrument compartment 1 is connected to the power supply unit 3 through the commutating switch 2 controlled by the onboard computer 5. Using other commutating switch 4, which supplies power to the low-frequency electromagnetic transmitter 8, the onboard computer 5 can modulate a signal emitted from the transmitter 8 in time. Onboard computer 5 is supplied with a low-voltage autonomous power supply unit.

The device operates in the following way. In the receiving trap after the tool kicking with the pressure increase guaranteeing the absence of explosible gas mixture in the launching trap, for example, 3 atm, the pressure alarm 7 activates and the onboard computer 5 generates a command to the power supply switch of the instrument compartment 2 for the connection of the power bus of the instrument compartment to the power supply unit. At the same time, according to the command of onboard computer 5 the low-frequency electromagnetic transmitter 8 is powered through the commutating switch 4 for the set in advance time corresponding, for example, to the signal - power is supplied to the instrument compartment. Next, a signal may follow - the tool is motionless etc. While the tool withdrawal in the receiving trap with the pressure drop to 3 atm the pressure alarm 7 activates, and the onboard computer 5 generates a command to the commutating switch 2 for the interruption of the instrument compartment 1 power supply.

At that moment the power supply to transmitter 8 is switched off, it stops the signal emission, and it means that it is possible to reduce pressure to atmospheric in the receiving trap and open it for the tool withdrawal.

In case of the unauthorized tool stop inside the linear part of a gas pipeline the signal - failure may follow with a subsequent disconnection of the instrument compartment power bus.