초록 ▼

A method of diagnosing corrosion risk of a buried pipe due to DC stray currents and/or AC voltages induced in soil employs a metal probe including a first, exposed part having a first specific resistivity, and a second, sealed reference part having a second specific resistivity. The probe is buried

A method of diagnosing corrosion risk of a buried pipe due to DC stray currents and/or AC voltages induced in soil employs a metal probe including a first, exposed part having a first specific resistivity, and a second, sealed reference part having a second specific resistivity. The probe is buried in the soil, and the AC current and voltage between the pipe and the probe are measured, from which the spread resistance is determined. The resistances of the first and second probe parts are determined by respectively passing first and second excitation currents through the first and second probe parts and measuring the voltages across them. The resistance measurements are stored, and the steps are repeated periodically. The corrosion of the first probe part is determined from the measurements according to an algorithm, and the pipe corrosion risk is diagnosed from an empirical combination of the corrosion of the first probe part, the spread resistance, and the AC voltage measured.

대표청구항 ▼

The invention claimed is: 1. A method of diagnosing corrosion risk of a pipe or a pipeline buried in soil due to DC stray currents and/or AC voltages induced in the soil, comprising: i) providing a two-part metal probe including a first probe part having a first metal element of a first size and a

The invention claimed is: 1. A method of diagnosing corrosion risk of a pipe or a pipeline buried in soil due to DC stray currents and/or AC voltages induced in the soil, comprising: i) providing a two-part metal probe including a first probe part having a first metal element of a first size and a first specific resistivity RC, said first probe part constituting an exposed element, and a second probe part having a second metal element of a second size and a second specific resistivity RR, said second probe part constituting an environmentally isolated reference element; ii) burying said two-part metal probe in said soil; iii) electrically connecting said two-part metal probe to said pipe or pipeline; iv) measuring an AC current flowing between said pipe or said pipeline and said two-part metal probe while said pipe or said pipeline and said two-part metal are electrically connected; v) electrically disconnecting said two-part metal probe from said pipe or pipeline; vi) measuring an AC voltage between said pipe or pipeline and said two-part metal probe while said pipe or pipeline and said two-part metal probe are disconnected from one another; vii) measuring a spread resistance based on said AC current determined in step iv) and said AC voltage measured in step vi) according to Ohm's Law; viii) passing a first excitation current through said first probe part and determining the voltage generated by said first excitation current across said first probe part for measuring the resistance of said first probe part according to Ohm's Law while said pipe or pipeline and said two-part metal probe are disconnected from one another; ix) passing a second excitation current through said second probe part and determining the voltage generated by said second excitation current across said second probe part for measuring the resistance of said second probe part according to Ohm's Law while said pipe or pipeline and said two-part metal probe are disconnected from one another; x) storing said measurements provided in steps iv), vi), vii), viii), and ix); xi) repeating said steps iii) through x) periodically, xii) determining an actual corrosion of said first probe part based on the measurements performed in steps viii) and ix) according to a mathematical corrosion algorithm; and xiii) diagnosing the risk of corrosion of said pipe or pipeline based on an empirical combination of the actual corrosion of said first probe part, said spread resistance determined in step vii) and said AC voltage measured in step vi). 2. The method according to claim 1, said first probe part and said second probe part having identical metal elements. 3. The method according to claim 1, said step xii being performed in accordance with the following equation: in which σ(t) denotes thickness of an element as a function of time. 4. The method according to any of the claims 1-3, said diagnosing of step xiii being performed in accordance with the following table: Event Active corrosion Spread resistance AC voltage Diagnose 1 No high (1-10 Ωm2) low (below No risk approx. 10 V) 2 No high (1-10 Ωm2) high No critical condition (above but monitor spread approx. resistance further 10 V) 3 No low (0.001-0.1 Ωm2) low (below No critical condition approx. but be aware of increased 10 V) AC voltage 4 No low (0.001-0.1 Ωm2) high Risk of AC corrosion (above incubation period approx. 10 V) 5 Yes low (0.001-0.1 Ωm2) high AC corrosion-take (above mitigation actions approx. 10 V) 6 Yes low (0.001-0.1 Ωm2) low (below Corrosion may approx. arise from DC stray 10 V) current 7 Yes high (1-10 Ωm2) low (below Corrosion may approx. arise from DC stray 10 V) current 8 Yes high (1-10 Ωm2) high Corrosion may (above arise from DC stray approx. current 10 V). 5. The method according to claim 4, wherein said spread resistance is high if the value of said spread resistance is above 1 Ohm, and low if the value of the spread resistance is below 0.1 Ohm. 6. The method according to claim 4, wherein said AC voltage is high if said voltage is higher than 10V. 7. The method according to any of the claims 1-3, said steps iii through x being repeated with a frequency of one or more days. 8. A system for diagnosing corrosion risk of a pipe or a pipeline buried in soil due to DC stray currents and/or AC voltages induced in the soil, comprising: i) a two-part metal probe including a first probe part having a first metal element of a first size and a first specific resistivity, said first probe part constituting an exposed element, and a second probe part having a second metal element of a second size and a second specific resistivity, said second probe part constituting an environmentally isolated reference element; ii) a switching device for the selective electrical connection and disconnection of said two-part metal probe and said pipe or pipeline; iii) a measuring apparatus electrically connected to said two-part metal probe and including: an AC current measuring circuit for measuring an AC current flowing between a pipe or pipeline and the two-part metal probe when said probe is buried in said soil while said two-part metal probe is electrically connected to said pipe or pipeline; an AC voltage measuring circuit for measuring an AC voltage between said pipe or said pipeline and said two-part metal probe when said two-part metal probe is buried within said soil while said two-part metal probe is electrically disconnected from said pipe or pipeline; a resistance measuring circuit connected to said AC current measuring circuit and said AC voltage measuring circuit for determining a spread resistance based on Ohm's Law; a current excitation circuit for (a) passing through said cable a first excitation current to said first probe part while said pipe or pipeline and said two-part metal probe are disconnected from one another; (b) for measuring the voltage generated by said first excitation current across said first probe part for measuring the resistance of said first probe part according to Ohm's Law; (c) for passing a second excitation current through said cable to said second probe part while said pipe or pipeline and said two-part probe are disconnected from one another; and (d) for determining the voltage generated by said second excitation current across said second probe part for measuring the resistance of said second probe part according to Ohm's Law; a data processor for determining an actual corrosion of said first probe part based on the measured resistances of the first and second probe parts according to a mathematical corrosion algorithm; a storage device for storing the measurements made by said AC current measuring circuit, said AC voltage measuring circuit, said spread resistance measuring circuit and said current excitation circuit; and a diagnosing circuit for diagnosing the risk of corrosion of said pipe or pipeline based on an empirical combination of the actual corrosion of said first probe part, said spread resistance and said AC voltage. 9. The system according to claim 8, wherein said measuring apparatus includes a micro processor constituting part of said AC current measuring circuit, said AC voltage measuring circuit, said spread resistance measuring circuit, said current excitation circuit, said storing circuit, and said diagnosing circuit, said micro processor controlling the overall operation of the apparatus for periodically repeating the measurements. 10. The system according to any of the claims 8 or 9, wherein said measuring apparatus includes two or more cable connectors for establishing connections to two or more two-part metal probes. 11. The system according to any of the claims 8-9, wherein said measuring apparatus further includes a data connector configured for connecting to an external device operable for receiving information regarding said two-part metal probe.