The corrosion condition of large diameter stainless steel pipe was detected by TEM method.Electrochemical corrosion, stray current corrosion and anaerobic bacteria corrosion, the result is quantity of metal corrosion and corrosion product scale product, cause the conductivity of the buried large diameter stainless steel pipe and the decline of permeability.Obviously, as long as detected by corrosion caused by the variation of the physical properties of position and degree of variation, with known (corrosion has occurred and no corrosion occurs) contrast, can be pointed out that the corrosion location and make evaluation of corrosion degree.

A horizontal and vertical primary field is built around a square excitation wire frame with pulse current.Instantaneous power, online around the box, including pipeline to be tested in lossy media to excite the eddy current decay over time, the secondary magnetic field associated with eddy current online box of normalized electromotive force in the receiving coil.

Normalized pulse transient response and the pipe body not only geometric parameters (size, shape, space) and the physical properties (electrical conductivity, magnetic permeability and dielectric constant), and circumference TuWu sexual (conductivity, magnetic permeability and dielectric constant) and distribution, but also with the position of the observation point, and the physical properties of pipe material.

If the influence of surrounding soil and backfill is not taken into account, the transient electromagnetic response of the pipeline can be expressed as follows:

Obviously, as a result of corrosion or conductive, made the wall thickness smaller permeability decreased, which resulted in increased d, attenuation faster, in a sense (l and the soil corrosion products of ∥ numerous as), the change of wall thickness Nai can be determined by a change.However, sufficient quantities of corrosion products are uncertain and should generally be higher than surrounding soil.Therefore, macro to tuoa2 as a suitable parameter: the increase of d or is due to the reduction of the thickness of the large diameter stainless steel pipe, or show that the corrosion of section electric and magnetic conductivity decreased.

The detection and evaluation of corrosion degree of buried pipeline by TEM is to study and identify the minor changes in the comprehensive physical properties of the pipeline under test.However, the following factors restrict the transient response.

(1) geometric factors: including buried depth, diameter and wall thickness of the pipeline under test;Shape, size, number of turns, spatial position and transceiver distance between the actuating loop and the receiving loop;Surface topography and cross section shape of canal trench backfill soil;

(2) medium factors: including the measured pipeline, the conveying medium in the pipeline, the surrounding soil (undisturbed soil), the conductivity, magnetic permeability and dielectric constant of the backfill soil;
(3) interference factors: they are mainly caused by "solar power", lightning and other "non-active" transient electromagnetic interference, including human interference.

Some of these factors can be identified and some can be simplified.For example, geometric parameters are all determinable factors, which will be greatly simplified after proper device design.For example, a common frame (loop) device with a pipe directly above it;Generally, it can be regarded as the groove shape under the condition of "infinite length".The size and space position of the pipeline under test;The distribution of land and backfill soil;The measured physical parameters have continuous contrast.Obviously, the above known or measurable parameters and determinable factors have some degree of time and space stability on the transient response, so they can be treated as background under certain conditions.Instantaneous interference can be suppressed by improving signal-to-noise ratio.After the mathematical physical model, modern data processing and inversion method, namely, or considering the soil, the geometry of backfill soil factors it can also achieve a medium of parametric variation of electromagnetic, the reason is that they are measurable and can be set.Obviously, the constraint conditions can be easily determined, and the non-uniqueness of the solution is greatly reduced.Large diameter stainless steel pipe, large diameter stainless steel pipe, large diameter thick wall pipe, thick wall stainless steel pipe,