Parallel HDDs for cathodic protection under a crude oil storage tank

In October 2023, Brownline Canada provided guidance services for several short parallel HDD crossings. At a crude oil storage facility in Alberta, horizontal directional drilling was used to install cathodic protection strings under a large storage tank.

Cathodic protection (CP) is a method to prevent corrosion (rust) that is also often used with steel pipelines. It involves connecting anode material to the structure and applying an electrical current. This causes an electro-chemical process which prevents corrosion on the steel structure, thus increasing its lifespan. In this project, aged cathodic protection anodes, previously installed around the perimeter of the tank were replaced to add continued corrosion protection on an already 20 year old storage tank with a diameter of 36.6 m / 120 ft.

11 HDDs required

The proposed system required installation of ten parallel anode strings under the tank, at a depth of 2 m / 6.6 ft. These anodes would need to be evenly distributed along the width of the tank, which meant the strings were spaced 3.3 m / 10.9 ft apart.

In addition, one diagonal crossing was planned above the anode strings, at 1.3 m / 4 ft below the bottom of the tank. With this diagonal crossing, an 80 mm / 3” PVC tube would be installed, which can be used to monitor the CP system. HDD contractor Precise Crossings carried out these drills.

Drilling with the highest accuracy

To ensure the most efficient operation of the cathodic protection system, it was very important that the anodes were installed at the specified depth and with the specified separation between the crossings. There was no room for deviations, so the highest accuracy was needed, without having to worry about interference from the steel infrastructure. This is why Brownline Canada was called in to use the Drillguide Gyro Steering Tool on this project. A small diameter GST (152 mm / 6”) was used to guide the drills under the storage tank.

The lengths of these crossings all ranged between 43 – 61 m / 141 – 200 ft. First, the Witness Tube (diagonal crossing) was drilled and installed, followed by the deeper ten (10) parallel anode strings. Each anode string and Witness Tube were installed with the highest accuracy, efficiency, and confidence.

The measured data for all crossings was recorded, and this data was used to visualize the exact placement of all installed materials. This allows the user of the CP system to determine the optimal settings to protect the storage tank from corrosion for decades to come.

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