Spool Piece Instalation

Spool Piece A spool piece is a smallish length of pipe used for two purposes:

  • To connect two pipeline systems
  • To handle thermal expansion (When a gas is heated, its molecules move faster. This causes a pressure increase which, if not constrained, causes the gas to expand over a larger volume)

Connecting two Pipelines

When laying subsea pipelines, there is a limit to how close to the target one can start and stop the pipeline. This is mainly due to the fact that platforms or ships stand in your way. There is also often a limit set by the owner of the system on how close your pipeline can come to other items on the seabed. Therefore the two pipeline ends to be connected together will be anything from 5 meters to 100 meters apart. In some cases this can be rectified by moving the pipeline while it is down on the seabed, but in most cases the problem is fixed by installing a spool piece.

Removing thermal expansion

If a pipeline carries a hot product, the material the line is made of will expand due to this added heat. This gives a slightly (mostly insignificant) larger diameter, but also (a very significant) lengthening of the pipeline. If the pipeline cannot expand, this lengthening will induce compression stresses in the pipeline and may cause buckling. By positioning an expansion spool on the ends of the pipeline this lengthening is allowed to happen, and the only stress increase one gets is a bending stress along the spool.

These “spool pieces” , in most cases, are made to fit(fabricated) for the job. As mentioned above, the gap between the two pipeline flanges is going to vary from job to job. Not only does the gap vary, but the angles at which the two pieces meet will almost always be different. In order to fabricate a piece(this is usually done on the boat or rig) Divers must enter the water and measure both the distance between the two flanges and their angles. This is done by using a distance or lengthxmjigs1.jpg measuring device, such as a tape measure, and what are known as Metrology Tables. Metrology, if you don’t know, is the Science of Measurement. As you can see to the right, the tables are actually tables , and not a series of formulas that I had initially thought. The tables sit nicely on top of each pipeline and butt up against the flange(the end of the pipe which connects to another piece). There is a wire line on one table that is pulled across and connected to the other table. The tables actually have the angles marked off on their surface, so that if the tables are set up correctly, the line will pass over the correct angle mark on the table. You can read them directly off the table. Once you have the correct angle, you will measure the distance between the two pieces. These measurements are then sent up to the boat and the “Spool Piece” is then created. Once the piece has been made, it is sent down and fastened between the two pipeline pieces with a large 0 ring inserted between both flange connections. This is where you would cross your fingers and hope that your measurements were correct and that the spool piece fits in between the two corresponding pipes. Can you imagine the time and money wasted if they were not? Regardless, there is going to be some manipulation involved in order to get the flanges to line up exactly.

Here at D.I.T, we do not really have the time to fabricate a spool piece each time we do the project, so a pretty simple system has been set up. In essence, we do the project backwards. We have a spool piece that has been prefabricated. In the water there are two stands, and on each stand sits a 4 foot piece of pipeline with the flanges facing one another(to an extent). Each stand can be adjusted for fore/aft position, lateral movement, and your up/down angle. This requires that you loosen small U-Bolts on the stand and rotate, slide, and tilt the pipes as needed. We know the angle and length of the spool piece ahead of time so we must adjust the pipes accordingly so that the spool piece will line up and fit in place. If not, the bolt holes will never line up and it will be impossible to fasten them together. Remeber, out in the field you have oil flowing through these pipes, and you can’t just have that Black Gold leaking out into the Sea. In order to adjust the pipes to our measurements, we simply fasten the Metrology tables to the pipes, connect the wire rope and read the angle. We can then loosen the U-Bolts and adjust the pipes until we get the angle that we need(this happens to be 75 degrees for our purposes). Once we have the angle in place, we can then measure the distance between the two flanges, loosen a few more U-bolts, and slide the pipe back or forward in the stand until we have the correct distance between pipes. In my opinion, performing this task in reverse is a bit more complicated than doing it from scratch. Each time you adjust the pipe, the angles and distances are, of course, going to change from our initial reading. So we try to get things lined up as close a possible, and then use some good ole human power to get the spool piece bolted in place. In case you were wondering, the pipes are sitting about 5 feet off the bottom, and the spool piece is heavy enough that even 10 divers could not lift it. We have two divers in the water, so we use a series of straps that are fastened to a lift bag(rated to 2000 lbs) in order to lift and move the piece around. Once connected, we can inflate inside the bag by using that small hose I’ve told about before, the Pnuemofathometer. We fill the bag just enough to allow us move the piece around with relative ease. Once the spool piece is in place, and bolted up snug, we then disassemble the entire project, and mess up the pipe alignments so that the next group pf divers can do the same thing all over again.

I worked on this project today, and was actually able to get it completed without any major difficulties. It was not easy by any means, but it sure was a lot of fun. In fact, it was the best time I’ve had while here at school. It’s nice to have a task that you can see through to completion. It’s satisfying. I hope to have a few more opportunities to work on this project before we move into salvage next weeek.

I know it’s a great deal to take in but I hoped you enjoyed reading anyway. Until next time…

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~ by Scott on Tuesday, March 20, 2007.

3 Responses to “Spool Piece Instalation”

  1. Thank you a great deal! It was useful info for me. Adn there is a question what we do if the pipes cannot be bolted, but welded. what do we do in this case?

  2. Nice post! It will be very helpful to readers especailly those who does not have experience in offshore pipeline jobs.

  3. nice post ,thanks

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