by Valery GOROSHEVSKY, Cand. Sc. (Tech.), Svetlana KAMAEVA, Cand. Sc. (Tech.), Igor KOLESNIKOV, Cand. Sc. (Tech.), TRANSKOR-K Scientific-Technical Center

Residents of any megalopolis are usually well aware of the fact that they are dwelling on top of yet another "metropolis" located under their streets and squares - an unimaginable maze of pipelines, cables and tunnels without which the urban life on the surface would have been simply impossible. And keeping this maze in working order is no simple task.

Experts in various countries are confronted with one common problem: how to check underground pipelines and cables under major cities where on-the-spot inspections are impossible. Some sections of such underground networks and their key junctions simply have to be "dug out" for inspection and maintenance, and in Russia these operations are conducted in line with a special "In-structions for Diagnostics of Technical Conditions of Underground Steel Gas Conduits". Such checks, however, fail to pinpoint specific "lesions" from corrosion or other causes which is necessary for having an authentic picture of metal wear all along a particular pipeline which would make it possible to prognosticate its lifespan.

The actual efficiency of urban conductor networks all over the world has to be determined by what specialists here call "factor of failure". And the causes for that in urban centers with millions of residents and hundreds of industrial units can be more than enough. These include, above all, unstable operating regimes of these pipes and conduits (sharp load variations) even within 24 hours, difficulties of conducting instrumental analysis of aggressive external factors (external-soil, microorganisms and internal-water, gas, liquid wastes, etc.) The difficulties of prognostication of metal defects in actual operating conditions are combined with the absence of a reliable system of risk assessments in emergencies.

Pages. 45

Naturally enough, one cannot anticipate and predict all kinds of problems associated with communal networks. Specialists try to increase their safety margin by trying to figure out chances of seal failures or decompressions. In doing that they rely on new methods like remote infrared inspection (for heating networks) and on the technical reliability factors of piping (for sewer and heating systems).

But the central problem today consists in the absence of special diagnostic equipment for different urban conditions. Municipal services in charge of these problems do have modern "tracer" instruments for inspecting communications of what they call passive and active types. The former operate on industrial frequencies (50 and seldom 100 Hz). And the latter help locate pipes which have no cathode chemical protection from corrosion-which emit no electric signals and have to be equipped with generators (usually rather large) of their own frequencies (5,000 - 20,000 Hz). Such emissions are "piped in" the approximate locations of the pipelines, and when reflected signals are picked up the exact positions are determined.

But the aforesaid instruments are incapable of identifying two parallel pipelines located, say, one meter away from one another or linked up with an electric "crosspiece"-a system of cathode protection. The above defect is shared even by the best foreign units like (British RD-400 locator) and Russian unit (TI-05Ts ZAO ERSTED).

The R&D Center TRANSKOR-K has been working on this problem for many years and ended up by suggesting a basically new approach. Our specialists developed in 2001 pipeline "tracer" POISK-A/03 with a built-in small-size generator. The detector can measure the depth of location of the pipelines and identify them with confidence. Incidentally, it will be an indispensable tool in the certification of underground piping because the client must know for sure the location of pipes which he intends to install or replace. We all know of cases when apartment houses are left without tap water.

Pages. 46

Corrosion detected under protective coating at gas-distribution networks of Noginskmezhraigaz (Moscow Region).

This often happens during repairs of a gas main whose exact position is not known.

Summing it up, we have been able to adapt to urban conditions new technology recently developed at our Center-of contactless magnetometric inspection of supply networks which makes it possible to assess their technical condition at distances of up to 15 diameters of a pipe.* Incidentally, the authors of this technique were awarded with a diploma of the Moscow Exhibition Pipeline Systems-2003 for the best unit of this kind. The new system has demonstrated its potential and has been used for inspection of more than 3,000 km of gas pipelines in Russia, Uzbekistan and Ukraine. It proved high authenticity of detection of different metal flaws, including such dangerous ones as internal lamination, or scaling, of metal which is unnoticeable in the beginning, but can gradually spread over the whole surface.

The new diagnostics technique is based on the interconnection of the phenomena of stress concentrations and alteration of polarity of the components of the magnetic field of the Earth. "Hot spots" with changing sign of the charge, and consequently, with the threat of metal failure, can be detected by SKIF magnetometers of the fourth generation. They detect spots with all kinds of damage and can be used for inspections of equipment located 21 - 23 m below ground. Using these devices, modified for urban conditions, experts have already inspected gas-distribution networks of what we call state unitary enterprises Mosgaz, Mosoblgaz, heating plants Lenenergo, water supply lines Mosvodokanal and Lenvodokanal having thus demonstrated the unlimited potentials of this technique.

And the main thing is that it makes it possible to detect areas of local corrosion located under scaled insulating coating. For example it has been possible to detect damage of this kind affecting 60 percent of the thickness of a pipe wall. That was done at a spot where, according to traditional electrometry, there were no deviations from the norms of such well-known parameters as the protective potential pipeline-ground and transitional resistance of the protective coating. Finally, our technology makes it possible to identify with confidence old and new communications, all possible metal flaws which are not caused by rusting, segments with shrinkage of pipelines and places with earth creeps and washouts which cause deformations.

Illustrations supplied by the authors

* See: S. Kamayeva, V. Goroshevsky, I. Kolesnikov, "'Seeing' Through the Earth", Science in Russia, No. 6, 2003. - Ed.

Permanent link to this publication: