Introducing: Magnesium Anode Bags
SIGMA is proud to introduce our new Magnesium Anode Bags, which protect municipal underground water piping systems from corrosion through sacrificial cathodic protection. These bags consist of a magnesium alloy core, often packaged in a cloth or cotton bag, surrounded by a special backfill material (typically a mix of bentonite, gypsum, and other compounds) to enhance electrical conductivity in soil. The bag is connected to the protected structure via an insulated copper wire, usually 8 AWG with XLPE/PVC insulation, and is buried near the structure.
SIGMA is currently stocking 9, 17, 32, and 48-pound bags in our Denver location and these can be immediately shipped nationwide. Midwest Region Branch Manager Charlie Kyle explains why SIGMA started supplying this product: “We began developing and producing SIGMA’s Magnesium Anode Bags in response to a customer who was having difficulty sourcing the product. We understand the frustrations dealing with shortages and dealing with numerous vendors. Having to enter and send multiple purchase orders to multiple vendors while trying to keep freight costs in check is time consuming and can be expensive. SIGMA has always been committed to providing quality products and the convenience of “one stop shopping” to our customers via our extended range product lines and the anode bags fit nicely into this category. The need of a few brought forth the opportunity to not only to help them, but to also offer this item to other customers facing similar challenges across the country.”
How They Work
Electrochemical Process: Magnesium is more reactive than steel (the material commonly used in water pipes). When connected to the steel pipe, the magnesium anode corrodes preferentially, releasing electrons that flow to the pipe, polarizing it and preventing it from corroding. This process counteracts the natural electrochemical reactions that cause rust.
High Driving Voltage: Magnesium anodes have a high electromotive voltage (typically 1.5V or 1.7V for high-potential alloys), making them effective in high-resistivity soils (up to 10,000 ohm-cm), which are common in municipal environments.
Backfill Role: The backfill in the bag reduces soil resistance, improving current flow from the anode to the pipe, and helps maintain moisture around the anode for consistent performance.
Use in Municipal Underground Water Piping Systems
In municipal water systems, magnesium anode bags are used to protect buried steel or iron water mains and piping from corrosion, which can lead to leaks, pipe failure, and costly repairs. Here's how they are applied:
Installation:
Placement: Anodes are buried 15–20 feet from the pipeline (or closer in low-resistivity soils) to ensure even current distribution. They can be installed parallel or perpendicular to the pipe, depending on space and design.
Connection: The anode’s copper wire is connected to the pipe, often through a test station or connection box, allowing for monitoring of the anode’s current output.
Quantity: The number of anodes depends on pipe size, soil resistivity, and coating quality. For example, a single 17-lb anode bag may protect a small section of pipe (1–2 km), while larger systems require multiple anodes.
Backfill and Wetting: The anode is placed in a prepared borehole, surrounded by backfill, and wetted with water (especially in dry soils) to enhance conductivity before burial.
Applications:
Water Mains and Service Lines: Magnesium anodes are ideal for protecting water mains, service pipes to buildings, and fittings like valves or flanges in urban areas with high-resistivity soils or where other buried utilities are present.
Temporary Protection: They are often used during pipeline construction before an impressed current cathodic protection (ICCP) system is activated.
Hot Spots: Anodes are installed in areas with aggressive soil conditions or damaged pipe coatings to provide localized protection.
Monitoring:
Monitoring equipment, such as reference electrodes and steel coupons, is installed to measure the cathodic protection level and ensure the pipe’s potential is maintained above -0.85V (relative to a copper/copper sulfate electrode) for adequate protection.
After installation, anodes are left to operate for about three weeks to stabilize current output, followed by potential surveys to adjust current if needed.
Key Features and Considerations
Anode Types: Magnesium anodes come in standard (1.5V) and high-potential (1.7V) alloys, with the latter being more effective in high-resistivity soils. Common weights include 9 lb, 17 lb, and 32 lb, with 17-lb bags being typical for municipal applications.
Lifespan: Anode lifespan is typically up to 5 years, depending on soil conditions, current output, and environmental factors. Regular inspections are needed to assess remaining anode mass.
Standards: Anodes are manufactured to standards like ASTM B843 or GB/T 17731-2009, ensuring quality and performance.
Limitations: Magnesium anodes self-corrode faster than zinc or aluminum, limiting their lifespan, especially in low-resistivity soils (<10,000 ohm-cm). For very high-resistivity soils (>10,000 ohm-cm) or uncoated pipes, engineers should be consulted for custom designs.
Benefits:
Cost-Effective: Magnesium anodes are economical for small-to-medium current requirements, reducing the need for expensive impressed current systems in many cases.
Reduced Maintenance: By preventing corrosion, anodes extend the lifespan of water pipes, minimizing leaks and replacement costs.
Environmental Safety: Magnesium anodes are non-toxic and safe for potable water systems.
To learn more about SIGMA’s new magnesium anode bags, please contact your regional office: https://www.sigmaco.com/regional-teams.