Recovery of a Pipe Coupon Located 4,000' from the Access Point

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Surge Shaft for Mohican Access

This project involved a hydroelectric intake tunnel where the customer had hot tapped the pressure piping in order to divert a portion of the water for another purpose. During the hot tapping by the contractor, there was a malfunction, and the pipe coupon could not be extracted by the hot tap equipment. The coupon fell into the pressure pipe. Since the coupon was of significant size, it posed a hazard to the hydroelectric facility and its turbines. The decision was made that it would have to be removed from inside the pipe. Since the location of the hot tap was approximately 4,000' from the location of the nearest access point into the tunnel at the surge shaft, Hibbard Inshore was called to provide an ROV and extraction tooling that could not only fly the distance to the coupon and locate it but also remove it through the pressure piping and shafts while the tunnel and piping remained flooded. Hibbard Inshore was up to the task, quickly devised a method, designed ROV tooling, and mobilized to site to assure the coupon would be removed.

Mohican ROV with 4 Function Manipulator

Due to the need for a Remotely Operated Vehicle (ROV) with the ability to retrieve the coupon, a larger light work ROV was used instead of a standard inspection ROV. It was decided that Hibbard Inshore's Sub-Atlantic Mohican ROV with 4 function hydraulic arm would be the proper vehicle to retrieve the coupon.

Upon arrival at site, it was assumed that the coupon was either in the immediate area of the hot tap or slightly downstream at the lower elbow of the vertical tunnel section. While traveling in the horizontal section, the ROV's forward looking sector scan sonar was used to image the invert of the tunnel and look for the coupon. When the coupon was located, the ROV manipulator picked up the coupon with a special hook. The hook was built specifically for the retrieval of the coupon by inserting the hook through the hole in the center of the coupon.

Mohican and Coupon Lowered to Ground

The ROV searched for the coupon as it entered the tunnel but focused on the lower elbow below the vertical section. Then, the ROV travelled up the vertical section and located the hot tap on sonar. The ROV moved to the hot tap location and quickly found the coupon in the invert of the pipe, immediately below the hot tap. A detailed visual inspection was performed of the hot tap to tunnel interface which was on the left spring line of the tunnel when facing up stream. Once the inspection was complete in the hot tap area, the manipulator engaged the coupon. Once engaged, the ROV travelled with the coupon downstream to the lower elbow of the surge shaft.

Recovered Steel Coupon

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After the coupon was recovered, a tunnel inspection was performed from the surge shaft upstream (approximately 3,800') to the lower elbow of the vertical section. The area above the vertical section was inspected during the coupon retrieval stage. Both the coupon retrieval and the tunnel inspection were performed with very low water clarity. The ROV Used two sonar heads, one recorded the cross section of the tunnel while the other scanned for features forward of the ROV during the inspection phase.

Corrosion is one of the important concerns across the world because it can affect water quality as well as damage the water carrying and purification equipment. To avoid this, different water monitoring techniques are used. At Cannon Water Technology, we provide corrosion monitoring coupon racks for corrosion monitoring in cooling water systems. Designed and developed by Cannon Water, these corrosion racks have been utilized for maximizing the value of aging water assets and minimizing the effects of corrosion.

Corrosion Coupon Rack Features Corrosion Coupon Rack, used for monitoring corrosion rates, scale formation and errosion of various alloy materials in cooling water systems. Available in PVC, CPVC, Carbon Steel and Stainless Steel, 3/4" or 1"...

What is Corrosion Monitoring and What Are Its Objectives?

Corrosion monitoring is a process performed to identify, access, and analyze the corrosion behavior of a system. Any corrosion monitoring is performed with two main objectives:

• To understand the operational condition of the equipment
• To understand the effect of different variables such as temperature, pH, water quality, and chemical treatment on different water systems

Using the right corrosion monitoring system enables users to meet these objectives, as well as achieve the following results:

• Identify the corrosion-related problems at different parts of the equipment and mitigate them effectively.
• Improve the life span of equipment, its components, structures, and process units.
• Minimize operating costs of the plant.
• Predict the maintenance needs of the equipment and design an effective maintenance program.

What Are Corrosion Coupon Racks and Corrosion Coupons?

The corrosion coupons are standard pre-weighed metal strips that are mounted on coupon racks. The coupon racks comprise several pipes and they are mainly used to estimate the metal corrosion rate of water systems like coolers. The coupons are weighed and exposed to water. Their weight is checked at regular intervals such as 60, 90, and 120 days to identify the rate of corrosion. They are available in various materials. At Cannon Water, we provide various types of coupons. You can choose between copper corrosion coupon, brass corrosion coupon, and carbon steel coupons.

Features of Corrosion Racks Provided by Cannon Water

The following features of corrosion coupon racks have contributed to their popularity with our clients.

• We provide standard coupon racks, which can be customized with one to six corrosion coupon holders. They come with inlet/outlet isolation valves.
• They can be equipped with PVC, CPVC, carbon steel, and stainless steel pipes of 3/4", and 1" diameter.
  • The PVC pipes are suited for most applications.
  • CPVC pipes are suited for applications that require moderately high temperatures.
  • Carbon steel and stainless steel pipes are ideal for applications where they would be exposed to high temperatures.
• The rack features a durable mounting frame and stainless steel safety chains that can hold the coupons in place.
• Our coupon racks are easy to install and feature quick-connect sample points.
• The racks can be customized with various optional features such as flow meters, Y-strainers, flow control valves, sample valves, and so on. The prices may vary depending on the customization.

Special Tips to Improve the Performance of Corrosion Racks

Corrosion coupon racks offer results based on different variables. Thus, it is important to install the rack such that it produces the most accurate results. The following pointers will be helpful in this case.

• Avoid touching the coupons with bare hands as any chemical or oil present on your palms may accelerate corrosion and alter the results.
• Ensure to maintain the flow of the rack at 3-5 feet per second. This is because flow rates below 3 will make the particulates rest on the coupons and the ones above it may erode metals like brass and copper.
• Arrange the coupons on the rack such that less noble materials such as carbon steel are mounted upstream followed by noble materials of higher-order like copper towards the downstream. This helps prevent copper ions from plating on the iron coupons and accelerating artificial corrosion rates.
• Avoid touching the coupons when they are in use and do not attempt to remove them until the testing period ends. This is because exposure to air may accelerate their corrosion rate.

If you have been facing the problem of corrosion in your aging cooling tower or water systems, then this coupon rack is the best option. Are you facing any other water treatment problems? Being at the forefront of water treatment and wastewater treatment technologies for a long time, we understand what solution works best for any situation. Feel free to discuss your water treatment requirements with our experts. We would be happy to help you.

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