How do you pull a stuck 6-inch diameter hardened steel pivot pin out of a million-pound navigational lock gate when you are out in the field?
This is the kind of challenge we live for at Altman Browning.
Most days, I work at our office doing design and analysis, but sometimes, as the Engineer of Record on a project, I’m required to be on the job site. Often, the site is a dam on the Columbia River where we’re helping to repair or upgrade the existing dam machinery. As you might imagine, this machinery is enormous and has been in continuous, hard service non-stop for 30 to 50 years.
On a recent project, we worked with a contractor on a dam’s navigational lock gate (the steel structure that holds back the water in the lock, allowing barge traffic to pass through the dam). The project included replacing the lower pivot point, called the “pintle.”
At Altman Browning, our piece of the project was to develop the jacking plan. The jacking plan is a documented step-by-step process for safely lifting and transporting the gates so the repairs can take place. The plan includes specifying the equipment to be used, the placement of the jacks, and the resulting stresses on the gates and lock foundations.
To understand what was at stake, you have to imagine how massive these lock gates are. Each gate weighs nearly a million pounds. They are 50 feet wide and 140 feet tall. One face is flat and the other is curved resulting in the top surface ranging from 2 feet wide at the ends to 10 feet wide at the center. It is a narrow strip of steel to stand on when you are 140 feet up in the air. Replacing the pintle is the equivalent of picking up a 14-story building, moving it 10 feet sideways and then putting it back in the original spot when the work is complete.
Along with all the challenges, the schedule was extremely tight. River commerce cannot be delayed, so the navigational locks are only closed for a short time in the winter and have to be reopened on time.
A Smooth Start Held Up by a Stubborn Part
To remove the pintle, we engineered a gate support system. The support system is a two-axis trolley system. The trolley supports the top of the gate when the bottom is lifted and slid sideways. Our solution was innovative and had not been employed before. We knew the physics of our design were solid but the rigging company crew was skeptical that the system would function correctly. We were challenged on all our assumptions and calculations throughout the review process.
If we were wrong it could result in injury (something that has NEVER happened as the result of one of our designs), or damage to the gate, which would result in delaying reopening the navigational locks.
With stakes that high, you bet we were there to monitor things during the jacking and sliding of the gates. Being out on a job site, especially with a project of this magnitude, is exhilarating. The millwrights and steel workers are amazing to watch. Well-trained and professional, they tackle the work with a can-do attitude in a tough, dangerous environment.
I watched as the gate support pins were pulled and the lock gate was supported by our frame system tied to the lock wall. Done. Perfect. Everything according to plan. All they had left to do was pull the remaining gate hydraulic operator pin and the gate, supported by our system was free to be moved.
And then it happened. Or rather, didn’t happen. The hydraulic operator pin on the gate wouldn’t budge. It was seized in place.
When a 300-ton Hydraulic Ram isn’t Enough
The seized pin was made of hardened steel, six inches in diameter and 16 inches long. I watched the millwrights apply all the jacking pressure they could muster. No movement. Not even a 300-ton hydraulic ram could not pull it out. Thirty years of service in outside conditions had taken their toll.
What could we do?
It was getting late in the day. We were getting behind schedule. We were hours from any city. The foreman was looking for direction. I knew to continue to try pulling the pin was futile. I suggested they “lance and freeze” the pin. After a quick discussion, the team agreed this was the best approach since the pin was already unsalvageable. The only other option was to try to drill a large hole down the length of the pin. However, with the tools at hand this would have taken an entire day. A day we did not have.
Using an oxygen lance (a demolition device typically used for quickly cutting thick steel plate), they bored a hole through the end of the pin and down the middle of its entire length in less than an hour.
This was not a typical use for an oxygen lance but we all agreed it was our best bet. Some of the crew had done it before, others had not. Having been around this before, I was able to advise them on the technique to use and the dangers associated with the process. By the way, have you seen one of these things in action? It is a steel tube about a half inch in diameter and 3 feet long filled with thermite. When you light it off it looks like a cross between a giant sparkler and a Jedi light saber. Potentially dangerous. But, boy, will it ever get the job done. When they lit the lance and started boring the hole in the pin it looked like a mini-volcano erupted on the end of it. Molten slag spewed out of the hole and ran like a river of molten slag onto the top of the gate. Amazing to experience.
Once the hole was bored, they poured a stream of liquid nitrogen into it in order to chill the pin, which shrank enough to allow the hydraulic ram to finally pull it out.
And let me tell you, when you have guys working on an ice covered, narrow strip of steel 14 stories up in the air in near-zero temperatures burning a hole in a pin holding a million-pound gate, it is nothing short of awe inspiring.
Showing the Next Generation How it’s Done
In the end, the engineering of our system was solid and the gate lifting and sliding went off without a hitch. I appreciated getting to be part of the team, providing thinking-on-your-feet transfer of knowledge that comes with the gray hair.
Best of all, I was able to include two of our junior engineers in the trip, and they got to experience the magnitude of the projects these “men of steel” take on every day. Eventually our newbies will be the gray-haired engineers giving advice to the steel workers on a job site. Maybe even replacing the very same components on that very same dam. You just never know.
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How do you pull a stuck 6-inch diameter hardened steel pivot pin out of a million-pound navigational lock gate when you are out in the field? This is the kind of challenge we live for at Altman Browning. Most days, I work at our office doing de...