US 4,843,319 AGranted

Transient electromagnetic method for detecting corrosion on conductive containers having variations in jacket thickness

AssigneeAtlantic Richfield Company

InventorPedro F. Lara

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Abstract

There is disclosed a method for detecting corrosion on the walls of conductive containers wherein a transmitting antenna induces a current into a portion of the container wall and the decay of the induced current is detected by a receiving antenna, with a record of the decay of the induced current being created. The record is interpreted to determine the thickness of the container wall portion and the presence or absence of corrosion is inferred. The effects of variations in distance between the transmitting antenna and the receiving antenna and the pipe wall at one location on the pipe and between the transmitting antenna and the receiving antenna and the pipe wall at another location on the record of the decay are corrected for by examining the rate of decay of the induced current.

Claims10

Dependent claims

A method of detecting corrosion in walls of container means, said walls being electrically conductive and having near surface and far surfaces, comprising the steps of:

a. placing transmitting antenna means and receiving antenna means in proximity of the near surface of that portion of the container means wall which is to be investigated for corrosion;
b. energizing the transmitting antenna means with current;
c. abruptly de-energizing the transmitting antenna means so as to induce current into the container means wall portion;
d. detecting the presence of and the decay of said induced current in said container means wall portion with the receiving antenna means;
e. creating a record of the decay of said induced current in said container means wall portion over a period of time, said record having intermediate and late time ranges, wherein said record of said induced current is influenced by variations in distance between said transmitting antenna means and said receiving antenna means and said container means wall caused by moving said transmitting antenna means and said receiving antenna means from one location to another location on said container means wall;
f. determining from the record with respect to time the derivative of the decay of said induced current, said derivative having intermediate and late portions corresponding to the intermediate and late time ranges of the record;
g. examining the derivative of the decay of the record and comparing the intermediate and late time portions of the derivative to intermediate and late time portions of the derivative to intermediate and late time portions of a derivative of a reference record to determine the wall thickness of said investigated container means wall portion, said reference record obtained from a reference container means with known wall thickness, wherein said wall thickness determination of said investigated container means wall portion is unaffected by said variations in distance and wherein the presence or absence of corrosion on said investigated container means wall portion can be inferred.

4 more elements

A method of measuring wall thickness to detect irregularities such as corrosion on electrically conductive walls of container means, comprising the steps of:

a. providing transmitting antenna means, receiving antenna means, transmitter means connected with said transmitting antenna means, and receiver means connected with said receiving antenna means;
b. placing said transmitting antenna means and said receiving antenna means in proximity to that portion of the container means wall which is to be investigated for irregularities;
c. providing an abruptly changing current to said transmitting antenna means from said transmitter means so as to induce current into the investigated container means wall portion;
d. detecting said induced current in said investigated container means wall portion with said receiving antenna means and said receiver means to produce a first received signal, said first received signal decaying into noise over a period of time, said first received signal having intermediate and late time ranges, said received signal being influenced by variations in distance between said transmitting and receiving antenna means and said container means wall, which variations are caused by moving said transmitting antenna means and said receiving antenna means from one location to another along said container means wall;
e. determining with respect to time the derivative of the received signal, said derivative having intermediate and late portions corresponding to the intermediate and late time ranges of said received signal;
f. comparing the intermediate and late time portions of the derivative of said received signal to intermediate and late time portions of a derivative of a reference received signal to determine the wall thickness of said investigated container means wall portion, said reference signal being obtained from a reference container means with known wall thickness, wherein the wall thickness of said investigated container means wall portion is determined without being influenced by variations in distance between the transmitting and receiving antenna means and the container means walls and the presence or absence of irregularities on the investigated container means wall portion can be determined.

3 more elements

Dependencies are inferred from the claim text.