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.
Classification of Corrosion Rates for Open Recirculating Cooling Water Systems
(Corrosion Rates, mpy)
| Description | Carbon Steel | Copper Alloys |
| Negligible or Excellent | Less than or equal to 1 |
Less than or equal to 0.1 |
| Mild or Very Good | 1 to 3 | 0.1 to 0.25 |
| Good | 3 to 5 | 0.25 to 0.35 |
| Moderate to Fair | 5 to 8 | 0.35 to 0.5 |
| Poor | 8 to 10 | 0.5 to 1 |
| Very Poor to Severe | >10 | >1 |
Classification of Corrosion Rates for Closed Recirculating Cooling Water Systems
(Corrosion Rates, mpy)
| Description | Carbon Steel | Copper Alloys |
| Excellent | Less than or equal to 0.2 | Less than or equal to 0.1 |
| Good | 0.2 to 0.5 | 0.1 to 0.25 |
| Moderate | 0.5 to 0.8 | 0.25 to 0.35 |
| Poor | 0.8 to 1 | 0.35 to 0.5 |
| Very Poor to Severe | Greater than or equal to 1 | Greater than or equal to 0.5 |
Source: Bennett P. Boffardi, Ph.D., FNACE. "Standards for Corrosion Rates", AWT Analyst, Spring 2000
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.
Why Install a Corrosion Coupon Rack?
Installing a corrosion coupon rack is one of the most cost-effective and reliable ways to monitor corrosion in water treatment systems. By exposing metal coupons to the same water conditions as your piping, these racks act as corrosion monitoring stations, allowing you to measure the rate of metal loss over time. This helps you:
- Detect early signs of corrosion before system failure or costly repairs occur.
- Validate the effectiveness of your water treatment program, including chemical dosing and filtration.
- Ensure compliance with industry-standard corrosion coupon testing procedures.
- Improve asset longevity by making informed decisions on maintenance and system adjustments.
Coupon Rack Installation Tips for Corrosion Monitoring
For accurate results, the proper installation of corrosion coupon racks is critical. The following are some essential tips to ensure correct installation and long-term performance.
- Install in a representative flow area: Place the corrosion coupon rack where it receives a consistent and representative flow of system water, typically in a bypass line or side-stream. This simulates real-world conditions experienced by your piping system.
- Follow corrosion coupon standards: Ensure coupon positioning, flow rate, and exposure time align with industry-recognized corrosion coupon standards. This guarantees that your corrosion data is valid and actionable.
- Maintain laminar flow: Avoid turbulent water flow through the corrosion test coupon rack. Laminar flow promotes uniform corrosion and accurate measurement.
- Use the right coupon material: Match the coupon material to the piping or system material. This ensures your corrosion monitoring station reflects true system conditions.
- Protect from environmental contaminants: Keep the installation area clean and dry. Contaminants can distort results and lead to incorrect conclusions about corrosion rates.
- Label and log everything: Each coupon should be clearly labeled with the date of installation and type of material. Maintain records as required by corrosion coupon standards for long-term tracking.
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.
Materials Used in Corrosion Monitoring Coupons
According to widely accepted corrosion coupon standards, coupons must be made from metals that match or closely resemble the piping materials in your system. Below are the most commonly used materials in corrosion monitoring coupons.
- Mild steel: It is widely applicable in industrial water systems, cooling towers, and closed loops, making it a standard choice for evaluating corrosion rates and the effectiveness of treatment programs.
- Copper and copper alloys. It is used in corrosion monitoring stations, wherein the system contains copper piping or components exposed to or submerged in water. These coupons help track corrosion specific to copper-based materials, which is important in potable water systems, HVAC applications, and closed-loop chillers.
- Stainless steel (304, 316): It is used in systems where stainless steel is the primary material. These are ideal for high-purity or corrosive environments and help identify issues such as pitting or crevice corrosion that may not be visible with other metals.
- Brass: Brass coupons are selected for systems that include brass fittings or mixed-metal piping. These help the monitor for problems such as dezincification, which can compromise system performance over time.
- Aluminum: It is used in specialty systems that incorporate aluminum components. Aluminum coupons provide valuable data in systems where lightweight, non-ferrous materials are part of the construction. This ensures the corrosion monitoring station delivers relevant results.
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.
Frequently Asked Questions (FAQs)
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How do I ensure compliance with corrosion coupon standards during coupon rack installation?
To meet recognized corrosion coupon standards, it’s critical to control flow rate, exposure duration, and coupon positioning. Flow should be laminar and representative of system conditions. Coupons must be installed clean, labeled properly, and removed within the specified timeframe for accurate analysis.
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What factors influence the corrosion rate readings from a coupon rack?
Several factors impact corrosion readings, including water chemistry, flow velocity, temperature, and microbiological activity. Improper installation or using the wrong coupon material can lead to misleading results.
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How frequently should corrosion coupons be replaced or evaluated?
The evaluation schedule depends on the system type and operational conditions. But a typical monitoring cycle lasts between 30 and 90 days. Coupons should be analyzed at regular intervals to track long-term trends, validate chemical treatment, and maintain reliable corrosion monitoring station data.