DECOMMISSIONING

FIELD OF THE INVENTION

This invention relates to a method of accelerated controlled uniform corrosion of a focused area of a metallic asset.

BACKGROUND OF THE INVENTION

Decommissioning metallic assets that have been impacted with naturally occurring hazardous materials which may include mercury, arsenic, lead and other contaminants have been traditionally costly to clean. These materials are often found embedded within the surface scale or corrosion layer. Standard industry practice to remove these materials can be achieved physically or chemically. The physical approach uses high pressure water jets to detach the surface scale or corrosion from the asset. This process typically generates a significant amount of wastewater and makes slow progress. The chemical approach commonly uses acidic chemistries that dissolved the inorganic scale or corrosion material.

As a result, this process generates a large volume of acidic waste. U.S. 10181706 describes a method to remove hazardous materials by accelerating the corrosion process on a focused area of the metallic asset into the surrounding conducting fluid.

Decommissioning of Subsea Pipelines can be prohibitively expensive if pipeline removal is required. Leaving pipelines in place is often the least risky alternative from an environmental perspective. Standard Industry practice during operation is to employ corrosion protection to preserve pipelines and prevent corrosion which may include cathodic protection- sacrificial anodes and/or impressed current. If removal of these types of pipelines and facilities is necessary, then the presence of impregnated metals and other impurities can add significant costs to the removal and disposal. Subsea pipelines can be flushed and pigged to remove internal hydrocarbons; however, this process will not remove contaminants impregnated into the metal.

SUMMARY OF THE INVENTION

An embodiment of the invention is controlled uniform corrosion on a focused area of a metallic asset to remove unwanted materials from the asset’s surface. The metallic asset is used as a sacrificial anode and coupled with a cathode assembly of lower redox potential than the asset. A non-conductive permeable spacer, and an electrolytic conducting fluid (e.g., seawater, water containing a corrosion enhancing agent, etc.) are used to complete the circuit between the anode and cathode. A preferred embodiment is an accelerated corrosion on the metal area of up to 0.1 mm thickness in one minute or less.

Another embodiment is a method of accelerating the corrosion of the focused area by increasing the conducting fluid circulation rate and/or temperature through the cathode assembly, adjusting the power, more specifically current, and/or adjusting the spacing between the cathode and the anode, and/or changing the type of non-conductive permeable spacer. The power source may be DC or AC. When the power supply is a DC power the amount of power per square meter will be higher than in an impressed system and the power delivered will depend on the number of brushes/brush heads employed. A preferred embodiment is 70 amps per 6 cm squared; 10 up to 50 Watts per cm squared. Another preferred embodiment is to adjust the power in bursts to corrode the metal section in intervals with subsequent scrubbing of the corroded area.

A further embodiment is the use of one or more magnetized moveable brush heads that enables repositioning of the anode for focused corrosion of a variety of areas across the surface of the metallic asset.

A preferred embodiment increases the temperature of the conducting fluid delivered to the corrosion area up to about 60 °C or alters the electrolytic chemistry of the solution to increase the reaction rate of the corrosion process. The temperature increase or solution chemistry can be combined with the increase in water circulation to further accelerate the focused corrosion.

A preferred embodiment is to fill the asset with the conducting fluid and submerge the cathode or multiple cathodes a given distance from the asset’s surface. In this embodiment 0.1-1 amp/cm2 may be applied over the course of multiple hours. The asset is then flushed of the conducting fluid and the corrosion material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG 1 is a plot of corrosion rates increase with increasing current density.

FIG 2 is a plot of the corrosion rate as a function of treatment time.

FIG 3 is a plot of steel equivalent corrosion rate v current density variable spacer type.

FIG 4 is a plot of steel equivalent corrosion rate v current density variable cathode sizes.

FIG 5 is a plot of steel equivalent corrosion rate v current density degree of corrosion. FIG 6 is a plot of power density v time with different spacers.

FIG 7 is a drawing of an embodiment of the brush pad or brush head for delivery of conducting fluid.

DETAILED DESCRIPTION OF THE INVENTION

Herein is described a method to remove a contaminant from facilities by focused uniform accelerated corrosion on an area of the metallic asset. The process as described herein would remove a key waste treatment step in the state of the art and improve the economy in the treatment of surface-contaminated metallic assets, including treatment & handling of process water and could be conducted offshore eliminating the need for costly on-shore treatment. “Contaminant” as used herein includes an unwanted area of the metallic asset that is targeted for removal.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurement.

“Metallic asset” as herein defined comprises an interior section of piping, pipeline, tank, separation or pressure vessel, process equipment and other equipment containing sufficient metal to corrode by the process employed herein.

“Conducting fluid” as used herein comprises water containing a corrosion or conductivity enhancing agent.

“Accelerated corrosion” as used herein consists of a corrosion time of the focused area of the metallic asset that is equal to or less than about one minute.

An embodiment of the invention is controlled uniform corrosion of a focused area of a metallic asset to remove unwanted materials from the asset’s surface. The metallic asset is employed as a sacrificial anode and coupled with a cathode assembly of lower redox potential than the asset comprising a non-conductive permeable spacer the cathode and the anode and an electricity conducting fluid including but not limited to seawater, water containing a corrosion enhancing agent and other fluids which are capable of conducting electricity known to one of skill in the art that is used to complete the circuit between the anode and cathode. A preferred embodiment is accelerated corrosion where the metal area of up to 0.1 mm thickness corrodes in one minute or less.

Another embodiment is a method of accelerating the corrosion of the focused area by increasing the conducting fluid circulation rate and/or temperature through the cathode assembly, adjusting the power, more specifically current, and/or adjusting the spacing between the cathode and the anode, and/or changing the type of non-conductive permeable spacer. The power source is a DC power supply wherein the amount of power per square meter will be higher than in an impressed system and the power delivered will depend on the number of brushes/brush heads employed. A preferred embodiment is 70 amps per 6 cm squared; 10 up to 50 Watts per cm squared. Another preferred embodiment is to adjust the power in bursts to corrode the metal section in intervals with subsequent scrubbing of the corroded area.

A further embodiment is the use of one or more magnetized moveable brush head or brush pad that enables repositioning of the anode for focused corrosion of a variety of areas across the surface of the metallic asset. The brush head or pad is a permeable nonconductive material affixed to the bottom of a four cornered plate wherein an irrigation hose is connected into the top of the plate for the flow of a conducting fluid through the brush head or pad. A further embodiment uses non-conductive rollers as spacers to allow the cathode to freely move across the corroding area.

A preferred embodiment is the use of increasing the temperature of the conducting fluid delivered to the corrosion area up to about 60 °C or the chemical make-up of the solution to increase the reaction rate of the corrosion process. The temperature increase or solution chemistry can be combined with the increase in water circulation to further accelerate the focused corrosion.

A preferred embodiment is to fill the asset with the conducting fluid and submerge the cathode or multiple cathodes a given distance from the asset’s surface. In this embodiment 0.1-1 amp/cm2 may be applied over the course of multiple hours. The asset is then flushed of the conducting fluid and the corrosion material. EXAMPLE 1 - Electrical Resistance is Reduced as Dry Steel Becomes More Saturated

During Treatment

4 areas treated sequentially, 2 minutes each area. Treatment began on dry steel surface at Area 1 , water flooding of all areas commenced at the beginning of treatment. Current density can be increased for the same power usage by pre-wetting the steel.

Area Pre-Treatment Current Density Power Density

Water Flood Time (Amps/cm2) Watts/cm2

(mins)

1 0 0.63 23.1

2 2 0.62 23.3

3 4 0.73 23.4

4 6 1.05 23.9