I’ve been a mechanical contractor for 30 years, but seldom have I encountered a situation like the one I found recently at a dairy plant in Ohio.
I had been called in to repair a piece of equipment that was tied into their ammonia pipe system. When we pulled off the insulation to get access to a coupling that would serve as our end point, we discovered some rust that we traced to one of the worst looking pipes I had ever seen. Pitted and brown, it clearly needed to be replaced—in fact, it looked as though it should have been addressed some time ago.
I asked the plant manager if he could give me more information about this section of pipe, hoping to find out when it was last inspected and what notes had been made.
Alas, he was unable to find the testing report he had received, but he told me Gamma Graphics Services (GGS) had examined the entire plant just three years prior. I had dealt with many of the GGS engineers in the past and found the quality of their work to be excellent, so it surprised me to think they would have missed something like this. A segment of pipe that appeared to be in such bad shape surely would have been detected.
I called Jim at GGS to see if he could provide some insight. He pulled a copy of the report and read to me the notes that had been made about this specific section. “We noted 7% wall loss, along with evidence of pitting and corrosion,” he said.
“But you didn’t recommend replacing them?” I asked.
“Well, no. That wasn’t necessary,” he replied.
Clearly, Jim didn’t realize how bad the condition of these pipes was. “I think you need to take a look at these pipes,” I said, and I e-mailed some images over to him.
Corroded pipe at dairy plant.
Same corroded pipe at dairy plant, cleaned.
Would you replace the pipes above if you discovered them in your plant?
“See, Jim?” I pressed, “Not only is it brown and covered in corrosion, but as you can see in the second photo, after we cleaned the pipe, the pitting is so significant you can see it from a few feet away! You have to admit, this needs to be replaced with new pipe.
Jim acknowledged, “No question, these pipes are ugly. But the presence of corrosion doesn’t necessarily equal wall loss significant enough to replace these pipes.”
He continued. “If we go solely by the eye test, you might as well throw out using non-destructive testing altogether. But you can’t do that. Had you not been at the plant to repair other parts of the system, the state of this pipe wouldn’t have raised any alarms, there was no visual indication there was a potential issue while it was wrapped in the insulation, right? You have to look at the data—and the data says that pipe is ok.”
Jim went on from there, noting that because of the change in the manufacturing process of pipe over the last 20 years, the existing, pitted old pipe might actually be more effective than the new pipe that we planned to install in its place.
“Even with the pitting, the remaining wall thickness on that pipe is more than you would have on a new section of pipe. If you simply cover that pipe in a protective gel and fix the breach in the vapor barrier, which you need to do anyway, you should see no additional corrosion on that section of pipe.“
There was a lot to consider here. Indeed, Jim was correct that any plant is going to do better with pipe that is more functional than it is beautiful. But it’s not always easy to convince a plant manager that some ugly segment like the one we had was actually more functional than a shiny new one. It would much simpler and safer to go with conventional thinking and just recommend replacing everything that looks corroded.
Once we got our hands on a new copy of the report and reviewed the results of testing three years prior, it was clear that at that time there were other parts of the plant that were a much higher priority than the 7% wall loss in this section.
For example, another section of pipe along this line was identified by the report happened to be the cause of corrosion on this section—the breach in the vapor barrier Jim was referring to. Since this had been resolved at the time of reporting, we coated the pipe, re-wrapped it insulation and salvaged this piece.
I learned a valuable lesson that day that has helped me save many of my customers from spending unnecessary time and money—piping is one book you can’t judge by its cover.
So look at the photo at the top of this piece one more time. Would you replace it?
The common answer is an emphatic “Yes!”
The correct answer is “No.”