The Adventures of Duke Waters: Chapter 4

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Municipal butterfly valves are built in accordance with American Water Works Association standard C504, which requires that every valve be tested to its full rating, 150 psig. The specs on this project indicated an operating pressure of only 75 psig, so, again, there should not be a problem. But because I had to fly in from a wintery Chicago, who can complain about a trip to Arizona?

I was escorted by Chon, the system engineer, to the piping gallery where I noticed miles of shiny new pipe. I asked, “Chon, what’s up with all the fancy pipe?”

He explained: “We employ ultraviolet light (UV) disinfection technology, so the inside of the pipe needs to be stainless steel.”

“I see,” I said and dragged my toolbox over to one of the 12-inch valves for a closer look.

Chon watched me shut and unbolt one of the valves and hoist it out of the pipe with the overhead crane. The unbolting went smoothly because the contractor used all stainless-steel bolts and stiff compressed fiber gaskets that did not stick to the pipe flanges, only the valve.

Looking at the valve, I said, “Chon, holy crap. It looks like this valve has been in service for 20 years. The edge of the disc is corroded away and the seat is barely still attached to it.”

Chon said, “That’s weird. I assure you that these were installed earlier this year.”

“This is really odd. The valve is coated with a high-service epoxy coating intended to last 50 years, yet all of the machined surfaces adjacent to the coating are toast.”

“You’re right, no wonder these valves leak,” Chon said.

I inquired, “Do you run sulfuric acid through these valves or something?”

“Of course not, it is just wastewater effluent.”

“Do they by chance operate at a temperature above 200°F?” I asked.

“No, just typical Arizona ambient temperatures,” he replied.

Without showing my frustration, I said, “Well then, to be honest, I can’t explain the condition of these valves and need to talk to a friend of mine about it and then we’ll get together in the morning to discuss it.”

I ran back to my hotel room, put my feet up and dialed my secret weapon, Duke Waters. If anybody had run across a problem like this, it would be that old semi-retired, freelance engineer Duke.

Duke was in for a change, so I explained my problem. “I’m in Tempe and have a couple dozen relatively new 12-inch, run-of-the-mill AWWA butterfly valves in wastewater effluent service that look like they are 20 years old. How can that be?”

Without hesitation, Duke said, “Johnny B, have you ever heard of galvanic corrosion?”

“Nope,” I sheepishly replied.

“I’ll bet your valves are being used as isolation in a UV disinfection system and the pipes are stainless steel.”

“Holy crap, you are exactly right. How did you know?”

Duke said, “The same thing happened to me on some check valves a few years ago. The valves lasted only about a year in service.”

“So what did you do?” I asked.

“First, we need to get you to understand the principle of galvanic corrosion and then we can talk about solutions. I am going to text you a diagram and then explain it to you.”

Duke explained, “Metals have varying propensities of giving up electrons and those that are very willing to corrode, such as iron, are designated as low on the galvanic series, or anodic. Metals that do not want to corrode, such as tin or stainless steel, are called cathodic and basically want to suck the electrons out of the anode when in physical contact and immersed in a conductive solution such as wastewater. Johnny, as shown in the diagram, you basically have a battery cell going on in the pipe and your iron valve is being eaten alive by the adjoining stainless-steel pipe.”

“It sounds like they should have bought a stainless-steel valve,” I offered.

Duke went on. “You are absolutely correct, but that is not always practical. The same thing occurs in your house where iron pipe is joined to copper pipe. Plumbers use a special insulated fitting so that the two metals never touch and the battery cell is not created.”

“That makes sense,” I said. “But I have a fiber gasket between the valve ends and the pipe, so isn’t my valve insulated?”

“Almost,” Duke said. “Unfortunately, the metal contact is completed by the flange bolts.”

“I don’t think I can buy plastic bolts strong enough, so what am I to do?”

Duke explained, “They make flange insulating kits that provide a plastic sleeve around the bolts and plastic washers for under the bolt heads and the nuts. That breaks the metal connection but you may need bigger bolt holes to pull it off.”

I thought for a minute and said, “That sounds more economical than buying new stainless-steel valves.”

Duke concluded, “I typically leave it up to the owner because in this case, it looks like you are buying new valves anyway.”

“That makes sense,” I said. “I can’t thank you enough for the lesson on galvanic corrosion.

“You bet,” said Duke, “and don’t forget to include my invoice in the price of the new valves.”

“Roger that. See you on the links.”

Up next in the series: While out playing golf Duke and Johnny B notice the course’s irrigation system acting up and offer a solution.

John V. Ballun, president and CEO of Val-Matic Valve, is a regular contributor to VALVE Magazine.