Wired!

Wire's important in cathodic protection. We have the anode lead going from the anode to the pipe, the joint bonds to maintain electrical continuity, test leads, and etc. Stranded or solid, THHN, RHW, #14-#1/0 (pronounced "one ought"), odds are in the Denver warehouse, we've got it in stock.

The smaller gauge wires, as you can see, come in a variety of colors--the color coding is important and varies by system owner. We've even got the purple wire required for waste water systems.

In cathodic protection, larger gauged wires (#8 and larger) tend to require HMW-PE insulation, or high molecular-weight polyethylene insulation. This is a heavy duty, thick casing that can withstand additional soil stress. We have one customer who requires a dual-jacketed wire with an additional layer because gophers keep chewing through the HMW-PE. Those are some determined gophers!

HMW-PE is common for joint bond wires, impressed current anode lead wires, and anode header cables.

Packaged or bare?

Bare Anode Ingots

Last week was the Rocky Mountain Section of NACE's short course. It was the biggest turn out yet with over 300 people attending! It's a great opportunity to meet customers (and competitors), and learn more about this rusty world. Every year is a Basic CP course that goes over the basics of electrochemistry, and what the corrosion cycle is. The nugget I garnered this year has to do with sacrifical anodes. A question I always have to ask when someone orders a mag (or zinc) anode is, do you want that packaged or bare?

When we talk about anodes, we talk about the bare weight of the ingot. "I want a 17 pound mag anode," means, I want an anode with 17 pounds of magnesium. The ingot is then silver soldered for a strong connection between the lead wire and the bare metal. Some anodes--bare anodes--are then finished.

The pictures on the left show bare ingot dimensions, where
the picture on the right shows a cross-section of a packaged
anode.

For a packaged anode, the ingot is then surrounded by a backfill and a cloth bag. This adds a significant amount of weight (at least doubling it; a 17# anode becomes 50#). The backfill is a standard mix of 75% gypsum, 20% bentonite, and 5% sodium sulfate. Each part plays an important part:

• The gypsum helps maintain a constant resistance between the anode and the structure being protected.
• The bentonite (clay) helps retain moisture (the electrolyte) against the ingot to help make sure the ingot is what corrodes, not the metal structure.
• The sodium sulfate helps keep the ingot from passivation, where the metal forms a film to protect itself.

The packaging of an anode obviously adds to freight costs, and the cost of the anode goes up by about 33%, but the benefits of ensuring an anode is protecting the neighboring communities explains why every specification I've worked with requires packaging.

Exothermic welding - explosion!

Once the materials have been ordered, and your handsome UPS driver has brought the supplies, you should now be the proud owner of

• a graphite mold with handle (mold appropriate to pipe material and wire size; typically they include a flint gun to start the ignition),
• a box of 20 weld metal (aka "shots," with a package of metal disks), and
• for #12 wire some copper sleeves (so the welding doesn't actually break off the wire)

After clearing away a spot on the pipe with a wire brush, going through the coating and baring a 3"x3" square, you slip the sleeve onto the bared end of the wire and crimp it on. Then, holding it against the pipe you press the mold down onto it. Into the mold you place the steel disk, then tap the contents of a weld metal shot into the crucible; the weld material is layered with starting powder, which dumps out last. A few grains need to be reserved for when the mold is closed, then poured onto the top to give you an easy place for igniting with the flint gun. It's really that simple!

To make it easier/safer, Erico and Continental have "one-step" options. Both include an electronic igniter with a 6'-15' lead, so you can be further away from the actual weld. For Erico, you purchase the "Plus" version of the correct weld metal. These are easy to use because you can simply drop the cup into your mold, attach the lead, walk off, hit a button and in theory it all fires off.

For Continental (ThermOWeld), you use the same weld metal and purchase the ignition fuse. Setting up the weld metal as usual, you slide the fuse into the crucible, attach the electronic lead, hit the button, and the weld should fire off. I like this idea because even if the batteries in your electronic igniter give out, you can still move along with a flint gun. The change in the cups for Erico makes adjusting for a broken igniter more difficult.

ThermOWeld's electronic ignition in practice:

Exothermic welding - ordering questions

From test leads to bond cables to anode wires, there are a lot of instances when wires need to be permanently attached to a pipe/metal substructure. How do you do that? It's a process known as exothermic welding, sometimes just known as welding or cadwelding. This is not brazing, a topic for a later time.

When people call, the first question out of my mouth is, "Are you welding to steel or ductile iron?" Steel is more susceptible to the welding process, where ductile (DIP) and cast iron require more stubborn materials to get the wire welded.

The second question, "What size wire are you welding?" A follow up is, "are you using a sleeve?" Cadweld welders are specific to 1) the material of the pipe, 2) the size gap left for the wire being welded, and 3) sometimes curved for a more secure fit against the pipe. The size of wire, and potentially the sleeve, will alter the size gap in the graphite welder.

