InterMoor completes largest suction pile ever

Final pile

We interviewed Michael Covello, Project Manager in charge of managing the project side of the pile fabrication. We extend our congratulations to everyone involved in this project, and particularly our fabrication crew in Morgan City, Louisiana, whose dedication and professionalism were paramount in the success of this challenging endeavor.

Q: Can you tell us a little about the Monster Pile?

A: Well it’s a suction pile. we make a lot of those and it will be installed by our client as a foundation for a massive pump that is currently being constructed in Norway.

Q: And what makes this pile different from other piles we may have done in the past?

A: In a word, size. The Monster pile is 32ft. in diameter and 55 ft. long That will make it, to anyone’s recollection, the largest pile ever installed in the Gulf of Mexico.

Q: Alright 32’x 55’ That doesn’t mean much to the average reader. Perhaps you could provide some comparisons?

A: OK, I guess first you need to understand how piles are made and what they do. Basically, we roll steel plates into cans, and then weld them together. The top can has a plate on the end, so it becomes a single open ended tube. Once the cans are assembled, you just add lifting padeyes, and other equipment that it needs to do its job. After it’s finished, we load it onto a vessel, where it gets over boarded and, lowered to the seafloor. As you start pumping water out of it. the suction draws the pile into the seabed. Once installed, it serves as a stable platform.

Most piles we fabricate are around 12’ to 16’ diameter. When the component cans are this size, they are fairly easy to move around and weld together. The largest pile we had built prior to this was 24’ diameter and that pretty much stretched our fabrication methodology as far as it could go.

With a 32’ diameter pile, the big challenge is component mass. At that size, individual pieces will collapse or deform under their own weight. Because of this, every component had to be engineered to be handled, so that it could be assembled without bending.

Rolling can plate
Rolling can plate

To complicate matters, there are a lot more steps to create a can assembly. In a normal sized pile, you roll a plate in one piece. You weld the ends together and you have a can. The Monster Pile was too big to fit a can that size in the building Additionally, steel can only be purchased in lengths around 40 feet long. To accommodate this, we needed to roll 3 plates into 1/3 can sections. We created a custom fixture to align the sections and keep them round as we welded them together. Then we had to add temporary stiffeners to keep it round while moving them. Like I said, everything needed to be analyzed to ensure we would not overstress the parts before they were assembled into their final configuration.

Finally, we had to modify our welding stations to fit the size of the pile. A standard subarc station goes up about 25 feet. Ours had to be elevated to join metal 32 feet in the air. This was managed by building very stiff towers to mount them on so that they would not wobble and allow discontinuities in the weld bead.

Checking Roundness
Checking Roundness

Q: So, which of those would you say was the most difficult challenge?

A: Probably none of the above. All those things I mentioned, we saw them coming and planned for them. What we did not see coming was the impact of the environment on our precision. Normally, a fabricated product has tolerances of around +/- 1/8” and can be checked with common inspection tools like a tape measure or square. There is nothing wrong with that, it has been the standard way of doing things in our industry forever. Engineers know this, and design accordingly.

On this pile however, we had very strict interface requirements with the pump that would sit on it. All the interface points needed to be located much more precisely and verified with a total station. If you have never seen a total station, it is a very clever transit that includes a laser range finder and a computer. It will tell you not only point to point distances, but will record an alignment map of all your key features relative to each other. Deviations that may not be perceptible to an inspector become glaring with a total station.

We brought our sister company UTEC in to help us with the total station. One of the things they picked up on right away was inconsistencies in their measurements. We sat down and talked about it together for a while and finally figured out that the problem was that we were building it outdoors in Southern Louisiana with temperatures ranging from 40°F degrees to 90°F degrees. Compounding this further, was the change in steel temperature by as much as 70°F when placed in the sun vs the shade.

Steel has a coefficient of thermal expansion. Every engineer knows this, and when dealing with common sized weldments it is negligible, but when your weldment is 32’ across, that expansion will stretch your material way beyond those tight tolerances.

Once we understood what was happening, we started monitoring temperature and performing our measurements when the steel was at or near a nominal temperature. UTEC was then able to survey everything in real time, allowing us to locate the components right where they needed to be.

Q: It sounds like the team was able to come up with solutions for all your problems and it worked out really well. Would you agree?

A: I would, and I would also say that the ability to do that comes from our culture. We have meticulous welders, who are managed by an outstanding team that really makes sure they have the tools to do their job well. We also have engineers that actually communicate with the fab shop on a daily basis, and a senior management team that supports us if we run into problems outside the norm. You couple that with a good client relationship where they understand and trust you, and the job just tends to work out.

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