COLUMN INSERT PLATE REPAIR

[jhb2011]

I need to replace the damaged pinholes on a jack up rig leg column. Im thinking removing the affected area and replacing it with new plate. I can't seem to find any information on the proper way to perform the procedure. For example I want to find out how long and wide the insert plate has to be. Can someone help me out with any procedures????

 

[dhengr]

Jhb2011:
There are potentially several different kinds of pin holes on that piece of pipe, you must explain. Provide a couple sketches. How does this thing work, what does it fit into or interact with? Show sizes, loads/forces and dimensions, etc., so we have an idea of proportions, etc. What are the various materials? Not everyone knows what a jack up rig leg column is or how it works. Nor do we know which is the top and bottom of that column. These are all important details or considerations for someone, even with an experienced eye, to start to understand your problem.

I assume that the outside dia. has to be maintained in the repair. I assume the top and bottom rectangular holes are o.k. and that the middle hole has been warn to that upper key-hole shape, and must be replaced. I would use a round cut-out shape, because square corners on a repair like this tend to be stress raisers and crack starters. I would cut the replacement out of a piece of pipe with the same O.D., but with a thicker wall; then I would machine the pin hole in it. The repair could be square or rectangular, but with generously radiused corners. You should have some idea of what caused this deformation of the hole so that your repair addresses this and prevents it in the future. You will have to clean up the pipe around the weld area, and I think you could nibble a bevel on the pipe so you left a land of only about 1/16 - 1/8". I assume you can’t get inside to weld the backside. So, you may have to live with a partial groove weld, without using considerably more detailing.

 

[jhb2011]

Thanks for your response dhengr. The column has 4 holes located horizontally around the column and are spaced 6 ft vertically. When arriving at location the legs are jacked down to the seafloor then the rig is raised entirely above the water. They use pins to lock into the holes. This rig was moved over seas by a ship (don't really know where), but in the process the holes were damaged by the pins. The materials vary from is ABS EH, CS and 1 1/2" thick. I attached some sketches to give you a better idea.

 

[jhb2011]

Here is another Sketch.

 

[dhengr]

Jhb2011:
This is a first class example of where a photo without any scale reference can be really misleading. Did you take that picture from an airplane? There isn’t anything about your photo which suggests 11' O.D. or 1.5" wall thickness. And, one wouldn’t imagine that the pin holes are 6' o/c vertically, and 12" high by 20" wide, although I can see a pin hole on the opposite side through the bottom hole. Once some scale is established, the proportions do seem to make sense. This should be a lesson to everyone here, how deceptive a photo and a few word description (your OP) can be without some sketches or means of scaling.

With that O.D., you can certainly get inside the leg to weld from both sides. You will have to pin down the various materials so you can establish proper welding procedures and processes. I would want to know more about what caused the damage and deformation in transit. What on the pins is 14.5" wide, and what is its condition? And, where those legs down in the water, aboard ship, and dragged around the world that way, wave action and all? And, you have to know what the normal working loads on the pins, the pin holes and the legs are so that you can check your welding stresses. You will have vertical loads (up or down, say 1 unit gravity downward) and lateral loads (any direction) on the leg; and that combination may well cause a pin load greater than 1 unit, on one pin. Maybe even a moment on pins across from each other with one pin at 1.4 units and the other at -.4 units, or some such; someone has to determine these load numbers, maybe from the original design calc. file. I think I understand the shape of the pin holes; the top and bottom are flat since they are the primary pin bearing surfaces; the sides need some bearing, but are cut out to ease pin insertion; the complex corner shaping is for corner stress raiser relief, similar to my first post comments about corners. I don’t see the stiffener plate behind and above the damage area, what’s that about? The 16" wide trapezoidal doubler pl. undoubtedly relates to the max. and normal bearing stress surface in use, and I think this is below the pin in normal use, but you must explain.

I’m not too surprised that you can’t find some nice text book example for fixing this problem. But, I think this is about what I’d try to design around and sell, assuming the repair is on the side (above?) away from the trapezoidal doubler pl. Also, assuming the damaged area is 14.5" wide and up to 14" high. Roll a piece of 1.5" thick compatible pl. mat’l. to 132" O.D. by 14"+ wide (your 14" high repair height) for your repair pieces. The next piece over would actually cut your 10" and 2.5" high repair pieces, but I don’t know how many of these you actually have. I would use a groove weld from both sides, maybe only 4 or 5 passes to fill the inside groove and get out of there; then back gouge the root pass and fill the outside groove. You might want to balance the welds a bit more, and pay attention to sequenceing the welds to minimize distortion. UT a few of the welds for QC and confidence in process, or maybe all of them. Radius the corners of the repair piece and cut hole if you can. But, in terms of max. width of repair piece stay away from the original complex pin hole corners if you can, you have about (20.75") - (2 x 1.625") - (14.5"+) to play with. You will want run-out tabs where the groove welds hit the pin bearing surface, and this will have to be cleaned up for the final pin bearing surface. Grind a small radius on the edges of the finished plate all around the pin hole to get rid of sharp edges. With good welding and welds, the weld stresses shouldn’t be a significant problem. Trying to replace 3 or 4 pieces 3' high and 2.5' wide, or some such, with a new pin holes in the middle, might do more damage (distortion) to the leg, or at least require much more work, than the above approach. This latter approach would also involve the stiffener pls. and the doubler pl. at each location.

This is your baby, not mine, so I’m just offering one possible solution to get you started thinking in the right direction. You do the actual design, with the help of your boss, or a senior engineer and a good welding engineer.