Cathodic protection testing tools

In our last primer on cathodic protection, we covered the basic principles of cathodic protection systems, offered a discussion on the strengths and weaknesses of sacrificial and impressed current systems, and addressed stray currents. Like anything performing a job at all hours of the day, different components start to burn out.

Underground piping systems and propane tanks can suffer severe corrosion without proper maintenance. Without routine testing and maintenance checks, your underground systems can potentially become volatile. Remember, your underground systems are constantly giving off an electrical charge. In some instances your systems may have an external power source. If at any point you want to speak directly to a cathodic protection engineer to answer specific questions unique to your current project, feel free to reach out to us.

You should perform maintenance testing and servicing every two to four years. Ensuring optimum anode health is absolutely crucial in safeguarding the longevity of your underground cathodic protection system. The anodes in your system are working overtime to protect the main structure of your CP system. Every hour of every day those anodes are taking the brunt of corrosion damage, diverting oxidation from underground piping systems.

As a direct result, those sacrificial anodes need replacing, as they are in a constant state of decay. However, failing to maintain the integrity of the anodes within your CP underground system will cause complications and may foment irrevocable damage to the internal structure in need of protection. Watch Out! Remember to Check for: Before launching into your work, remember you may be entering an unintentionally hostile environment.

Be careful not to disturb them. Corrosionpedia Terms. Anodize This: The Brilliance of Anodizing. Top Corrosion Mitigation Technologies to Watch for in Soluble Salts and Coating Performance. Introduction to Electroplating Interview with Jane Debbrecht. Metallizing Why is Stainless Steel Corrosion Resistant? An Introduction to Hydrogen Embrittlement. An Intro to Pipeline Corrosion in Seawater.

Follow Connect with us. Sign up. Thank you for subscribing to our newsletter! Connect with us. Key Takeaways. Source: sylvar is licensed with CC BY 2. Share This Article. Senior cathodic protection engineer interested in all corrosion branches. This is referred to as an impressed current cathodic protection ICCP system. CP Systems protect infrastructure assets from corrosion. These structures include:. CP engineers can design systems for maximum life and ease of replacement. To be the most effective and economical, CP systems must be designed properly.

CP design is the scientific discipline involving:. Design engineers possessing the right expertise and knowledge of the structure to be protected from corrosion should perform all phases of system design.

On an unprotected pipeline, potential variations occur naturally. Wherever you go from a minor positive to a minor negative, current flows and galvanic pipeline corrosion will occur. Cathodic Protection CP is an electro-chemical process that slows or stops corrosion currents by applying DC current to a metal. When applied properly, CP stops the corrosion reaction from occurring to protect the integrity of metallic structures.

Cathodic protection works by placing an anode or anodes external devices in an electrolyte to create a circuit. Current flows from the anode through the electrolyte to the surface of the structure. Corrosion moves to the anode to stop further corrosion of the structure. An anode is one of the key components in a Cathodic Protection system. It is the component from which DC current will be discharge. It is the source of electrons in the CP system.

It is the component that is more negative relative to the structure being protected. The cathode is the structure being cathodically protected and is where current flows to after discharging from the anode. It is the component that is more positive relative to the structure being protected. As the cathode receives electrons, it becomes polarized, or more electrically negative.

An electrolyte, for cathodic protection purposes, is an environment around the cathode structure being protected that is electrically conductive enough to allow current to flow from the anode to the cathode. The anode and cathode must both be in this environment that allows cathodic protection current to flow from the anode to the cathode.

In some cases, there might be multiple electrolyte layers or types through which the current might flow. Several buried or submerged structures require or can benefit from the proper application of cathodic protection. This includes all oil and gas steel pipelines, steel and ductile iron water piping systems, the tank bottoms on large diameter above ground storage tanks, ductile iron fire hydrant risers, and HVAC transmission tower guide wire anchors are examples of structures that are commonly protected using CP.

For marine structures, cathodic protection is commonly applied to steel pilings and sheet pile walls on a wide range marine near shore structures. Additionally, ships and other large vessels commonly use CP. These are some of the common CP applications but there are numerous others as well. This shift is in potential is called polarization. The amount of polarization is a measure of the effectiveness of the cathodic protection current and once the polarization is sufficient, the structure is deemed cathodically protected.

The time it takes to fully polarize a structure can vary depending on the structure and its environment but in some cases a structure can take weeks to fully polarize. When the cathodic protection current stops flowing from the anode to the structure being cathodically protected, the polarized structure will begin to depolarize.

The rate of depolarization can vary depending on the structure and its environment. There are two basic criteria per NACE International standards that can be used to confirm that the structure is considered cathodically protected. The first criteria is mV of polarization — this is a pretty simple criteria to apply in that you measure the potential of the structure without any CP being applied native potential and then after applying cathodic protection for a sufficient period of time for polarization, measure the potential again and if the potential difference is greater than mV — this is commonly known as the mV shift criteria.

The other criteria is the mV Off potential criteria. In this case, it is not necessary that there be a native potential to use as a baseline — this criteria simply requires that the potential of the structure be more negative than mV after accounting for all current sources by turning them off for an instant. Instant off refers to the process of taking measurements at the instant that the power is turned off on an impressed current CP system.

When there are multiple current sources, they all need to be turned off simultaneously using interrupters that are synchronized. The purpose of turning all the current sources off is to eliminate the IR drops in the circuit. When attempting to measure the level of polarization, it is important to eliminate the IR drops in the circuit that are the result of current flow creating these IR drops.

By instantaneously turning the current off these IR drop readings are immediately reduced to zero because the current I is now zero. This means that the polarization being measured immediately after the current is turned off is the true polarization current.

Timing is critical because with the current turned off the structure will immediately depolarize and the polarization potential will begin to decay.

The goal of instant off polarization readings is to catch the polarization level as the power is turned off and before the depolarization process begins.

Anodes can be broken down into two basic anode types — galvanic anodes frequently referred to as sacrificial anodes and impressed current anodes. The galvanic series anodes use the natural voltage differential between the anode and the structure to drive current off the anode and to the structure.

The impressed current anodes use an external power supply to drive current off the anode and to the structure. Galvanic anodes are basically metal castings that do not utilize an external power supply to drive current.

They rely on the natural potential differences between the two metals to drive the cathodic protection current. There are three primary types of galvanic anodes. Magnesium which is the most active of the galvanic anodes and is used primarily in soil applications.

Zinc which is les active a metal and is commonly used in low resistivity soils and brackish water. Zinc is also the primary metal in galvanized applications. And finally, Aluminum which is used primarily in seawater applications. Note that galvanic anodes are often call sacrificial anodes because they are consumed during the CP reaction — this is also true of many impressed current anodes as well.

The term sacrificial implies no power supply and the use of anodes these anodes that are more active than the structure being protected. There are two major advantages of galvanic anode systems.