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New Acoustic-Emission Systems for Different Objects Including UnderwaterBELOV V.M., PODLEVSKIKH M.N.
Eltest Inc., Moscow, Russia
Gosgortechnadzor, Moscow, Russia.
Only during last four years (1996-1999) Eltest corporation personnel test more than 700 km of pipelines, 300 dangerous crossings of pipelines with the highways and railroads, 270 pressure vessels, where we find more than 10 thousands of different defects, including 314 very dangerous defects, which must be immediately removed to prevent a failure
With 1997 our corporation produces new model of the device "Locus - D", all digital, having the expanded set of an measured parameters, and also a lot of new functions. The model provides conventional qualities of devices of developing of the "Eltest" corporation - minimum overall dimensions and weight (no more than 7,5 kgs for the 16-channel device), the maximum immunity to exposures - dust, moisture, temperature, vibration and shocks (up to IP66), and also lower consumed power at a feed from accumulators, that in the total provides maximum productivity of the control at absence of loss of the data.
Now we develop a new generation of AE sensors that allow to test the underwater crossings of pipelines with the rivers and lakes up to 20 meters deep, being installed by the divers.
Keywords: acoustic emission, acoustic emission system, underwater sensor, pipeline testing, pressure vessel
Only during last four years (1996-1999) Eltest corporation personnel test more than 700 km of pipelines, 300 dangerous crossings of pipelines with the highways and railroads, 270 pressure vessels, where we find more than 10 thousands of different defects, including 314 very dangerous defects, which must be immediately removed to prevent a failure.
There are permanently carried out researh works, due to which one the procedure of the AE control of underwater pipe lines crossings with usage specialized underwater AE sensors is designed and approved.
We consider, that the detection of defects in a wall of the pipe line is most effective at the following program of loading:
In some cases on stage II of loading the rise of pressure can be exchanged with its decreasing up to 0,9 Po with subsequent rising of pipeline pressure on stage III up to operating, but in these cases, according to our opinion, the groups of finded defects should be revised. The researh carried out by Eltest Ltd on the experimental proving ground (the pipe line a dia 720 mms and a length 450m) have shown, that the degree of hazard of the retrieved defects at the given program of loading should be magnified by 1-2 levels.
As examples of finded defects detected with applying of our instrumentation and an offered procedure, we shall cause following.
Example 1. Inadmissible defects detected at AE control (Fig.1) of a main oil pipeline "Omsk - Irkutsk" with a dia 720 mms and wall thickness 8 mms. The defects represent cracks in welds by depth of 5,5 mms and overall length accordingly 40 and 150 mms (from left to right).
|Fig 1: Summary amplitudes of AE events vs. its X-coordinates on the main oil pipeline "Omsk-Irkutsk".|
Example 2. Permissible defects (Fig.2) detected in welds of the pressure vessel in Nevinnomyssk (operating pressure 55 aTM, height 10100 mms, diameter 3800 mms, wall thickness 100 mms).
|Fig 2: Summary amplitudes of AE events (color marked) vs. its XY-coordinates on the pressure vessel (Nevinnomyssk).|
What demands should be maked to AE systems intended for pipe lines diagnostics?
For build-down of labour input of diagnostics it is necessary to magnify distance between sensors, therefore the AE system should provide maximum sensitivity and minimum level of a self-noise.
If the intensive exploitation of a system in field or industrial conditions is supposed, for its moving to object of tests, failure-free operation and the non-admissions of diagnostic data loss are indispensable:
Stages of development of our AE instrumentation
Maiden AE instruments of the corporation (AE-1) were designed in middle of 80th years, were single-channel and placed in a strong steel rectangular box. There was only indication of coming pulses, and, naturally, no computer.
The instruments of following modification - AE-2160 - were designed in the begining of 90th, had already up to 16 channels, took an imposing box by the size about the small TV set and weighed about 25 kg.
The recording of pulses was carried out on crossing two thresholds (lower and upper), which one were set simultaneously for all channels. They have shown themselves rather reliable, and the majority from made instruments is successfully exploited to this day. Subsequently computer - notebook was adjoined to them, that has allowed to realise data record in a file, linear and planar location.
The instruments of the third modification -AE-3080 - were designed in 1995. There were made as one large card having the own processor and located in the docking station of a base computer - notebook. The new chips of a heightened scale of integration were applied. Naturally, the set of an measured parameters was sharply magnified, of weight was decreased up to 9 kgs (it at 8 channels!). Small power consumption of the instrument began possible the powering from an automobile accumulator through the special converter. The instrument was supplied with the simple and user-friendly Windows - similar software of own development. Some crews of the technicians of the corporation, permanently working on this instruments in field and industrial conditions, gave a guidelines promoted to perfecting of the instrument construction much.
In following year - 1996 - the fourth modification of portable AE instruments was designed, which one contained already up to 16 channels, did not require the docking-stations and placed in a body of an industrial computer - notebook. In result the instrument has received the expanded temperature range, moisture- and shock-proof capability, and also capacity to endure full disappearance of an external power supply about 5 minutes. In the total was created really field rugged multichannel AE instrument.
The given modification of the instrument has passed check in field and industrial conditions within three years at diagnostics of substantial manufacturing objects - pipe lines, pressure vessels etc., having ensured for this time detection more than 138 confirmed defects. A lot of this instruments is successfully exploited in different organizations of Russia and CIS countries to this day. However designers of the corporation were not stopped on reached. With 1997 the new model of the instrument "Locus - D", alldigital, having the expanded set of an measured parameters, and also lot of new functions is produced.
Principled difference of the new architecture of the instrument is the alldigital processing of a signal realised on power FPGAs (fully programmed gate arrays).
Former there were conventional qualities of the Eltest corporation instruments - minimum overall dimensions and weight (no more than 7,5 kgs for the 16-channel instrument), the maximum stability to external conditions - dust, moisture, temperature, vibration and impacts (up to IP66), and also lower consumed power at supply from accumulators, that in the total provides maximum productivity of the AE control at absence of data loss.
The software supports activity with the instrument up to 80 channels with autodetection of their number (in a mode « Plug and play »). It allows individually to set all parameters of each channel, provides an autotuning, floating threshold, filtering on any instrument parameters separately and in aggregate, postprocessing, graphical representation of the data.
More in-depth information on these systems is released in .
Now we develop a new generation of AE sensors that allow to test the underwater crossings of pipelines with the rivers and lakes up to 20 meters deep, being installed by the divers. This solves the problem of long underwater crossings AE control. This sensors contains the built-in preamplifier, six strong rare-earth magnets and strengthened signal cable.
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