Quantitative transient analysis of localized corrosion

• US 20050211570A1
• Filed: 03/21/2005
• Published: 09/29/2005
• Est. Priority Date: 03/26/2004
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Menendez, Carlos M., Jovancicevic, Vladimir, Hammonds, Paul, Mok, Wai Yeung
• Granted Patent: US 7,368,050 B2
• Time in Patent Office: Days
• US Class Current: 205/775.500
• CPC Class Codes: G01N 17/02 Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement

Abstract

The invention provides an electrochemical noise method, apparatus and system for estimating parameters of interest related to corrosion rates of an electrically conductive article, the method comprising: placing a working electrode, a reference electrode, and a counter electrode in an environment of interest; measuring potential at open circuit between the working electrode and the reference electrode over time; placing the working electrode under a potentiostatic control; measuring current between the working electrode and the counter electrode for a predetermined period of time, the period of time of measurements may be extended to include a transient event; and estimating the corrosion rate.

Claims

1. A method for estimating localized corrosion of an electrically conductive article comprising:

(a) placing a working electrode, a reference electrode, and a counter electrode in an environment of interest, wherein the working electrode has substantially the same composition as the electrically conductive article;

(b) placing the working electrode under potentiostatic control;

(c) measuring a current between the working electrode and the counter electrode;

(d) measuring a transient substantially over a duration of a localized corrosion event; and

(e) estimating the localized corrosion from the measured potential and current data.

2. The method of claim 1 wherein the localized corrosion is selected from the group consisting of:

i) the number of corrosion events, ii) the duration of corrosion events, iii) surface area of a pit associated with the corrosion event, iv) depth of penetration of a pit associated with the corrosion event, v) rate of penetration of a pit associated with the corrosion event, vi) volume of metal displaced by the corrosion event and vii) a type of localized corrosion event.

3. The method of claim 1 further comprising:

estimating a rate of penetration of a pit associated with the localized corrosion from a time rate of change of the measured potential and current data.

4. The method of claim 1 further comprising:

determining a type of localized corrosion from the measured transient; and

estimating a geometry of a pit associated with the type of localized corrosion.

5. The method of claim 1 further comprising:

estimating a surface area of a pit associated with localized corrosion.

6. The method of claim 1 further comprising:

estimating rates of penetration of multiple pits associated with localized corrosion according to a sum of ratios;

$\frac{1}{R}=\underset{n=1}{\overset{n}{\sum <br><br>}}<br><br>\left(\frac{1}{R_n}\right)$

where each R_n is given substantially as

$R_n<br><br>\left(t+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)=R<br><br>\left(t+\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>t\right)·<br><br>\frac{\underset{n=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{PD}}_n^2<br><br>\left(t\right)}{{\mathrm{PD}}_n^2<br><br>\left(t\right)}.$

7. An apparatus for estimating localized corrosion of an electrically conductive article comprising:

(a) a working electrode having substantially the same composition of the electrically conductive article;

(b) a reference electrode;

(c) a counter electrode; and

(d) a sensor for measuring current transient data between the working electrode and the counter electrode until initiation of a current transient due to a localized corrosion event, wherein the current transient is measured substantially over the duration of the localized corrosion event; and

(e) a sensor for measuring potential transient data between the working electrode and the reference electrode until initiation of a potential transient due to a localized corrosion event, wherein the potential transient is measured substantially over the duration of the localized corrosion event; and

(f) a processor for estimating the localized corrosion from the measured transient data.

8. The apparatus of claim 7 wherein the localized corrosion is selected from the group consisting of:

i) the number of corrosion events, ii) the duration of corrosion events, iii) surface area of a corrosion event, iv) depth of penetration of a corrosion event, v) rate of penetration of a pit associated with the corrosion event, vi) volume of metal displaced by corrosion event and vii) the type of localized corrosion event.

9. The apparatus of claim 7 wherein the localized corrosion is a rate of penetration of a pit associated with the localized corrosion event is estimated from a time rate of change of the measured potential and current data.

10. The apparatus of claim 7 wherein localized corrosion is estimated from the measured transient to obtain geometry of a pit.

11. The apparatus of claim 7 wherein the localized corrosion is a rate of penetration of pits estimated according to a sum of ratios:

12. A localized corrosion measuring system for an electrically conductive article in an environment of interest comprising:

(a) an electrically conductive fluid-conduit composed of a material of interest;

(b) a working electrode which is substantially composed of the material of interest;

(c) a counter electrode;

(d) a reference electrode; and

(e) a measurement system connected to the working electrode, the counter electrode, and the reference electrode for monitoring transients events indicative of localized corrosion, wherein the transient events are monitored between the working electrode, the counter electrode and the reference electrode substantially over the duration of the transient event.

13. The system of claim 12 wherein the counter electrode and the reference electrode are substantially inert in an environment of interest.

14. The system of claim 12 for monitoring current transient events indicative of localized corrosion selected from the group consisting of:

i) the number of corrosion events, ii) the duration of corrosion events, iii) surface area of a corrosion event, iv) depth of penetration of a corrosion event, v) rate of penetration of a pit associated with the corrosion event, vi) volume of metal displaced by corrosion event and vii) the type of localized corrosion event.

15. The system of claim 12 wherein a rate of penetration of a pit associated with the localized corrosion is estimated from a time rate of change of the monitored transient.

16. The system of claim 12 wherein localized corrosion is estimated from the measured transient to obtain a geometry of a pit.

17. The system of claim 12 wherein the electrically conductive fluid conduit in an environment of interest, for example:

i) a pipeline; and

ii) a well bore tubular, etc., is utilized.

18. The system of claim 12 wherein the localized corrosion is a rate of penetration of pits estimated according to a sum of ratios: