What is a coupon rack for water treatment?

When metal meets moisture, you get rust. Everyone knows that, but rust is only the surface issue in this highly corrosive relationship. Simply put, water eats metal. Thats why your industrial water needs to be treated with a corrosion inhibitor. Even then, if you dont have the right chemical feed rates or the right formulation, you can eat away at costly metal components and end up having to replace them before their time.

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So how do you know if your treatment is actually working? A visual inspection would tell you, but critical heat-transfer surfaces are often hidden away inside your heating, cooling, and process systems, and cant be seen without a borescope or some major dismantling. Thats where corrosion coupons come in.

What are Corrosion Coupons?

No, these coupons wont give you a discount on your next purchase. Corrosion coupons are small strips of metal that represent the metal components contained in your buildings recirculating water systems. Each coupon strip is measured and pre-weighed. They are then placed in your treated water loop, typically in a coupon rack, to expose them to the conditions of the system for a period of 90 days. After 90 days, you can remove the coupons, visually check them for corrosion and send them to a lab to be cleaned, weighed, and analyzed. The weight loss in the coupon and exposure time will be translated to a corrosion rate in the system for that metal type. The results are a good indication of how the actual metal surfaces inside your systems are faring.

Corrosion coupon materials include stainless steel, copper/copper alloys, low carbon steel, galvanized steel, and aluminum. Its important to properly identify the metals used in your heating and cooling systems. For instance, if your open cooling loop flows across steel and copper, testing an aluminum coupon wont tell you anything useful.

How Do You Conduct the Test?

Coupons are held in a pipe system called a coupon rack, which is installed into your recirculating loop at a point after the water has cycled through your cooling or heating system. Within the rack, the most active metal is placed in the first position in the downstream flow of water. This is to prevent noble metals from depositing onto active metals and producing a false coupon reading.

Additionally, the broad face of each metal strip should be in a vertical orientation to reduce the accumulation of debris, which can likewise throw off test results.

Corrosion rates are measured in mils per year (MPY). To get the most accurate rating, coupons are exposed to treated water for 90 days. At that point, the coupons are removed, cleaned, and weighed to determine metal loss and corrosion rating.

Are Corrosion Coupons Worth the Effort?

Corrosion coupons are an easy and inexpensive way to protect your costly HVAC or process components. There is an upfront cost to install the rack, and the lab analyses may or may not be covered in your service contract (contact your water treatment provider if youre unsure) but these are minor expenses when compared to the cost of having to replace corroded equipment, or even to perform a cleaning.

Beyond that, a corrosion coupon rack puts one more set of eyes on your water treatment program, letting you see and measure the results youre getting from the dollars you already spend. It also allows your treatment professional to make necessary adjustments and stay ahead of the corrosion curve. Source water chemistry can change over time and require a different dosage of inhibitor. Adjusting other treatment chemicals can also impact corrosion. For instance, if a spike in microbial activity forces you to increase your oxidizing biocide feed, this may adversely affect your corrosion protection. Coupons are a tangible way to monitor the impact of these variables.

Understanding the Test Results

A coupons corrosion rate is based on metal loss over a designated time period. The coupons are carefully weighed and logged before and after to determine metal loss. Corrosive pitting is also quantified by measuring pitted surface area.

There are several factors that affect corrosion rate, including location, exposure time, pH, water temperature, coupon design/placement, flow velocity, and current water treatments.

Once evaluated, the technician will calculate the rate in mils per year. Each metal or alloy used has its own acceptable corrosion rates.

Stainless Steel

Evaporative Water Systems Closed Water Systems Acceptable <0.1 MPY <0.1 MPY Unacceptable >0.1 MPY >0.1 MPY

Copper and Copper Alloys

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Evaporative Water Systems Closed Water Systems Excellent <0.1 MPY 0.1 MPY Very Good 0.1-0.25 MPY 0.1-0.15 MPY Good 0.25-0.35 MPY 0.15-0.20 MPY Fair 0.35-0.5 MPY 0.2-0.3 MPY Poor 0.5-1.0 MPY 0.3-0.5 MPY Unacceptable >1.0 MPY 0.5 MPY

Low Carbon Steel

Evaporative Water Systems Closed Water Systems Excellent 1.0 MPY 0.2 MPY Very Good 1.0-3.0 MPY 0.2-0.3 MPY Good 3.0-5.0 MPY 0.3-0.5 MPY Fair 5.0-8.0 MPY 0.5-0.8 MPY Poor 8.0-10.0 MPY 0.8-1.0 MPY Unacceptable >10 MPY 1.0 MPY

Aluminum

Evaporative Water Systems Closed Water Systems Acceptable <0.2 MPY <0.2 MPY Marginal 0.2-0.25 MPY 0.2-0.25 MPY Unacceptable >0.25 MPY >0.25 MPY

Acceptable corrosion rates from the Association of Water Technologies.

I Know My Corrosion Rate. Now What?

If your corrosion rate comes back within an acceptable range, no action is needed. But dont forget to place new coupon strips in your rack. This is an ongoing tool that will help you monitor the health of your system components. A number of different variables can change over time, affecting the protection level of your treated water.

If your corrosion rate comes back above the acceptable range, you can work with your water treatment team to create or modify your plan of action. This may require some additional diagnostics to get to the root cause of the problem, but a knowledgeable water treatment professional should be able to get you back on course in short order.

If you would like more information about corrosion coupons or corrosion protection, dont hesitate to contact us. An experienced HOH Water Quality Engineer will be happy to answer your questions. And while youre at it, you can ask him or her about the latest automated technology that will give you an instantaneous corrosion reading.

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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