EXPERT TIP #32 – MAKING EFFECTIVE CATHODIC PROTECTION CONNECTIONS TO A STRUCTURE

Background

During a typical cathodic protection (CP) field survey, the CP technician must make effective electrical connections to the structure under test and other metallic components.

Often, the technician will encounter an existing above-ground test station where a conductor (cable) is permanently attached to the structure under test and the other end is terminated to the test station panel. In this case, the connection to the structure is already made and is typically effective.

However, when a ground-level or “flush-mount” test station is encountered, the enclosure may be flooded or may have been at some point, presenting testing challenges. The technician will still need to connect directly to the structure via the test station cables, but connection points or cables are often corroded, and a sound electrical connection may be challenging. If this is the case, a poor structure connection can result in inaccurate CP readings. Therefore, the connections and cables must be cleaned before testing. Cleaning methods include a file, wire brush, sandpaper or similar to clean the connection points.

Making Good Electrical Connections

A test station is not required when a technician can make a direct electrical connection to the structure under test, such as an above-ground pipe or storage tank. However, some conditions can make it challenging to establish a good electrical connection for CP testing. Rust or corrosion deposits on a steel structure are good electrical insulators and, conversely, poor electrical conductors.

In cases where you need to obtain a CP reading on a rusty structure, it is imperative that you get through the corrosion layers and down to clean metal to obtain an accurate CP measurement.

Typical tools and techniques include:

• An “awl” is a tool with a steel shaft with a pointed end used for punching holes in soft materials, such as leather. The point of the awl can usually get through the rust deposit or protective coating. Once contact with the steel structure is made with the awl, the technician can use a test or “alligator” clip to connect the meter test wire to the awl shank.
  • Pros – An inexpensive solution that works well in most situations.
  • Cons – Damages the structure's protective coatings; the tool may dull quickly depending on the metal quality of the awl.
• The corner of a flat or square file can be used to cut through a rust deposit or protective coatings. It is best to use the file on an edge or small-diameter component of the structure, such as a flange. Once the connection to the structure is made with the file, the technician can again use a test or alligator clip to connect the meter test wire to the file in contact with the structure. This is the author’s favorite connection technique.
  
  • Pros – Effective and inexpensive, a well-made file will last years.
  • Cons - Damages the structure's protective coatings; the tool may dull quickly depending on the metal quality of the awl.
• If working in a marine environment, especially on offshore structures, multiple layers of surface corrosion can be encountered, making it a challenge to conduct testing. If the surface of the structure allows, use a pair of locking pliers or Vise Grips to obtain a connection. Do this by tightly clamping the pliers to the structure and then rotating the pliers back and forth to break through the layers of corrosion. When the pliers reach steel, remove the pliers, and clean away the corrosion particles on the pliers and the structure. Once clean, reattach the pliers back to the same clean structure location and clamp the pliers as tightly as possible. Once again, rotate the pliers to obtain a connection to bare metal. When done, leave the pliers locked to the structure and connect the meter test-lead wires to the pliers to get a CP reading.
• To connect a large gauge wire (#10 to # 6 AWG) to a structure for current testing, use the above locking plier method to clean a test location. When clean, clamp the cable to the structure with the jaws of the locking pliers.
• A “C-clamp” with the flat shoe removed from the tool and the threaded end sharpened to a point works well for current testing where you need to make a structure connection for an extended period. To prepare the C-clamp for the cable connection, drill a hole in the body of the clamp, install a bolt in the hole, and connect the cable to the C-clamp using a cable ring or fork terminal.
• There are many magnetic connecting tools available that may work for CP testing. Magnetic connections work best when the structure under test has clean and bright metal at the magnet contact area. Depending on the situation, magnets may have limited applications.
• Need a CP reading on a structure you cannot quite reach? Extension poles that painters use to get extra reach for a paint roller may help. In this case, you can clamp (use hose clamps) a flat or square file to the extension pole. Then, connect a test-lead cable to the file and your meter. This method works well for taking readings in a below-ground vault and eliminates confined space access issues. You can also find commercially available extension systems built especially for this requirement.