The third question is the size of the pipe. For smaller steel lines (3.5" and smaller), the molds are curved. For DIP and cast iron lines <24", the specific pipe sizes all have their own mold. For projects welding to multiple sizes, you can use a product called mold sealer that will help the hot weld metal keep from running out.

The main manufacturers we work with are Erico Cadweld and Continental Therm-O-Weld.

Test Station Assemblies

We put a lot of money into protecting our pipes. How do we know the coatings, joint bonds, flange isolation kits, anodes, etc., are all doing their jobs? We test these things. There's this magic number (-0.85 volt) in cathodic protection, that when epoxy, anodes, and the moon align, we should achieve perfect harmony for the pipes, and they will go on to live happily ever after. Periodically along a pipe, the pipe's owner will typically (required: gas, option: water, sewer) require test station boxes to help them determine if they are meeting that value. Too low, and the pipes are sick. Too high, and you could be damaging the coating.

A big part of what I do is look at drawings to determine the test station. There are variables (above-ground, below-ground, for instance), but typically it requires:

• A box with terminals (posts for attaching wires)
• Wires (running between the box and the pipe)
• Welding (a method of connecting the wires to the pipe)
• And a protective coating for the weld.

The box can be above-ground (mounted on a post) or flush-mounted (even with the ground). Denver Water in particular likes to use the Testox 917, a metal post-mounted option that is expandable from 1-10 terminals. Denver Water typically supplies the post for the 917, otherwise you would need: galvanized conduit, conduit straps, and a sturdy chunk of wood. Another option for a post-mounted test station is a polycarbonate nearly-indestructible plastic version that is actually pretty common, the red photo below by Tinker & Rasor. They come brightly colored, which means it is easy to identify a water line (blue) from a sewer line (purple) from a gas line (typically orange).

A lot of different wires feed into the test station. Typically there are 2 lead wires going between the test station and the pipe. Often in cathodic protection you will see twin sets of materials, as this is literally your pipe's insurance policy, and backups are essential. If the test station occurs where one pipe crosses another, you might have 2 sets (of 2) test leads, one in color A and another in color B so you can easily tell if both pipes are doing well. Other wires that might feed into the test station include: anode lead wires (which would utilize the previously-mentioned shunt), permanent reference electrode wires, or test leads that are on opposite sides of an isolated flange. Test stations can also be modified to act as coupon test stations, but that is a concept that requires additional research on my part and will be touched on later.

A good item to consider for the test station includes ring tongue compression lugs. These are part metal sleeve that encase the end of one wire, and a metal ring that loops onto the terminal (typically 1/4" diameter post in the test station), which eases removal for testing and etc.

The test station lead wires are welded onto the pipe, an exothermic process that includes PPE and explosions (aka: fun!). Up next!

What is a shunt?

Just had a great customer call in and ask a seemingly easy question: What is a shunt? Well, 3 office people later, I had to call in the NACE C. P. Specialist big gun to answer the question.

A shunt is a precision resistor that allows you to measure the amperage or current in a circuit by measuring the voltage drop across the shunt. A shunt is important because you can measure the current without breaking the circuit. Breaking the circuit is generally frowned upon (it's what protects the metal substructure!), and can be time consuming: instead of clipping your multimeter's alligator clamps onto the shunt, you need to remove the test leads from each of the terminals, connect them to the meter, then remove them from the meter and put them back on the test station. Repeat that 20x a day and tell me if it isn't worth a $5-$9 little instrument?

Ideally when selecting a shunt, you would choose one with the least amount of resistance; particularly for sacrificial systems you would want to choose a 0.01-ohm or 0.001-ohm resistance shunt. An impressed current system can handle the resistance better and a 0.1-ohm resistance shunt may be appropriate.

Cathodic what?

For over two years, now, I've been working in sales for a company that specializes in materials and engineering for cathodic protection. For those two years, people have asked me what I do, and when I tell them, I can actually see their eyes glaze over. Maybe I can just direct them to this blog post, now!

So, what is cathodic protection? Essentially it's an electrochemical process of protecting metal structures from corroding--mostly stopping rust on pipes, tanks, boats, etc.. I joke around that I'm superwoman, as in I help protect our nation from exploding pipes.

99% of the external protection system is completed by a good coating. The remaining 1% that gives complete protection is trickier, involving dissimilar metals, applying current, and so forth.

For that 99% of the protection, a good coating is what's essential. Coatings are relatively simple, but much like data entry, despite being simple it requires a high attention to detail and requires perfection every single time. For the most part, coatings include tapes, heat shrink sleeves, and epoxies.

For that 1% of the protection, you look at distances, soil conditions, and application.

Upon completing the coatings and electrical steps, there is a whole world of testing, analysis, and upkeep.

It has taken me two years to get a good grasp on what's what--not just the process, but the materials a person uses to the best advantage to protect people from potential disaster. My inner teacher and inner writer come together here, at Kate's Corrosion Corner, in an effort to educate other people coming into this industry based off my own experiences.