EXPERT TIP #36 – HMWPE vs. Halar/HMWPE CABLE INSULATION
From a system longevity standpoint, the selection of a proper anode cable insulation is important when installing impressed current anodes, most commonly cast iron, graphite and MMO. The following guide will help determine the best cable insulation solution for the application.
- HMWPE (High Molecular Weight Polyethylene) cable insulation is a flexible and durable cable insulation used very commonly in the cathodic protection industry. It is used for anodes, negative connections, test leads, bonds and more.
- Halar/HMWPE cable insulation is comprised of two separate or dual cable insulations. The inner or primary HalarTM insulation, or ECTFE (ethylene chlorotrifluoroethylene), is very tough and chemically resistant. The outer insulation is HMWPE, the same material described above. This dual cable insulation type is almost exclusively used for impressed current anodes for the reasons below.
Deciding which cable insulation to use for impressed current anodes depends on installation parameters. A single layer of HMWPE insulation is a good choice for anodes but is not chemically resistant. Therefore, the insulation can deteriorate when exposed to certain chemicals, such as chlorine gas, causing premature cable failure. Adding a primary layer of Halar provides a very chemically resistant protective layer to the copper cable. It is the best choice when significant chlorine gas is produced in the anode well and in contact with anode cable.
With impressed current anode systems, some amount of chlorine gas will be produced. The amount of gas depends on several factors, including the salinity of the soil/water and the level of DC current produced by the anodes. The more DC current generated by the anodes and the higher the salinity of the environment, the more chlorine is produced.
Determining the best type of cable insulation for a CP system is a bit of a guess. If the system designer knows their CP system is designed to provide high DC current outputs, Halar/HMWPE cable insulation is likely the best choice, albeit a bit more expensive. If the design calls for very low anode current outputs, then HMWPE may be suitable.
This is a simplified explanation. Other factors may affect the selection of the proper cable insulation and if needed, technical experts can help.
