Cathodic protection is a term we hear often as Piping Designers. However, as much as it is a simple topic, it can also be very complicated depending on how far you want to reach into the details of the materials science side of things. However, looking at it through the eyes of a Piping Designer, there's only so much you need to know. You need to know how to identify it on a P&ID, you need to know what components to model in CADWorx or whichever modeling software you are using, and you need to know how to identify a cathodically protected pipeline or tank when you are in the field on an as-build.
So what is Cathodic Protection? Cathodic Protection is an electrochemical corrosion control technique commonly used with underground piping and storage tanks. Some examples include above ground storage tanks (bottom of tank), the internal surfaces of water storage tanks, heat exchangers, and other equipment subjected to the environment. For most piping designers, especially those who work for EPC's in oil and gas, you will most often be dealing with pipelines and underground tanks.
So what is Cathodic Protection? Cathodic Protection is an electrochemical corrosion control technique commonly used with underground piping and storage tanks. Some examples include above ground storage tanks (bottom of tank), the internal surfaces of water storage tanks, heat exchangers, and other equipment subjected to the environment. For most piping designers, especially those who work for EPC's in oil and gas, you will most often be dealing with pipelines and underground tanks.
Cathodic Protection only applies to metals, and most metals that are in contact with an aqueous environment (dirt/earth) can be cathodically protected. Cathodic protection involves the use of sacrificial metals connected to the piping or equipment which are more easily corroded, hence the term "sacrificial". The connected sacrificial metal acts as the anode in an electrochemical cell. Common anode materials (sacrificial metals) are magnesium, zinc, and aluminum.
Side note: A few types of anodes are: stand off, flush mounted, and bracelet. You may hear these terms from time to time. Standoff has the anode situated near but not on the pipe, and connected to it with arms/brackets, which keeps the sacrificial anode off of the pipe. Flush mount is directly on the pipe, and bracelet is wrapped around the pipe.
Did you know that cathodic protection is considered a secondary level of protection? The first and primary form of protecting a pipe or pipeline from corrosion is with the pipe coating. This typically means yellow jacket (YJ) or similar, or fusion bond epoxy powder coating (FBE). When dealing with off-shore pipelines the coating becomes a lot more complicated with multiple layers of coatings involved.
If you are looking at a P&ID, how do you even know if the pipeline is cathodically protected, or intended to be? In general, the presence of isolation kits is a dead give away, as these are mandatory components in a cathodic protection system. If you want to know more, check out this post on isolation kits. Another place to check is the notes section on the P&ID, which in some cases my list the requirement.
If you are in the field on an as-build, refer to this post for how to identify an isolation kit in the field: isolation kits.
If you are modelling a pipeline riser or underground tank, your flanges will need isolation kits instead of a regular gasket. So when you insert a flange mating up to the nozzle on the tank, for example, you must ensure that an isolation kit is there instead of a gasket. If you don't have that component in your list, ask your CAD Manager/Administrator to add the component, and confirm with your client specs what to use. If it's a pipeline you are modelling, it's often the first flange above ground where the isolation kit is found, but refer to your P&ID first and model it exactly where the P&ID indicates. You should never model BEFORE you have a P&ID, so it should be there! If it isn't there, ask your Project Manager if it should be or not. It's all about being proactive and showing due diligence. Now get out there and show them who the best designer is!
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