US 6,476,624 B1Granted

Crack monitoring method and apparatus

AssigneeMitsubishi Heavy Industries, Ltd.

InventorsYasuharu Chuman, Masafumi Yamauchi, Nobuhiko Nishimura, Masahiro Umata

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Abstract

A method and apparatus for monitoring crack inside piping suitable for high temperature environment including an electrode attachment process for attaching a pair of heat resistant current input-output electrodes to an outer circumferential surface of the piping such that the crack is positioned between electrodes. Measuring intra-crack potential difference by a pair of heat resistant potential difference measuring electrodes attached to outer circumferential surface of the piping and placed between the input output electrodes by supplying alternating current between the input-output electrodes. Crack length is calculated from the measured electric potential difference after correcting the intra-crack electric potential difference as a function pipe temperature and pressure by an intra-crack electrode potential difference correction process.

Claims22

Dependent claims

A method for monitoring a crack that is generated within a welded portion of a high temperature, thick-walled piping of a plant, which method is accomplished during the operation of the plant, comprising:

attaching a pair of heat-resistant current input-output electrodes to an outer circumferential surface of the welded portion of the piping such that the crack whose position is previously specified is put between the pair of heat-resistant current input-output electrodes;
attaching at least one pair of heat-resistant crack electric potential difference measuring electrodes to the outer circumferential surface of the piping such that they are put between the current input-output electrodes;
alternately supplying an alternating current of a frequency of either 10 Hz or lower or 50 Hz or higher between said current input-output electrodes;
measuring an electric potential difference between said crack electric potential difference measuring electrodes;
correcting the electric potential difference between said crack electric potential difference measuring electrodes;
protecting the heat resistant current input-output electrodes and the electric potential difference measuring electrodes by enclosing those electrodes in a protective box;
and
calculating the length of the crack on the basis of said electric potential difference obtained by said intra-crack electric potential difference correction process.

5 more elements

An apparatus for monitoring a crack that is generated within a welded portion of a high temperature, thick-walled piping of a plant during the operation of the plant comprising:

a pair of current input-output electrodes made of heat-resistant material attached to an outer circumferential surface of the welded portion of the piping;
a sensor head having at least one pair of crack electric potential difference measuring electrodes made of a heat-resistant material attached to the outer circumferential surface of the welded portion of said piping such that they are put between said current input-output electrodes;
an electric alternating current power supply for alternately supplying an alternating current of a frequency of either 10 Hz or less or 50 Hz or greater between said current input-output electrodes of said sensor head;
a crack electric potential difference measurement means for measuring an electric potential difference between said crack electric potential difference measuring electrodes of said sensor head;
an intra-crack electric potential difference correction means for correcting the electric potential difference between said crack electric potential difference measuring electrodes of said sensor head measured by said crack electric potential difference measurement means;
and
a crack length calculation means for calculating the length of said crack on the basis of said electric potential difference obtained by said intra-crack electric potential difference correction means.

4 more elements

Dependencies are inferred from the claim text.