Compliance with Cathodic Protection
Written by: Brian Pottebaum, Director of Training Services
Corrosion is the gradual degradation of materials, specifically metal, by chemical reaction with its environment. Metallic corrosion can be mitigated or controlled, and this is sometimes referred to as cathodic protection. In addition to steel tanks and piping, all other metal components in direct contact with the ground or liquid that routinely contain fuel -- such as flexible connectors, pipe fittings, and submersible turbine pumps -- must be protected from corrosion.
What methods of corrosion or cathodic protection are there?
If the underground storage tank (UST) system was installed properly, all metal components are being cathodically protected in one of three ways: cathodic isolation, galvanic (sacrificial) anode system, or an impressed current system. All three of these systems are beneficial and simple to operate and manage.
Cathodic isolation prevents the metal components from being in contact with the corrosive environment like water or soil/backfill. Without the water or soil/backfill electrolyte, the corrosion cell is not complete, and corrosion is safely minimized or eliminated. This type of cathodic protection is generally used with metal pipe fittings and flexible connectors and is relatively maintenance free. Metallic components are isolated by wraps, boots, sumps, or simply being above the ground surface.
Galvanic (sacrificial) anode protection is a self-contained cathodic protection system. The anodes are attached directly to the tank or piping, and nearly everything is kept below the ground surface. In this type of installation, the metal has to be in contact with the soil/backfill or water to work properly. The anodes are engineered to protect the metallic structure they are attached to by corroding instead of that structure. One of the more common applications of this method is the STI-P3 tank. The anodes are fastened directly to the steel tank in the factory. Another common application of this method is on metal fittings below dispensers and at submersible pumps that are not contained, i.e. the “spike anode” installation. The anode is placed in the backfill or water and then attached to the metal fitting with a lead wire and clamp. Keep in mind that these anode additions must also be tested periodically, just like the STI-P3 tanks.
Impressed current protection systems require a little more management. With this type of installation, the tank system and anodes are below the ground surface, similar to the galvanic sacrificial system; however, the system is energized with electricity and the wiring runs from the structure being protected to the rectifier and back out to the anodes. The anodes are buried around the structures to be protected, and are also sacrificed instead of those protected structures. Inside the building, there is a rectifier control box that hangs on the wall and is usually located in the back room by the tank monitor. This box has a power indicator light (red/green) and usually several output gauges as well: hour meter, amp meter, and volt meter. It is essential that this rectifier is powered on and operational through the life of the structure it is protecting.
How do you know if your UST system is being protected from corrosion?
You must routinely inspect each accessible part of each protection method you are implementing, and, if you utilize protection by isolation, ensure that these components are free from contact with soil/backfill and liquid. This may include cleaning liquid and debris from piping sumps if observed during the inspection. Galvanic tank systems are installed below the surface, and in most cases do not have anything at the surface to inspect. However, if you have added galvanic spike anodes to a metal pipe fitting or flex connector, you should check each lead wire and clamp to make sure it has a good connection to the metal fitting. Also, check the anode to make sure it doesn’t appear depleted along with the condition of the component it is protecting. With the impressed current system, you should be recording all the rectifier output values (amps, volts, hours) every 30-60 days, as well as inspecting the anode wiring runs to ensure none of the wires are exposed to vehicle traffic. If any of these wires get damaged, part of your cathodic protection system will no longer operate. At most sites, wiring is installed through the concrete in a “saw cut”, being sealed with a packing and caulking material. The anode wiring should never be exposed to the surface at any part of the system. It is very important that the impressed current system always stay “on” and operational to adequately protect your UST system from corrosion.
How often do you need to have your system tested?
Both galvanic and impressed current systems require testing, or certification within 6 months of installation or repair and then recertification every 3 years thereafter. The spring season is the optimal time for testing due to the amount of ground moisture, since dry and frozen ground conditions can cause interference that will affect the test results. The certifications must be reported on an acceptable form, please note that some states have a prescribed form. Furthermore, the certifications must be conducted by a trained and knowledgeable technician; there are industry standards they must follow. The State of Iowa requires the individual to be trained and licensed before this work can be done in the state. Having the system certified is very important because these systems will wear out over time, and the sooner you correct the problem the less likely you are to have a major fuel release from your tank system. If your system fails the certification, you must notify the local regulatory department as well as your insurance provider immediately. From there, you will need to make arrangements with a cathodic protection technician to adjust the system to meet minimum industry standards.
What records do you need to keep?
If you are performing routine inspections of any isolated metallic components, spike anodes, or the impressed current wiring system, it is recommended that you keep a log or journal of the condition and maintenance at that time. The logs should be kept at the facility as they will be reviewed during a UST compliance inspection, along with the two most recent system certifications. Keeping all certifications is recommended as they may prove important during file review or system protection analysis. Impressed current systems also require periodic rectifier operation checks as described earlier. These logs must be maintained and available for review upon request. When you are recording these values, you should also analyze them. If any of the numbers have changed dramatically or the output gauge is displaying a “0”, you should contact your licensed tester to have the system evaluated further.
If you remember to follow the guidelines explained in this article, you should have very little trouble with metal corrosion in your underground tank system.